6 or 8 inches front disc?
Colin
If you are given a choice to choose between a 6" and an 8" disc rotor for
your front disc brake on a single
crown fork, on a full-sus XC/epic bike, which would you go for? why? would
you also opt for the 8" rear?
There are people who would say that a 6" will serve the purpose on an XC,
and is "more than enough" braking power, too much braking power will make
you endo, lost control on loose soil, etc...
There are also people who would say that "more is better", better
modulation, better heat transfer, etc.....
What's your thought and comment?
jim beam
squeal, pads getting so hot both they and the disk were turning blue...
the "recommended" solution was 8" rotors, but i was reluctant for the
reasons you state, too much liklihood of endo, etc. effectiveness
wasn't the problem - 6" rotors are already /way/ more effective than any
rim brake solution i've ever tried.
i tried "one last thing" before going down the big rotor road - a
different brand of pad. all problems ended! great braking, excellent
modulation, no squeal, no overheating... i now use e.b.c. pads rather
than shimano and would never bother with a 6" rotor.
jb
Jose Rizal
Make sure your forks are warrantied for an 8" rotor. Most manufacturers
limit rotor size on their particular forks, and void warranties if
greater than 6" rotors are used.
An 8" rotor is overkill for most off-road applications; only the
steepest downhill courses *may* justify these.
Tim McNamara
The choices are 6" rotors and 8" rotors. The 8" rotors, it appears,
have more stopping power since they are referred to as being
"overkill" amd "more likely to cause endos." Am I with you so far?
Now, if these statements are accurate, then it seems to me that the
post powerful braking system possible for a mountain bike would be the
one that uses 22" rotors: rim brakes!
Simon Brooke
> Hmm. Interesting thread. Let me make sure I've got this straight.
>
> The choices are 6" rotors and 8" rotors. The 8" rotors, it appears,
> have more stopping power since they are referred to as being
> "overkill" amd "more likely to cause endos." Am I with you so far?
What gives more stopping power is, ultimately, ability to dissipate
heat, since brakes essentially convert kinetic energy to heat energy
and then dump the heat energy into the environment. Other things being
equal, a larger rotor has a larger radiant surface and is able to dump
more heat.
> Now, if these statements are accurate, then it seems to me that the
> post powerful braking system possible for a mountain bike would be the
> one that uses 22" rotors: rim brakes!
If you dump too much heat into the system which holds your tyres on,
you're going to blow tyres.
--
si...@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/
;; in faecibus sapiens rheum propagabit
Simon Brooke
The advantage of a bigger rotor is primarily larger cooling surface;
the disadvantage is greater weight. Unless you are doing very long
downhill sections at high speed (as in downhill racing) I find it hard
to believe that you need the greater cooling area, and if you're doing
an epic you certainly don't want to carry more weight.
In this case, less is more: less weight to heave up each hill means
more distance covered.
Jose Rizal
> Hmm. Interesting thread. Let me make sure I've got this straight.
>
> The choices are 6" rotors and 8" rotors. The 8" rotors, it appears,
> have more stopping power since they are referred to as being
> "overkill" amd "more likely to cause endos." Am I with you so far?
No, you're not. I don't know where you got the "more likely to cause
endos" bit. "Endos" aren't solely reliant on brakes (let alone the type
of brake) but involve riding position as well, among other things. The
overkill claim comes from the fact that 6" disc rotors provide ample
stopping ability for all but the most demanding incline, eg steep muddy
downhills with a relatively heavy rider/bike *and* very short distance
stopping requirements, such as those in some downhill mountainbiking
courses. However, larger disc rotors exert larger bending moments on
caliper mounts despite the smaller stopping force exerted by the
calipers (compared to smaller disc rotors), and therefore require
relatively stronger mounts than those designed for smaller disc rotors.
> Now, if these statements are accurate, then it seems to me that the
> post powerful braking system possible for a mountain bike would be the
> one that uses 22" rotors: rim brakes!
You're over-simplifying to an erroneous extent. You would know by now
the main mechanical differences between rim brakes and disc brakes; if
not, Google will come up with many threads and pages about that in
cycling-related newsgroups and websites. By now you must also be aware
of the different features of both types of brakes, as well as the pros
and cons of both so there is no need to rehash all of that here.
If the purpose of your post, however, is to try to dismiss bicycle disc
brakes as unnecessary in any case, you need to come up with a lot better
argument than what you've posted, addressing all the relevant issues
that have been discussed and argued for several years now.
Phil, Squid-in-Training
> > post powerful braking system possible for a mountain bike would be the
> > one that uses 22" rotors: rim brakes!
>
> You're over-simplifying to an erroneous extent.
I think he was being sarcastic... lol
--
Phil, Squid-in-Training
Tim McNamara
> Tim McNamara <tim...@bitstream.net> writes:
>
> > Hmm. Interesting thread. Let me make sure I've got this
> > straight.
> >
> > The choices are 6" rotors and 8" rotors. The 8" rotors, it
> > appears, have more stopping power since they are referred to as
> > being "overkill" amd "more likely to cause endos." Am I with you
> > so far?
>
> What gives more stopping power is, ultimately, ability to dissipate
> heat, since brakes essentially convert kinetic energy to heat energy
> and then dump the heat energy into the environment. Other things
> being equal, a larger rotor has a larger radiant surface and is able
> to dump more heat.
Humm. And a rim would have a much larger surface than a 6" or 8"
rotor, which again would indicate that the rim brake would have
greater stopping power than either size disc brake. Thanks for
clarifying that for me.
> > Now, if these statements are accurate, then it seems to me that
> > the post powerful braking system possible for a mountain bike
> > would be the one that uses 22" rotors: rim brakes!
>
> If you dump too much heat into the system which holds your tyres on,
> you're going to blow tyres.
I've heard of that happening, although in the 30+ years I've been
riding bikes as an "enthusiast," it's never happened to me. Of
course, I've also never lived in mountainous terrain with the long
steep descents necessary to heat a rim up that much. OTOH in my tour
in the Alps in 2002, I never had a problem with rims heating up.
My wife and I have never ridden our tandem in the mountains; that's a
situation that I could easily see resulting in very warm rims and
might warrant a hub brake- but since my wife hates climbing, it's not
something I'll ever be likely to test.
Kelly Johnson
You would have a point IF rim brakes generated as much pressure
between the pads as disk brakes do.
The appeal of disk brakes is not that they provide more stopping power
than rim brakes, but rather they the stopping power they provide is
almost constant regaurdless of the conditions. Wet, Dry, Muddy,
Icey...disk brakes work more or less the same in all those conditions.
That is certainly not a claim that can be made by rim brakes.
Carl Fogel
Dear Colin,
The trails that you ride might be what really matters.
The first Montesa trials motorcycles had huge brakes:
"The brakes are borrowed from Montesa's
other dirt models; of 7-inch diameter, they require a
delicate touch."
--"Sammy Miller On Trials"
Miller was being unreasonably polite--the damn things
were virtually useless in tricky downhill sections
because a single finger's pressure would lock up the
front wheel. The next model had much smaller brakes
that allowed real control at low speed instead of the
giant on-off switches stolen from the motocross line.
It would be worth trying to arrange a test ride or two
on a familiar trail to see which kind of brakes appeal
to you. If you do fairly fast, smooth riding, then larger
brakes are likely to be what you want. If you do more
low-speed riding with switchbacks, awkward rock sections,
and so forth, then smaller brakes may offer the necessary
light touch for control.
Keep in mind that brakes are far more important off-road
for bicycles than motorcycles. Descending long bad sections
of trail is much harder on a bicycle with nothing but brakes
and a useless freewheel, compared to a motorcycle with brakes
and a throttle to provide engine braking. This is why bicycle
rear brakes are more impressive--they're actually used.
Carl Fogel
(Pete Cresswell)
>There are also people who would say that "more is better", better
>modulation, better heat transfer, etc.....
>
>What's your thought and comment?
I've got 8" on my front wheels, but with 6":
- Interchangability: If you wind up with a spare somehow, it'll fit any of your
wheels instead of just fronts for just backs.
- Simpler: I had to get an add-on bracket to make Avid mechs fit the 8" rotor.
- More bulletproof (this is a stretch...but it seems logical) because there's
less leverage on the thing when you bang it up against, say, a big rock.
- Safer (another beeeeg stretch....) because there's less area for a stick or
something to find it's way into while you're under way.
Besides fade resistance (which is moot for the kind of riding I do) the only
theoretical con I can come up with is the leverage/front wheel ejection thing.
Bigger rotors move the pad further out, creating less ejection force for a given
amount of braking. How much? Does it matter? Dunno.
--
PeteCresswell
Werehatrack
<col...@no---spam.tm.net.my> may have said:
>Hi all,
>
>If you are given a choice to choose between a 6" and an 8" disc rotor for
>your front disc brake on a single
>crown fork, on a full-sus XC/epic bike, which would you go for?
8"
>why?
Better mechanical advantage.
>would
>you also opt for the 8" rear?
No. In fact, I wouldn't spend the bucks for a disc on the rear at
all.
>There are people who would say that a 6" will serve the purpose on an XC,
>and is "more than enough" braking power, too much braking power will make
>you endo, lost control on loose soil, etc...
There are, and will always be, alarmists for any given piece of new
tech, often persisting well after the new tech has become old.
>There are also people who would say that "more is better", better
>modulation, better heat transfer, etc.....
>
>What's your thought and comment?
In most cases, there is no need for a disc brake on a bicycle. Disc
brakes have some small, often purely subjective and somewhat
infrequent advantages in normal use which do not objectively outweigh
the high cost for most people. On the other hand, for a rider who
does a lot of prolonged descents, the disc has some significant
advantages in the area of removing the heat buildup from the rims.
There is also a consideration to be weighed in the area of safety, in
that on rare occasions, ejection of the front wheel from the fork has
been attributed to the way that the disc brake setups are designed.
In my personal opinion, these reports do not constitute a serious
enough cause for concern to keep me from buying or using a disc brake
setup.
I wouldn't disqualify a bike from consideration because it had disc
brakes, but I would not spend a lot of extra money to step up into
one, either, unless I was contemplating a lot of downhill braking.
--
My email address is antispammed; pull WEEDS if replying via e-mail.
Yes, I have a killfile. If I don't respond to something,
it's also possible that I'm busy.
Words processed in a facility that contains nuts.
Tim McNamara
>
> If the purpose of your post, however, is to try to dismiss bicycle
> disc brakes as unnecessary in any case, you need to come up with a
> lot better argument than what you've posted, addressing all the
> relevant issues that have been discussed and argued for several
> years now.
Jose, you need to check your sense of humor. It seems to need a
tune-up. You also need to re-read what was previously written by
other posters. The implication was clear that the larger disk rotors
offer more stopping power, which is erroneous.
Also, the math done in other threads addressed the fact that the
smaller rotors place a higher ejection force on the axle, with current
fork and caliper designs. I'm afraid I'll have to ask you to explain
how the larger rotors create a larger bending force on the fork leg,
since I'm having trouble perceiving that.
Disk brakes are unnecessary in most cases, as far as that part of your
critique goes. I was merely poking a bit o' fun at some of the logic
thus far in the thread. You disk-brakers seem to be kind of touchy on
the subject!
Carl Fogel
Dear Pete,
Pardon an innocent's fascination, but I love lists of
advantages like this and am intrigued by your "more
bulletproof" idea for the smaller 6" rotor.
I can see that a 6" rotor would hit fewer rocks to start
with because it's an inch higher than the 8" rotor, a
world of difference in nasty places.
But I'm not sure that I follow your idea of "less
leverage when you bang it up"--do you mean that a
smaller rotor is less likely to bend inward toward
the spokes when mashed sideways against a rock because
it doesn't stick out as far from its supports? Or am
I missing something better?
Carl Fogel
Colin
Thank you very much for all your feedback and comment.
On the other hand, do you think that we should also take into considerations
of the tire's traction? Given the same circumstances, a "grippier" tire
would benefit more from the braking as compare to one with less grip.
Do you think that there's a point where additional braking would be of no
use when the tire starts to loose traction? Especially on mud, loose gravel,
etc.
Although I am just a novice, I think the braking power (of any brakes) will
best benefit while riding on asphalt (or optimal traction), other than that,
its just too much "waste". Am I right or there are other issues such as
braking technique, etc.?
Simon Brooke
> Simon Brooke <si...@jasmine.org.uk> writes:
>
> > Tim McNamara <tim...@bitstream.net> writes:
> >
> > > Hmm. Interesting thread. Let me make sure I've got this
> > > straight.
> > >
> > > The choices are 6" rotors and 8" rotors. The 8" rotors, it
> > > appears, have more stopping power since they are referred to as
> > > being "overkill" amd "more likely to cause endos." Am I with you
> > > so far?
> >
> > What gives more stopping power is, ultimately, ability to dissipate
> > heat, since brakes essentially convert kinetic energy to heat energy
> > and then dump the heat energy into the environment. Other things
> > being equal, a larger rotor has a larger radiant surface and is able
> > to dump more heat.
>
> Humm. And a rim would have a much larger surface than a 6" or 8"
> rotor, which again would indicate that the rim brake would have
> greater stopping power than either size disc brake. Thanks for
> clarifying that for me.
Well, you're trying to be smart but in general I would agree that rim
brakes have a number of advantage WRT disks. The chief among these is
that they don't impose a torque loading on the wheel.
The primary disadvantages of rim brakes are
(i) it's difficult to keep them out of the dirt, so in muddy
conditions the braking surfaces are contaminated, and
(ii) it's difficult to keep them perfectly true, so the brakes have to
work at much less precise tolerances
However, if you're doing the sort of sustained braking that the true
downhill loonies do, and you dumped that much heat into your rims, you
probably would blow tyres.
--
si...@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/
;; better than your average performing pineapple
Simon Brooke
> Jose Rizal <_@_._> writes:
>
> >
> > If the purpose of your post, however, is to try to dismiss bicycle
> > disc brakes as unnecessary in any case, you need to come up with a
> > lot better argument than what you've posted, addressing all the
> > relevant issues that have been discussed and argued for several
> > years now.
>
> Jose, you need to check your sense of humor. It seems to need a
> tune-up. You also need to re-read what was previously written by
> other posters. The implication was clear that the larger disk rotors
> offer more stopping power, which is erroneous.
No, it's not, actually. While the instantaneous stopping power is
(other things being equal) may be the same, the ability to sustain
that stopping power over time is greater because the radiant area is
greater.
Mark Hickey
>Keep in mind that brakes are far more important off-road
>for bicycles than motorcycles. Descending long bad sections
>of trail is much harder on a bicycle with nothing but brakes
>and a useless freewheel, compared to a motorcycle with brakes
>and a throttle to provide engine braking. This is why bicycle
>rear brakes are more impressive--they're actually used.
Carl, if we ever end up riding off-road motorcycles together, I'm
going to insist you ride in front.
Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame
Mark Hickey
>Hi gentlemen,
>
>Thank you very much for all your feedback and comment.
>
>On the other hand, do you think that we should also take into considerations
>of the tire's traction? Given the same circumstances, a "grippier" tire
>would benefit more from the braking as compare to one with less grip.
>
>Do you think that there's a point where additional braking would be of no
>use when the tire starts to loose traction? Especially on mud, loose gravel,
>etc.
Bingo. Every new brake type that comes along is lauded for having
"greater stopping power", even though those that came before had more
than enough "stopping power" to send the rider over the handlebars.
>Although I am just a novice, I think the braking power (of any brakes) will
>best benefit while riding on asphalt (or optimal traction), other than that,
>its just too much "waste". Am I right or there are other issues such as
>braking technique, etc.?
It's really the same issue either way - you can only use so much
brake. If you can lift your rear wheel with your front brake, you
have enough brake - and that's something my old cantis and single
pivot calipers do fine.
Carl Fogel
Dear Mark,
Actually, I almost always ride sweep. No one
can stand waiting behind an unreformed trials
rider given to digressions.
But you needn't worry about my inability to find
the rear brake pedal (I think it's on the right on
the Honda, but it was on the left on the Bultaco).
After all, chopping the throttle on a four-stroke
TL-348 chirps the rear tire on pavement. In fact,
some of the Honda team's RTL machines ran brakeless
spool rear wheels to reduce unsprung weight.
As for bicycles, well, anyone stuck riding behind
me off-road or on pavement will get a lot of practice
doing trackstands or coasting.
Slowly yours,
Carl Fogel
David Damerell
>overkill claim comes from the fact that 6" disc rotors provide ample
>stopping ability for all but the most demanding incline, eg steep muddy
>downhills with a relatively heavy rider/bike *and* very short distance
>stopping requirements, such as those in some downhill mountainbiking
>courses.
Er, a steep downhill reduces the maximum possible deceleration.
--
David Damerell <dame...@chiark.greenend.org.uk> Kill the tomato!
Matt O'Toole
> Hi gentlemen,
>
> Thank you very much for all your feedback and comment.
>
> On the other hand, do you think that we should also take into considerations
> of the tire's traction? Given the same circumstances, a "grippier" tire
> would benefit more from the braking as compare to one with less grip.
No. Any brake has enough power to either lock the front wheel or flip you over
the handlebars.
> Do you think that there's a point where additional braking would be of no
> use when the tire starts to loose traction? Especially on mud, loose gravel,
> etc.
Exactly, and that's the reality most of the time riding on dirt.
> Although I am just a novice, I think the braking power (of any brakes) will
> best benefit while riding on asphalt (or optimal traction), other than that,
> its just too much "waste". Am I right or there are other issues such as
> braking technique, etc.?
Good technique is everything.
Disks are an advantage in muddy or snowy/icy conditions, but otherwise probably
a waste of money. Some people like the modulation for stunt-type riding. But
for normal riding, properly adjusted standard brakes are more than good enough
for most people. Save your money for other stuff that will make far more
difference in your riding experience -- good shoes and clothing, for example.
Or a trip to a great riding area.
Some mid-level mountain bikes come with disks anyway. In that case, take them
and be happy. But don't spend extra for them. With over 15 years experience in
the sport, I would still not buy disks if I were building my "dream bike"
today -- unless I lived where the trails were always muddy/snowy.
Matt O.
Tim McNamara
> Tim McNamara <tim...@bitstream.net> writes:
>
> > Jose Rizal <_@_._> writes:
> >
> > >
> > > If the purpose of your post, however, is to try to dismiss
> > > bicycle disc brakes as unnecessary in any case, you need to come
> > > up with a lot better argument than what you've posted,
> > > addressing all the relevant issues that have been discussed and
> > > argued for several years now.
> >
> > Jose, you need to check your sense of humor. It seems to need a
> > tune-up. You also need to re-read what was previously written by
> > other posters. The implication was clear that the larger disk
> > rotors offer more stopping power, which is erroneous.
>
> No, it's not, actually. While the instantaneous stopping power is
> (other things being equal) may be the same, the ability to sustain
> that stopping power over time is greater because the radiant area is
> greater.
I think there may be a difference in ease of modulation between a 6"
and 8" disk, but that's different than what you call "instantaneous
stopping power." I suspect some of the posters have confused the
two. Both will lock the wheel up just fine, which is the limit of
braking power.
In reference to the radiant area, I presume you are referring to the
ability to brake longer without vaporizing the pad material down to
the metal backing plate. In that case, 8" brakes might last longer
than 6" ones, but both would be inferior to the 22" disk brake that
has been in use for years. ;-)
Tim McNamara
> Tim McNamara <tim...@bitstream.net> writes:
>
> > Humm. And a rim would have a much larger surface than a 6" or 8"
> > rotor, which again would indicate that the rim brake would have
> > greater stopping power than either size disc brake. Thanks for
> > clarifying that for me.
>
> Well, you're trying to be smart
Guilty!
> but in general I would agree that rim brakes have a number of
> advantage WRT disks. The chief among these is that they don't impose
> a torque loading on the wheel.
Well, less load. The FEAs show that braking does have some effect on
spoke tension, which I presume indicates some loading in torque. But
a disk brake would probably wind 'em up much more. Or any hub brake,
for that matter- drum, roller or coaster brake.
> The primary disadvantages of rim brakes are
>
> (i) it's difficult to keep them out of the dirt, so in muddy
> conditions the braking surfaces are contaminated, and
>
> (ii) it's difficult to keep them perfectly true, so the brakes have
> to work at much less precise tolerances
Which is why they run at a 4:1 ratio for single-pivot sidepulls and
(IIRC) a 2.7:1 ration for dual-pivot sidepulls and (IIRC) a 2:1 ratio
for V-brakes. With a disc brake, you could run a 10:1 ratio and still
have clearance because the disk is smaller and more laterally rigid.
> However, if you're doing the sort of sustained braking that the true
> downhill loonies do, and you dumped that much heat into your rims,
> you probably would blow tyres.
There may be some situations where disk brakes are more effective
because of the mud/ice/snow issue and sustained high braking forces on
insane grades. The odds of me- or most people- riding in those
circumstances are pretty low. And the major disadvantage of current
disk brakes, the ejection force problem, is a complete deal-breaker
for me.
(Pete Cresswell)
>do you mean that a
>smaller rotor is less likely to bend inward toward
>the spokes when mashed sideways against a rock
Yes - but I would reiterate that this may be a stretch....perhaps purely
theoretical..
--
PeteCresswell
(Pete Cresswell)
>some small, often purely subjective and somewhat
>infrequent advantages in normal use which do not objectively outweigh
>the high cost for most people.
Depends on "normal use". If it includes much mud, discs definately have an
advantage in that the rims don't get worn out.
--
PeteCresswell
Ryan Cousineau
This I can see, but the local terrain depends a lot. See below.
> With over 15 years experience
> in
> the sport, I would still not buy disks if I were building my "dream bike"
> today -- unless I lived where the trails were always muddy/snowy.
In general, I would feel exactly the way you do, and to look at my bike,
I'm clearly a fan of the V-brake: my MTB (a hardtail) does not have
discs.
That said, I have been on several rides in the past year that have made
it painfully clear what the advantage of discs might be, besides the
obvious mud issues.
Because of their design (mainly that reduced clearances allow much
greater mechanical advantage) a disc brake can be modulated with more
precision and much less lever effort than other brakes (the proverbial
"1-finger stop" which discs are famous for).
Now this isn't important if you just want to do one-off braking contests
with your buddies. Everyone will stop at about the same point, discs or
rims. Where it makes a difference is that discs are more easily
modulated with less effort, so they tend to get used more effectively by
riders of all ability, and perhaps most importantly, they require less
hand strength after repeated efforts.
This last point was hammered home for me after a few local XC races. In
the Vancouver area, a cross-country course seems to mean brutal climbs,
rocks, dirt, and roots, water is not unheard of, and then you come down
the hill, so it's a steep descent, typically with switchbacks, drops,
and lots of other fun.
For these local conditions, I found that on the descents, I was using my
brakes so frequently and hard that at the end of the ride my arm had
"pumped" badly. I couldn't brake as effectively. The guys on discs
wouldn't have had that problem.
If you're riding substantially flat trails, that sort of pretty
smooth-singletrack-through-the-forest that features in beauty shots from
back east, I'd say there was no need for discs, especially if you don't
go out in the wet. But around here it's not like that, and for riders
who ride when it's wet or do steep descents, I think discs have real
value.
The disc-ejection issue is a problem, though: through-axle designs have
trickled down to some pretty normal forks, so a fix is really a matter
of making sure you get a QR20 or similar setup.
Share & Enjoy,
--
Ryan Cousineau, rcou...@sfu.ca http://www.sfu.ca/~rcousine
President, Fabrizio Mazzoleni Fan Club
Dave Wilson
[...]
> and be happy. But don't spend extra for them. With over 15 years experience in
> the sport, I would still not buy disks if I were building my "dream bike"
> today -- unless I lived where the trails were always muddy/snowy.
What about crash resistance? When I first started I was riding a
WalMart special, and laying it down a lot. Very often it would bang
the brakes and they would rub until I adjusted them again. And
tweaking the rims would also make them rub. So when I built a decent
bike I put on Hayes disks, and I have zero none nada problems with
them. Although I do crash a lot less now. Plus I just like the neato
tech solution.
I did recently build up another bike, and it didn't have disk mounts
in the back, so I used a Shimano v-brake, and I was surprised at how
well it works (basically as well as the disk). But I have already
bent the rim a little and had to readjust the brake so it won't rub.
Dave
(Pete Cresswell)
>QR20
?
--
PeteCresswell
Chalo
> "Colin" <col...@no---spam.tm.net.my> wrote:
>
> >Do you think that there's a point where additional braking would be of no
> >use when the tire starts to loose traction? Especially on mud, loose gravel,
> >etc.
>
> Bingo. Every new brake type that comes along is lauded for having
> "greater stopping power", even though those that came before had more
> than enough "stopping power" to send the rider over the handlebars.
You forgot the rest of the conditions: Those brakes that came before
had enough stopping power to send the rider over the handlebars IF the
rider were lightweight, on a short-wheelbase upright single bicycle
with a forward-leaning riding position and not carrying a heavy load;
if the wheels were clean, dry, and true; if the brakes were properly
set up and adjusted.
That's a lot of ifs. Packing more brakes than you need is far better
than not having enough.
In my experience, though, discs of any size are worse than the best
rim brakes at delivering big heaps of braking torque.
> It's really the same issue either way - you can only use so much
> brake.
Right, and I can use more than you can use. And you can use more on
your tandem, and I can use even more on my cargo sidehack. What's the
matter with a brake that's strong enough to do it all?
Chalo Colina
Ryan Cousineau
"(Pete Cresswell)" <x@y.z> wrote:
> RE/
> >QR20
>
> ?
Marzocchi's oversized axle setup. It's a quick-release through-axle,
thanks to a combination of a skewer and quick-releasing flaps under the
axle. So the axle can't just drop out.
The original Marzocchi URL was 421 characters. I like the name tinyurl
came up with.
This URL is for a Z1 FR fork, one of several models to use the QR20. The
original URL was 506 characters:
What the heck is with Marzocchi's site?
Simon Brooke
Not at all.
I'm not arguing to be cussed and I'm not an unequivecal supporter of
disk brakes on bikes - they have serious problems and in most
situations are not the appropriate solution.
However, downhillers routinely have problems with hydraulic fluid
boiling. This implies very high temperatures at the disk surface. If
you back the disk with a thermal insulator - for example, a reservoir
of trapped air - which retains that heat, you will achieve even higher
temperatures.
Horses for courses. Disk brakes cause far more stress on the wheel
structure generally and because they take up width at the hub lead to
a structure which is under higher tension and which is weaker
laterally. They're also heavier for equal stopping power than a
caliper or cantilever brake. Finally, they're more expensive to
engineer. So they are not a good general solution to bicycle braking
problems.
But there are niches in which they have advantages. Those niches are
constrained by dirt and contamination, and by sustained braking over
long periods. In these fairly limited niches, disks outperform other
bicycle brakes to an extent which tilts the cost-benefit in their
favour.
--
si...@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/
/-\ You have discovered a security flaw in a Microsoft product. You can
|-| report this issue to our security tesm. Would you like to
| | * Be completely ignored (default)
| | * Receive a form email full of platitudes about how much we care
\_/ * Spend hours helping us fix this problem for free?
Simon Brooke
> Simon Brooke <si...@jasmine.org.uk> writes:
>
> > However, if you're doing the sort of sustained braking that the true
> > downhill loonies do, and you dumped that much heat into your rims,
> > you probably would blow tyres.
>
> There may be some situations where disk brakes are more effective
> because of the mud/ice/snow issue and sustained high braking forces on
> insane grades. The odds of me- or most people- riding in those
> circumstances are pretty low. And the major disadvantage of current
> disk brakes, the ejection force problem, is a complete deal-breaker
> for me.
I have a lefty :-)
--
si...@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/
(Pete Cresswell)
>This URL is for a Z1 FR fork, one of several models to use the QR20. The
>original URL was 506 characters:
>
>http://tinyurl.com/tos3
>
>What the heck is with Marzocchi's site?
Probably the same thing as with their so-called manuals.
--
PeteCresswell
Jose Rizal
> Jose Rizal <_@_._> writes:
>
> >
> > If the purpose of your post, however, is to try to dismiss bicycle
> > disc brakes as unnecessary in any case, you need to come up with a
> > lot better argument than what you've posted, addressing all the
> > relevant issues that have been discussed and argued for several
> > years now.
>
> Jose, you need to check your sense of humor. It seems to need a
> tune-up. You also need to re-read what was previously written by
> other posters. The implication was clear that the larger disk rotors
> offer more stopping power, which is erroneous.
Since I made no such claim, and I don't know how you define power, I'm
not inclined to delve into it that much further. However, what is clear
is that the larger the rotor, the less friction force required for the
same stopping rate (ie distance to stop a given weight from a given
speed).
> Also, the math done in other threads addressed the fact that the
> smaller rotors place a higher ejection force on the axle, with current
> fork and caliper designs. I'm afraid I'll have to ask you to explain
> how the larger rotors create a larger bending force on the fork leg,
> since I'm having trouble perceiving that.
In qualitative terms, although for a given stopping rate the friction
force required with a larger rotor is smaller than with a smaller
diameter rotor, the moment arm from the caliper mounts to the pad/rotor
contact area is longer with the former, so that the bending moment is
higher than with a smaller diameter rotor.
In quantitative terms, consider a free body diagram of a fork and disc
brake system, and for simplicity assume that the caliper mounting posts
are parallel to the radial line from the axle to the center of the
caliper contact area. Also assume that the caliper center is exactly
between the tips of the mounting posts.
fork leg
| |
| | upper mounting post
| | /
| | / + caliper center
| | /
| |/ / lower mounting post
| | /
| | /
| |/
---O--
dropout
Now in the case of a small rotor with diameter Ro, the force exerted by
the caliper Fo is taken up by the two mounting posts. Assume for
simplicity that each post takes up exactly half the caliper force, or
0.5*Fo. The moment about the base of each post will then be
1) 0.5 * Fo * Lo,
where Lo is the length of the mounting post.
Now consider the case of a larger rotor with diameter R1. It can be
resonably assumed that the mounting posts are lengthened by the same
amount as the increase in radius for the larger rotor, that is,
2) R1 - Ro = L1 - Lo
and the posts are still parallel to the axle-caliper radial line.
Since the moment about the axle needs to be the same as with the smaller
rotor, then
3) F1 * R1 = Fo * Ro.
and so
4) F1 = Fo * Ro/R1.
The moment about the base of each post will now be
5) Moment = 0.5 * F1 * L1 = 0.5 * Fo * Ro/R1 * L1
But L1 = (R1 - Ro + Lo) from 2) above, so the moment on each post is
6) Moment = 0.5 * Fo * Ro/R1 * (R1 - Ro + Lo).
Plugging in typical numbers show clearly that the larger the disc brake
rotor, the greater the moment exerted on the fork leg brake mounts.
Example: let Ro = 76.2mm (6" rotor), Lo = 15mm, and R1 = 101.6mm (8"
rotor)
Plug into 1) and 6) above and it's clear that the moment on each
mounting post is about 2 times greater for the 8" rotor than for the
6" rotor. This is why suspension fork manufacturers void warranties on
most of their QR-dropout-equipped forks if greater than 6" rotors are
used.
Jose Rizal
> The primary disadvantages of rim brakes are
>
> (i) it's difficult to keep them out of the dirt, so in muddy
> conditions the braking surfaces are contaminated, and
>
> (ii) it's difficult to keep them perfectly true, so the brakes have to
> work at much less precise tolerances
Add to this a significant issue: when you've worn away the rim, you need
to build a new wheel.
Jose Rizal
> There may be some situations where disk brakes are more effective
> because of the mud/ice/snow issue and sustained high braking forces on
> insane grades. The odds of me- or most people- riding in those
> circumstances are pretty low.
But wearing down your rim is an inevitability, as is the requirement for
a new wheel, and disc brakes involve a lot less effort in this area.
Chalo
> Any brake has enough power to either lock the front wheel or flip you over
> the handlebars.
Hello? No it doesn't. Folks say this as if it will somehow become
true through repetition.
There are conditions under which, say, a single-pivot caliper brake
will deliver nose-wheelie quality braking:
- the bike must have a short wheelbase
- the bike must be of the upright type
- the bike must be for a single rider
- the rider must be of average or smaller size and weight
- the rider must be using a forward-leaning body position
- the rider must have abundant grip strength
- the bike must carry no heavy cargo
- the wheels must be clean, dry, and true
- the brakes must be well adjusted
- the brake pads must be of good quality and in good condition
If all these conditions do not apply, the braking will be less than
optimal. Because of the rider size, weight, and positioning issues, I
am unable to get the kind of braking you describe on 16 of my 17
bikes. It ain't because I don't squeeze the bejeebers out of them,
either.
I had to make my own brakes for the other bike! They give me all the
stopping power I can use.
In my experience, nothing short of a loose, wet, or otherwise slippery
surface will allow a bike of conventional layout to skid the front
tire.
If you and Jobst are happy with weak brakes, great. You can have
them; they don't work for me. They fail to work well for a lot of
other people too.
Chalo Colina
Tim McNamara
> Tim McNamara:
>
> > Jose Rizal <_@_._> writes:
> > >
> > > If the purpose of your post, however, is to try to dismiss
> > > bicycle disc brakes as unnecessary in any case, you need to come
> > > up with a lot better argument than what you've posted,
> > > addressing all the relevant issues that have been discussed and
> > > argued for several years now.
> >
> > Jose, you need to check your sense of humor. It seems to need a
> > tune-up. You also need to re-read what was previously written by
> > other posters. The implication was clear that the larger disk
> > rotors offer more stopping power, which is erroneous.
>
> Since I made no such claim, and I don't know how you define power,
> I'm not inclined to delve into it that much further. However, what
> is clear is that the larger the rotor, the less friction force
> required for the same stopping rate (ie distance to stop a given
> weight from a given speed).
I was responding to several posts, as I recall without citing them, in
which it was clearly implicated that larger rotor disks had greater
stopping power. It was that logic that I was having some fun with. I
don't recall that any of your posts made any such claim, although for
some reason you seem to have taken it that I was criticizing something
you wrote.
> > Also, the math done in other threads addressed the fact that the
> > smaller rotors place a higher ejection force on the axle, with
> > current fork and caliper designs. I'm afraid I'll have to ask you
> > to explain how the larger rotors create a larger bending force on
> > the fork leg, since I'm having trouble perceiving that.
>
> In qualitative terms, although for a given stopping rate the friction
> force required with a larger rotor is smaller than with a smaller
> diameter rotor, the moment arm from the caliper mounts to the pad/rotor
> contact area is longer with the former, so that the bending moment is
> higher than with a smaller diameter rotor.
<snip> Thanks. Now, looking at your diagram, I see that the mounts
for the calipers stick out from the fork and are longer for the larger
disk, naturally. Now, if the caliper was mounted directly to the fork
leg, does that change the math? (It shouldn't as far as I can tell).
And by extension, a 22" rotor (the rim) should result in extremely
high bending forces on the fork.
Tim McNamara
I can't recall ever having worn out the brake track on a rim in >35
years of riding bike. I've had some wheels that were in service on my
road bikes for >20 years. Of course, I don't use pre-machined rims
that have had 25-30% of the sidewall thickness removed before the rim
was ever laced to a hub.
Jose Rizal
> Because of the rider size, weight, and positioning issues, I
> am unable to get the kind of braking you describe on 16 of my 17
> bikes.
You have 17 bikes? Are you a collector or a pack rat?
Jose Rizal
> Jose Rizal <_@_._> writes:
>
> > Tim McNamara:
> > > Also, the math done in other threads addressed the fact that the
> > > smaller rotors place a higher ejection force on the axle, with
> > > current fork and caliper designs. I'm afraid I'll have to ask you
> > > to explain how the larger rotors create a larger bending force on
> > > the fork leg, since I'm having trouble perceiving that.
> >
> > In qualitative terms, although for a given stopping rate the friction
> > force required with a larger rotor is smaller than with a smaller
> > diameter rotor, the moment arm from the caliper mounts to the pad/rotor
> > contact area is longer with the former, so that the bending moment is
> > higher than with a smaller diameter rotor.
>
> <snip> Thanks. Now, looking at your diagram, I see that the mounts
> for the calipers stick out from the fork and are longer for the larger
> disk, naturally. Now, if the caliper was mounted directly to the fork
> leg, does that change the math? (It shouldn't as far as I can tell).
Not if the mounts do not change positions, ie Lo just becomes shorter.
The analysis is different for calipers mounted further up the fork leg,
ie close to the rim as in typical rim brakes.
> And by extension, a 22" rotor (the rim) should result in extremely
> high bending forces on the fork.
Only if the brake caliper mounts remain near the dropout. The bending
moment on rim brake mounts are quite low since the moment arms from the
pad contact area to the mounts is quite short, these being quite close
to the rim. Coupled with the lower forces required for a given stopping
rate (compared to disc brakes), fork strength for brake mounts is not as
big a design issue with rim brakes.
David Damerell
>Jose Rizal
>>But wearing down your rim is an inevitability, as is the requirement
>>for a new wheel, and disc brakes involve a lot less effort in this
>>area.
>I can't recall ever having worn out the brake track on a rim in >35
>years of riding bike. I've had some wheels that were in service on my
>road bikes for >20 years.
I wore out a front rim after about 13 years, but perhaps I ride in more
bad weather conditions?
Irrespective, I agree it's hard to see it as a serious concern. :-)
A Muzi
>>>There may be some situations where disk brakes are more effective
> Jose Rizal <_@_._> writes:
>>But wearing down your rim is an inevitability
-snip-
Tim McNamara wrote:
> I can't recall ever having worn out the brake track on a rim in >35
> years of riding bike. I've had some wheels that were in service on my
> road bikes for >20 years. Of course, I don't use pre-machined rims
> that have had 25-30% of the sidewall thickness removed before the rim
> was ever laced to a hub.
I wondered about that, too. I have never worn through a rim
and some are quite old. I do notice that many customers'
bikes require brake shoes every season and their rims are
gouged deeply. Maybe it is a difference of style to ride
the brakes often?? I still have the same front pads on my
fixed from its build in 1995. City miles, too.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971
Mike Latondresse
news:m2n0ba9...@localhost.bitstream.net:
>
> I can't recall ever having worn out the brake track on a rim in
> >35 years of riding bike. I've had some wheels that were in
> service on my road bikes for >20 years. Of course, I don't use
> pre-machined rims that have had 25-30% of the sidewall thickness
> removed before the rim was ever laced to a hub.
Commuting in Vancouver winters I used to wear out a rim in about 6
months. Wet street grit is a great abrader.
Carl Fogel
Dear Jose,
Let us say that Chalo is a man of interests both broad
and deep, with ample storage space and yet not even a
different bike for every day of the month, fer chrissake.
At least his stable includes a wide variety of bicycles
for different purposes. My modest holdings consist of
only three identical models, two of which live frightened
lives, hanging from the rafters and waiting either for
visiting friends to abuse them or else for me to cannibalize
them for quick parts.
Let's see . . . road bike, tandem, mountain bike, Moulton,
penny-farthing, recumbent, fixed-wheel, BMX--two of each
kind and Chalo would have 16 bikes. Maybe the 17th is
actually a tricycle?
Carl Fogel
Carl Fogel
Dear Chalo,
I liked your list of braking conditions for nose-wheelies.
My only success met them all. Well, maybe not the abundant
grip strength, being well-adjusted (the brakes, that is),
the wheel being well-trued, or the average or smaller size
and weight rider, but I was pedalling upright no-hands at
a good clip on a dry concrete path in the countryside,
frantically tearing my helmet off to deal with an angry wasp,
when two fishermen deep in conversation walked out of the
trees in front of me and I lunged forward, desperately
grabbed the brakes, and learned why the penny-farthing
design was replaced with the so-called safety bicycle,
which provided a classic endo and shoulder-roll.
Do your tall-boy bicycles count as uprights?
More seriously, given your size, bicycling experience,
and machinist's expertise, it would be fascinating if
you have the time to describe how and why you made
your own brakes--bigger pads, longer or stronger arms,
cable-attachment improvements, better leverage points,
levers able to withstand someone like you squeezing
the bejeebers out of them?
Carl Fogel
Gary Young
<snip>
> I had to make my own brakes for the other bike! They give me all the
> stopping power I can use.
I'm curious what you came up with.
Simon Brooke
I can remember fitting a set of new brake blocks on my road bike, and
two days later having to fit another set. Mind you, I'd been over the
Kirkstone pass in the interim, and this was thirty years ago whan
blocks were less good and rims were steel (at least on the quality of
bike I was then riding).
Hill bikes do go through brake blocks faster than road bikes, but I've
never worn through a rim.
--
si...@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/
do not sail on uphill water
- Bill Lee
Tim McNamara
> Tim McNamara:
>
> > And by extension, a 22" rotor (the rim) should result in extremely
> > high bending forces on the fork.
>
> Only if the brake caliper mounts remain near the dropout. The
> bending moment on rim brake mounts are quite low since the moment
> arms from the pad contact area to the mounts is quite short, these
> being quite close to the rim. Coupled with the lower forces
> required for a given stopping rate (compared to disc brakes), fork
> strength for brake mounts is not as big a design issue with rim
> brakes.
Ah. Got it. Thanks!
Tim McNamara
> Tim McNamara <tim...@bitstream.net> wrote:
>
> >I can't recall ever having worn out the brake track on a rim in >35
> >years of riding bike. I've had some wheels that were in service on
> >my road bikes for >20 years.
>
> I wore out a front rim after about 13 years, but perhaps I ride in
> more bad weather conditions?
Given your .uk e-mail address, I think that may be a possibility.
:-).
Tim McNamara
Jobst has talked about this issue, noting that he's done extended
tours in the Alps where it rained basically every day for 3 weeks.
Wet weather riding seems far more likely to wear out a rim, and of
course mountain riding would involve more use of the brakes than the
basically flat to rolling riding I do. MTB'ers are more likely to
ride in mud, which presumably acts as both an abrasive and a lubricant
(no brakes, but chews up your rims).
I also think that some pads tend to entrap grit and such, either in
grooves in the surface or in the material itself. My Scott/Mathauser
brake pads don't seem to do this. For one thing there are no grooves,
and for another the material seems to be tough enough that particles
don't get embedded.
Jose may ride more in wet weather and/or the mountains, or off-road in
mud, than I do and so his perceptions may be different than mine.
Jose Rizal
> Tim McNamara <tim...@bitstream.net> wrote:
> >Jose Rizal
> >>But wearing down your rim is an inevitability, as is the requirement
> >>for a new wheel, and disc brakes involve a lot less effort in this
> >>area.
> >I can't recall ever having worn out the brake track on a rim in >35
> >years of riding bike. I've had some wheels that were in service on my
> >road bikes for >20 years.
>
> I wore out a front rim after about 13 years, but perhaps I ride in more
> bad weather conditions?
>
> Irrespective, I agree it's hard to see it as a serious concern. :-)
I assume both of you are referring to road riding? I've gone through a
set of wheels using rim brakes in just over 2 years of off-road riding,
not doing too many miles within that period. The conditions were a
little too dirty for getting long mileage out of rim brakes.
Rim wear is certainly not a major justification for disc brakes,
especially for most riding conditions but it's a nice baggage to drop
for those conditions that promote it.
jobst....@stanfordalumni.org
>> But wearing down your rim is an inevitability, as is the
>> requirement for a new wheel, and disc brakes involve a lot less
>> effort in this area.
> I can't recall ever having worn out the brake track on a rim in >35
> years of riding bike. I've had some wheels that were in service on
> my road bikes for >20 years. Of course, I don't use pre-machined
> rims that have had 25-30% of the sidewall thickness removed before
> the rim was ever laced to a hub.
You didn't say how many miles that was or in what weather you rode. I
have a stack of MA-2 rims in the basement, 20 or so of them from my
use and most of which were retired for wear, some having only 0.5mm
(0.020") wall remaining. Many of these served on the same hubs and
spokes I am riding now, certainly more than 200,000mi. On the other
hand I also have a couple of wheels >20 years old that have almost no
wear... but I don't use them.
Jobst Brandt
jobst....@stanfordalumni.org
Mark Hickey
I've seen them (Chalo sent me photos). They are very, very, very
robust brakes that appear to be quite well-designed and well-made (and
capable of stopping a typical motorcycle). For all my talk about
belief in over-engineering, I don't pretend to hold a candle to Chalo
(who actually NEEDS a lot of that over-engineering to prevent
failures). If I were ever to build a quad (four-seater), I'd call up
Chalo to get lots of the parts.
Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame
Chalo
> You have 17 bikes? Are you a collector or a pack rat?
Habitual bike builder. With a 2-car garage and no car.
Chalo
Tim McNamara
> Tim McNamara writes:
>
> >> But wearing down your rim is an inevitability, as is the
> >> requirement for a new wheel, and disc brakes involve a lot less
> >> effort in this area.
>
> > I can't recall ever having worn out the brake track on a rim in
> > >35 years of riding bike. I've had some wheels that were in
> > service on my road bikes for >20 years. Of course, I don't use
> > pre-machined rims that have had 25-30% of the sidewall thickness
> > removed before the rim was ever laced to a hub.
>
> You didn't say how many miles that was or in what weather you rode.
Or terrain. That particular wheel set was a pair of Rigida 13-19 27"
rims laced onto the low-end Avocet (Ofmega) hubs- Model I's IIRC. The
rims were very similar to the MA-2 in design and finish, although now
I can't recall if they had nipple sockets or just a simple ferrule
("single eyelet"). I used 14g Trois Etoiles spokes- are those even
made any more?
I built these in the summer of 1978- the first wheels I built from
scratch, following instructions published in Bicycling! Magazine, as I
recall. Don't know who wrote the article, might even have been Jobst
or Sheldon. Anyway, I rode those as my primary wheels until 1992
using them for two different bikes, and then only occasionally until
1999 or 2000, on flat to rolling terrain and almost never in the rain
(I hate riding in the rain). I'd guess those wheels had only about
50,000 to 55,000 miles on them. I finally dismantled them since I had
no need for 27" wheels any more, and the hubs were used on a fixed
gear project for a while. I recall breaking several axles in the rear
wheel after respacing it for 6 speed.
My rim of choice has been the MA-2 after having repeated failures of
anodized "fancy" rims, and I only have a couple of new ones left.
Last summer saw the premature demise of two of them thanks to a
well-hidden pothole and airport bagage handlers somewhere between
Minneapolis and Paris.
(Pete Cresswell)
>I wore out a front rim after about 13 years, but perhaps I ride in more
>bad weather conditions?
What was the failure mode when the rim finally did go?
i.e. Catastrophic, as in coming apart at speed...or gradual...
--
PeteCresswell
Matt O'Toole
<jobst....@stanfordalumni.org> wrote in message
news:7Lyqb.4416$Wy2....@typhoon.sonic.net...
How many miles do you get out of your rims? I imagine at least 20k.
I've never kept track -- partly because I didn't use computers for a long time,
and partly because it was mostly mountain biking, where conditions are so varied
anyway. Pulverized granite and grainy sand seem to be the worst, slimy clay not
as bad.
Matt O.
Chalo
> I had to make my own brakes for the other bike! They give me all the
> stopping power I can use.
Carl Fogel very kindly posted a couple of photos of my brake to his
webspace:
http://home.comcast.net/~carlfogel/download/red_brake.JPG
http://home.comcast.net/~carlfogel/download/redfront.JPG
My thanks go to Carl for the favor.
The brake in the pictures is the strongest I have ever seen attached
to a bicycle. It outperforms boosted Self Energizing cantilevers, any
and all V-brakes, Magura rim brakes, and every disc brake I have ever
had occasion to try. 8" Hayes hydraulic discs do not approach the
braking torque this brake provides.
I made the brake to replace a set of Avid Tri-Align brakes that I had
broken. The fork was a pair of Bontrager legs stuck in a deep-arch
magnesium crown I made in order to accept the 700c wheel because the
legs were for 26". When I decided to invest the effort of making my
own brakes, I sought out some suspension fork legs. The ones I got
were Specialized Future Shock Carbon legs, because they were available
cheap, legs only, at a local shop. They've since been heavily
reworked to shorten and stiffen the travel and to reinforce the
bushings.
I made a new fork brace, both to clear the 700c tire and to provide a
new location for the brake pivots. Those pivots are 12.7mm (1/2") in
diameter rather than the usual 8mm, and they fit more closely than the
studs do in most cantilever or V brakes. They are brass for its
improved bearing qualities against aluminum.
I made a booster arch that holds the fork arch at three points. The
former brake pivots were used to anchor the booster to the fork legs
for more extra additional bonus redundancy.
The brake arms are longer overall than regular V-brakes, but have
lower
mechanical advantage due to the relocated pivot points. The pads are
Kool-Stop Thinline. When I used the brake levers shown in these
pictures (Snafu Ultimate Levers), I was able to switch from
linear-pull leverage to cantilever leverage, and either one worked
just fine. The feel was different, but either ratio gave plenty of
braking without running out of travel.
I had not seen Shimano V-brakes at the time I made these. I used
Marinovative Cheap Trick brakes as a design guide, but the box brace
was my
own invention. I had already observed that booster arches helped me
get strong braking, and I had seen that boosters tended to flex
forward visibly during hard stops. I chose to bolt the booster to the
fork brace at top, and I provided a more mechanically rigid interface
at the pivots.
I am convinced that all the improvement in power over an ordinary
brake (and it is quite a bit) is attributable to the lack of flex in
the system. Neither cable force nor pad frictional force can twist
the brake into a less effective configuration. It takes a relatively
small force at the lever to get lots of braking, which I believe
supports my impression that flex is the primary source of most brakes'
inability to directly proportion lever force to braking force. There
is nothing else so different about these brakes as to account for the
improvement in braking force over commercially available brakes.
After making this brake, I soon had to make a new fork crown, because
the enhanced braking bent the steerer and caused the fork stanchions
to crawl up in their clamps. I made a stem and fork crown to match
each other, so that they could be joined with a rod to resist bending
loads on the steerer. At one point I attempted to swap this front end
onto a lugged steel frame, but the braking forces bent the frame (!)
and I was obliged to switch back.
Chalo Colina
Tim McNamara
> The brake in the pictures is the strongest I have ever seen attached
> to a bicycle.
Good grief! What does it weigh?
jobst....@stanfordalumni.org
>> I had to make my own brakes for the other bike! They give me all
>> the stopping power I can use.
> http://home.comcast.net/~carlfogel/download/red_brake.JPG
> http://home.comcast.net/~carlfogel/download/redfront.JPG
> My thanks go to Carl for the favor.
> The brake in the pictures is the strongest I have ever seen attached
> to a bicycle. It outperforms boosted Self Energizing cantilevers,
> any and all V-brakes, Magura rim brakes, and every disc brake I have
> ever had occasion to try. 8" Hayes hydraulic discs do not approach
> the braking torque this brake provides.
The only thing you missed was getting some red Kool-Stop pads.
However, what you have there is a brute force V-brake. Not having a
head-on view, I can't estimate its mechanical advantage but while you
were at it, you could have dropped the brake arm pivot point another
centimeter or two to reduce cosine error. What you have conclusively
proven, is that sponge is the enemy of good braking. I assume the
other dimensions are fairly standard.
> I made the brake to replace a set of Avid Tri-Align brakes that I
> had broken. The fork was a pair of Bontrager legs stuck in a
> deep-arch magnesium crown I made in order to accept the 700c wheel
> because the legs were for 26". When I decided to invest the effort
> of making my own brakes, I sought out some suspension fork legs.
> The ones I got were Specialized Future Shock Carbon legs, because
> they were available cheap, legs only, at a local shop. They've
> since been heavily reworked to shorten and stiffen the travel and to
> reinforce the bushings.
The problem is that the forks shown have an extra weak crown with
respect to spreading from cantilevers. This crown should contain most
of the metal that is in the brake bridge, going straight across to th
other side. The whole design looks like a machinists make work, hewn
from solid blocks of aluminum.
> I made a new fork brace, both to clear the 700c tire and to provide a
> new location for the brake pivots. Those pivots are 12.7mm (1/2") in
> diameter rather than the usual 8mm, and they fit more closely than the
> studs do in most cantilever or V brakes. They are brass for its
> improved bearing qualities against aluminum.
You should have dropped them down and extended the brake arms
proportionally up.
> I made a booster arch that holds the fork arch at three points. The
> former brake pivots were used to anchor the booster to the fork legs
> for more extra additional bonus redundancy.
Well the fork isn't contributing much, as bad as the crown is.
> The brake arms are longer overall than regular V-brakes, but have
> lower mechanical advantage due to the relocated pivot points. The
> pads are Kool-Stop Thinline. When I used the brake levers shown in
> these pictures (Snafu Ultimate Levers), I was able to switch from
> linear-pull leverage to cantilever leverage, and either one worked
> just fine. The feel was different, but either ratio gave plenty of
> braking without running out of travel.
Where are the pivots? What it the length ratio to regular V-brakes?
> I had not seen Shimano V-brakes at the time I made these. I used
> Marinovative Cheap Trick brakes as a design guide, but the box brace
> was my own invention. I had already observed that booster arches
> helped me get strong braking, and I had seen that boosters tended to
> flex forward visibly during hard stops. I chose to bolt the booster
> to the fork brace at top, and I provided a more mechanically rigid
> interface at the pivots.
> I am convinced that all the improvement in power over an ordinary
> brake (and it is quite a bit) is attributable to the lack of flex in
> the system. Neither cable force nor pad frictional force can twist
> the brake into a less effective configuration. It takes a
> relatively small force at the lever to get lots of braking, which I
> believe supports my impression that flex is the primary source of
> most brakes' inability to directly proportion lever force to braking
> force. There is nothing else so different about these brakes as to
> account for the improvement in braking force over commercially
> available brakes.
Well, that's one discovery I think many manufacturers never made. That
"sponge" is the enemy of good braking is evident from adjusting
sidepull brakes so they have little pad clearance. They seem to have
more power suddenly, when in fact it is the better handful the grip
makes when it isn't nearly closed. Add to that a brake that doesn't
flex and you have a large handful (two fingers) of brake available.
> After making this brake, I soon had to make a new fork crown,
> because the enhanced braking bent the steerer and caused the fork
> stanchions to crawl up in their clamps. I made a stem and fork
> crown to match each other, so that they could be joined with a rod
> to resist bending loads on the steerer. At one point I attempted to
> swap this front end onto a lugged steel frame, but the braking
> forces bent the frame (!) and I was obliged to switch back.
You should have done all this as a grade school bikie and saved yourself
a lot of work by starting out with a better design on paper rather
than in hardware. This takes too long. Each iteration being
expensive and slow. Doing this on a CAD screen with the experience
you have gained is rewarding... but don't let that stop you. We may
yet benefit from some of these things.
Jobst Brandt
jobst....@stanfordalumni.org
Rado bladteth Rzeznicki
> In quantitative terms, consider a free body diagram of a fork and disc
> brake system, and for simplicity assume that the caliper mounting posts
> are parallel to the radial line from the axle to the center of the
> caliper contact area.
This is great oversimplification, since these two lines are never
parallel. Usually the angle between them is about 45 degrees, which
changes things substantially and complicates the calculations a bit.
I am not going to do them here, but as I look at quick drawn diagram,
bending moment on top mount is just a tad greater (or lower, depends
on the adapter shape) with larger rotor and significantly greater on
bottom mount. However, I have not seen a broken lower mounting post
yet - have you? I think it is more dependent on adapter shape. Some
of them are more like a piece of art than part designed with
mechanics in mind.
--
Best regards,
Rado bladteth Rzeznicki
http://www.widzew.net/~bladteth/rower.html
mailto:blad...@iprimus.com.au
MCM #252
Dave Kahn
> You should have done all this as a grade school bikie and saved yourself
> a lot of work by starting out with a better design on paper rather
> than in hardware. This takes too long. Each iteration being
> expensive and slow. Doing this on a CAD screen with the experience
> you have gained is rewarding... but don't let that stop you. We may
> yet benefit from some of these things.
I think Jobst just paid Chalo a compliment. Wow, I'd hate to be on the
end of a roasting!
--
Dave...
Jose Rizal
> Jose Rizal wrote:
>
> > In quantitative terms, consider a free body diagram of a fork and disc
> > brake system, and for simplicity assume that the caliper mounting posts
> > are parallel to the radial line from the axle to the center of the
> > caliper contact area.
>
> This is great oversimplification, since these two lines are never
> parallel. Usually the angle between them is about 45 degrees, which
> changes things substantially and complicates the calculations a bit.
It's not an invalid simplification, since the bending moment arms can be
resolved along lines which are parallel to the radial line of the rotor.
In fact these can be resolved along any line you choose; just
substitute the resolved forces into the equations. Calculations and
visualisation are made a lot simpler though by taking up the said
assumptions.
It doesn't change things "substantially"; show your analysis if you
think otherwise.
> I am not going to do them here, but as I look at quick drawn diagram,
> bending moment on top mount is just a tad greater (or lower, depends
> on the adapter shape) with larger rotor and significantly greater on
> bottom mount.
I don't see that adapter shape has any effect on the analysis. The
caliper remains halfway between the mounting post tips on any adapter
I've seen, although the shapes of these varied a bit. The only
significant effect is if the distance between mounting post tip and fork
dropout is changed. With rotors > 6" it's typically the case that the
top mounting post is slightly extended by adapters, and hence the
bending moment will be slightly higher but it's still valid to assume
that each mounting post will take up equally the braking force from the
caliper.
> However, I have not seen a broken lower mounting post
> yet - have you? I think it is more dependent on adapter shape. Some
> of them are more like a piece of art than part designed with
> mechanics in mind.
The broken mounting posts I've seen were due to stripped mounting post
threads; either the operator overtorqued the bolts or there was a flaw
in the fork leg casting (I've seen the latter on new Manitou forks). I
don't see how adapter shape by itself affects mounting post integrity;
it wouldn't be surprising though if the shapes were chosen for aesthetic
effects only.
David Damerell
>David Damerell:
>>I wore out a front rim after about 13 years, but perhaps I ride in more
>>bad weather conditions?
>What was the failure mode when the rim finally did go?
The sidewalls bent outwards, making it difficult to fit tyres. I suppose
eventually they would have ripped off, but nothing catastrophic happened
before I noticed.
--
David Damerell <dame...@chiark.greenend.org.uk> flcl?
Jose Rizal
> Chalo Colina writes:
>
> >> I had to make my own brakes for the other bike! They give me all
> >> the stopping power I can use.
>
> > http://home.comcast.net/~carlfogel/download/red_brake.JPG
> > http://home.comcast.net/~carlfogel/download/redfront.JPG
>
> > My thanks go to Carl for the favor.
>
> > The brake in the pictures is the strongest I have ever seen attached
> > to a bicycle. It outperforms boosted Self Energizing cantilevers,
> > any and all V-brakes, Magura rim brakes, and every disc brake I have
> > ever had occasion to try. 8" Hayes hydraulic discs do not approach
> > the braking torque this brake provides.
>
> The only thing you missed was getting some red Kool-Stop pads.
> However, what you have there is a brute force V-brake. Not having a
> head-on view, I can't estimate its mechanical advantage but while you
> were at it, you could have dropped the brake arm pivot point another
> centimeter or two to reduce cosine error. What you have conclusively
> proven, is that sponge is the enemy of good braking. I assume the
> other dimensions are fairly standard.
But dropping the pivot point means a longer arm, which increases bending
moment and potentially flex. There needs to be a happy medium between
pivot/pad length and mechanical advantage.
> > I made a new fork brace, both to clear the 700c tire and to provide a
> > new location for the brake pivots. Those pivots are 12.7mm (1/2") in
> > diameter rather than the usual 8mm, and they fit more closely than the
> > studs do in most cantilever or V brakes. They are brass for its
> > improved bearing qualities against aluminum.
>
> You should have dropped them down and extended the brake arms
> proportionally up.
Which might mean beefing up the arms to counteract the increased bending
moment trying to flex the arm or pivot.
> Well, that's one discovery I think many manufacturers never made. That
> "sponge" is the enemy of good braking is evident from adjusting
> sidepull brakes so they have little pad clearance. They seem to have
> more power suddenly, when in fact it is the better handful the grip
> makes when it isn't nearly closed. Add to that a brake that doesn't
> flex and you have a large handful (two fingers) of brake available.
I've always assumed that the cyclicts' interpretation of the term
"sponge" involves flex of the brake arms and/or the pads themselves
(evident when there is a noticeable toe-in, depending on how thin the
pads); that is, once at least part of the pads are in contact with the
rim and some braking starts, and the brake levers are squeezed further,
corresponding further movement of the pads due to flexing of some part
of the system gives the "spongy" feeling. Pad clearance results merely
in changing brake lever travel before braking starts.
Carl Fogel
Dear Tim,
Chalo's brake may weigh less than you and I both
thought at first glance.
If you look at the front view carefully, the massive
front U-arm appears to have a deep, smoothly-machined
U-shaped indentation, making it more of a girder
than a solid billet bent into a U.
The close-up from the front also also exaggerates
the size of the brake--switch back and forth
between the close-up picture and the view from
the side and you get a better idea of the real
size.
It's still a substantial chunk of metal.
Of course, a few minutes with a drill press would
leave it looking like Swiss cheese from the front
and still almost as strong. (Well, a few minutes
for Chalo--I'd break the drills and ruin the piece.)
In any case, the extra weight may not matter as much
to a rider who weighs roughly as much as you and I
combined.
Carl Fogel
Werehatrack
said:
>RE/
>>some small, often purely subjective and somewhat
>>infrequent advantages in normal use which do not objectively outweigh
>>the high cost for most people.
>
>Depends on "normal use". If it includes much mud, discs definately have an
>advantage in that the rims don't get worn out.
True, but my observations of the folks riding locally would seem to
indicate that even in this sodden climate, "normal use" involves the
assiduous avoidance of mud for the vast majority of riders. For the
most common classes of user, then, that advantage does not seem to
apply.
(OTOH, there was a Wal-crap bike in the clearance bin at a Mall-wart
near Dallas which had clearly been ridden through the Abrasive Mud Pit
Of All Hells before it was returned to the store; the front rim's
walls were eroded at least half a millimeter. The rest of the bike
looked pristine. *That* bike could certainly have made good use of a
disc brake on the front, but given that it was only a $65 bike, I
doubt that it would have been sold to the abuser if it had been a
disc-equipped unit in the first place.)
--
My email address is antispammed; pull WEEDS if replying via e-mail.
Yes, I have a killfile. If I don't respond to something,
it's also possible that I'm busy.
Words processed in a facility that contains nuts.
Carl Fogel
>
[snip Chalo]
>
> The only thing you missed was getting some red Kool-Stop pads. . . .
> What you have conclusively proven, is that sponge is the enemy
> > I made the brake to replace a set of Avid Tri-Align brakes that I
> > had broken.
[snip]
> > The pads are Kool-Stop Thinline.
[snip]
> You should have done all this as a grade school bikie and saved yourself
> a lot of work by starting out with a better design on paper rather
> than in hardware. This takes too long. Each iteration being
> expensive and slow. Doing this on a CAD screen with the experience
> you have gained is rewarding... but don't let that stop you. We may
> yet benefit from some of these things.
>
> Jobst Brandt
Dear Jobst,
Well, since Chalo was already an impressively grown man
and replacing a broken set of brakes, he might have needed
a time machine to go back and design it in grade school,
not that a lot of grade schools hereabouts offer that
kind of shop class.
Given a machine shop and a broken bicycle rather than any
scheme to stand the manufacture of brakes on its head, the
Chalo Mark I looks pretty good.
Since it's powerful enough to bend ordinary frames with
Chalo's payload, further mechanical improvements may
satisfy the engineering soul, but are arguably of little
practical value unless they reduce weight, long-term wear,
or unexpected fragility.
It's nice that you both agree that sponge in the metal
parts of brakes is a problem, but I've already skidded
past the metal-arm side of braking and want to know:
What's the difference between the red (or salmon) Kool-Stop
brake pads that everyone seems to agree are the best anchors
available and Chalo's black Kool-Stop Thinline pads?
Are the red brake pads stickier, softer, harder, wider,
more expensive, shorter-lived, or what?
I seem to recall that you've explained that adding color
pigment to tire rubber gets in the way of the rubber and
traction (sorry if this is wildly inaccurate), so I'm
puzzled when the cheerful red brake pads outperform
the drab black ones. Are they getting better traction
on the rims?
I'm pretty sure (often a warning sign) that brake pads
aren't tires and that rims aren't pavement, but I don't
know enough to explain the difference. Should Kool-Stop
engineers get to work on their CAD screens and make me
some red tires?
Carl Fogel
jobst....@stanfordalumni.org
>> I wore out a front rim after about 13 years, but perhaps I ride in
>> more bad weather conditions? What was the failure mode when the
>> rim finally did go?
> The sidewalls bent outwards, making it difficult to fit tyres. I
> suppose eventually they would have ripped off, but nothing
> catastrophic happened before I noticed.
I don't think the sidewall bent. From my experience with rims wearing
out and from strength of materials considerations, once the sidewall
begins to yield, it will fail completely. That is, the tire will no
longer stay on the rim. What appears to be spreading of the rim walls
is really worn hollow cheeks. Measuring the inside width in
comparison to a new rim would verify that.
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
>> The only thing you missed was getting some red Kool-Stop pads.
>> However, what you have there is a brute force V-brake. Not having
>> a head-on view, I can't estimate its mechanical advantage but while
>> you were at it, you could have dropped the brake arm pivot point
>> another centimeter or two to reduce cosine error. What you have
>> conclusively proven, is that sponge is the enemy of good braking.
>> I assume the other dimensions are fairly standard.
> But dropping the pivot point means a longer arm, which increases
> bending moment and potentially flex. There needs to be a happy
> medium between pivot/pad length and mechanical advantage.
Only if you insist on staying with the flimsy levers conventional
brakes have. This is an experiment in brake design and getting rid of
a large cosine error is part of the problem. When riding in rapid pad
wear conditions, repositioning pads is not acceptable. Therefore,
deducing pad dive is important. Parallelogram links help greatly but
add complexity and clearances that could introduce chatter.
>>> I made a new fork brace, both to clear the 700c tire and to
>>> provide a new location for the brake pivots. Those pivots are
>>> 12.7mm (1/2") in diameter rather than the usual 8mm, and they fit
>>> more closely than the studs do in most cantilever or V brakes.
>>> They are brass for its improved bearing qualities against
>>> aluminum.
>> You should have dropped them down and extended the brake arms
>> proportionally up.
> Which might mean beefing up the arms to counteract the increased
> bending moment trying to flex the arm or pivot.
Yes, so what's wrong with that? It doesn't change the force at the
pivot unless the ME is changes. I didn't suggest that. In fact, with
a more rigid brake the ME could probably go back to 4:1 as in the days
of yore.
>> Well, that's one discovery I think many manufacturers never
>> made. That "sponge" is the enemy of good braking is evident from
>> adjusting sidepull brakes so they have little pad clearance. They
>> seem to have more power suddenly, when in fact it is the better
>> handful the grip makes when it isn't nearly closed. Add to that a
>> brake that doesn't flex and you have a large handful (two fingers)
>> of brake available.
> I've always assumed that the cyclists' interpretation of the term
> "sponge" involves flex of the brake arms and/or the pads themselves
> (evident when there is a noticeable toe-in, depending on how thin
> the pads); that is, once at least part of the pads are in contact
> with the rim and some braking starts, and the brake levers are
> squeezed further, corresponding further movement of the pads due to
> flexing of some part of the system gives the "spongy" feeling. Pad
> clearance results merely in changing brake lever travel before
> braking starts.
Yes, that's my take on that as well. However, it all eats up hand
lever travel and gets into the region of ones grip that isn't as
strong as when the lever is nearer its free position. One of the
features of dual pivot brake levers is that part of the return spring
is in the hand lever so that the caliper does not have to pull as
hard. This reduces cable tension in the pad-clearance take up stroke,
and therefore, reduces friction that makes the transition from free
travel to braking more distinct and also makes brakes lock up more
easily on application.
I was made more aware of this while walking a bicycle with these
brakes down a steep trail. The transition between rolling and wheel
lock-up was hard to control in comparison to my 4:1 Campagnolo Record
brakes as I reported in my tour report 2003.
Jobst Brandt
jobst....@stanfordalumni.org
jobst....@stanfordalumni.org
> What's the difference between the red (or salmon) Kool-Stop brake
> pads that everyone seems to agree are the best anchors available and
> Chalo's black Kool-Stop Thinline pads?
None, because the same material is available in that product line:
http://www.koolstop.com/brakes/#thinline
> Are the red brake pads stickier, softer, harder, wider, more
> expensive, shorter-lived, or what?
They have a more consistent friction coefficient and do not generate
aluminum particles as readily as other pads, such as those of the
major brake manufacturers or even other Kool-Stop pads.
> I seem to recall that you've explained that adding color pigment to
> tire rubber gets in the way of the rubber and traction (sorry if
> this is wildly inaccurate), so I'm puzzled when the cheerful red
> brake pads outperform the drab black ones. Are they getting better
> traction on the rims?
I don't know what goes into a brake pad. I just know that I stumbled
onto these years ago and had a hard time breaking brakes away from
their shiny metal brake show holders and onto Kool-Stop Continentals.
Now the salmon red compound is available in most inserts that they
offer. I am told that it is rouge (iron oxide) while the others do
not contain this material.
> I'm pretty sure (often a warning sign) that brake pads aren't tires
> and that rims aren't pavement, but I don't know enough to explain
> the difference. Should Kool-Stop engineers get to work on their CAD
> screens and make me some red tires?
The function of tire tread is well understood by the major tire
companies and it is tested in highly paid racing arenas. Brake pads
for bicycles are unique and do not have that kind of financial
backing. Where Kool-Stop got this compound is unclear to me, but I
got to them after trying Matthauser pads, the worst pads I used
because they melted and locked up on descents. Kool-Stop made salmon
pads for Matthauser after that. I still have one of these melting
pads as a memento. My riding pal recalls how close I was to hitting
the deck on that descent, skidding the front wheel in a fast turn.
Jobst Brandt
jobst....@stanfordalumni.org
jim beam
>>bending moment and potentially flex. There needs to be a happy
>>medium between pivot/pad length and mechanical advantage.
>
> Only if you insist on staying with the flimsy levers conventional
> brakes have. This is an experiment in brake design and getting rid of
> a large cosine error is part of the problem. When riding in rapid pad
> wear conditions, repositioning pads is not acceptable. Therefore,
> deducing pad dive is important. Parallelogram links help greatly but
> add complexity and clearances that could introduce chatter.
xt brake levers have an interesting mechanism that mitigates some of
this problem, at least at the lever end. basically, the cable is
anchored to a small roller that is free to move closer to the pivot
point the nearer the lever gets to the bar - effectively increasing the
mechanical advantage as the lever is pulled. i've not done the math on
it to see how much difference it really makes but when activated, it
seems to work really well and allows people with small hands and one
finger to stop on a dime.
jb
Chalo
I don't know. The bike it's attached to, which has similarly uprated
wheels, crank, BB, stem, bars, seat, etc., weighs 37 lbs ready to
ride.
That's without my special stainless steel pump, which weighs 2.2 lbs.
Chalo Colina
Tim McNamara
> The function of tire tread is well understood by the major tire
> companies and it is tested in highly paid racing arenas. Brake pads
> for bicycles are unique and do not have that kind of financial
> backing. Where Kool-Stop got this compound is unclear to me, but I
> got to them after trying Matthauser pads, the worst pads I used
> because they melted and locked up on descents. Kool-Stop made
> salmon pads for Matthauser after that. I still have one of these
> melting pads as a memento.
Were those the old Mathauser pads with the phony cooling fins on them?
I remember those looked cool, but I could never feel any indication of
them shedding heat. The pads and holders never got warmer than air
temp at all. Turns out, I am told many years later, that the brake
pad material is an insulator and doesn't conduct heat.
The current Mathauser design, referenced in the URLs earlier, aren't
removeable from the holders. The holders surround the pad on five
sides.
jobst....@stanfordalumni.org
>> The function of tire tread is well understood by the major tire
>> companies and it is tested in highly paid racing arenas. Brake
>> pads for bicycles are unique and do not have that kind of financial
>> backing. Where Kool-Stop got this compound is unclear to me, but I
>> got to them after trying Matthauser pads, the worst pads I used
>> because they melted and locked up on descents. Kool-Stop made
>> salmon pads for Matthauser after that. I still have one of these
>> melting pads as a memento.
> Were those the old Matthauser pads with the phony cooling fins on
> them? I remember those looked cool, but I could never feel any
> indication of them shedding heat. The pads and holders never got
> warmer than air temp at all. Turns out, I am told many years later,
> that the brake pad material is an insulator and doesn't conduct
> heat.
They were inserts for Campagnolo brake pad holders. The cooling fin
design convinced me that Matthauser was in fact not an engineer
capable of anything more than designing a brake caliper that looked
like pliers. I think he had no idea of how a friction pair works. Of
course that's the case with many others in the business who are not
aware of what insulating coatings on rims do to pad surface
temperatures.
> The current Matthauser design, referenced in the URLs earlier,
> aren't removable from the holders. The holders surround the pad on
> five sides.
I don't believe Mr Matthauser has anything to do with all that these
days. On the web, I notice that these are more than four times as
expensive than mainline brand inserts.
Jobst Brandt
jobst....@stanfordalumni.org
Chalo
> Chalo Colina writes:
>
> >> I had to make my own brakes for the other bike! They give me all
> >> the stopping power I can use.
>
> > http://home.comcast.net/~carlfogel/download/red_brake.JPG
> > http://home.comcast.net/~carlfogel/download/redfront.JPG
>
> The only thing you missed was getting some red Kool-Stop pads.
> However, what you have there is a brute force V-brake.
Yes, that's how it applies force to the rim. How it applies a LOT of
force to the rim has more to do with the integrated brace than with
the arms, though.
Later, I was able to apply my design principles to a normal V-brake
(Marinovative Cheap Trick) for a friend's trials bike. I made two
arches from 1/8" plate, bolted one behind the brake studs and the
other in front, with a screw and a standoff joining them together at
the top. The resulting system was much more powerful than the same
brake with a conventional booster.
> The problem is that the forks shown have an extra weak crown with
> respect to spreading from cantilevers. This crown should contain most
> of the metal that is in the brake bridge, going straight across to th
> other side. The whole design looks like a machinists make work, hewn
> from solid blocks of aluminum.
Your critique of the proportion of the fork crown to the fork brace
ignores the fact that this fork is telescopic; that if the legs are
not braced they will not only move up and down independently, but they
will also freely rotate about their axes. Furthermore, there is
necessary clearance between the fork stanchions and the fork bushings.
The structure in which the brake pivots are rooted is the fork brace
and not the fixed portion of the fork legs. The crown is actually
unable to contribute any of its rigidity to the brake pivots.
Therefore, the cross section of the fork crown "arms" is oriented to
match the applicable loads: large fore-to-aft and smaller laterally.
The crown was not more sophisticated due to the limitations at that
time of my CNC mill (2 axis, 1.5HP, no coolant) and my CAD/CAM system
(graph paper and a trig calculator).
> > I made a new fork brace, both to clear the 700c tire and to provide a
> > new location for the brake pivots.
>
> You should have dropped them down and extended the brake arms
> proportionally up.
I limited the total length of the arms so that they would not
intersect the downtube even if suspension pressure were lost. There's
a lot of inertia in the rotating assembly of my bikes, and I did not
want to bungle a non-replaceable frame I had just made dedicated parts
for.
I could have lowered the pivots more without lengthening the arms
above the pads. As it is, I can use up the limited pad thickness
without having to reposition the pads, so a flatter pad trajectory
would not help in that regard.
> > I made a booster arch that holds the fork arch at three points. The
> > former brake pivots were used to anchor the booster to the fork legs
> > for more extra additional bonus redundancy.
>
> Well the fork isn't contributing much, as bad as the crown is.
My chief motivation for bolting to the legs at the studs was that it
gave me another adhesive-bonded part to hold mechanically. I reckoned
if the thing were glued in four places and one broke loose, that would
be better than if it were glued in only two places. The fact that the
booster arch thus attached at 5 points instead of 3 was a bonus.
> Where are the pivots? What it the length ratio to regular V-brakes?
The pivots are brass sleeves over the 3/8" stainless socket head cap
screws whose heads protrude from the front. They are in the
neighborhood of 40mm below the rim sidewall, compared to about 25mm
for V-brakes. The upper arms are longer than those of V-brakes, but
not by much. I don't have the drawings handy, but the ratio of cable
travel to pad throw is about 3:1, which is about the lower end of the
possible leverage range for V-brakes.
> You should have done all this as a grade school bikie and saved yourself
> a lot of work by starting out with a better design on paper rather
> than in hardware.
The pictured system _is_ the better design, inasmuch as everything
else bent or broke or flexed too much or offered inadequate braking.
In the years since I built the system you see, I have changed only the
handlebars in order to get a different bend, and the fork internals.
It is the only front end in my big pile of bikes that doesn't want for
anything. Its only significant shortcoming is higher weight than most
other sytems, and I'll happily accept that to enjoy the benefits.
Chalo Colina
jobst....@stanfordalumni.org
>>>> I had to make my own brakes for the other bike! They give me all
>>>> the stopping power I can use.
http://home.comcast.net/~carlfogel/download/red_brake.JPG
http://home.comcast.net/~carlfogel/download/redfront.JPG
>> The only thing you missed was getting some red Kool-Stop pads.
>> However, what you have there is a brute force V-brake.
> Yes, that's how it applies force to the rim. How it applies a LOT
> of force to the rim has more to do with the integrated brace than
> with the arms, though.
I agree, rigidity is most of the battle and it seems to get ignored
most of the time.
> Later, I was able to apply my design principles to a normal V-brake
> (Marinovative Cheap Trick) for a friend's trials bike. I made two
> arches from 1/8" plate, bolted one behind the brake studs and the
> other in front, with a screw and a standoff joining them together at
> the top. The resulting system was much more powerful than the same
> brake with a conventional booster.
I don't know who invented the term "booster" but I guess we're stuck
with it. It's really a brake bridge that closes the force loop of pad
pressure rather than dump it into the fork blades that wold bind in
their compression without it. Even solid forks have suffered from
this with cantilevers spreading with brake force. Suspension brought
that to a head and it has been marginally addressed since.
>> The problem is that the forks shown have an extra weak crown with
>> respect to spreading from cantilevers. This crown should contain
>> most of the metal that is in the brake bridge, going straight
>> across to th other side. The whole design looks like a machinists
>> make work, hewn from solid blocks of aluminum.
> Your critique of the proportion of the fork crown to the fork brace
> ignores the fact that this fork is telescopic; that if the legs are
> not braced they will not only move up and down independently, but
> they will also freely rotate about their axes. Furthermore, there
> is necessary clearance between the fork stanchions and the fork
> bushings. The structure in which the brake pivots are rooted is the
> fork brace and not the fixed portion of the fork legs. The crown is
> actually unable to contribute any of its rigidity to the brake
> pivots.
Just the same the fore and aft forces tend to spread this crown, it
being a triangle with the front side missing. Bending loads on a
straight across crown would not be a problem at the cross section
used.
> Therefore, the cross section of the fork crown "arms" is oriented to
> match the applicable loads: large fore-to-aft and smaller laterally.
> The crown was not more sophisticated due to the limitations at that
> time of my CNC mill (2 axis, 1.5HP, no coolant) and my CAD/CAM
> system (graph paper and a trig calculator).
It looks that way, but I'm sure a straight across crown with a strut
back to the steering axis would be better in weight and rigidity. A
bit more reduction of the I-bean cross sections wouldn't hurt.
>>> I made a new fork brace, both to clear the 700c tire and to
>>> provide a new location for the brake pivots.
>> You should have dropped them down and extended the brake arms
>> proportionally up.
> I limited the total length of the arms so that they would not
> intersect the downtube even if suspension pressure were lost.
> There's a lot of inertia in the rotating assembly of my bikes, and I
> did not want to bungle a non-replaceable frame I had just made
> dedicated parts for.
As you mentioned below, you changed the pad operating radius. I
couldn't tell from the views shown.
> I could have lowered the pivots more without lengthening the arms
> above the pads. As it is, I can use up the limited pad thickness
> without having to reposition the pads, so a flatter pad trajectory
> would not help in that regard.
That's what I was getting at.
>>> I made a booster arch that holds the fork arch at three
>>> points. The former brake pivots were used to anchor the booster to
>>> the fork legs for more extra additional bonus redundancy.
>> Well the fork isn't contributing much, as bad as the crown is.
> My chief motivation for bolting to the legs at the studs was that it
> gave me another adhesive-bonded part to hold mechanically. I reckoned
> if the thing were glued in four places and one broke loose, that would
> be better than if it were glued in only two places. The fact that the
> booster arch thus attached at 5 points instead of 3 was a bonus.
>> Where are the pivots? What it the length ratio to regular V-brakes?
> The pivots are brass sleeves over the 3/8" stainless socket head cap
> screws whose heads protrude from the front. They are in the
> neighborhood of 40mm below the rim sidewall, compared to about 25mm
> for V-brakes. The upper arms are longer than those of V-brakes, but
> not by much. I don't have the drawings handy, but the ratio of
> cable travel to pad throw is about 3:1, which is about the lower end
> of the possible leverage range for V-brakes.
Sounds good. Now the package needs to get smaller without losing the
gains made. I think that can be done.
>> You should have done all this as a grade school bikie and saved
>> yourself a lot of work by starting out with a better design on
>> paper rather than in hardware.
> The pictured system _is_ the better design, inasmuch as everything
> else bent or broke or flexed too much or offered inadequate braking.
> In the years since I built the system you see, I have changed only the
> handlebars in order to get a different bend, and the fork internals.
> It is the only front end in my big pile of bikes that doesn't want for
> anything. Its only significant shortcoming is higher weight than most
> other systems, and I'll happily accept that to enjoy the benefits.
This project seems to support my thoughts on brakes in that a rigid
system is more important than a high ME one and without power brakes
we have only a limited stroke at the rim given by the reach of the
human hand. That's what makes this a difficult problem but one that
is just about within reach, so to speak.
Just think how much was wasted in the Campagnolo Delta brake that was
ultimately rigid but had a variable ratio ME, and terrible cosine
error to boot. When I see things like that, I wonder where all the
engineers went. This stuff is known outside the bicycle world but it
cant get in.
Jobst Brandt
jobst....@stanfordalumni.org
Chalo
> What's the difference between the red (or salmon) Kool-Stop
> brake pads that everyone seems to agree are the best anchors
> available and Chalo's black Kool-Stop Thinline pads?
The Kool-Stop "salmon" pads (actually more like brick-colored if you
ask me) use an iron-rich friction material invented and brought to
market by Mathauser back in days of yore. It has a terrific
combination of very high frictional coefficient, especially in the
wet, and very low abrasiveness combined with exceptional durability.
Mathauser faded into obscurity and was for all intents lost to the
marketplace for some time. Kool-Stop, whose own innovation had been a
brake pad molded around an aluminum plate which served as a heat sink,
licensed the Mathauser formula from the senescent company. Now
Kool-Stop makes Mathauser "salmon" pads alongside several other
formulations in their line.
If they were all the Mathauser formula, that would suit me fine. But
they offer other kinds, and sometimes the other kinds are all you can
get at your LBS when you go down there. Know what I mean?
To be fair, some brakes are eager to squeal, honk, scream, or
otherwise fuss when fitted with Mathauser/Kool-Stop salmon pads. A
few are so obstinate that some other, lesser brake pad must be
resorted to.
> Are the red brake pads stickier, softer, harder, wider,
> more expensive, shorter-lived, or what?
Stickier, harder, longer-lived.
Chalo Colina
Chalo
> Chalo's brake may weigh less than you and I both
> thought at first glance.
>
> If you look at the front view carefully, the massive
> front U-arm appears to have a deep, smoothly-machined
> U-shaped indentation, making it more of a girder
> than a solid billet bent into a U.
I machined the front arch into a channel shape and the rear one into
an I-beam shape. I arbitrarily chose .125" as a decent section
thickness, and wherever solid metal was not required for threads or
clamped areas, I machined reliefs into the sections until the
remaining webs were .125" thick.
I think the weight of this brake compares to that of a bicycle drum
brake-- it's lighter than an Arai drum, for instance. But it's safely
heavier than any caliper, cantilever, or V-brake ever made. It
performs well for me on a braking-energy-per-gram basis, though.
> It's still a substantial chunk of metal.
Oh yes.
The rear brake on that bike is a last-generation Pedersen Self
Energizing cantilever. It provides more than half the braking potency
of the front brake, while weighing less than half as much. It is much
more demanding to set up and much more temperamental than the big
brake, though.
Chalo Colina
Carl Fogel
Dear Jobst,
I browsed through the link that you provided at:
http://www.koolstop.com/brakes/#thinline
and things seem ever stranger.
First, I hadn't realized that red isn't the same
as salmon, but KoolStop eventually makes the distinction
quite clear and salmon is apparently what everyone
loves, not the different red--sorry about any
confusion of the two in my earlier post.
Second, KoolStop at least claims that the material is
different, way down at the very bottom of the long
page, with black being for dry condtions and salmon
for extreme wet, mud, and dry. (The other colors
are apparently good enough for government work,
being described as good for all conditions.)
Third, KoolStop offers two weird-looking hybrid pads,
again at the very bottom of the page, one with the
front half salmon and the back half black, "for a
fusion of the two finest compounds . . . for all
conditions," and another hybrid with black and a
yellow tip that KoolStop claims "eliminates chatter
and squeal as high friction compound makes contact
with the rim."
Am I right in thinking that these hybrids are the
triumph of marketing over engineering, or would you
expect a half-salmon, half-black pad to show any
advantages, or a low-friction yellow leading-tip to
quiet brake chatter and squeal?
Carl Fogel
jobst....@stanfordalumni.org
> Am I right in thinking that these hybrids are the triumph of
> marketing over engineering, or would you expect a half-salmon,
> half-black pad to show any advantages, or a low-friction yellow
> leading-tip to quiet brake chatter and squeal?
I've talked to the Kool-Stop folks every time I get to InterBike and
have gotten the feeling that they don't bring engineers to the show,
or maybe there are none to bring along. I have badgered them about
these pads and that the salmon colored ones are the only ones that I
found to work well, in all conditions, not as their ad material says.
They used to tout them as "For steel rims" and grey ones for aluminum.
Iron oxide is not bright red but the (salmon) color of polishing
rouge, iron oxide. If Kool-Stop Continental Salmon pads will fit your
brake, use them. It took me a long time to find pads that didn't
gouge my rims and that worked well under all conditions.
Jobst Brandt
jobst....@stanfordalumni.org
Mark Hickey
Hefty steer tubes for a 360 pound guy, I understand...
A custom-made brake that would stop a Harley, I understand...
But a 2.2 pound air pump?
Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame
Carl Fogel
Dear Mark,
A) Because it was not there, but now it is?
Machinists have a restless urge to make things.
There's the famous story of the fellow who made
the first hat turned on a lathe and used it to
win a job at the dawn of the Steam Age:
http://www.trainingscotland.i12.com/murdoch/timmer.htm
Since then, machinsts have been making bowler
hats on lathes in their idle moments. Chalo is
probably the only boy on his block with a stainless
steel pump that he built himself--I don't know about
you, but I'm simply jealous.
B) Would you like to be an ordinary hand-pump in
Chalo's paws? He can probably be quite delicate,
but it's easy to get carried away when pumping
up tires. Recall his cheerful phrase about
squeezing the bejeebers out of a front brake
lever and spend a moment in silent sympathy
for any equipment that he gives a workout.
C) At 37 pounds, the bike is about 10% of the rider's
weight--which corresponds to about 15-22 pounds for
about 95% of rec.bicycles.tech posters. So a 1 kg pump
that you and I might sweat to carry may be almost an
airy nothing to Chalo.
D) Chalo, got a picture of that pump?
Carl Fogel
Rado bladteth Rzeznicki
> It's not an invalid simplification, since the bending moment arms can be
> resolved along lines which are parallel to the radial line of the rotor.
Of course, but resolved components will be different. Take a look at
these calipers:
http://www.magura.com/english/pop/images/pop_louise_01.jpg
This is standard 160 mm Magura Louise. The force vector tangent to the
disc rim at the caliper center passes just below top mount. Therefore
normal component is quite small and so is bending moment. The distance
to the bottom mount is shorter, but normal component of the force is
significantly greater and bending moment as well.
Now, let's look at second scenario:
http://www.magura.com/english/pop/louise_fr_2002_pop.jpg
Pictured is 180 mm Magura Louise FR. No adapter here, but the caliper
is moved 10 mm away from the dropout. As you can see, the caliper is
simply rotated about top mount to compensate for larger disc diameter.
Here force vector passes almost exactly through the top mount and the
bending moment about it is even smaller than in previous case. As for
the bottom mount, the distance is significantly greater and normal
component of the force is also larger. Since the force itself is
smaller due to disc diameter difference, I would say that bending
moment about the bottom mount is approximately two times greater than
in 160 mm disc scenario. Yet, only failures I have seen were broken
tabs on older Marzocchi forks (silly thin mounting posts) or the whole
slider leg just above the caliper top mount. The latter, however, is
more likely with smaller diameter disc as it was probably proven on
this group before. Mounting posts on modern forks are IMHO quite beefy
and nicely recessed into slider leg, so I do not think they will brake
that easily. I asked leading fork manufactures about it, and according
to the replies, the restrictions are based not on increased bending
moments' issue, but on unfounded (and plainly wrong) fear of hub
ejection. This is obviously less probable with larger disc.
I do not have other picures at hand, but as you can see, the caliper
for larger rotor can be positioned everywhere as long as it passes
the disc properly. This location depends on adapter's shape and size.
The farther the caliper is from the mounting posts, the greater bending
moments get. Now, it is up to the adapter's designer.
Jose Rizal
> Jose Rizal wrote:
>
> > It's not an invalid simplification, since the bending moment arms can be
> > resolved along lines which are parallel to the radial line of the rotor.
>
> Of course, but resolved components will be different. Take a look at
> these calipers:
>
> http://www.magura.com/english/pop/images/pop_louise_01.jpg
>
> This is standard 160 mm Magura Louise. The force vector tangent to the
> disc rim at the caliper center passes just below top mount. Therefore
> normal component is quite small and so is bending moment. The distance
> to the bottom mount is shorter, but normal component of the force is
> significantly greater and bending moment as well.
You are resolving forces in irrelevant directions. Normal component of
the pad force doesn't matter; the load vector on each caliper mount
which counteracts the pad force, multiplied by the equivalent mount
length perpendicular to this counteracting force, is what gives the
bending moment on each mount. The equations in my analysis apply. In
the Magura brakes' case, bending moment on each mount is lower compared
to other forks since Lo is quite small.
> Now, let's look at second scenario:
>
> http://www.magura.com/english/pop/louise_fr_2002_pop.jpg
>
> Pictured is 180 mm Magura Louise FR. No adapter here, but the caliper
> is moved 10 mm away from the dropout. As you can see, the caliper is
> simply rotated about top mount to compensate for larger disc diameter.
> Here force vector passes almost exactly through the top mount and the
> bending moment about it is even smaller than in previous case. As for
> the bottom mount, the distance is significantly greater and normal
> component of the force is also larger. Since the force itself is
> smaller due to disc diameter difference, I would say that bending
> moment about the bottom mount is approximately two times greater than
> in 160 mm disc scenario. Yet, only failures I have seen were broken
> tabs on older Marzocchi forks (silly thin mounting posts) or the whole
> slider leg just above the caliper top mount. The latter, however, is
> more likely with smaller diameter disc as it was probably proven on
> this group before.
Maguras are unique in their fork mount arrangements. You will find that
other fork manufacturers have mounts which stick out more significantly
and hence have greater bending moments concern. This is also why Magura
is the only fork manufacturer I know which do not limit disc rotor size
on any of their forks.
> Mounting posts on modern forks are IMHO quite beefy
> and nicely recessed into slider leg, so I do not think they will brake
> that easily.
Thinking and knowing are two different things. For your sake I hope you
are right, but even then only Magura will honour your warranty.
> I asked leading fork manufactures about it, and according
> to the replies, the restrictions are based not on increased bending
> moments' issue, but on unfounded (and plainly wrong) fear of hub
> ejection.
Which ones did you ask? Fox and Answer both stated to me that it is the
increased stresses on the mounts with larger disc rotors that invalidate
their warranties.
> This is obviously less probable with larger disc.
>
> I do not have other picures at hand, but as you can see, the caliper
> for larger rotor can be positioned everywhere as long as it passes
> the disc properly.
Obviously. Anything can be better if the design is well though out.
> This location depends on adapter's shape and size.
> The farther the caliper is from the mounting posts, the greater bending
> moments get. Now, it is up to the adapter's designer.
No, it is up to the fork manufacturers to specify the adapter which they
are willing to incorporate into their warranty cover.
Zog The Undeniable
> I can't recall ever having worn out the brake track on a rim in >35
> years of riding bike. I've had some wheels that were in service on my
> road bikes for >20 years. Of course, I don't use pre-machined rims
> that have had 25-30% of the sidewall thickness removed before the rim
> was ever laced to a hub.
If you only ride in dry weather you are much less unlikely to wear out a
rim. In wet weather you pick up lots of grit and the aluminium dust
stays on the rim as a nice black grinding sludge. One day you're riding
along (hopefully not far from home) and your brakes catch because the
tyre pressure has split the paper-thin rim. Thankfully it's the rear
rim that tends to go first (assuming the rims are the same age), because
the rear wheel gets all the crud sprayed up from the front one, despite
not doing as much braking. A good case for a fixed wheel and no rear
brake in winter?
Zog The Undeniable
> If you dump too much heat into the system which holds your tyres on,
> you're going to blow tyres.
>
This is pretty unlikely unless you're running at excessive pressures
already - modern hook bead rims will cope with well over the
"recommended" pressure before the tyre pops off, and the overpressure
from a mountain descent is only about 25% [1]. Maybe this could be a
problem with an 18mm tyre and a wide-ish rim starting at 150psi - oops,
that describes one of my wheelsets! Tub cement melting on long
descents, leading to the tyres solling off in corners, *is* a real
problem in the mountains (and may account for the unimpressive
descending of many pro riders), but this applies to a miniscule
percentage of non-professional riders.
The best rationale I heard for disc brakes was that you could use a
disc-specific rim with no brake track, so it could be optimised to be
lighter or stronger, and with no need for surface hardness. However,
most disc-equipped bikes I see have rims with nicely machined surfaces
for their non-existent V-brakes ;-)
[1] John Forester did a descending test and couldn't even get his front
rim up to 200 deg F (366K), but if the tyres were filled at 20 deg C
(293K), the pressure at 200 deg F would only have been the ratio of the
Kelvin temperatures = 125% of the starting pressure. A mountain bike
tyre at 40psi is only going to reach 50psi at the bottom of a really big
mountain. Not an issue at all.
Tim McNamara
Yah, Jobst was making the same point, I think. Rims last a long time
for me for two reasons, one being not riding in the rain if I can
avoid it and the other being that I don't live or ride in mountainous
terrain. So I just don't use the brakes much.
I did used to fixed-gear in the winter, but don' thave a fixie right
now. I've got a single speed track bike with a Bendix coaster brake
hub in back, which is mucho fun to ride. Those hubs are remarkably
smooth when properly adjusted. FWIW, this wheel has the only anodized
rim on a rear wheel that hasn't failed within 2,000 miles from spoke
cracking- an MA-3. I attribute that to being a 36 spoke wheel with
zero dish, versus the 32 spokers I usually use with 7/8/9 speed.
I've seen one rim that split in this way, a friend who was a TT'er and
had part of the rim sidewall blow off. Fortunaely he was riding
rollers at the time, so it was rather dramatic but not particularly
inconvenient. I recall Chris Juden of the CTC bringing this issue up
in his articles for the CTC magazine- living in England (or Britain,
or the UK, or whatever is the correct name for it), he'd be riding in
the rain a lot I suspect and this problem may be more frequent in such
climates.
Tim McNamara
> Tub cement melting on long descents, leading to the tyres solling
> off in corners, *is* a real problem in the mountains (and may
> account for the unimpressive descending of many pro riders), but
> this applies to a miniscule percentage of non-professional riders.
I remember reading that Indurain used clinchers on mountain stages for
this reason.
jobst....@stanfordalumni.org
>> If you dump too much heat into the system which holds your tyres
>> on, you're going to blow tyres.
> This is pretty unlikely unless you're running at excessive pressures
> already - modern hook bead rims will cope with well over the
> "recommended" pressure before the tyre pops off, and the
> overpressure from a mountain descent is only about 25% [1]. Maybe
> this could be a problem with an 18mm tyre and a wide-ish rim
> starting at 150psi - oops, that describes one of my wheelsets!
> Tubular tyre cement melting on long descents, leading to the tyres
> rolling off in corners, *is* a real problem in the mountains (and
> may account for the unimpressive descending of many pro riders), but
> this applies to a miniscule percentage of non-professional riders.
The problem is not rolling off the rim as is often surmised, but
rather the tire creeping around the rim, piling up against the stem
and either blowing out there or making such a lump that it jams on the
fork crown. This I have seen and done. Tubular tires roll mainly
from side slip on loose traction and regaining traction. Otherewise,
there are no side forces on tires.
Clincher tires at below 100psi can be blown off rims, especially when
descending cautiously. At high speeds, not much energy goes into rims
because most is taken by wind drag, and rims are better cooled. I and
fellow riders have all had tire blow-offs, my latest one was a few
years ago while descending slowly, waiting for a friend who was taking
pictures.
> The best rationale I heard for disc brakes was that you could use a
> disc-specific rim with no brake track, so it could be optimised to
> be lighter or stronger, and with no need for surface hardness.
> However, most disc-equipped bikes I see have rims with nicely
> machined surfaces for their non-existent V-brakes ;-)
I don't see that much can be spared in rim weight by that rationale.
How would you prevent people from using them with rim brakes?
> [1] John Forester did a descending test and couldn't even get his
> front rim up to 200 deg F (366K), but if the tyres were filled at 20
> deg C (293K), the pressure at 200 deg F would only have been the
> ratio of the Kelvin temperatures = 125% of the starting pressure. A
> mountain bike tyre at 40psi is only going to reach 50psi at the
> bottom of a really big mountain. Not an issue at all.
I have crossed paths with Forester in accident reconstruction law
suits and found his testimony to be based on myth and lore. I have
little faith in his tests. I for on have generated steam from water
that got inside tubular tire rims while normally descending a mountain
pass with fast straight sections between hairpins.
Jobst Brandt
jobst....@stanfordalumni.org
jim beam
> I don't see that much can be spared in rim weight by that rationale.
> How would you prevent people from using them with rim brakes?
you don't prevent them. some shops commonly build disk wheels with
traditional rims because they're either cheaper or just happen to be
what they have in stock. and besides, as you will have seen here on
r.b.t, some people want dual-purpose wheels.
>>[1] John Forester did a descending test and couldn't even get his
>>front rim up to 200 deg F (366K), but if the tyres were filled at 20
>>deg C (293K), the pressure at 200 deg F would only have been the
>>ratio of the Kelvin temperatures = 125% of the starting pressure. A
>>mountain bike tyre at 40psi is only going to reach 50psi at the
>>bottom of a really big mountain. Not an issue at all.
>
> I have crossed paths with Forester in accident reconstruction law
> suits and found his testimony to be based on myth and lore. I have
> little faith in his tests. I for on have generated steam from water
> that got inside tubular tire rims while normally descending a mountain
> pass with fast straight sections between hairpins.
who won the lawsuit?
steam doesn't mean massively elevated temperatures. my tea is steaming
right now.
Chalo
> Simon Brooke wrote:
>
> > If you dump too much heat into the system which holds your tyres on,
> > you're going to blow tyres.
> >
> This is pretty unlikely unless you're running at excessive pressures
> already - modern hook bead rims will cope with well over the
> "recommended" pressure before the tyre pops off, and the overpressure
> from a mountain descent is only about 25% [1].
...
> [1] John Forester did a descending test and couldn't even get his front
> rim up to 200 deg F (366K). A mountain bike
> tyre at 40psi is only going to reach 50psi at the bottom of a really big
> mountain. Not an issue at all.
You ignore the fact that nylon and latex are not nearly as strong at
200F or even more elevated temperatures as they are at ambient temps.
The fact that your tire pressure might have gone up by 25% or 50%
would have a minor role in a blowoff resulting from thermal breakdown
of the casing.
Chalo Colina
jobst....@stanfordalumni.org
> who won the lawsuit?
His testimony was easily refuted. Either he is not aware of the cause
of some bicycle failures or he is prostituting himself for the
plaintiff. There are such people in the business, like John Howard
and Eugene Sloan and above all, Jim Green of North Carolina whose
testimony I had discredited without knowing what it was, mainly
because he testified against Huffy and Trek using the same evidence to
prove opposite conclusions. Even Forester finds fault with him:
http://www.johnforester.com/Consult/green_intro.htm
> steam doesn't mean massively elevated temperatures. my tea is
> steaming right now.
I think you are using the colloquial term for water vapor rather than
steam. I generated hissing steam (an invisible gas) rushing from the
valve stem hole while braking. At the heat of vaporization of water,
this requires substantial braking heat in the rim. Tandem riders and
shops that cater to tandem tourists can tell about many tire blow-offs
reported. I testified on such a case where the rider was trying to
sue the bicycle shop and rim manufacturer. That was an easy case once
I saw the evidence.
Jobst Brandt
jobst....@stanfordalumni.org
jim beam
> His testimony was easily refuted. Either he is not aware of the cause
> of some bicycle failures or he is prostituting himself for the
> plaintiff.
horror!! people /do/ such things??? in a court of law???!!!
> There are such people in the business, like John Howard
> and Eugene Sloan and above all, Jim Green of North Carolina whose
> testimony I had discredited without knowing what it was, mainly
> because he testified against Huffy and Trek using the same evidence to
> prove opposite conclusions. Even Forester finds fault with him:
>
> http://www.johnforester.com/Consult/green_intro.htm
>
>
>>steam doesn't mean massively elevated temperatures. my tea is
>>steaming right now.
>
>
> I think you are using the colloquial term for water vapor rather than
> steam.
yes.
> I generated hissing steam (an invisible gas) rushing from the
> valve stem hole while braking. At the heat of vaporization of water,
> this requires substantial braking heat in the rim.
true! my best example is disk brakes where the steel has gone blue with
heat. that's about 600F.
jb
Rado bladteth Rzeznicki
> Normal component of
> the pad force doesn't matter; the load vector on each caliper mount
> which counteracts the pad force, multiplied by the equivalent mount
> length perpendicular to this counteracting force, is what gives the
> bending moment on each mount.
Sorry, I still do not get it. Perhaps it is my English, perhaps we have
different mounting posts in mind or I am just missing something. Could
you draw a force diagram using Magura pictures? Thanks.
> Maguras are unique in their fork mount arrangements. You will find that
> other fork manufacturers have mounts which stick out more significantly
> and hence have greater bending moments concern.
You should have used past tense. Take a look at IS mounts on almost
every modern XC fork and you will see they are just like Magura tabs
- as close to the slider leg as possible, even Fox:
http://www.pinkbike.com/photo/pbpic114389.jpg
Curiously, caliper mounts on downhill forks, which are suitable for 8"
discs without question, usually stick out much more and nobody seems to
be worried by that:
http://www.magura.com/english/pop/images/pop_gustavm_02.jpg
> Which ones did you ask?
Marzocchi and... Fox (different guy?).
Jose Rizal
> Jose Rizal wrote:
>
> > Normal component of
> > the pad force doesn't matter; the load vector on each caliper mount
> > which counteracts the pad force, multiplied by the equivalent mount
> > length perpendicular to this counteracting force, is what gives the
> > bending moment on each mount.
>
> Sorry, I still do not get it. Perhaps it is my English, perhaps we have
> different mounting posts in mind or I am just missing something. Could
> you draw a force diagram using Magura pictures? Thanks.
"Normal" component means a component which is perpendicular to the
tangent. On a circle, normal to the circumference means a radial line.
On fork mounting posts, it doesn't make sense to refer to normal or
tangent unless you specify to what surface these apply.
> > Maguras are unique in their fork mount arrangements. You will find that
> > other fork manufacturers have mounts which stick out more significantly
> > and hence have greater bending moments concern.
>
> You should have used past tense. Take a look at IS mounts on almost
> every modern XC fork and you will see they are just like Magura tabs
> - as close to the slider leg as possible, even Fox:
>
> http://www.pinkbike.com/photo/pbpic114389.jpg
One example does not mean "almost every". Look at Manitou forks and you
will see just the opposite. XC Marzocchis also have mounts which stick
out.
You're missing the point that there is a significant increase in bending
moments when going from a 6" to an 8" rotor, no matter what mounting
arrangement there is. Granted that designs which have very short mounts
may be better able to cope with this increase, but manufacturers
skimping out on their warranties with users using larger rotors does not
inspire confidence that their designs are adequate.
> Curiously, caliper mounts on downhill forks, which are suitable for 8"
> discs without question, usually stick out much more and nobody seems to
> be worried by that:
>
> http://www.magura.com/english/pop/images/pop_gustavm_02.jpg
One doesn't have to worry about it if the section has been designed to
cope with the forces and moments involved. Most XC suspension forks
have been designed for rim brakes, with disc mounts being added only as
the latter became more popular. It's only the sturdier (and heavier)
fork models meant for downhill or "freeride" that seemingly have had
larger design loads considered, as 20mm thru axles and larger stanchions
indicate.
> > Which ones did you ask?
>
> Marzocchi and... Fox (different guy?).
I've been told the increased stress with larger rotors voiding XC
warranties reason by Answer and Fox long before the wheel ejection issue
became popular. I think you need to talk to their design, not
marketing, people. Even then be prepared to be told rhubarb.
Simon Brooke
another, so excuse me if I merge them to respond.
chump...@hotmail.com (Chalo) writes:
jim beam <u...@ftc.gov> writes:
> [Jobst Brandt had written]
>
> > I generated hissing steam (an invisible gas) rushing from the
> > valve stem hole while braking. At the heat of vaporization of water,
> > this requires substantial braking heat in the rim.
>
> true! my best example is disk brakes where the steel has gone blue
> with heat. that's about 600F.
I think we all agree that most bicycles operated in normal bicycling
conditions never achieve through braking a rim temperature which is
dangerous. However, it's also clear that in some extreme conditions,
specifically extended mountain descents, it does happen. Having a tyre
blow is nasty at the best of times and having it blow at speed or when
negotiating a difficult bend is particularly nasty.
So it seems to me that while disk brakes on bicycles may in many cases
be a fashion statement (as Tim has suggested), and do have a number of
clear disadvantages, there are nevertheless applications in which they
are the most sensible choice.
--
si...@jasmine.org.uk (Simon Brooke) http://www.jasmine.org.uk/~simon/
Morning had broken, and there was nothing left for us to do
but pick up the pieces.