please tell me all about braking
Carl Fogel
wheel-ejection thread that might be deserve their own
thread.
I asked what the basis is for an assumption of a
maximum braking on a typical disk brake mountain bike
of 0.6 g. That is, can we confirm this figure as
significantly low, reasonably correct, or significantly
high?
Obviously, the kind of tires, the slope of the ground,
the nature of the surface, and the details of the bike
(suspension, frame geometry, and rider position, for
example) may affect braking.
A clean start might help things, so I'll name no one.
Some early posters are now moving from theory to testing.
Others, like me, are merely waffling hopefully and looking
for answers.
First, what do we mean by braking? Stopping distance,
force in terms of g, practical measurements, or
theoretical calculations?
(I think that we're ignoring rider reaction time and
just talking about what happens after we actually drop
the anchor.)
Do bicycle-style disk brakes offer better braking than
rim-caliper brakes? Given the same bicycle and front
tire, how far will each kind need to stop from 20 mph
on flat dry pavement?
Do mountain-bikes with disk brakes and knobby tires
brake better, as well, or worse off-road than street
bikes with caliper brakes and thin tires on flat dry
pavement? Imagine two appropriate riders, side by side,
one on the street and the other on the dirt shoulder.
Who stops shortest?
For that matter, would mountain-bikes with disk brakes
and knobby tires brake better on the same flat dry
pavement than thin-tire caliper-brake street bikes?
Does a downhill slope affect braking? That is, does
it matter that the bike is already in a slightly
tipped-forward position? Does a downhill angle
affect traction? Does a bicycle braking from 20 mph
to 0 mph at the same rate require more braking force
and traction descending a slope than it would on
level ground? Does front (or rear) suspension affect
braking? Do rear brakes work better on downhills?
It might be well to test any theories involving slope
on uphills as well as downhills and level roads.
Details about skidding, tipping, tread, tire pressure,
gravel, and anything else to do with braking are welcome.
I only hope that we can avoid any spelling argument about
disk versus disc. As always, any links to tables or studies
would be nice.
Thanks,
Carl Fogel
Christopher Brian Colohan
> I asked what the basis is for an assumption of a
> maximum braking on a typical disk brake mountain bike
> of 0.6 g. That is, can we confirm this figure as
> significantly low, reasonably correct, or significantly
> high?
It sounds like the right ballpark to me. But please don't ask me to
do the math -- my last dynamics course was 11 years ago. :-)
> Do bicycle-style disk brakes offer better braking than
> rim-caliper brakes? Given the same bicycle and front
> tire, how far will each kind need to stop from 20 mph
> on flat dry pavement?
If you could apply them both smoothly, then they should be the same,
since both offer sufficient braking force to stop the wheel and go
into a skid. If one let you control the braking better, and avoid a
skid (which I hear disk brakes are good at), then that one might be
able to stop sooner.
On the other hand, if your traction is good enough that you will go
over the bars before your front tire will skid (which should be the
case on flat dry pavement) then this is not an issue. Both brakes
have more than enough force to make you do a faceplant.
> Do mountain-bikes with disk brakes and knobby tires
> brake better, as well, or worse off-road than street
> bikes with caliper brakes and thin tires on flat dry
> pavement? Imagine two appropriate riders, side by side,
> one on the street and the other on the dirt shoulder.
> Who stops shortest?
If the dirt was slippery and caused a skid, then the road rider stops
first. If the mountain biker got as good a grip on the dirt as the
road rider does on the road, then they should be the same.
> Does a downhill slope affect braking? That is, does
> it matter that the bike is already in a slightly
> tipped-forward position?
If this means the rider is in a slightly more tipped-forward position,
then yes, this affects braking. By moving the center of gravity
further forward you give the bicycle more leverage on the bicyclist,
meaning less braking force will be required to cause the rider to go
over the bars. If the bicyclist is able to lean far enough back (such
that they are in the same position as they are on level ground) then
this should not be an issue.
Also, when braking in a downhill the brakes are countering both the
force of gravity on the bike/bicyclist as well as reducing the
momentum of the bike/bicyclist, so you can not slow down as quickly as
on level ground.
> Does a downhill angle affect traction? Does a bicycle braking from
> 20 mph to 0 mph at the same rate require more braking force and
> traction descending a slope than it would on level ground?
To answer this properly you need to strictly define traction. I am
too tired to do this now. :-) My gut feeling is this: if by "same
rate" you mean "constant acceleration", on a downhill your brake has
to both counter the force of gravity (pulling you down the hill) and
reduce your velocity, which means it has to do more work. So more
braking force is required to slow you down at a fixed rate on a
downhill slope.
> Does front (or rear) suspension affect braking?
On perfectly flat pavement front suspension could cause the rider
position to shift slightly forward, which would make braking worse.
On rough ground front suspension could keep your wheel in contact with
the ground, which makes braking better.
> Do rear brakes work better on downhills?
No -- but if you use rear brakes you reduce the risk of the front
wheel skidding and hence a loss of steering control.
Chris
--
Chris Colohan Email: ch...@colohan.ca PGP: finger col...@cs.cmu.edu
Web: www.colohan.com Phone: (412)268-4751
S. Anderson
"Carl Fogel" <carl...@comcast.net> wrote in message
news:8bbde8fc.04032...@posting.google.com...
> I asked what the basis is for an assumption of a
> maximum braking on a typical disk brake mountain bike
> of 0.6 g. That is, can we confirm this figure as
> significantly low, reasonably correct, or significantly
> high?
I can't say really..I know motorcycles can stop in the 1g range, so I don't
think this number is wildly out of the question. It might be a little
high..1g is about 35km/h to 0km/h in 1 sec, right? (10m/s * 60s * 60m /1000
= km/h). So .6g is about 20km/h to 0 in 1 sec? I think that's a pretty
good braking feat..so maybe a bit high but not out of the question in
extreme situations and for brief periods of max deceleration.
> First, what do we mean by braking? Stopping distance,
> force in terms of g, practical measurements, or
> theoretical calculations?
I take braking to mean stopping distance. Decelerative g's are interesting,
but stopping distance decides whether you're going to hit the car or not! I
think you could use either, but g's, unless measured continuously, are hard
to judge stopping by. There is fade, the g's can vary up and down according
to conditions even within the stop. I'd use stopping distance.
>
> Do bicycle-style disk brakes offer better braking than
> rim-caliper brakes? Given the same bicycle and front
> tire, how far will each kind need to stop from 20 mph
> on flat dry pavement?
I think both are pretty equal in terms of braking force. Fade and
modulation are where the difference are between the two (ignore the
serviceability and wet-braking arguments I think for this discussion). I
can lift the rear wheel of my MTB when braking with v-brakes (you mentioned
"rim-caliper" but I'll throw v-brakes into that category..) and that's
pretty much max braking on a bicycle. So I don't think v-brakes are lacking
in stopping power. Fade and modulation..well, arguments could be made to
those. Modulation especially as that's pretty much the "feel" of the brake.
>
> Do mountain-bikes with disk brakes and knobby tires
> brake better, as well, or worse off-road than street
> bikes with caliper brakes and thin tires on flat dry
> pavement? Imagine two appropriate riders, side by side,
> one on the street and the other on the dirt shoulder.
> Who stops shortest?
Pavement bike. Simply more traction. I personally find it easier to
control my MTB while stopping quickly and that may mean I stop more quickly
on pavement than on a road bike, but I suspect it's simply due to comfort
level.
> For that matter, would mountain-bikes with disk brakes
> and knobby tires brake better on the same flat dry
> pavement than thin-tire caliper-brake street bikes?
I think this would be down to the available traction at the front wheel for
both. Brakes I don't think would make a difference, or not much.
>
> Does a downhill slope affect braking? That is, does
> it matter that the bike is already in a slightly
> tipped-forward position? Does a downhill angle
> affect traction? Does a bicycle braking from 20 mph
> to 0 mph at the same rate require more braking force
> and traction descending a slope than it would on
> level ground? Does front (or rear) suspension affect
> braking?
Downhill would affect braking. How much would be the debate. If your Cg is
already forward and you start braking, you would be able to use less braking
force before the rear wheel lifts. Therefore, you will have longer stopping
distances. You would actually have more traction at the front wheel but you
would also go over sooner. And since you are going downhill, you would
require more distance to stop since you're also countering gravity.
Suspension affects Cg and would alter the forward weight transfer and rear
wheel lifting accordingly.
> Do rear brakes work better on downhills?
No. Not from a braking distance perspective.
Sheldon Brown
> Some questions about braking arose in the disk-brake
> wheel-ejection thread that might be deserve their own
> thread.
>
> I asked what the basis is for an assumption of a
> maximum braking on a typical disk brake mountain bike
> of 0.6 g. That is, can we confirm this figure as
> significantly low, reasonably correct, or significantly
> high?
That's reasonably correct for bicycles of normal upright geometry. Has
nothing to do with whether it's a mountain bike nor whether the brakes
are discs.
With good brakes of any available type, the minimum braking distance
depends on traction and the angle formed between the front tire patch
and the center of gravity of the bike/rider.
> First, what do we mean by braking? Stopping distance,
> force in terms of g, practical measurements, or
> theoretical calculations?
All of the above.
> (I think that we're ignoring rider reaction time and
> just talking about what happens after we actually drop
> the anchor.)
>
> Do bicycle-style disk brakes offer better braking than
> rim-caliper brakes? Given the same bicycle and front
> tire, how far will each kind need to stop from 20 mph
> on flat dry pavement?
No difference.
> Do mountain-bikes with disk brakes and knobby tires
> brake better, as well, or worse off-road than street
> bikes with caliper brakes and thin tires on flat dry
> pavement? Imagine two appropriate riders, side by side,
> one on the street and the other on the dirt shoulder.
> Who stops shortest?
Road rider can stop shorter because the traction is better.
> For that matter, would mountain-bikes with disk brakes
> and knobby tires brake better on the same flat dry
> pavement than thin-tire caliper-brake street bikes?
The brakes make no difference, assuming they're in good condition, but
knobby tires get worse traction on hard surfaces, so the mountain bike
would have a longer stopping distance.
> Does a downhill slope affect braking? That is, does
> it matter that the bike is already in a slightly
> tipped-forward position?
Yes, because this steepens the angle between the
tire-patch/center-of-gravity.
> Does a downhill angle
> affect traction?
It does, it improves front traction and reduces rear traction.
> Does a bicycle braking from 20 mph
> to 0 mph at the same rate require more braking force
> and traction descending a slope than it would on
> level ground?
Yes, because the brake is working against both momentum and gravity.
> Does front (or rear) suspension affect
> braking?
In some conditions suspension can improve traction, mainly at higher speeds.
> Do rear brakes work better on downhills?
No, they work worse.
>
> It might be well to test any theories involving slope
> on uphills as well as downhills and level roads.
>
> Details about skidding, tipping, tread, tire pressure,
> gravel, and anything else to do with braking are welcome.
> I only hope that we can avoid any spelling argument about
> disk versus disc. As always, any links to tables or studies
> would be nice.
You might find my article on Braking and Turning enlightening:
http://sheldonbrown.com/brakturn
Sheldon "Friction" Brown
+-------------------------------------------------+
| Men and nations behave wisely once they |
| have exhausted all the other alternatives. |
| -- Abba Eban |
+-------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone 617-244-9772 FAX 617-244-1041
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com
jim beam
reasonable wost-case estimate; it's the /underestimation/ of pull-out
force necessary to cause ejection that's not being addressed properly.
pull-out is dramatically affected by the serrations manufacturers put on
their axle facings. these create corresponding indentations on the
relatively soft fork material of the mtb fork - easy to see with the
naked eye. so now, assuming a properly clamped skewer, pull-out has to
overcome not simple friction, but material shear.
the force necessary to shear through only 25mm^2 of serration
engagement, [a conservative estimate given that a shimano xt mtb disk
hub has a minimum outside serrated face diameter of 17mm & an inside of
13mm - you check the math] and assuming a very conservative shear stress
of only 200N/mm^2 for the fork material, would be over 5,000N.
suddenly, the 1825N pull-out force supposed to be generated by a disk
brake is insufficient to be any major worry. and that's /before/ any
consideration of factors that would reduce it like lack of traction,
blah blah blah blah blah blah.
it's late. and this debate has a cT of 0.9.
meb
56-.57 g is the nominally cited road bike decel rate before endo.
If you lower cg or move the mass backwards on a bike, you don’t see a
huge increase because you aren’t that much away from the limits of
adhesion for a road bike tire on pavement. A mountain bike tire would
have less adhesion than the road bike. LWB and MWB recumbents and
tandems will have higher decel rates since 1endos are removed from the
braking limits and adhesion will become the new limiting factor.
Lowracers with their low cg resulting in a small moment about the front
patch will have a more optimal weight distribution for adhesion.
Unless specified otherwise, decel rate in G’s is the most frequent and
practical criterion for comparative measurement because all others are a
function of either speed and/or weight. Decel reate is a near constant,
so stopping time is a product of speed and decel rate. Stopping distance
is proportional to the square of speed over stopping time. Force is mass
times decel rate. Another measure includes heat dissipation rate
(measured in watts) for downhill situations in which you are pressing
the BRAKE’S heat dissipation limits, and still another measure heat
dissipated.
Disc brakes are more resistant to the effects of the elements than rim
brakes such as rain, dirt, mud or snow and for that reason are favored
in mountain bike use. The lighter weight rim brakes are preferred for
road bikes. Discs can be more effective whenever brakes become a
limiting factor such as long downhills, particularly with tandems or
recumbents.
The reason a mountain bike tire has less adhesion on dry pavement that
a road tire are: 1) those gaps in the rubber are no longer abutting
portions of the road- the flexible rubber conforms to the small
dimples and irregularities in the pavement providing additional side
resistance in the direction of decel 2) the knobs sometimes add some
small bumping of the tire off the road reducing contact and contact
forces with the road.
If front and rear tires are identical, optimal braking occurs when the
dynamic weight (not the standing weight) on each tire is equal. From a
practical standpoint, the further back you get the weight the more even
the dynamic tire weight distribution in a high decel condition. The
notable exception can be a long wheelbase lowracer recumbent which can
actually achieve a static weight distribution far enough back to be
beyond optimal in a likely overly optimistic .8 g decel.
On a downhill, front traction is improved less than rear traction is
degraded. 3 reasons: the gravity downforce on each the tire is reduced
by: 1-cosine (slope angle) so the friction is reduced, with net of the
tire pair reduced by this amount even though there will be more front
traction on mild downgrades; a rearward force is added to the bike from
the slight downgrade equal to the mass times g times the sine (slope
angle); weight is transferred to the front tire from the rear tire
deviating further in high decel conditions from the optimal equal weight
distribution (excepting the long wheelbase lowracer).
Suspension can help braking by maintaining constant force on the tires
which in turn maintain a constant footprint when traversing road
undulations even small ones thereby eliminating pitching the bike up and
down-even if vertical pitching is so slight as to not be humanly
perceptible. Suspension can adversely effect braking because: upon
initial application, the bike and rider pivot forward relative the tires
creating a latency before the bike and rider start slowing down; also
the bike-rider combination can start harmonically oscillating on their
rotation path adding components in yaw axis and roll axis directions
which will reduce braking effectiveness.
--
Zog The Undeniable
The disc (disk) [1] brake starts off at a disadvantage because it's such
a small diameter. A lot more frictional force is needed than with rim
brakes to get the bike to slow down at the same rate (open a door by
pushing on the hinge edge and you'll see what I mean). This means the
pads have to be run close to the rim so that an actuation mechanism with
high mechanical advantage can be used. A good choice of pad and disc
material can also add to friction, but my school physics tells me this
can never exceed the squeezing force applied by the caliper, do the
latter is the limiting factor.
Against this you have the advantage that they stay out of the mud, are
stiffer so they run more true, and allow rim designs that aren't
compromised by the need for a flat braking track. The latter is,
however, rarely exploited on production bikes.
[1] Did you know that a digital Compact Disc is always spelt with a "c"
even in the US? The spelling is part of the Philips/Sony "Red Book"
standard...
James Annan
> pull-out is dramatically affected by the serrations manufacturers put on
> their axle facings. these create corresponding indentations on the
> relatively soft fork material of the mtb fork - easy to see with the
> naked eye. so now, assuming a properly clamped skewer, pull-out has to
> overcome not simple friction, but material shear.
>
> the force necessary to shear through only 25mm^2 of serration
> engagement, [a conservative estimate given that a shimano xt mtb disk
> hub has a minimum outside serrated face diameter of 17mm & an inside of
> 13mm - you check the math] and assuming a very conservative shear stress
> of only 200N/mm^2 for the fork material, would be over 5,000N.
> suddenly, the 1825N pull-out force supposed to be generated by a disk
> brake is insufficient to be any major worry. and that's /before/ any
> consideration of factors that would reduce it like lack of traction,
> blah blah blah blah blah blah.
Nevertheless, it moves. Not always, but not never either.
James
Tom Sherman
> ...
> The disc (disk) [1] brake starts off at a disadvantage because it's such
> a small diameter. A lot more frictional force is needed than with rim
> brakes to get the bike to slow down at the same rate (open a door by
> pushing on the hinge edge and you'll see what I mean). This means the
> pads have to be run close to the rim so that an actuation mechanism with
> high mechanical advantage can be used. A good choice of pad and disc
> material can also add to friction, but my school physics tells me this
> can never exceed the squeezing force applied by the caliper, do the
> latter is the limiting factor.
However, as the wheel diameter decreases, the effective braking force
available from brakes that act at the hub (disc and drum) is increases,
and the rim diameter/disc diameter ratio is of course much smaller.
> Against this you have the advantage that they stay out of the mud, are
> stiffer so they run more true, and allow rim designs that aren't
> compromised by the need for a flat braking track. The latter is,
> however, rarely exploited on production bikes.
There are now rims being made for trikes that do not have a rim braking
surface. (All but the cheapest trikes use hub brakes).
--
Tom Sherman - Quad Cities (Illinois Side)
Rick Onanian
wrote:
>Do bicycle-style disk brakes offer better braking than
>rim-caliper brakes? Given the same bicycle and front
>tire, how far will each kind need to stop from 20 mph
>on flat dry pavement?
Here's the thread I mentioned where I had questioned braking:
http://groups.google.com/groups?&threadm=2Pk*P10aq%40news.chiark.greenend.org.uk
David Damerell does a great job of summing it up in a single
message.
--
Rick Onanian
Rick Onanian
<hroth...@yahoo.com> wrote:
>[1] Did you know that a digital Compact Disc is always spelt with a "c"
>even in the US? The spelling is part of the Philips/Sony "Red Book"
>standard...
Disc brakes have sometimes been spelled with a 'c' in the US for 25
years, at least. I remember a 1978 Chevy dumptruck whose brake pedal
said "Disc brakes" on it, and a 1990 GMC dumptruck that may have
said the same. The memory is a bit fuzzy, me having been a child,
but I remember my fascination with the 'c' spelling.
--
Rick "Fuzzy memories" Onanian
Chris Zacho The Wheelman
bike than any other kind, as far as actual power is concerned. The
surface the tires are traveling is the deciding factor there.
The main advantage is water and mud, because these brakes are mounted on
the hub, away from these contaminants. Also, they offer a better "feel"
than calipers, thereby offering more precise control. A plus for braking
on road/trail surfaces offering questionable traction.
As for tandems bikes, this is a different story. These bikes, because of
their greater weight to frontal area ratio, require much more braking on
downhills, lest they get going too fast. Here the main advantage is rim
heating. Again, solved by the mounting f the stopping surface on the
hub.
I have discs on my ATB, and they stop no faster or slower then my linear
pulls on my road tourer.
- -
"May you have the wind at your back.
And a really low gear for the hills!"
Chris Zacho ~ "Your Friendly Neighborhood Wheelman"
Chris'Z Corner
http://www.geocities.com/czcorner
G.T.
"Chris Zacho "The Wheelman"" <Chrisz...@webtv.net> wrote in message
news:25914-40...@storefull-3173.bay.webtv.net...
> Disc brakes, on mountain bikes, are really no better at _stopping_ the
> bike than any other kind, as far as actual power is concerned. The
> surface the tires are traveling is the deciding factor there.
>
> The main advantage is water and mud, because these brakes are mounted on
> the hub, away from these contaminants. Also, they offer a better "feel"
> than calipers, thereby offering more precise control. A plus for braking
> on road/trail surfaces offering questionable traction.
>
They also take less effort to stop with, I can leave three fingers and my
thumb wrapped around the grip with discs which is important to relieve hand
fatigue on long, bumpy descents.
Greg
ZeeExSixAre
> can lift the rear wheel of my MTB when braking with v-brakes (you
mentioned
> "rim-caliper" but I'll throw v-brakes into that category..) and that's
> pretty much max braking on a bicycle.
Absolutely not. You can lift the rear (brake-only) on ANY
properly-maintained bicycle, and yet be nowhere near maximum braking. You
have to lean almost as far back as you can, almost to the point where the
front wheel would rather skid than hold, before you can reach maximum
deceleration.
Sheldon explains it well... body position is absolutely critical to
acheiving optimal braking performance.
--
Phil, Squid-in-Training
ZeeExSixAre
> gravel, and anything else to do with braking are welcome.
Carl, I feel that braking can be summed up easily:
1. More braking power can be effected with a farther-back handlebar
position. Ergo, mountain bikes are inherently better brakers than road
bikes with drop bars. This is also due to the obviously more perpendicular
brake-lever action of the flat bars. You can get perpendicular in the
drops, but this puts you farther forward over the front wheel, decreasing
your braking effectiveness.
2. All recent brake designs have enough power for either skidding the front
wheel or flipping the rider over the bars, disc or caliper (don't know about
hub brakes)
3. On pavement, the front brake is always the primary brake, except in wet,
sandy, icy conditions. This includes downhills. Thus, road bikes should
primarily use the front brake.
4. Off-road on MTB, the front brake either tends to take the backseat or
works more so in conjunction with the rear brake, as front-wheel slideouts
while turning are more common in loose sand, leaves, pine needles, etc. and
often unrecoverable. Sliding the rear, as we all know, rarely ends in a
crash.
4. Straight offroad extreme-angle short downhills (> 70 degrees) on MTBs can
be descended initially with both brakes, and then usually with the rear
throughout. It requires more skill than most have, though.
--
Phil, Squid-in-Training
Tom Sherman
Or you can ride a bicycle that puts the seat close to the ground and
near the rear wheel, so the angle (relative to the ground) from the
front tire contact patch to the combined bicycle/rider center of mass is
small.
G.T.
>>Details about skidding, tipping, tread, tire pressure,
>>gravel, and anything else to do with braking are welcome.
>
>
>
> works more so in conjunction with the rear brake,
That's a bit of a stretch, the front brake is still the primary brake. If
you're using more rear than front you're not braking very efficiently. The
exception is your 2nd number 4, very steep pitches..
Greg
jim beam
and if you feel rejected because you're only trying to save fools from
themselves, don't. it's called evoluton.
James Annan wrote:
<snip>
James Annan
> you're crying wolf.
No, just quoting Lennard Zinn, among others.
Ok, it wasn't a direct quote. But this is:
"I have noticed on my own mountain bikes, all of which have disc brakes,
that if I use a skewer where the lever is aluminum with an off-center
hole at its rounded end to create the cam, I get downward movement of
the axle in the dropout. After riding, I notice this by flipping the
front skewer open when the bike is standing on its wheels. If the fork
drops down a bit to clunk back down onto the axle, I know that that hub
moved down in the dropout while riding."
Lennard Zinn, author of "Zinn and the art of mountain bike maintenance"
(and other books), and also various technical Q&A columns in cycling
publications.
Shame none of the manufacturers seem to read him.
James
ZeeExSixAre
> you're using more rear than front you're not braking very efficiently.
The
> exception is your 2nd number 4, very steep pitches..
Now that I think about it, I agree. The case with me is that I don't
usually brake unless I'm in a turn, though. Therefore, most of my braking
is with the rear. However, after a long straight downhill before a turn,
then yes, both the front and rear come into play.
--
Phil, Squid-in-Training
jim beam
yesterday, i passed a mtb rider and noticed his front q.r. lever
dangling & swinging back & forth. clearly, it was not tight so only
lawyer lips were holding his wheel in. so i stopped him and told him of
his problem. and i learned two things:
1. he was pissed for my not minding my own business.
2. he was happy with the notion that the q.r. was just a fancy lever
for twiddling the thread against the thumb screw.
bottom line, he didn't want to know - "finger tight" was good enough.
and he'd "never had a problem".
so james, should i launch on a crusade to try & enlighten the ignorant
across the nation? should i campaign for legislation to save fools from
themselves? or should i just let darwin take care of those unwilling to
read the instructions?
as far as your "fork design flaw" theory is concerned, my opinion is
that lawyer lips take care of everything, even my friend above.
as far as your q.r. skewer design comments are concerned, zinn is just
confirming what sheldon & others have been saying for ever - the
enclosed cam design of shimano & campy is superior and utterly reliable.
period.
i /have/ had a q.r. slip, on the rear of a road bike. it was a ritchey
ocr wheel with a ti "open cam" skewer, and it just wouldn't hold.
interestingly, the axle did not have the same axle facing serration
design as the campy or shimano i usually use, and the frame has
horizontal steel ends, not aluminum, so they weren't taking the bite.
after two rides with slippage, i took it all back to the shop & got my
money back. but guess what? as i was packing it all back into the box,
at the bottom, there was a little note: "not designed for use with
horizontal dropouts". so, was this design flaw or darwin?
Mike Jacoubowsky
> dangling & swinging back & forth. clearly, it was not tight so only
> lawyer lips were holding his wheel in. so i stopped him and told him of
> his problem. and i learned two things:
>
> 1. he was pissed for my not minding my own business.
> 2. he was happy with the notion that the q.r. was just a fancy lever
> for twiddling the thread against the thumb screw.
>
> bottom line, he didn't want to know - "finger tight" was good enough.
> and he'd "never had a problem".
>
> so james, should i launch on a crusade to try & enlighten the ignorant
> across the nation? should i campaign for legislation to save fools from
> themselves? or should i just let darwin take care of those unwilling to
> read the instructions?
That's why it's my job, on every bike I sell, to demonstrate how tight a
quick release needs to be to work properly, and to show that you don't screw
them on (just twist them, without using the cam). If I assume that somebody
who's been riding for a long time knows this, I'm frequently assuming
WRONGLY.
We see such bikes (with improperly-tightened QRs) coming in all the time for
repair, and the standing rule (often overlooked) is that a note must be
placed on the tag and the owner shown how it works when the bike is picked
up.
In my opinion, QRs work very well, when used properly. Unfortunately, it's
far too easy to use them improperly. It's definitely a design in need of
improvement, not because they don't work, but because it's apparent that
proper use is not intuitive to many people.
--Mike-- Chain Reaction Bicycles
http://www.ChainReactionBicycles.com
G.T.
>>That's a bit of a stretch, the front brake is still the primary brake. If
>>you're using more rear than front you're not braking very efficiently.
>
> The
>
>>exception is your 2nd number 4, very steep pitches..
>
>
> Now that I think about it, I agree. The case with me is that I don't
> usually brake unless I'm in a turn, though.
You should always brake before the corner. If you have a blind decreasing
radius corner than braking mid-turn is understandable. But if you usually
brake in a turn, well, you're not anticipating very well.
Greg
Mark Hickey
>We see such bikes (with improperly-tightened QRs) coming in all the time for
>repair, and the standing rule (often overlooked) is that a note must be
>placed on the tag and the owner shown how it works when the bike is picked
>up.
>
>In my opinion, QRs work very well, when used properly. Unfortunately, it's
>far too easy to use them improperly. It's definitely a design in need of
>improvement, not because they don't work, but because it's apparent that
>proper use is not intuitive to many people.
It's not hard to see why the CPSC and fork manufacturers would be
skeptical of a new "skewer unscrewing claim" - given the fact that
lots and lots of people are out there riding around with their skewers
improperly adjusted.
Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $695 ti frame
James Annan
> as far as your q.r. skewer design comments are concerned, zinn is just
> confirming what sheldon & others have been saying for ever - the
> enclosed cam design of shimano & campy is superior and utterly reliable.
> period.
I don't believe that Sheldon has ever said or implied that anyy skewer
in "utterly reliable", even in the narrow context of slipping under the
load of a disc brake. He has said they are more reliable, which appears
to be true. Although pointing the finger at the skewer seems misplaced
since the fault is in the fork design. If the skewers are faulty, then
they should not be sold, but if they are in fact fully up to normal
standards then the problem is in a design which expects too much of them.
That aside, I'm interested in exploring in a bit more detail your
comments about the knurling biting into the dropout and causing damage
when it moves. I believe Jose Rizal also thinks that this disproves
everything I have said. How different would this damage be from the
general wear and tear of a soft metal dropout?
FWIW, although you used "a very conservative shear stress of only
200N/mm2" in your calculations, the first two references I googled on
gave about 140 for magnesium. Perhaps a different alloy or something,
but I was surprised at the discrepancy.
James
jim beam
>>yesterday, i passed a mtb rider and noticed his front q.r. lever
>>dangling & swinging back & forth. clearly, it was not tight so only
>>lawyer lips were holding his wheel in. so i stopped him and told him of
>>his problem. and i learned two things:
>>
>>1. he was pissed for my not minding my own business.
>>2. he was happy with the notion that the q.r. was just a fancy lever
>>for twiddling the thread against the thumb screw.
>>
>>bottom line, he didn't want to know - "finger tight" was good enough.
>>and he'd "never had a problem".
>>
>>so james, should i launch on a crusade to try & enlighten the ignorant
>>across the nation? should i campaign for legislation to save fools from
>>themselves? or should i just let darwin take care of those unwilling to
>>read the instructions?
>
>
> That's why it's my job, on every bike I sell, to demonstrate how tight a
> quick release needs to be to work properly, and to show that you don't screw
> them on (just twist them, without using the cam). If I assume that somebody
> who's been riding for a long time knows this, I'm frequently assuming
> WRONGLY.
>
> We see such bikes (with improperly-tightened QRs) coming in all the time for
> repair, and the standing rule (often overlooked) is that a note must be
> placed on the tag and the owner shown how it works when the bike is picked
> up.
new shimano hubs come with such a tag attached to the q.r. too. mike,
it's great someone cares.
>
> In my opinion, QRs work very well, when used properly. Unfortunately, it's
> far too easy to use them improperly. It's definitely a design in need of
> improvement, not because they don't work, but because it's apparent that
> proper use is not intuitive to many people.
this is the crux of the issue. but how far do we go with this? we all
take a driving test to make sure we have the basic skills necessary for
the task, yet we've all see people competing for darwin awards with the
way they drive. how about construction sites? foundries? and of
course, kitchen implements. now /there's/ a dangerous working
environment...
personally, i think good quality q.r's to be far superior to any solid
axle/nut design, and based on the many millions of rider miles since
their introduction, they are sufficiently intuitive for /most/ people.
this is really the only practical way of addressing the issue, not
mandating a radical overhaul of the entire industry because of the
/chance/ of failure.
example: the lug nuts on large commercial vehicles have l/h threads on
the left side and r/h threads on the right side. this is to prevent the
nuts loosening under high load, just like pedal threads. presumably, we
all agree this is a good idea. so why don't manufacturers use l/h
threads on the left side of passenger cars & light trucks? the same
loosening principle applies to them as it does for heavy vehicles... so
what's up?
the answer is that, in practice, light vehicles almost /never/ have a
problem, unless the nuts are not torqued to spec. and even then, on a
light vehicle, you notice pretty much straight away and can stop before
the wheel falls off. a loose wheel on the rear of a big rig of course,
you'd never know until separation.
so, the practical reality is, based on the huge number of items in use,
and their extensive daily deployment, either q.r's or lug nuts, are
/not/ a statistical problem. and the benefits of q.r's and the ease
with which you can change wheels without tools, is quite excellent.
ZeeExSixAre
"G.T." <getn...@dslextreme.com> wrote in message
news:oaH9c.15756$CI6....@newssvr27.news.prodigy.com...
Haha... I misstated that again. Yes, braking before the turn so as to have
both wheels as firmly planted on the ground as possible. And if need be,
additional rear braking during the turn itself.
--
Phil, Squid-in-Training
jim beam
> jim beam wrote:
>
>
>> as far as your q.r. skewer design comments are concerned, zinn is just
>> confirming what sheldon & others have been saying for ever - the
>> enclosed cam design of shimano & campy is superior and utterly reliable.
>> period.
>
>
>
> I don't believe that Sheldon has ever said or implied that anyy skewer
> in "utterly reliable", even in the narrow context of slipping under the
> load of a disc brake. He has said they are more reliable, which appears
> to be true. Although pointing the finger at the skewer seems misplaced
> since the fault is in the fork design. If the skewers are faulty, then
> they should not be sold, but if they are in fact fully up to normal
> standards then the problem is in a design which expects too much of them.
get over it james. planes kill people. is flying fundamentally wrong?
the fact is, as we've discussed before, q.r's do /not/ suffer any
serious pull-out problems when properly deployed on disk brakes.
otherwise all the calls & enquiries i made after your first post on this
subject would have turned up a positive result. but it didn't then, and
hasn't since, so, with respect, you're outside the curve.
>
> That aside, I'm interested in exploring in a bit more detail your
> comments about the knurling biting into the dropout and causing damage
> when it moves. I believe Jose Rizal also thinks that this disproves
> everything I have said. How different would this damage be from the
> general wear and tear of a soft metal dropout?
"damage" is an emotive term. the "bite" /is/ a design feature. just
like the bite when the cable clamp on my brake calipers gets indented by
the cable.
if you're asking whether general repeated clamping & unclamping will
cause wear & tear over time, yes it will, but that is unlikely to cause
any reduction on the pull-out force. if anything, it will make pull-out
harder, not easier because indentations will get deeper.
>
> FWIW, although you used "a very conservative shear stress of only
> 200N/mm2" in your calculations, the first two references I googled on
> gave about 140 for magnesium. Perhaps a different alloy or something,
> but I was surprised at the discrepancy.
ok, so 25mm^2 x 140N/mm^2 = 3500N. still not a problem. to be honest,
i have no idea /which/ "magnesium" alloy is used in which fork, but
let's assume it's not something /too/ cheap & rubbishy. again, i can't
say this is the case with forks, but in the automotive industry, not all
alloys billed as magnesium are that. most are predominantly aluminum
with a magnesium component.
best
jb
>
> James
>
>
Tom Sherman
> That's why it's my job, on every bike I sell, to demonstrate how tight a
> quick release needs to be to work properly, and to show that you don't screw
> them on (just twist them, without using the cam). If I assume that somebody
> who's been riding for a long time knows this, I'm frequently assuming
> WRONGLY.
>
> We see such bikes (with improperly-tightened QRs) coming in all the time for
> repair, and the standing rule (often overlooked) is that a note must be
> placed on the tag and the owner shown how it works when the bike is picked
> up.
>
> In my opinion, QRs work very well, when used properly. Unfortunately, it's
> far too easy to use them improperly. It's definitely a design in need of
> improvement, not because they don't work, but because it's apparent that
> proper use is not intuitive to many people.
And I thought it was silly that the QR lever had "open" and "close"
inscribed on it - it is ridiculously obvious how the thing works.
Since I am in a cranky mood, I am of the opinion that if people can not
figure out a QR lever, then that is their problem. I do believe however,
that QR's should be of the internal cam rather than exposed cam design
(as the superiority of the internal cam design is not immediately obvious).
James Annan
> if you're asking whether general repeated clamping & unclamping will
> cause wear & tear over time, yes it will, but that is unlikely to cause
> any reduction on the pull-out force. if anything, it will make pull-out
> harder, not easier because indentations will get deeper.
Yes, I've certainly heard from people who say they have significant
indents in the dropout which interlock well with the skewer (and
presumably the same is possible with the hub, although harder to
notice and IME hub locknuts are often more just rough than really
deeply serrated.
Obviously these people do not experience wheel movement (at least,
they have not yet) and this will be one factor which separates the
failures from the rest. Just checking on my (rim-braked) bikes I see
that there is minimal damage to the hard steel dropouts and in fact
there is even still quite a lot of paint (albeit crimped and damaged)
on the fork ends of the less-used bike. I have no QR suspension forks
to examine and experiment with right now.
But I'll get to my point. I'm trying to work out exactly what you are
talking about in terms of damage that you would expect from skewer
slip and not from general wear and tear. Is it fair to say that you
would expect to see stable indents (at least assuming the metal is not
quite as hard as my steel fork ends, AIUI most MTB fork ends are Al/Mg
etc alloys) from a serrated QR that does not slip, and actually expect
the fork dropouts to wear down if (and only if) slippage occurs?
Thanks,
James
G.T.
> jim beam <u...@ftc.gov> wrote in message news:<TpI9c.15785$tw7....@newssvr27.news.prodigy.com>...
>
>
>>if you're asking whether general repeated clamping & unclamping will
>>cause wear & tear over time, yes it will, but that is unlikely to cause
>>any reduction on the pull-out force. if anything, it will make pull-out
>>harder, not easier because indentations will get deeper.
>
>
> Yes, I've certainly heard from people who say they have significant
> indents in the dropout which interlock well with the skewer (and
> presumably the same is possible with the hub, although harder to
> notice and IME hub locknuts are often more just rough than really
> deeply serrated.
>
I have a new fork, from Fox, and new XT hubs and QRs. Starting with my
ride today I'm going to check my QRs post-ride after dabbing on a little
fingernail polish. After today's ride, short at 75 minutes, I can see no
movement whatsover. There were two 5 minute, bumpy, sustained 30 mph
descents along with several shorter ups and downs.
I'll be hampered a bit since I usually drive to the trailhead removing my
front wheel before and after the ride. I won't get a good sample until I
have a chance to do some longer descents.
Greg
jim beam
> jim beam <u...@ftc.gov> wrote in message news:<TpI9c.15785$tw7....@newssvr27.news.prodigy.com>...
>
>
>>if you're asking whether general repeated clamping & unclamping will
>>cause wear & tear over time, yes it will, but that is unlikely to cause
>>any reduction on the pull-out force. if anything, it will make pull-out
>>harder, not easier because indentations will get deeper.
>
>
> Yes, I've certainly heard from people who say they have significant
> indents in the dropout which interlock well with the skewer (and
> presumably the same is possible with the hub, although harder to
> notice and IME hub locknuts are often more just rough than really
> deeply serrated.
>
> Obviously these people do not experience wheel movement (at least,
> they have not yet) and this will be one factor which separates the
> failures from the rest. Just checking on my (rim-braked) bikes I see
> that there is minimal damage to the hard steel dropouts and in fact
> there is even still quite a lot of paint (albeit crimped and damaged)
> on the fork ends of the less-used bike. I have no QR suspension forks
> to examine and experiment with right now.
>
> But I'll get to my point. I'm trying to work out exactly what you are
> talking about in terms of damage that you would expect from skewer
> slip and not from general wear and tear. Is it fair to say that you
> would expect to see stable indents
yes. i'd show you my fork ends if i had a digicam with sufficient close
zoom - they're a perfect fit for the hub - and stable.
> (at least assuming the metal is not
> quite as hard as my steel fork ends, AIUI most MTB fork ends are Al/Mg
> etc alloys) from a serrated QR that does not slip, and actually expect
> the fork dropouts to wear down if (and only if) slippage occurs?
i don't think wear would be much of a problem unless you lose a
significant quantity of dropout material. and you'd have to be putting
up with a really lousy setup for a long time for that to happen.
>
> Thanks,
>
> James
Andrew Price
jim beam wrote -
> dangling & swinging back & forth. clearly, it was not tight so only
> lawyer lips were holding his wheel in. so i stopped him and told him of
> his problem.
On the usual Sunday bunch ride last year (starts in the dark in winter) it
had been a quicker than usual first 2 hours so we were all glad to stop at
the usual service station/ food shop.
And as we were sitting around shooting the breeze one of the more
experienced riders had his attention drawn to the fact that his front QR was
undone and in the condition you described.
He quietly did it up and remembered he had been in a tearing hurry after
dropping the fork onto the wheel and had just plain forgot to check it. Two
hours of steady riding and he hadn't noticed it.
And a few said silent prayers about various things ...
best, Andrew
James Annan
> James Annan wrote:
>> But I'll get to my point. I'm trying to work out exactly what you are
>> talking about in terms of damage that you would expect from skewer
>> slip and not from general wear and tear. Is it fair to say that you
>> would expect to see stable indents
>
>
> yes. i'd show you my fork ends if i had a digicam with sufficient close
> zoom - they're a perfect fit for the hub - and stable.
>
>> (at least assuming the metal is not
>> quite as hard as my steel fork ends, AIUI most MTB fork ends are Al/Mg
>> etc alloys) from a serrated QR that does not slip, and actually expect
>> the fork dropouts to wear down if (and only if) slippage occurs?
>
>
> i don't think wear would be much of a problem unless you lose a
> significant quantity of dropout material. and you'd have to be putting
> up with a really lousy setup for a long time for that to happen.
Ok, I thought that was what you meant and thank you for your patience
and clarity. I wanted to make sure we were not talking at cross purposes
- I basically agree with you on the main principle, but as you will see
I think you are perhaps too optimistic on the magnitude and reliability
of the indentation.
I suspect that given your comments above that you will be as gobsmacked
as I was by this on page 9 of the Fox '04 manual:
"Over time the knurled surfaces of the hub on the front wheel and
quick-release skewer wear the drop-out region of the lower leg."
"Inspect and measure the thickness of the dropouts every 6 months or 100
hours that any point on the surface is above the minimum thickness of
6.20mm. (Fig 1)" [sic]
"Replace the lower leg assembly if the dropout thickness is at the
minimum specification or smaller."
Figure 1 shows 2 pictures of a worn dropout being measured. Left hand
side, naturally :-) The picture isn't good enough for me to really see
clearly how worn it is. According to you (and I agree) this wear is
proof of relative motion of the surfaces under substantial load.
Moreover, the fact that this wear is described in the manual is surely
proof that Fox are well aware that this problem is reasonably common, in
direct contradiction of their public comments.
(NB I do not claim that motion is ubiquitous, as agreed above if
substantial indents are formed then that will greatly reduce the
likelihood of slip. There will be many people whose dropouts do not wear
down, ever.)
I can guess that the remaining critics will try to claim that this is
just "normal wear and tear" that one might equally expect with rim
brakes, but I don't buy it. As I said, I've still got some paint (albeit
crimped and chipped, it will come off eventually) on the dropouts of my
rim-braked single. The whole concept of "wearing out" dropouts is
completely new to me, and I cannot think of any other situation where
tightly bolted surfaces with no relative motion generate significant wear.
In fact, according to your comments above, the riders who are wearing
down their dropouts to the point at which replacement is required are
probably "putting up with a really lousy setup for a long time".
Oh, the Fox manual is at
<http://www.foxracingshox.com/BackOffice/UploadedFiles/OwnersManual/04%20Forx%20Manual%20English.pdf>
James
David Damerell
>Here's the thread I mentioned where I had questioned braking:
>http://groups.google.com/groups?&threadm=2Pk*P10aq%40news.chiark.greenend.org.uk
>David Damerell does a great job of summing it up in a single
>message.
Thank you.
I've slapped this up as
http://www.chiark.greenend.org.uk/~damerell/bikes/brake.txt
FWIW.
It seems to me that the last piece of the picture would be to confirm that
the CoG/front contact angle is just as low with heavy panniers as with
one's bottom behind the saddle.
--
David Damerell <dame...@chiark.greenend.org.uk> flcl?
Carl Fogel
[snip]
The center of mass has been mentioned frequently.
There seems to be an assumption that this point is
roughly at the rider's hips.
While this assumption works fairly well for someone
walking upright, I wonder whether the center of mass
is shifted significantly (in terms of braking) for
a rider using the lower part of touring bars, a
straight-handlebar mountain bike, or a recumbent
tricycle like Tom Sherman's:
http://www.ihpva.org/incoming/2002/Dragonflyer/df2.jpg
Once the center of mass question has been settled for
normal riding positions, please tell me all about how
far a rider can shift it and how much the shift matters
for braking.
Thanks again,
Carl Fogel
James Annan
anyone, is prepared to argue that normal use of a QR will "wear down" a
dropout to the point at which replacement is needed, other than through
slipping under disk brake forcing while firmly clamped. Certainly from
Jim Beam's previous comments on the matter, he does not think that this
is possible.
James
mojo deluxe
"James Annan" <still_th...@hotmail.com> wrote in message
news:4069ef54$0$23541$44c9...@news3.asahi-net.or.jp...
> This post appears to have gone unanaswered.
>
My gear is holding up just fine. No slippage, or movement. 80 miles since I
last touched my QRs.
Slacker
at night.
--
Slacker
carlfogel
> [snip]
> Can we just get this lawsuit going already... The suspense is keeping
> --
> Slacker
Dear Slacker,
I fear that, somewhere deep down in the fussy wives-can't-be-forced-to-testify-against-
husbands fine print, there may be something about needing standing in
order to sue.
That is, you may need someone who has actually suffered from the alleged
negligence, incompetence, poor taste, or bad cooking. You can't just
jump in and file suit against anyone who offends your sense of justice.
There is indeed a fellow who may be in the process of claiming in a
lawsuit that his injuries were caused by a defective disk brake design,
but it sounds as if his lawyers have suggested that he keep his mouth
shut and as if things go a bit slower than the second half-hour of "Law
and Order" might suggest.
In this thread, I seem to recall that he's mentioned that the bicycle in
question hasn't even been examined.
Otherwise, the woods don't seem to be full of other potential
plaintiffs.
With luck, some of our real-life attorneys will now explain where I
dozed off during "Rumpole of the Bailey" and how legal actions could
be brought.
Carl Fogel
--
Russ
mojo deluxe <voud...@hellsouth.nett> wrote in message
news:w4oac.30162$b_2....@bignews4.bellsouth.net...
>
> "James Annan" <still_th...@hotmail.com> wrote in message
> news:4069ef54$0$23541$44c9...@news3.asahi-net.or.jp...
> > This post appears to have gone unanaswered.
> >
> Or ignored??
I for one didn't pick it up
> My gear is holding up just fine. No slippage, or movement. 80 miles since
I
> last touched my QRs.
Lucky You
Russ
Russ
Slacker <slac...@sbcglobal.net> wrote in message news:c4d60k$2evtv2$1@ID-
> Can we just get this lawsuit going already... The suspense is keeping up
> at night.
That's the trouble with the youth of today. No patience, no sense of drama,
want immediate results. These things take time.
I blame TV
Russ :-)
mojo deluxe
"Russ" <nom...@nowhere.com> wrote in message
news:406aa...@mk-nntp-2.news.uk.tiscali.com...
>
> mojo deluxe <voud...@hellsouth.nett> wrote in message
> news:w4oac.30162$b_2....@bignews4.bellsouth.net...
> >
> > "James Annan" <still_th...@hotmail.com> wrote in message
> > news:4069ef54$0$23541$44c9...@news3.asahi-net.or.jp...
> > > This post appears to have gone unanaswered.
> > >
> > Or ignored??
>
> I for one didn't pick it up
>
> > My gear is holding up just fine. No slippage, or movement. 80 miles
since
> I
> > last touched my QRs.
>
> Lucky You
>
Or maybe quality gear that's properly installed.
Russ
> > > My gear is holding up just fine. No slippage, or movement. 80 miles
> since
> > I
> > > last touched my QRs.
> >
> > Lucky You
> >
> Or maybe quality gear that's properly installed.
I do hope so - I seem to remember thinking (and saying) exactly the same
thing but in spite of being extremely diligent about having 'quality gear
that's properly installed' I'm still in a wheelchair for the rest of my
life.
Still it's ok though - you're confident it can't happen to you. No need to
make sure that if all your lottery numbers come up and the worst happens and
the QR does fail (for whatever reason) then you can brake safely to a stop,
much better that the geometry of the fork/caliper forces the wheel out and
stuffs you over the handlebars at high speed hey ?
Still there's absolutely no way possibly it could ever, not in a million
years, happen to you or one of your friends is there? You can be quite
confident that there'll never be that occurence can't you?
Russ
mojo deluxe
on the way to work.
I can't guarantee my carbon bar won't snap, or my chain won't break, either.
There is nothing really safe about this sport, but I do my best to reduce
the risks.
Slacker
--
Slacker
mojo deluxe
Russ
mojo deluxe <voud...@hellsouth.nett> wrote in message news:Ouzac.4
>
> I can't guarantee my carbon bar won't snap, or my chain won't break,
either.
> There is nothing really safe about this sport, but I do my best to reduce
> the risks.
>
So how does arguing that positioning the disc brake caliper shouldn't be
positioned differently sit with doing your best to reduce the risks then -
because it clearly would do just that?
Russ
mojo deluxe
bomba
>> So how does arguing that positioning the disc brake caliper shouldn't be
>> positioned differently sit with doing your best to reduce the risks then -
>> because it clearly would do just that?
>>
> It's not enough to keep me off my bike.
And the award for 'Inappropriate Comment' goes to...
--
a.m-b FAQ: http://www.j-harris.net/bike/ambfaq.htm
a.bmx FAQ: http://www.t-online.de/~jharris/bmx_faq.htm
mojo deluxe
"bomba" <myar...@hotmail.com> wrote in message
news:pan.2004.03.31....@hotmail.com...
> On Wed, 31 Mar 2004 08:49:57 -0600, mojo deluxe wrote:
>
> >> So how does arguing that positioning the disc brake caliper shouldn't
be
> >> positioned differently sit with doing your best to reduce the risks
then -
> >> because it clearly would do just that?
> >>
> > It's not enough to keep me off my bike.
>
> And the award for 'Inappropriate Comment' goes to...
>
He threw the question out.
I answered.
'You' commented.
Ambrose Nankivell
mojo deluxe <voud...@hellsouth.nett> typed:
<whoooooooosh>
I think something just went right over your head there.
Russ
mojo deluxe <voud...@hellsouth.nett> wrote in message
Did I say it should be ?
Russ
mojo deluxe
"Stephen Baker" <saild...@aol.comnospam> wrote in message
news:20040331102814...@mb-m22.aol.com...
> Mojo D says:
>
> >> And the award for 'Inappropriate Comment' goes to...
> >>
> >You silly man.
> >
> >He threw the question out.
> >
> >I answered.
>
>
> http://groups.google.com/groups?q=russel+pinder&hl=en&lr=&ie=UTF-8&selm=b5
> c4vc%24omj%241%40lust.ihug.co.nz&rnum=1
>
> (sorry about the wrapping....)
>
> Then start again.
>
Damn, thanks for the heads up.
Russ, if my answer came across as cold, my apologies.
mojo deluxe
bomba
> Damn, thanks for the heads up.
>
> Russ, if my answer came across as cold, my apologies.
The odd thing is that you obviously didn't read Russ' posts in this
thread. Three posts up from your foot in mouth effort, in reply to
you, Russ wrote: "I seem to remember thinking (and saying) exactly the
same thing but in spite of being extremely diligent about having 'quality
gear that's properly installed' I'm still in a wheelchair for the rest of
my life."
--
mojo deluxe
>
> > Damn, thanks for the heads up.
> >
> > Russ, if my answer came across as cold, my apologies.
>
> The odd thing is that you obviously didn't read Russ' posts in this
> thread. Three posts up from your foot in mouth effort, in reply to
> you, Russ wrote: "I seem to remember thinking (and saying) exactly the
> same thing but in spite of being extremely diligent about having 'quality
> gear that's properly installed' I'm still in a wheelchair for the rest of
> my life."
>
bomba
> James, you are right.
You're having a good day today: my name's Jon :)
AndyP
> That's the trouble with the youth of today. No patience, no sense of
drama,
> want immediate results. These things take time.
>
> I blame TV
I blame the old people.
Ian G Batten
Russ <nom...@nowhere.com> wrote:
> So how does arguing that positioning the disc brake caliper shouldn't be
> positioned differently sit with doing your best to reduce the risks then -
> because it clearly would do just that?
Moving the caliper to the front of the fork leg would expose it to more
risk of impact damage. That may, or may not, improve overall safety.
It would certainly expose the point at which the brake line enters the
caliper to more damage. That too may, or may not, improve overall
safety.
You're assuming that things you believe caused your accident can be
changed in a manner which makes your accident less likely, but does not
make other accidents any more likely. That may be possible. It may not
be.
ian
Russ
"Chris Phillipo" <cphi...@ramsays-online.com> wrote in message
news:MPG.1ad4ce1f6...@news.eastlink.ca...
> In article <406ad21c$1...@mk-nntp-2.news.uk.tiscali.com>,
> nom...@nowhere.com says...
> > >
> > > I can't guarantee my carbon bar won't snap, or my chain won't break,
> > either.
> > > There is nothing really safe about this sport, but I do my best to
reduce
> > > the risks.
> > >
> >
> > So how does arguing that positioning the disc brake caliper shouldn't
be
> > positioned differently sit with doing your best to reduce the risks
then -
> > because it clearly would do just that?
> >
> > Russ
>
> as being high. I mean I've seen more hubs spontaneously fly apart at
> the flange (2), pedals snap off at the crank (2), Handlbars break at the
> stem (5) than properly closed QRs hubs slip out of fork drop outs
> (none).
And there's your problem - QR's are notoriously fickle things - and OK lets
assume every instance of QR's coming loose is operator error (a position I
find difficult to accept but that's not the point here) then there's plenty
of occurences and there'll be a huge amount more as discs get onto cheaper
and cheaper bikes. - what's better a system that allows people to brake to a
halt or one that throws them over the bars - it's such any easy fix for
future production that's it really is stupid in the extreme to say it's not
necessary.
> All those breakages have the same potention to F you up. So in
> the grand scheme of things there are more pressing matters to attend to
> if you are going to uproot the industry and start redesigning things.
And the indusrty doesn't redesign it's forks every year then ? It's
difficult to see how handlebars/pedals/hubs can be made to fail safe but
it's very easy to see it with disc brakes / QR's. If it could be done with
handlebars/hubs/pedals then are you saying that it wouldn't be a good idea
because it would uproot the industry. Sure stuff fails - we all accept that
possibility but if the result of that failure can be mitigated against are
you really trying to say it's not a good idea to do so?
> If you want to spend the money you can have your own bike made that
> addresses every issue that anyone has ever come accross, just don't
> expect it to be $599 at the LBS.
And the extra cost of mounting the caliper in the front or altering drop out
angles on next years (or the following years or whichever years is on the
drawing board at the moment) bike would be nil- that's nothing, zero, just
takes a couple of minutes on the CAD machine.
Your arguments just don't stack up I'm afraid. It's a no cost solution to a
real problem with no downside to the rider on the trail.
Just because you think it wont happen to you it will happen to someone
somewhere soon, it may be because they didn't do it up properly, it may be
for some other reason but rather than being able to brake safely to a stop
they'll be in a wheelchair too and all because everyone (the majority) said
not to rock the boat (read 'uproot the industry and start redesigning
things).
Russ
Tony Raven
>
> Since just about every trials guy knows that rear brakes have been
> tearing off of frames almost since the beginning because they are
> subjected to this "pulling" force when they hop on the rear wheel rather
> than the intended compression force.
Sorry Chris, you must be mistaken about that happening. Jobst has already
told us in no uncertain terms that there is nothing wrong with brake mountings
being in tension rather than compression. So what you claim is happening can't
have ;-)
Tony
PS Someone here a while ago mentioned that early trials motorbikes had tried
the caliper on the front but they had to give it up. Was I dreaming it or can
anyone shed any light on it?
Russ
"Tony Raven" <ju...@raven-family.com> wrote in message
news:c4f4mg$2hqmq1$1...@ID-178940.news.uni-berlin.de...
> Chris Phillipo wrote:
>
> >
> > Since just about every trials guy knows that rear brakes have been
> > tearing off of frames almost since the beginning because they are
> > subjected to this "pulling" force when they hop on the rear wheel rather
> > than the intended compression force.
>
>
> Sorry Chris, you must be mistaken about that happening. Jobst has already
> told us in no uncertain terms that there is nothing wrong with brake
mountings
> being in tension rather than compression. So what you claim is happening
can't
> have ;-)
>
> Tony
Any metal, whether in tension or compression will fail if stressed enough -
of course it will happen if the mounts aren't strong enough (or the welds
are poorly done) I think you'll find that there's no need for it to fail at
all. It's a spurious argument at best against front mounting calipers. It's
easy to make the mounts sufficiently strong.
However is is an incontrovertible fact that metals are equally as strong in
tension as they are in compression as any qualified structural engineer will
tell you - Ah yes that'll be me then.
If bike designers choose to put too little metal around the mounting tab
then that's another question entirely.
Russ
carlfogel
> Chris Phillipo wrote:
> >
> > Since just about every trials guy knows that rear brakes have been
> > tearing off of frames almost since the beginning because they are
> > subjected to this "pulling" force when they hop on the rear wheel
> > rather than the intended compression force.
> Sorry Chris, you must be mistaken about that happening. Jobst has
> already told us in no uncertain terms that there is nothing wrong with
> brake mountings being in tension rather than compression. So what you
> claim is happening can't have ;-)
> Tony
> tried the caliper on the front but they had to give it up. Was I
> dreaming it or can anyone shed any light on it?
Dear Tony,
As far as I can tell, trials machines use leading caliper front
disk brakes:
http://www.gasgas.com/Pages/2004's/300-pro-big-pics.html
or
Carl Fogel
--
Russ
"carlfogel" <usenet...@cyclingforums.com> wrote in message
news:%MFac.77529$sb5....@fe26.usenetserver.com...
Wonder why the mounts don't rip off ? It'll be because trials motor bikes
generate smaller forces than mtbs can I expect.
Wonder why they put it there? It's bound to be damaged more but that
wouldn't be an issue on a trials bike would it?
After all they don't put themselves in that sort of situation do they?
Thanks for the link Carl
Russ
James Annan
> Besides looking ridiculous
Of course that is the most important reason of all.
All this 'what should they do about it' is somewhat beside the point as
far as I am concerned. Yes, of course a change requires that a better
design is found, but I'd settle for a spot of honesty from the
manufacturers. I've explained what happens when skewers 'mysteriously'
come loose mid-ride, and rather than _thank_ me for solving a problem
that has obviously been beyond their massed ranks of 'engineers' for the
last decade, they have done nothing but evade, dissemble and bullshit.
FWIW, the front-mounted disk seems like a very obvious and
straightforward solution, and most of the criticisms seem father feeble.
For instance, if such a position is really vulnerable, we would already
be seeing plenty of damage to the rotor which is far weaker. And I don't
know about you, but the hoses from my front brakes go up the inside of
the fork where it is very well protected.
James
carlfogel
> "carlfogel" <usenet...@cyclingforums.com> wrote in message news:%MFa-
> c.77529$sb5....@fe26.usenetserver.comnews:%MFac.77529$sb5.43871@fe26.-
> usenetserver.com...
> > Tony Raven wrote:
> > > Chris Phillipo wrote:
> > > >
> > > > Since just about every trials guy knows that rear brakes have
> > > > been tearing off of frames almost since the beginning because
> > > > they are subjected to this "pulling" force when they hop on the
> > > > rear wheel rather than the intended compression force.
> > > Sorry Chris, you must be mistaken about that happening. Jobst has
> > > already told us in no uncertain terms that there is nothing wrong
> > > with brake mountings being in tension rather than compression. So
> > > what you claim is happening can't have ;-) Tony
> > > PS Someone here a while ago mentioned that early trials motorbikes
> > > had tried the caliper on the front but they had to give it up.
> > > Was I dreaming it or can anyone shed any light on it?
> >
> >
> >
> > Dear Tony,
> >
> > As far as I can tell, trials machines use leading caliper front
> > disk brakes:
> >
> > http://www.gasgas.com/Pages/2004's/300-pro-big-
> >
> > or
> >
> > http://tinyurl.com/yrvrbhttp://tinyurl.com/yrvrb
> >
> > Carl Fogel
> Wonder why the mounts don't rip off ? It'll be because trials motor
> bikes generate smaller forces than mtbs can I expect.
> Wonder why they put it there? It's bound to be damaged more but that
> wouldn't be an issue on a trials bike would it? After all they don't put
> themselves in that sort of situation do they?
> Thanks for the link Carl
> Russ
Dear Russ,
I should point out that the position of the disk brake on a motorcycle
has nothing to do with wheel ejection.
Trials machines, like practically all motorcycles, use front through-
axles.
Our idea of a quick-release is to weld a big handle on the axle nut to
eliminate the need for a wrench.
Same for the rear axle.
Carl Fogel
--
James Annan
> mojo deluxe <voud...@hellsouth.nett> wrote in message
> >
> > "James Annan" <still_th...@hotmail.com> wrote in message
> > news:4069ef54$0$23541$44c9...@news3.asahi-net.or.jp...
> > > This post appears to have gone unanaswered.
> > >
> > Or ignored??
>
> I for one didn't pick it up
It was originally on a different thread in r.b.t. alone, I saw an
opportunity and jim beam obligingly walked straight into the bear
trap:-) Sorry jim, but a few people have already insisted that
grinding down a dropout to a dangerously thin state is "normal wear
and tear that could happen equally with rim brakes" and I wanted to
eliminate that option before coming out with the punchline.
James
Eric Murray
Early trials motorcycles had drum brakes. Discs only became popular
on trials bikes in the late 80s.
Most trials bikes have the calipers on the front of the fork legs.
Even my newest bike ('03 Scorpa) has the caliper on the front.
It might be slightly less succeptible to damage and packing with
mud there than mounted on the back of the fork leg, MTB style. But
I have bikes that have their calipers mounted that way and I haven't
damaged them or packed them with mud.
Street/roadrace is different.
When discs became popular on street motorcycles in the early 1970s
most calipers were on the front of the fork legs. But putting them
on the back puts the mass of the calipers closer to the steering
axis (which is behind the forks). Early calipers were pretty heavy
so moving them to the back of the fork legs made for quicker steering.
Cafe racers (and real race bikes) in the 70's often had their fork legs
reversed to obtain the desired position. All street and road bikes
come with calipers mounted on the back of the fork legs now.
But there's no other reason for motorcycle caliper position that I
know of.
Eric
Tom Sherman
> ...
> However is is an incontrovertible fact that metals are equally as strong in
> tension as they are in compression as any qualified structural engineer will
> tell you - Ah yes that'll be me then....
Gray cast iron has an ultimate unconfined compressive strength
approximately 4 times that of its ultimate tensile strength.
--
Tom Sherman - Quad Cities (Illinois Side)
mojo deluxe
>
> > James, you are right.
>
> You're having a good day today: my name's Jon :)
>
post, mostly out of laziness, hence the 'foot in the mouth' thingy. I'm not
a cruel person.
carlfogel
Dear Eric,
I browsed a bit through Honda, Yamaha, and Kawasaki. It's not just their
street machines that have trailing calipers. Their off-road and
motocross machines all seem to have trailing disk calipers, too, just
like the street bikes.
From this, I conclude that all the other kinds of machines are mistaken,
since trials machines are of course the acme of creation.
Now I have to ask around and find out why the hell the trials machines
put the caliper on the front.
Carl Fogel
--
jobst....@stanfordalumni.org
http://www.gasgas.com/Pages/2004's/300-pro-big-pics.html
> Wonder why the mounts don't rip off ? It'll be because trials motor
> bikes generate smaller forces than MTB's can I expect.
For the same reason regular caliper brakes don't "rip off" of bicycle
forks used on most bicycle. The parts are properly dimensioned. The
Idea that tension is not allowed in attachments is an imagined hazard.
Automobiles are full of tension joints as are aircraft. Where did
this notion arise?
> Wonder why they put it there? It's bound to be damaged more but
> that wouldn't be an issue on a trials bike would it? After all they
> don't put themselves in that sort of situation do they?
There is no danger of damage that isn't there otherwise, the disk,
regardless of caliper position is more fragile and more exposed to the
imagined contact with solid objects.
Jobst Brandt
jobst....@stanfordalumni.org
Slacker
> "Slacker" <slac...@sbcglobal.net> wrote in message
> news:c4egjj$2f8uoq$1...@ID-191655.news.uni-berlin.de...
>
>>Russ wrote:
>>
>>>Slacker <slac...@sbcglobal.net> wrote in message
>
> news:c4d60k$2evtv2$1@ID-
>
>>>
>>>>Can we just get this lawsuit going already... The suspense is keeping up
>>>>at night.
>>>
>>>
>>>That's the trouble with the youth of today. No patience, no sense of
>
> drama,
>
>>>want immediate results. These things take time.
>>>
>>>I blame TV
>>>
>>>Russ :-)
>>>
>>>
>>>
>>
>>hehehe.... I blame baby formula and no natural breast milk :-)
>>
>
> I was breast fed. Maybe that's why I turned out so well.
>
<just finished reading your conversation with Russ>
Are we regretting this comment too. You're giving breast feeding a bad
name ;-)
--
Slacker
mojo deluxe
and my time management skills have gone to shit, so at night, I've been
skimming through any post I read. Well, I had a few hours this morning, and
found myself doing it again over coffee.
I'm going to stop now, before I insert the size 13 foot again.
carlfogel
> Dear Eric,
> I browsed a bit through Honda, Yamaha, and Kawasaki. It's not just their
> street machines that have trailing calipers. Their off-road and
> motocross machines all seem to have trailing disk calipers, too, just
> like the street bikes.
> From this, I conclude that all the other kinds of machines are mistaken,
> since trials machines are of course the acme of creation.
> Now I have to ask around and find out why the hell the trials machines
> put the caliper on the front.
> Carl Fogel
I asked a friend who might know:
>> Why do modern trials bikes have their disk brake calipers in front,
>> while the off-road, motocross, and street machines all use trailing
>> calipers?
My anonymous former mechanic informant replied:
> I suppose there are several things at work.
> A trials bike has a very small disk and only one of them. The idea of
> placing the calipers behind the fork legs was to get them closer to
> the center of the steered mass.
> Also, road racers have narrow bars, so you've got less leverage. So
> get 2 big calipers in front of the forks and steer with a narrow
> bar at high speed, and you'd probably find it better to place them
> in back.
> I think on a bike with a leading axle fork the caliper itself is a
> little less vulnerable when placed in front. It's higher and away from
> rocks. Of course, other off-road bikes have the calipers in back. But
> they have bigger brakes due to higher speeds and more weight than a
> trials bike.
> Rear calipers are more difficult to work on and around, so, barring
> compelling reasons to place them in back, front placement has its own
> advantages.
So possibly modern bicycles simply imitated the rear-calipers of non-
trials motorcycles?
Carl Fogel
--
jim beam
both these /are/ the structural reasons not to front mount. period.
jim beam
James Annan wrote:
> jim beam wrote:
>
>> James Annan wrote:
>>
>>> But I'll get to my point. I'm trying to work out exactly what you are
>>> talking about in terms of damage that you would expect from skewer
>>> slip and not from general wear and tear. Is it fair to say that you
>>> would expect to see stable indents
>>
>>
>>
>> yes. i'd show you my fork ends if i had a digicam with sufficient
>> close zoom - they're a perfect fit for the hub - and stable.
>>
>>> (at least assuming the metal is not
>>> quite as hard as my steel fork ends, AIUI most MTB fork ends are Al/Mg
>>> etc alloys) from a serrated QR that does not slip, and actually expect
>>> the fork dropouts to wear down if (and only if) slippage occurs?
>>
>>
>>
>> i don't think wear would be much of a problem unless you lose a
>> significant quantity of dropout material. and you'd have to be
>> putting up with a really lousy setup for a long time for that to happen.
>
>
> Ok, I thought that was what you meant and thank you for your patience
> and clarity. I wanted to make sure we were not talking at cross purposes
> - I basically agree with you on the main principle, but as you will see
> I think you are perhaps too optimistic on the magnitude and reliability
> of the indentation.
>
> I suspect that given your comments above that you will be as gobsmacked
> as I was by this on page 9 of the Fox '04 manual:
>
> "Over time the knurled surfaces of the hub on the front wheel and
> quick-release skewer wear the drop-out region of the lower leg."
>
> "Inspect and measure the thickness of the dropouts every 6 months or 100
> hours that any point on the surface is above the minimum thickness of
> 6.20mm. (Fig 1)" [sic]
>
> "Replace the lower leg assembly if the dropout thickness is at the
> minimum specification or smaller."
>
> Figure 1 shows 2 pictures of a worn dropout being measured. Left hand
> side, naturally :-) The picture isn't good enough for me to really see
> clearly how worn it is. According to you (and I agree) this wear is
> proof of relative motion of the surfaces under substantial load.
> Moreover, the fact that this wear is described in the manual is surely
> proof that Fox are well aware that this problem is reasonably common, in
> direct contradiction of their public comments.
>
> (NB I do not claim that motion is ubiquitous, as agreed above if
> substantial indents are formed then that will greatly reduce the
> likelihood of slip. There will be many people whose dropouts do not wear
> down, ever.)
>
> I can guess that the remaining critics will try to claim that this is
> just "normal wear and tear" that one might equally expect with rim
> brakes, but I don't buy it. As I said, I've still got some paint (albeit
> crimped and chipped, it will come off eventually) on the dropouts of my
> rim-braked single. The whole concept of "wearing out" dropouts is
> completely new to me, and I cannot think of any other situation where
> tightly bolted surfaces with no relative motion generate significant wear.
>
> In fact, according to your comments above, the riders who are wearing
> down their dropouts to the point at which replacement is required are
> probably "putting up with a really lousy setup for a long time".
>
> Oh, the Fox manual is at
>
> <http://www.foxracingshox.com/BackOffice/UploadedFiles/OwnersManual/04%20Forx%20Manual%20English.pdf>
>
ok, so how are you going to account for wear resulting from regular
clamping & unclamping, wheel insertion & removal, clamping & removal
from roof racks, etc? i'd call that "normal wear & tear". perhaps if
you call fox you can get their clarification as well.
i can see i'll have to borrow a digicam. just got back from another
sketchy downhill. still absloutely zero shifting of the q.r. my fork's
been disk braked 2 or 3 times a week for well over a year now.
>
> James
>
jim beam
> In article <c4et6u$h8k$1...@news-out.ftel.co.uk>, I.G.B...@batten.eu.org
> says...
> tearing off of frames almost since the beginning because they are
> subjected to this "pulling" force when they hop on the rear wheel rather
> the caliper on the opposite side of the fork leg. No, I think the
> solution already exists, the 20mm thru axle, if you want it, buy it.
> There is no further engineering needed on this issue.
whoops! who let the sense enter this argument? time to go. goodnight.
Russ
<jobst....@stanfordalumni.org> wrote in message
news:EaLac.2966$Fo4....@typhoon.sonic.net...
I'm with you totally here Jobst - I just didn't know the emoticon for very
heavy sarcasm. But it does prove to all the doubters that there's absolutely
no reason not to relocate the disc caliper.
Russ
Russ
I realise the point about QR's Carl but there were a number of people here
maintaining that repositioning the caliper in front of the fork leg would
inevitably result in calipers ripping off and / or being damaged. I think
you've just shown that these claims are entirely unfounded.
Russ
bomba
>> > James, you are right.
>>
>> You're having a good day today: my name's Jon :)
>>
> Well, fjvck me then. I have a bad habit of skimming through way too many
> post, mostly out of laziness, hence the 'foot in the mouth' thingy. I'm not
> a cruel person.
I know. That's why I phrased my comment in a jokey sort of way. If for one
second I'd thought you were being malicious, my reply would have been very
different.
Shaun Rimmer
> On Wed, 31 Mar 2004 19:09:40 -0600, mojo deluxe wrote:
>
> >> > James, you are right.
> >>
> >> You're having a good day today: my name's Jon :)
> >>
> > Well, fjvck me then. I have a bad habit of skimming through way too many
> > post, mostly out of laziness, hence the 'foot in the mouth' thingy. I'm
not
> > a cruel person.
>
> I know. That's why I phrased my comment in a jokey sort of way. If for one
> second I'd thought you were being malicious, my reply would have been very
> different.
And I do believe almost the entire ng would have ripped him a big ol' new
one, too.
Shaun aRe
Shaun Rimmer
"AndyP" <An...@ajp100.freeserve.no-spam.co.uk> wrote in message
news:c4er8e$473$1...@news8.svr.pol.co.uk...
Old people are just young people with all the air let out.
Shaun aRe
Tim McNamara
> i can see i'll have to borrow a digicam. just got back from another
> sketchy downhill. still absloutely zero shifting of the q.r. my
> fork's been disk braked 2 or 3 times a week for well over a year
> now.
And you haven't adjusted or reclamped the QR in that entire time?
Amazing!
Tim McNamara
> thank you tom! and to chris as well for the point about welds.
>
> both these /are/ the structural reasons not to front mount. period.
Try a free body diagram of the stresses again. You'll see that they
are no different whether the caliper is in front or behind the fork
leg. This is a red herring.
Ian Smith
> However is is an incontrovertible fact that metals are equally as
> strong in tension as they are in compression as any qualified
> structural engineer will tell you - Ah yes that'll be me then.
I'm not sure what you mean by qualified structural engineer, but I'm a
chartered civil engineer working mostly with structures, and I
disagree.
Given your UK email address, I'd refer you to the Highways Agency
Design Manual for Roads and Bridges, specifically Vol 3 Highway
structures: Inspection and Maintenance, Section 4 Assessment, Part 3:
BD21/01 - The Assessment of Highway Bridges and Structures
Clause 4.10:
"The compressive stress in cast iron due either to the permanent load
or to the combined permanent and live load shall not exceed 154 N/mm2.
The tensile stress due either to the permanent load or to the combined
permanent and live load shall not exceed 46 N/mm2. In addition, for a
given value of permanent load stress, the live load stress shall not
exceed the permissible tensile or compressive live load stresses
obtained from figure 4.1."
That is, a maximum compressive stress of 154 is allowed, but a maximum
tensile of only 46 - rather less than one third of teh compressive.
In fact, the material behaviour is even odder than that, because teh
actual range of allowable stresses is a function of teh long term
stresses in teh material - this is what's shown in figure 4.1. At
this point it's difficult to show in plain ascii text, but if you want
to look at http://www.astounding.org.uk/ian/temp/CI_props.html you can
see teh equations and graphs (if you have a graphical browser -
they're all images 'cos that's how teh program I used writes equations
in html). Note that teh last graph has a log scale.
You'll see that at any long term stress more compressive than
17.5 N/mm2 compression, teh capacity in compression is actually at
least 10 times that in tension. The tensile and compressive
allowable stresses are equal only if teh long term stress equals about
12 N/mm2.
regards, Ian SMith
--
|\ /| no .sig
|o o|
|/ \|
Russ
news:MPG.1ad642b1...@news.eastlink.ca...
> In article <m2r7v7z...@Stella-Blue.local>, tim...@bitstream.net
> says...
> > jim beam <u...@ftc.gov> writes:
> >
> > > thank you tom! and to chris as well for the point about welds.
> > >
> > > both these /are/ the structural reasons not to front mount. period.
Cast Iron is a lot of a red herring, it's not like you see a lot of cast
iron on bikes and the Al was stronger in tension. Still it's all a moot
point as in any material it's not difficult to design sufficently strong
mounts.
Also very odd that Trials motorbikes front mount their disc calipers if
these are real reasons for not doing so. I think we've well and truly put
that one to bed
> >
> > Try a free body diagram of the stresses again. You'll see that they
> > are no different whether the caliper is in front or behind the fork
> > leg. This is a red herring.
> >
>
> That would be quite impossible because no one here has put forth a
> design for a front caliper mount, simply turning the current one around
> would not work, not even slightly.
Put it on the opposite fork and it'll work just fine (you might have to turn
the wheel round too!), even the hose would work, wouldn't even need a
caliper redesign, just need mounts on the fork in a different place which
could easily be done as manufacturers like RS / Manitou / Fox / Marozochi
roll out their new forks every year (or possibly two).
But it wouldn't suit Chris's arguments to admit that it could possibly be
that simple.
Russ
jobst....@stanfordalumni.org
>> I can see I'll have to borrow a digicam. Just got back from
>> another sketchy downhill. Still absloutely zero shifting of the
>> q.r. My fork's been disk braked 2 or 3 times a week for well over
>> a year now.
> And you haven't adjusted or reclamped the QR in that entire time?
> Amazing!
I'm not amazed. I visited our local bicycle shop recently and wanted
to see how severely a wheel locks when the left end of the axle is
ejected by the disc brake. First, I was amazed at the small diameter
of the disc whose working radius was 1/4 the tire radius, which makes
the ejection force as much as 4x rider weight. Anyway, when I tried
to open the QR, it was so tight that it took all I could do to open it
without tools. I guess people are aware of suspension fork-disc brake
loosening syndrome.
Jobst Brandt
jobst....@stanfordalumni.org
James Annan
Chris Phillipo wrote:
> I think a few people here are having trouble visualizing this so I took
> a picture of what an international standard disk brake looks like fitted
> to the front of a fork:
>
> http://www.ramsays-online.com/pictures/frontbrake.jpg
>
> As you can see it is not as simple as flipping the fork leg around.
The calliper flips around to the front of the RIGHT leg!
For forks where the offset is added at the crown rather than dropout,
abbsolutely no change is required, simple swapping the left and right
lowers would suffice.
Some people have already done this switch (Erickson tandems). All it
takes, on any fork, is correct placement of the mount on the front of
the rihht hand blade. The calliper already works fine in that position.
And depite the dire warnings that some have come out with here, these
callipers have not ripped off, even with tandem braking forces.
This solution is already working fine.
James
James Annan
> I'm not amazed. I visited our local bicycle shop recently and wanted
> to see how severely a wheel locks when the left end of the axle is
> ejected by the disc brake. First, I was amazed at the small diameter
> of the disc whose working radius was 1/4 the tire radius, which makes
> the ejection force as much as 4x rider weight. Anyway, when I tried
> to open the QR, it was so tight that it took all I could do to open it
> without tools. I guess people are aware of suspension fork-disc brake
> loosening syndrome.
Yes, they know all about it...
http://www.velonews.com/tech/report/articles/5432.0.html
"No matter what, you need to tighten your front skewer about as hard as
you can with a front disc brake." Lennard Zinn
Of course when the skewer snaps or thread strips, you know you got it
too tight.
James
mojo deluxe
> On Wed, 31 Mar 2004 19:09:40 -0600, mojo deluxe wrote:
>
> >> > James, you are right.
> >>
> >> You're having a good day today: my name's Jon :)
> >>
> > Well, fjvck me then. I have a bad habit of skimming through way too many
> > post, mostly out of laziness, hence the 'foot in the mouth' thingy. I'm
not
> > a cruel person.
>
> I know. That's why I phrased my comment in a jokey sort of way. If for one
> second I'd thought you were being malicious, my reply would have been very
> different.
>