Rim bulge - Can it be repaired?
HarryB
recumbent tandem has a bulge. At the bulge, the rim is about 0.75mm
wider than the rest of the rim and about the length of three spoke
holes. I assume I must have hit something with the wheel, but don't
remember it, nor do I see any damage to the tire or rim other than the
bulge. The wheel has approximately 3,000 miles on it, so I don't think
it is because the rim is worn from braking.
Can this be safely repaired, maybe by squeezing the bulged area in a
vice? I don't want to replace the rim if I don't have to, but neither
do I wish put my wonderful stoker in jeopardy by riding on an unsafe
wheel.
If the rim can't be safely repaired, is it safe to ride this rim until
I can find a replacement?
TIA,
Harry
531Aussie
I've experienced this twice, and the bike shop guys said they were
faulty rims which should be replaced, so I did.
I only noticed it it because of the shuddering braking :)
--
531Aussie
jim beam
if it's just a dent, maybe, but it's difficult to get right. if it's a
symptom of a worn rim, it's the bulge that precedes outright rim
failure. suggest tire removal and close inspection, including under the
rim tape. asap. and it would /not/ be safe to ride if any cracking or
excess brake wear is evident. in either case, the safest solution is
rim replacement.
Phil, Non-Squid
> I discovered that one side of the rim (20" Velocity DeepV) on my
> recumbent tandem has a bulge. At the bulge, the rim is about 0.75mm
> wider than the rest of the rim and about the length of three spoke
> holes. I assume I must have hit something with the wheel, but don't
0.75mm is not a big deal. Across three spoke holes is. This is not likely
to happen from a pothole encounter. I would say replace.
> remember it, nor do I see any damage to the tire or rim other than the
> bulge. The wheel has approximately 3,000 miles on it, so I don't think
> it is because the rim is worn from braking.
Send pics if you can.
--
Phil
Tim McNamara
jim beam <spamv...@bad.example.net> wrote:
> HarryB wrote:
> > I discovered that one side of the rim (20" Velocity DeepV) on my
> > recumbent tandem has a bulge. At the bulge, the rim is about 0.75mm
> > wider than the rest of the rim and about the length of three spoke
> > holes. I assume I must have hit something with the wheel, but don't
> > remember it, nor do I see any damage to the tire or rim other than
> > the bulge. The wheel has approximately 3,000 miles on it, so I
> > don't think it is because the rim is worn from braking.
> >
> > Can this be safely repaired, maybe by squeezing the bulged area in
> > a vice? I don't want to replace the rim if I don't have to, but
> > neither do I wish put my wonderful stoker in jeopardy by riding on
> > an unsafe wheel.
> >
> > If the rim can't be safely repaired, is it safe to ride this rim
> > until I can find a replacement?
>
> if it's just a dent, maybe, but it's difficult to get right. if it's
> a symptom of a worn rim, it's the bulge that precedes outright rim
> failure. suggest tire removal and close inspection, including under
> the rim tape. asap. and it would /not/ be safe to ride if any
> cracking or excess brake wear is evident. in either case, the safest
> solution is rim replacement.
Those were my thoughts too. I wondered particularly about the rim
cracking along the spoke bed where it meets the sidewall, causing it to
bulge outward from tire pressure. jim's right, this wheel should not be
used until it has been inspected and the cause of the bulge determined.
Having the sidewall blow out while riding would be a bad deal.
The Velocity USA web site doesn't list a 20" version but there is a
cutaway drawing:
Steve knight
out in the rain.
HarryB
Yes, that picture is what the rim looks like. I have looked at the
inside and outside of the rim with a magnifying glass and don't see
any cracking anywhere.
What I should have mentioned is that the bulge is most pronounced at
the edge of the rim (by the hook) and that there is no bulge at the
braking surface nearest the hub. It certainly appears like the rim is
"dented" outward as if it had been hit with something blunt from the
inside.
Harry
HarryB
Although I could take a picture, I doubt it would show anything
clearly. (And, I'm not sure where I could post such a picture.)
Maybe I didn't do a good job of explaining the bulge: maybe I should
have written that as I slowly turn the wheel, the outward part of the
rim (by the hook) gradually becomes wider on one side of the wheel for
about the distance of about 1 1/2 spoke holes and then gradually
narrows back to the normal width the over the same distance. Since
this is a 20" 36 hole rim, the total distance that is deformed is
about 8cm. I should also have noted that the part of the rim's braking
surface nearest the hub does not increase in width at all.
Harry
HarryB
Yes, that is the way that I also noticed it. I think it came on
suddenly and assumed that I needed to true the wheel. I forgot about
it after the ride (we only ride this particular tandem occasionally)
and was again reminded of it on the next ride. When I went to true the
wheel I noticed that it was a bulge.
Harry
carl...@comcast.net
>On Tue, 3 Apr 2007 03:05:27 -0400, "Phil, Non-Squid"
><REMOVEph...@hotmail.com> wrote:
[snip]
>>Send pics if you can.
[snip]
>Although I could take a picture, I doubt it would show anything
>clearly. (And, I'm not sure where I could post such a picture.)
[snip]
Dear Harry,
Try www.tinypic.com to post pictures.
Click on browse, choose the file to upload, and cut and paste the
resulting link into your post or email.
Here's an example, a picture of a highwheeler in another thread:
http://i12.tinypic.com/2mzl8jb.jpg
TinyPic is free, doesn't even require a login, and allows a short
caption to let you search for the file if you lose the link.
There are other free hosting services that let you log in and group
your pictures in galleries and upload multiple pictures, but for most
people TinyPic is as quick and easy as it gets.
Cheers,
Carl Fogel
Ron Hardin
rims you just bent it back with vise grips, putting some unbendable
object between the grip and the good side of the rim, so it didn't
get bent inwards.
Then you bought a new rim.
--
Ron Hardin
rhha...@mindspring.com
On the internet, nobody knows you're a jerk.
Tim McNamara
HarryB <No...@none.net> wrote:
That usually takes the form of an acute "V" bulging out from the
centerline of the rim or indented in towards the centerline the rim.
Usually about 1/2" long or so. It takes a pretty good whack, you'd
remember it.
John Thompson
> I discovered that one side of the rim (20" Velocity DeepV) on my
> recumbent tandem has a bulge. At the bulge, the rim is about 0.75mm
> wider than the rest of the rim and about the length of three spoke
> holes. I assume I must have hit something with the wheel, but don't
> remember it, nor do I see any damage to the tire or rim other than the
> bulge. The wheel has approximately 3,000 miles on it, so I don't think
> it is because the rim is worn from braking.
>
> Can this be safely repaired, maybe by squeezing the bulged area in a
> vice? I don't want to replace the rim if I don't have to, but neither
> do I wish put my wonderful stoker in jeopardy by riding on an unsafe
> wheel.
There's the Bicycle Research "Rim Saver" tool:
But be aware that impact damage not only causes a bulge, but also often
flattens the rim at the impact site, so you will likely have a bit of a
"hop" in the rim regardless of how well you repair the bulge.
I am a bit concerned about the extend of the bulge you describe, though.
Most impact damage is very restricted in extent; this sounds more like
the rim wall itself might be deformed. Can you take it to a shop for
someone to check in person? I
> If the rim can't be safely repaired, is it safe to ride this rim until
> I can find a replacement?
Assuming it is just impact damage, it should be ok. If it is the rim
wall failing you may suffer a blowout with the tire coming off the rim.
Get it checked.
--
John (jo...@os2.dhs.org)
HarryB
>On Tue, 03 Apr 2007 11:54:49 -0500, HarryB <No...@none.net> wrote:
>
>>On Tue, 3 Apr 2007 03:05:27 -0400, "Phil, Non-Squid"
>><REMOVEph...@hotmail.com> wrote:
>
>[snip]
>
>>>Send pics if you can.
>
>[snip]
>
>>Although I could take a picture, I doubt it would show anything
>>clearly. (And, I'm not sure where I could post such a picture.)
>
>[snip]
>
>Dear Harry,
>
>Try www.tinypic.com to post pictures.
>
[snip]
>
>Cheers,
>
>Carl Fogel
Carl,
Thanks for the link. I have taken some pictures and uploaded them to
that site. Taking pictures of a dark colored wheel is difficult. If I
was a photographer the pictures would be much better...
Harry
HarryB
<REMOVEph...@hotmail.com> wrote:
Here are some pictures I took of the rim. (Taking close-up pictures of
a rim is difficult!)
The first picture shows the area of the bulge. The line that runs
through the middle of the braking surface is a gouge, not a crack,
that goes all the way around the rim. The piece of tape points to the
widest part of the bulge:
http://i11.tinypic.com/29gbv4p.jpg
The next picture shows the inside of the rim at the bulge area:
http://i9.tinypic.com/2cnw3n5.jpg
The bulge is on the right side in this last picture:
http://i10.tinypic.com/4hip6xd.jpg
Harry
Tim McNamara
HarryB <No...@none.net> wrote:
> Here are some pictures I took of the rim. (Taking close-up pictures
> of a rim is difficult!)
>
> The first picture shows the area of the bulge. The line that runs
> through the middle of the braking surface is a gouge, not a crack,
> that goes all the way around the rim. The piece of tape points to the
> widest part of the bulge: http://i11.tinypic.com/29gbv4p.jpg
Is that a set of parallel cracks in the sidewall, about 1/2 and 1/2 of
the way up?
> The next picture shows the inside of the rim at the bulge area:
> http://i9.tinypic.com/2cnw3n5.jpg
>
> The bulge is on the right side in this last picture:
> http://i10.tinypic.com/4hip6xd.jpg
There's no impact mark on the edge of the rim, which I think argues
against having hit something. I think you're looking at a failing rim.
jobst....@stanfordalumni.org
I think you are looking at a brand new rim, the brake track of which
hasn't even shown brake wear. The way the rim is shown, I cannot see
the "bulge". If the rim were lying on a flat surface, bulge downward,
and photographed on edge, we might be able to see what is claimed.
Jobst Brandt
jim beam
because of reflection on #2, it's not possible to say for sure, but the
combination of #1 & #2 lead me to think this rim is cracking. suggest
you replace asap.
also for future reference, stick to /rim/ manufacturer tire pressure -
you don't say what you're running, but i'll bet it's not 60lbs!
Tim McNamara
jobst....@stanfordalumni.org wrote:
> Tim McNamara writes:
>
> >> Here are some pictures I took of the rim. (Taking close-up pictures
> >> of a rim is difficult!)
>
> >> The first picture shows the area of the bulge. The line that runs
> >> through the middle of the braking surface is a gouge, not a crack,
> >> that goes all the way around the rim. The piece of tape points to
> >> the widest part of the bulge: http://i11.tinypic.com/29gbv4p.jpg
>
> > Is that a set of parallel cracks in the sidewall, about 1/2 and 1/2
> > of the way up?
Should have been "1/4 and 1/2 of the way up."
> >> The next picture shows the inside of the rim at the bulge area:
> >> http://i9.tinypic.com/2cnw3n5.jpg The bulge is on the right side in
> >> this last picture: http://i10.tinypic.com/4hip6xd.jpg
>
> > There's no impact mark on the edge of the rim, which I think argues
> > against having hit something. I think you're looking at a failing
> > rim.
>
> I think you are looking at a brand new rim, the brake track of which
> hasn't even shown brake wear. The way the rim is shown, I cannot see
> the "bulge". If the rim were lying on a flat surface, bulge downward,
> and photographed on edge, we might be able to see what is claimed.
If you look at http://i11.tinypic.com/29gbv4p.jpg there are two lines
that look different from the machining artifacts; they are brighter than
the "album groove" machining marks, have distinct ends and are
apparently centered in the bulge. The lower one is about 1/4 of the way
up the brake track and is about 1 1/4 the length of a span between
spokes. On my LCD screen the lines become more obvious if I tilt my
monitor back slightly to increase contrast. Above that is another line,
but that one is harder to differentiate as there seems to be a groove
all the way around at the middle of the brake surface (some
manufacturers put some kind of wear indicator on rims these days, this
might be one of those).
There's no impact mark on the edge of the rim, though, so I doubt that
the bulge is due to hitting something.
I like the idea of laying the rim on a flat surface or placing a
straightedge along the rim and photographing it from the edge to
highlight the bulge. Seeing both sides of the rim this way would be
helpful, to see if both sides deviate.
A Muzi
>> I discovered that one side of the rim (20" Velocity DeepV) on my
>> recumbent tandem has a bulge. At the bulge, the rim is about 0.75mm
>> wider than the rest of the rim and about the length of three spoke
>> holes. I assume I must have hit something with the wheel, but don't
>> remember it, nor do I see any damage to the tire or rim other than the
>> bulge. The wheel has approximately 3,000 miles on it, so I don't think
>> it is because the rim is worn from braking.
>> Can this be safely repaired, maybe by squeezing the bulged area in a
>> vice? I don't want to replace the rim if I don't have to, but neither
>> do I wish put my wonderful stoker in jeopardy by riding on an unsafe
>> wheel.
John Thompson wrote:
> There's the Bicycle Research "Rim Saver" tool:
> http://www.biketoolsetc.com/index.cgi?id=594510960559&d=single&c=Tools&sc=Wheel-and-Rim&tc=Rim-Repair-Tools&item_id=BR-RS1
-snip 'check for safety'-
Back to esoterica, where there's a will, there's a way:
http://www.yellowjersey.org/photosfromthepast/RIMTRUE.JPG
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971
Tim McNamara
A Muzi <a...@yellowjersey.org> wrote:
> Back to esoterica, where there's a will, there's a way:
> http://www.yellowjersey.org/photosfromthepast/RIMTRUE.JPG
I remember having one of those at the first bike shop I worked at,
although I think it was a VAR and not as old as that one looks. I have
had occasion to wish I still had one of those in the past few years.
data...@yahoo.com
not bend rims inward laterally.
AMuzi's tool bends rims outward radially while possibly deforming
outside the tools grasp inward radially?
an orbital jigsaw 'might' cut 3/4" ply or particle board-or two 1/2"
bolted to the correct inside rim circumference if you fabricate a
jigsaw trammel rod from strap stock-home depot/used bedframes.
center the radial bend, screw the center to the circumference
blocks,possibly screw each nipple hole down then tap rim to set the
rebend.
but the jigsaw 'might' not cut the ply or particle board at a 90
degree angle leaving the work with another trammel cut this time with
a router.
very experimental.
A Muzi
> A Muzi <a...@yellowjersey.org> wrote:
>> Back to esoterica, where there's a will, there's a way:
>> http://www.yellowjersey.org/photosfromthepast/RIMTRUE.JPG
Tim McNamara wrote:
> I remember having one of those at the first bike shop I worked at,
> although I think it was a VAR and not as old as that one looks. I have
> had occasion to wish I still had one of those in the past few years.
We use it once or twice a year when normal conditions are exceeded.
Where a new rim can be sold it's a better wheel than using this tool.
HarryB
Jobst,
In order to get a better look at the bulging area I cleaned it up with
a 3M ScotchBrite pad. As I wrote in my initial post, the rim has about
3,000 miles on it.
I tried to take a picture the way you suggested, but was unable to
show the bulge that way either. I did however take a short,
unfortunately poor quality, video of the wheel in my truing stand. I
do think it shows that there is a bulge even though it doesn't shed
any light on what caused it:
http://video.tinypic.com/player.php?v=2cn8fuv
Harry
HarryB
Tim,
You guys are sharp! I think this is what you are referring to:
http://i9.tinypic.com/2h3mw09.jpg
The top groove goes all the way around the rim and so I assume it is a
groove from something that was in the brake pad. The lower one, you
noted, is different, and probably is a crack. It must be located about
here: http://i7.tinypic.com/301nhc2.jpg
As I noted in my reply to Jobst, I couldn't figure out how to get a
decent picture of the rim on a flat surface since the rim only bulges
out about 0.75mm. However, I did take a video that shows that there is
a bulge on one side only:
http://video.tinypic.com/player.php?v=2cn8fuv
I am now convinced that the wheel is unsafe to ride (we hadn't ridden
the bike since I discovered the bulge) and will go about looking for a
replacement rim. I do wonder, however, how something like this can
happen. A manufacturing defect maybe?
I have been biking less than four years and that something like this
could happen never occurred to me. I can now see how this could lead
to a catastrophic failure of the rim. I'm so glad I posted my concern
here because we often hit speeds in excess of 30, and sometimes 40mph,
on some local downhills on our tandems. I don't like to think about
the possible consequences of the tire blowing off at that kind of
speed.
Thanks so much for taking the time to discover what was staring me in
the face, but I didn't see, due to my inexperience.
Harry
HarryB
You are right about the pressure - I ran between 85 and 95psi on this
wheel. I contacted the manufacturer and was told that they do not have
a maximum recommended pressure on any of their rims.
I have examined the rim more closely, especially after Tim McNamara's
observations, and now agree that the rim is cracking. It will be
replaced!
Thank you,
Harry
jobst....@stanfordalumni.org
>>>> Here are some pictures I took of the rim. (Taking close-up pictures
>>>> of a rim is difficult!)
>>>> The first picture shows the area of the bulge. The line that runs
>>>> through the middle of the braking surface is a gouge, not a crack,
>>>> that goes all the way around the rim. The piece of tape points to
>>>> the widest part of the bulge: http://i11.tinypic.com/29gbv4p.jpg
>>> Is that a set of parallel cracks in the sidewall, about 1/2 and 1/2
>>> of the way up?
>>>> The next picture shows the inside of the rim at the bulge area:
>>>> http://i9.tinypic.com/2cnw3n5.jpg The bulge is on the right side in
>>>> this last picture: http://i10.tinypic.com/4hip6xd.jpg
>>> There's no impact mark on the edge of the rim, which I think argues
>>> against having hit something. I think you're looking at a failing
>>> rim.
>> I think you are looking at a brand new rim, the brake track of
>> which hasn't even shown brake wear. The way the rim is shown, I
>> cannot see the "bulge". If the rim were lying on a flat surface,
>> bulge downward, and photographed on edge, we might be able to see
>> what is claimed.
> In order to get a better look at the bulging area I cleaned it up with
> a 3M ScotchBrite pad. As I wrote in my initial post, the rim has about
> 3,000 miles on it.
I'm sorry, I missed that. For this exercise I suppose leaving the rim
as it was last used would have been easier to assess its problem.
> I tried to take a picture the way you suggested, but was unable to
> show the bulge that way either. I did however take a short,
> unfortunately poor quality, video of the wheel in my truing stand. I
> do think it shows that there is a bulge even though it doesn't shed
> any light on what caused it:
http://video.tinypic.com/player.php?v=2cn8fuv
It seems to have radial and lateral deformation. I notice that I can
see the inside of the rim on part of the revolution. As you say, it's
hard to see what is occurring but the rim is not in good shape from
that video.
If it has the crack that is hardly visible, you should be able to bend
it in and out manually without much effort.
Jobst Brandt
jobst....@stanfordalumni.org
>> because of reflection on #2, it's not possible to say for sure, but
>> the combination of #1 & #2 lead me to think this rim is cracking.
>> suggest you replace asap.
>> also for future reference, stick to /rim/ manufacturer tire
>> pressure - you don't say what you're running, but i'll bet it's not
>> 60lbs!
> You are right about the pressure - I ran between 85 and 95psi on
> this wheel. I contacted the manufacturer and was told that they do
> not have a maximum recommended pressure on any of their rims.
You should be able to run more than 100psi considering downhill
braking can raise that to 130psi. I can' imagine a reputable rim
manufacturer saying you can't use this rim for descending. They need
to survive at least 150psi as I see it.
> I have examined the rim more closely, especially after Tim
> McNamara's observations, and now agree that the rim is cracking. It
> will be replaced!
Who pays? And who rebuilds the wheel?
Jobst Brandt
data...@yahoo.com
send it to harris they'll resell it
data...@yahoo.com
looks like you could take-hahahaha this is a trip right-two 1x6 or
better 2x6 or 8" long enough to cover the bend then brace the straight
part with equal thickness lumber on a FLAT concrete floor, cover the
bend with the 'extra' 2x, kneel on that peice and bang it with a heavy
hammer
bang once take a look at it, bang twice ect...work up to getting it
straight in incremental blows
then drink 2 quarts urine every day for two weeks
data...@yahoo.com
HarryB
>Harry B? writes:
>
>>> because of reflection on #2, it's not possible to say for sure, but
>>> the combination of #1 & #2 lead me to think this rim is cracking.
>>> suggest you replace asap.
>
>>> also for future reference, stick to /rim/ manufacturer tire
>>> pressure - you don't say what you're running, but i'll bet it's not
>>> 60lbs!
>
>> You are right about the pressure - I ran between 85 and 95psi on
>> this wheel. I contacted the manufacturer and was told that they do
>> not have a maximum recommended pressure on any of their rims.
>
>You should be able to run more than 100psi considering downhill
>braking can raise that to 130psi. I can' imagine a reputable rim
>manufacturer saying you can't use this rim for descending. They need
>to survive at least 150psi as I see it.
>
My choice of words may have been poor. What I meant is that I agreed
that I did not run 60psi - I ran 85-95psi. When I spoke with the
person at Velocity he said that they don't have a maximum recommended
pressure. From the context (I told him what pressures I ran on that
rim) I understood him to mean that their rims are capable of handling
the pressure of any tire that can be mounted on their rims.
>> I have examined the rim more closely, especially after Tim
>> McNamara's observations, and now agree that the rim is cracking. It
>> will be replaced!
>
>Who pays? And who rebuilds the wheel?
>
>Jobst Brandt
I was told that Velocity stopped making this particular rim (20" DeepV
BMX) at least five years ago. (The bike is a 2005 model.) When I spoke
with Velocity I hadn't yet realized that the rim was failing due to a
crack and so didn't ask if they stand behind this rim that is at least
five years old that apparently has a manufacturing defect. I'll try to
call about this tomorrow.
Harry
jobst....@stanfordalumni.org
> I was told that Velocity stopped making this particular rim (20"
> DeepV BMX) at least five years ago. (The bike is a 2005 model.) When
> I spoke with Velocity I hadn't yet realized that the rim was failing
> due to a crack and so didn't ask if they stand behind this rim that
> is at least five years old that apparently has a manufacturing
> defect. I'll try to call about this tomorrow.
I have a better idea. Buy a new better quality rim and transfer the
spokes over and build your own wheel. This could be the beginning of
a new mode of DIY maintenance.
Jobst Brandt
HarryB
Interesting that you should mention this because I have thought about
doing exactly that. However, I'm hesitant: Although I am a DIY'er,
have the tools, and have trued our wheels a number of times, I have
never built a wheel. Do I want to practice on the front wheel of one
of our tandems? This is a 20" wheel, so my Park Tool tensiometer won't
work on it. And since I would have to dismantle the defective wheel in
order to reuse the hub, I wouldn't have another 20" wheel to which I
could compare the tone. And, the wheel is dished because the hub was
designed for a disk brake (why would RANS select a hub like that for
the front wheel of their Screamer?). I will have to give it some more
thought.
Harry
PS: My wife/stoker gave me a book called, "The Bicycle Wheel" for
Christmas. One of the first things I learned from this book was that I
was wrong! I had sometimes mused out loud about how our loaded tandem
actually hung from a couple of thin spokes and my stoker agreed that
this was rather amazing. But, the author claims otherwise! He writes
that our loaded tandem actually stands on a couple of its spokes. So,
I had to explain to my wife that I was wrong. (No big deal she told me
- we've been married for more than three decades and I've had to admit
to being wrong many times...)
daveornee
Why not start with a non-disc hub?
Since you will not likely be able to re-use the spokes either since
finding another Deep V 20" rim or other rim with the same ERD, you will
need new spokes too.
I have a little experience with the 20" (406) Deep V rims. I built a
pair for a local friend. His daughter uses it on her BMX. She uses
the bicycle regularly and the wheels have stayed true. The hubs are
32H Avocet so there is minimal spokes compared to most 48H BMX wheels.
David Ornee, Western Springs, IL
--
daveornee
data...@yahoo.com
but before you go, try straightening the rim.
as with the JB method, holding the straight section fast avoiding a
secondary effect from banging on the bulge-the collision test videos?-
is essential.
if a local pile if used pallets/skid is available, find hardwood for
the banging pieces. grease them. leaving room for the rim's two points
at the end of the bulge for sliding back into a factory length rather
than freezing to the wood surface then deforming the bulge when the
hammer force dams is also essential.
also tops is placing a stationary vice of two boards-basswood #2-
immediately behind the points the bulge take off from. and find a fat
friend to stand on those fixing planks.
i haven't tried this but i'm certian the other posters have: use a
vise with the bulge spokes removed. cover the vises metal jaws with
hardwood/formica particle board/delrin rectangles and grease the
rectangles.
if you suckseed then you have a spare wheel! if not, experience.
tell him about the electrical tape...
Tim McNamara
HarryB <No...@none.net> wrote:
> You guys are sharp! I think this is what you are referring to:
> http://i9.tinypic.com/2h3mw09.jpg
Yes, that's it.
> The top groove goes all the way around the rim and so I assume it is
> a groove from something that was in the brake pad. The lower one, you
> noted, is different, and probably is a crack. It must be located
> about here: http://i7.tinypic.com/301nhc2.jpg
The crack would be either just above or below the rim bed (the "floor"
of the rim as you look at it edge-on). Since the rim is bulging out on
the side with the crack, I'd guess it's just above the rim bed and that
tire pressure flexes it outwards. I'd also guess that the bulge is
worse with the tire installed and inflated.
As for cause, someone with more knowledge of materials and engineering
than I would have to speculate on that. Flaw in the rim extrusion,
perhaps? I would hope that tire pressure would not be an issue, rim
should be able to withstand large pressures (150 psi) to provide a
margin of safety. As Jobst notes, descending with lots of braking can
raise rim temperatures well over the boiling point of water which in
turn raises tire pressure quite a bit. I'd hate to have a rim so
fragile that it cracks while going down a mountain from the increase in
pressure!
jobst....@stanfordalumni.org
>>> I was told that Velocity stopped making this particular rim (20"
>>> DeepV BMX) at least five years ago. (The bike is a 2005 model.)
>>> When I spoke with Velocity I hadn't yet realized that the rim was
>>> failing due to a crack and so didn't ask if they stand behind this
>>> rim that is at least five years old that apparently has a
>>> manufacturing defect. I'll try to call about this tomorrow.
>> I have a better idea. Buy a new better quality rim and transfer
>> the spokes over and build your own wheel. This could be the
>> beginning of a new mode of DIY maintenance.
> Interesting that you should mention this because I have thought
> about doing exactly that. However, I'm hesitant: Although I am a
> DIY'er, have the tools, and have trued our wheels a number of times,
> I have never built a wheel. Do I want to practice on the front
> wheel of one of our tandems? This is a 20" wheel, so my Park Tool
> tensiometer won't work on it. And since I would have to dismantle
> the defective wheel in order to reuse the hub, I wouldn't have
> another 20" wheel to which I could compare the tone. And, the wheel
> is dished because the hub was designed for a disk brake (why would
> RANS select a hub like that for the front wheel of their Screamer?).
> I will have to give it some more thought.
I haven't used a tensiometer in years although I have a few among my
tools. Tone is more important because you need to adjust spokes that
are out of line in tension as you work and reaching for a tensiometer
all the time is tedious. You can get the idea of how tight, as you
say from other working wheels, but probably a bit tighter.
> Harry PS: My wife/stoker gave me a book called, "The Bicycle Wheel"
> for Christmas. One of the first things I learned from this book was
> that I was wrong! I had sometimes mused out loud about how our
> loaded tandem actually hung from a couple of thin spokes and my
> stoker agreed that this was rather amazing. But, the author claims
> otherwise! He writes that our loaded tandem actually stands on a
> couple of its spokes. So, I had to explain to my wife that I was
> wrong. (No big deal she told me - we've been married for more than
> three decades and I've had to admit to being wrong many times...)
Ooh, I had no idea writing such stuff could cause family discord.
Good work in bridging that faux pas.
Jobst Brandt
daveornee
it was delivered to you and tried to straighten it ,,, and it started
to crack at that point in time. Deep V used in the 20" is the same
extrusion as used in the 26" MTB rims. I used over 200 of them without
any problems and have a 40H pair on our tandem with over 8,000 miles
without any problems.
Despite all of that, you should replace the rim. You will need to
evaluate the hub and spokes as to possible re-use.
What rear rim do you use?
Is matching important?
--
daveornee
jim beam
> Harry B? writes:
>
>>> because of reflection on #2, it's not possible to say for sure, but
>>> the combination of #1 & #2 lead me to think this rim is cracking.
>>> suggest you replace asap.
>
>>> also for future reference, stick to /rim/ manufacturer tire
>>> pressure - you don't say what you're running, but i'll bet it's not
>>> 60lbs!
>
>> You are right about the pressure - I ran between 85 and 95psi on
>> this wheel. I contacted the manufacturer and was told that they do
>> not have a maximum recommended pressure on any of their rims.
>
> You should be able to run more than 100psi considering downhill
> braking can raise that to 130psi. I can' imagine a reputable rim
> manufacturer saying you can't use this rim for descending. They need
> to survive at least 150psi as I see it.
mavic open pros are not rated for that. and the pressure rating drops
as the tire width goes up. the point the op needs to consider is
whether the pressure is appropriate to the tire /and/ rim. running a
2.5" tire at 130psi is /not/ appropriate! blanket statements, as usual
jobst, don't work.
jim beam
> On 06 Apr 2007 02:24:58 GMT, jobst....@stanfordalumni.org wrote:
>
>> Harry B? writes:
>>
>>>> because of reflection on #2, it's not possible to say for sure, but
>>>> the combination of #1 & #2 lead me to think this rim is cracking.
>>>> suggest you replace asap.
>>>> also for future reference, stick to /rim/ manufacturer tire
>>>> pressure - you don't say what you're running, but i'll bet it's not
>>>> 60lbs!
>>> You are right about the pressure - I ran between 85 and 95psi on
>>> this wheel. I contacted the manufacturer and was told that they do
>>> not have a maximum recommended pressure on any of their rims.
>> You should be able to run more than 100psi considering downhill
>> braking can raise that to 130psi. I can' imagine a reputable rim
>> manufacturer saying you can't use this rim for descending. They need
>> to survive at least 150psi as I see it.
>>
> My choice of words may have been poor. What I meant is that I agreed
> that I did not run 60psi - I ran 85-95psi.
that's high for a 20" wheel.
> When I spoke with the
> person at Velocity he said that they don't have a maximum recommended
> pressure.
that's not encouraging. there /has/ to be a maximum limit. if they
haven't bothered to check, i'd not use their rims. more likely however,
you need to drill deeper into the organization and find the right person
that knows.
> From the context (I told him what pressures I ran on that
> rim) I understood him to mean that their rims are capable of handling
> the pressure of any tire that can be mounted on their rims.
there has to be a limit.
jim beam
of course, if the rim was perfectly rigid, then you wouldn't be jumping
to that conclusion. you're simply looking at some of the spokes and
drawing a hasty conclusion. [just like most of the rest of your
"engineering" hypotheses].
data...@yahoo.com
clean rim "crack" with thinner and brush/abrasive pad/razor
shine intense light on clean crack
examine
place PCblaster on flat screwdriver end
spread blaster on "crack"
hold upside down.
watch blaster seep thru crack
schedule eye exam
drink 1 quart urine evry day for a week
Tim McNamara
jim beam <spamv...@bad.example.net> wrote:
> jobst....@stanfordalumni.org wrote:
> > Harry B? writes:
> >
> >>> because of reflection on #2, it's not possible to say for sure,
> >>> but the combination of #1 & #2 lead me to think this rim is
> >>> cracking. suggest you replace asap.
> >
> >>> also for future reference, stick to /rim/ manufacturer tire
> >>> pressure - you don't say what you're running, but i'll bet it's
> >>> not 60lbs!
> >
> >> You are right about the pressure - I ran between 85 and 95psi on
> >> this wheel. I contacted the manufacturer and was told that they do
> >> not have a maximum recommended pressure on any of their rims.
> >
> > You should be able to run more than 100psi considering downhill
> > braking can raise that to 130psi. I can' imagine a reputable rim
> > manufacturer saying you can't use this rim for descending. They
> > need to survive at least 150psi as I see it.
>
> mavic open pros are not rated for that. and the pressure rating
> drops as the tire width goes up.
Hmmm. If that's true, then it is a further sign of increasing
ineptitude at Mavic. Their rims from 20 years ago could withstand high
pressures and largish (26-28 mm) tires without any problem. It seems
that Mavic's progress continues to be retrograde.
Tim McNamara
jim beam <spamv...@bad.example.net> wrote:
Yes, but perhaps the limit is 200 psi so the point would be moot.
data...@yahoo.com
carl...@comcast.net
Dear Tim,
Just to keep things straight, the rim in question in this thread is a
20" Velocity rim, not a Mavic:
"I discovered that one side of the rim (20" Velocity DeepV) on my
recumbent tandem has a bulge."
http://groups.google.com/group/rec.bicycles.tech/msg/a6ef4fe1763d0333
Later, the original poster asked the manufacturer what the maximum
pressure is for that rim, and received a less than impressive answer:
"I contacted the manufacturer and was told that they do not have a
maximum recommended pressure on any of their rims."
Rims do have limits. Things get worse with heavy loads (like tandems),
too-wide tires, and excessive infaltion.
Here's a lurid picture of what happened when 275-lb rider put 500
miles on cxp33 rim with a too-wide tire and what he mistakenly thought
was an acceptable pressure:
http://members.cox.net/younggg/Wheel1.jpg
Numerous posters insisted that the disaster was due to a bad
manufacturer. I argued that it was due to a 275-lb rider inflating an
oversized 37mm tire to 90 psi on a rim rated for a maximum of 117 psi
with a maximum 28mm tire:
http://groups.google.com/group/rec.bicycles.tech/msg/bae2bdf666aeeab7
Velocity apparently doesn't give out maximum tire widths and
inflations, but Mavic does, which is what Jim Beam probably had in
mind when he mentioned a Mavic Open Pro rim as an example.
Below are a few Mavic recommended rim limits. Maximum pressure rises
as the tire narrows and exerts less force on the rim.
max__psi tire_mm
track/triathlon
cxp33 117..146 28..19
open pro 117..146 28..19
reflex 117..146 28..19
road
kys es 103..146 32..19
cosmic e 103..146 32..19
road
a719 103...66 50..28
a119 103...66 50..28
a319 103...66 50..28
mtb
xc717 113...59 53..25
xm317 69...49 58..48
ex721 49...32 76..58
http://www.mavic.com/ewb_pages/p/produit_jante_cxp33.php?onglet=3&gamme=route
You can see specific Mavic rim limits by clicking on products in the
link above, choosing a category (road, for example), picking a rim,
and finally clicking on "technical information" (not "technical
features").
Again, this picture shows what can happen in 500 miles if a rider
ignores recommended pressures, tire widths, and loads:
http://members.cox.net/younggg/Wheel1.jpg
Cheers,
Carl Fogel
Gary Young
> HarryB wrote:
>> On 06 Apr 2007 02:24:58 GMT, jobst....@stanfordalumni.org wrote:
>>
>>> Harry B? writes:
>>>
>>>>> because of reflection on #2, it's not possible to say for sure, but
>>>>> the combination of #1 & #2 lead me to think this rim is cracking.
>>>>> suggest you replace asap.
>>>>> also for future reference, stick to /rim/ manufacturer tire
>>>>> pressure - you don't say what you're running, but i'll bet it's not
>>>>> 60lbs!
>>>> You are right about the pressure - I ran between 85 and 95psi on
>>>> this wheel. I contacted the manufacturer and was told that they do
>>>> not have a maximum recommended pressure on any of their rims.
>>> You should be able to run more than 100psi considering downhill
>>> braking can raise that to 130psi. I can' imagine a reputable rim
>>> manufacturer saying you can't use this rim for descending. They need
>>> to survive at least 150psi as I see it.
>>>
>> My choice of words may have been poor. What I meant is that I agreed
>> that I did not run 60psi - I ran 85-95psi.
>
> that's high for a 20" wheel.
>
What's the diameter of the rim got to do with it?
Recumbent riders often use 20" tires rated to 100 psi or more:
http://gaerlan.com/bikeparts/parts/451wheel/wheel.html
http://gaerlan.com/bikeparts/parts/406wheel/wheelbmx.html
The Mavic recommendations seem to show that the width of the tire is the
important factor. In what way does a small diameter lessen the rim's
ability to withstand high pressures?
data...@yahoo.com
>
> The Mavic recommendations seem to show that the width of the tire is the
> important factor. In what way does a small diameter lessen the rim's
good question. the ERTRO people and whoever in asia tried to give us
interchangability so we wouldn't get confused, wreck equipment, throw
up and go away as we're not up to sheldon brown
encyclopediocyclecompandium standards of swapping the corn bolt from a
'57 whiplet to the '63
brevet 250.
assume this is true of the tire wall at rim edge and below AND the
ridge the rim has to hold the tire.
IS THAT TRUE?
i don't know...
butbutbut if using the vise for squeezing a bulge out iudong the
formica/particle board/grease/spokes behind bulge but not in the vise
method, it's wize to put a bit of pressure on the rim, not enough to
actually move it, then bash the vize with a hammer, unleash rim, and
reset-avoiding dimpling the formica in one spot causing it to jamb
there, and off course regreasing.
but i don't know if that method works? maybe if I erect a sign then
set it on fire...
Tim McNamara
carl...@comcast.net wrote:
Indeed. I was replying to a comment about Mavic Open Pros.
Tim McNamara
> Here's a lurid picture of what happened when 275-lb rider put 500
> miles on cxp33 rim with a too-wide tire and what he mistakenly
> thought was an acceptable pressure:
>
> http://members.cox.net/younggg/Wheel1.jpg
Another reason to not use current Mavic products. The company seems
intent on going from strength to weakness.
carl...@comcast.net
Dear Tim,
Do you know of any manufacturers who post maximum recommended rim
widths and pressures for their rims that are higher?
Cheers,
Carl Fogel
Gary Young
It's hard to draw any conclusions from Mavic's recommendations
without further information. Such recommendations are sometimes a sign of
fragility, not strength -- for instance, titanium-spindled pedals typically
carry a maximum weight recommendation, whereas steel spindles usually
don't.
Mavic may have more concern for safety than velocity, or it may push the
envelope more than velocity, or it may just have more nervous lawyers than
velocity. Not to mention the fact that we don't seem to know anything
about how Mavic derived its recommendations.
carl...@comcast.net
wrote:
Dear Gary,
No offense, but I draw the conclusion that Mavic is saying that those
are the maximum recommended pressures for tires of those widths on
those rims.
If other manufacturers say nothing, they say less than Mavic.
If they say more, I'd love to add the link to my list.
Here's Sheldon's edited table of a German table for safe tire widths
versus rim widths, with this comment from Sheldon:
If you use a very wide tire on a narrow rim, you risk sidewall or rim
failure.
http://www.sheldonbrown.com/tire_sizing.html#width
Here's the original table:
http://tandem-fahren.de/Technik/Reifentips/index.html
True, we don't know the details of how the table was devised, but a
picture like this after 500 miles suggests that a combination of too
much pressure, load, and tire width is indeed a bad idea:
Gary Young
I have no quarrel with that, but you seemed to be drawing the conclusion
that Mavic's recommendations speak to the robustness of its rims.
Otherwise why bring it up in reply to Tim's comment? For what it's worth,
though I avoid Mavic rims, I think Tim's to-hell-in-a-handbasket comment
was likewise under-determined by his evidence.
>
> If other manufacturers say nothing, they say less than Mavic.
And that says what about the quality of their rims?
>
> If they say more, I'd love to add the link to my list.
>
> Here's Sheldon's edited table of a German table for safe tire widths
> versus rim widths, with this comment from Sheldon:
>
> If you use a very wide tire on a narrow rim, you risk sidewall or rim
> failure.
>
> http://www.sheldonbrown.com/tire_sizing.html#width
>
> Here's the original table:
>
> http://tandem-fahren.de/Technik/Reifentips/index.html
Unfortunately, my high-school German has all but evaporated, but if google
translate is any good, then the table is derived from recommendations by
the European Tire and Rim Technical Organisation (and was made a
standard in DIN7800?).
The only factors in that table are the width of the rim bed and of the
tire. In other words, all it seems to say is that a tire of a certain
width will work with a rim of a certain width regardless of whether the
rim is made by Mavic or Velocity or whomever.
If Mavic's recommendations are drawn from ERTRO, then they don't tell us
anything about the quality of Mavic's rims in particular. I'll have to see
if I can track down the standard.
> True, we don't know the details of how the table was devised,
but a
> picture like this after 500 miles suggests that a combination of too
> much pressure, load, and tire width is indeed a bad idea:
>
> http://members.cox.net/younggg/Wheel1.jpg
>
I'm not disputing that certain combinations are bad (though was a rim
defect ever ruled out in that failure?). What I dispute is the idea that
publishing a table of recommendations is very probative
evidence of quality, especially since such
recommendations are often given when a less-than-robust part is put on the
market (as with titanium pedal spindles).
Gary Young
<snip>
> If Mavic's recommendations are drawn from ERTRO, then they don't tell us
> anything about the quality of Mavic's rims in particular. I'll have to see
> if I can track down the standard.
>
ETRTO has a website, but there are fees for its standards and
recommendations:
HarryB
>HarryB wrote:
[snip]
>> My choice of words may have been poor. What I meant is that I agreed
>> that I did not run 60psi - I ran 85-95psi.
>
>that's high for a 20" wheel.
The tire that was on the rim is a Primo Comet 20x1.5 which is rated at
100psi max. When I spoke with the person at Velocity he said that the
pressures I ran were no problem for that rim. And I wouldn't feel
comfortable running much lower pressures on a tandem.
>
>> When I spoke with the
>> person at Velocity he said that they don't have a maximum recommended
>> pressure.
>
>that's not encouraging. there /has/ to be a maximum limit. if they
>haven't bothered to check, i'd not use their rims. more likely however,
>you need to drill deeper into the organization and find the right person
>that knows.
>
Peter White, who has a reputation among many tandemists as building
some of the best wheels, notes that the Velocity DeepV "...is by far
my strongest 26" rim." Knowing Peter White's opinion of the DeepV rim
and then hearing that the person at Velocity had no concerns at all
about running 95psi on our rim on our tandem leaves me with a
comfortable feeling about Velocity's DeepV rims, this apparent
manufacturing defect not withstanding.
>> From the context (I told him what pressures I ran on that
>> rim) I understood him to mean that their rims are capable of handling
>> the pressure of any tire that can be mounted on their rims.
>
>there has to be a limit.
>
Harry
jim beam
> On Fri, 06 Apr 2007 10:58:39 -0700, jim beam
> <spamv...@bad.example.net> wrote:
>
>> HarryB wrote:
> [snip]
>>> My choice of words may have been poor. What I meant is that I agreed
>>> that I did not run 60psi - I ran 85-95psi.
>> that's high for a 20" wheel.
> The tire that was on the rim is a Primo Comet 20x1.5 which is rated at
> 100psi max.
ok, that's the tire. now let's look at the rim. a 1.5" tire is ~43mm.
using a linear model on the mavic numbers, they recommend a 3.22psi
drop per mm increase in tire width. that would give ~70psi max for your
tire width. unless you /know/ the velocity to be stronger with respect
to its extrusion axis, you should regard the mavic numbers as a max for
your rim too.
When I spoke with the person at Velocity he said that the
> pressures I ran were no problem for that rim. And I wouldn't feel
> comfortable running much lower pressures on a tandem.
>>> When I spoke with the
>>> person at Velocity he said that they don't have a maximum recommended
>>> pressure.
>> that's not encouraging. there /has/ to be a maximum limit. if they
>> haven't bothered to check, i'd not use their rims. more likely however,
>> you need to drill deeper into the organization and find the right person
>> that knows.
>>
> Peter White, who has a reputation among many tandemists as building
> some of the best wheels, notes that the Velocity DeepV "...is by far
> my strongest 26" rim." Knowing Peter White's opinion of the DeepV rim
> and then hearing that the person at Velocity had no concerns at all
> about running 95psi on our rim on our tandem leaves me with a
> comfortable feeling about Velocity's DeepV rims, this apparent
> manufacturing defect not withstanding.
the real determinant of tire pressure is handling and bottoming. next
time, try the lower pressure and see how it goes. the # on a tire
sidewall has /nothing/ to do with what the tire should be run at in any
particular application.
daveornee
Since Harry is going to replace the rim, what width rim should he go
with to allow him use the maximum inflation (assuming he wants to stay
with the same tire)?
--
daveornee
jim beam
er, yes, 38.1. it helps not having your calculator on octal. well
spotted! that gives max inflation pressure of ~85psi.
> Since Harry is going to replace the rim, what width rim should he go
> with to allow him use the maximum inflation (assuming he wants to stay
> with the same tire)?
better to just get the rim, then worry about the tire and pressure.
Tim McNamara
Gary Young <garyy...@gmail.com> wrote:
> On Fri, 06 Apr 2007 23:28:01 -0600, carlfogel wrote:
>
> > On Fri, 06 Apr 2007 22:36:27 -0500, Gary Young
> > <garyy...@gmail.com> wrote:
> >
> >>On Fri, 06 Apr 2007 20:46:48 -0600, carlfogel wrote:
> >>
> >>> On Fri, 06 Apr 2007 20:59:41 -0500, Tim McNamara
> >>> <tim...@bitstream.net> wrote:
> >>>
> >>>>In article <3ibd13d4b8kb3ckbm...@4ax.com>,
> >>>> carl...@comcast.net wrote:
> >>>>
> >>>>> Here's a lurid picture of what happened when 275-lb rider put
> >>>>> 500 miles on cxp33 rim with a too-wide tire and what he
> >>>>> mistakenly thought was an acceptable pressure:
> >>>>>
> >>>>> http://members.cox.net/younggg/Wheel1.jpg
> >>>>
> >>>>Another reason to not use current Mavic products. The company
> >>>>seems intent on going from strength to weakness.
> >>>
> >>> Do you know of any manufacturers who post maximum recommended rim
> >>> widths and pressures for their rims that are higher?
> >>>
> >>
> >>It's hard to draw any conclusions from Mavic's recommendations
> >>without further information. Such recommendations are sometimes a
> >>sign of fragility, not strength -- for instance, titanium-spindled
> >>pedals typically carry a maximum weight recommendation, whereas
> >>steel spindles usually don't.
> >>
> >>Mavic may have more concern for safety than velocity, or it may
> >>push the envelope more than velocity, or it may just have more
> >>nervous lawyers than velocity. Not to mention the fact that we
> >>don't seem to know anything about how Mavic derived its
> >>recommendations.
> >
> > No offense, but I draw the conclusion that Mavic is saying that
> > those are the maximum recommended pressures for tires of those
> > widths on those rims.
>
> I have no quarrel with that, but you seemed to be drawing the
> conclusion that Mavic's recommendations speak to the robustness of
> its rims. Otherwise why bring it up in reply to Tim's comment? For
> what it's worth, though I avoid Mavic rims, I think Tim's
> to-hell-in-a-handbasket comment was likewise under-determined by his
> evidence.
Fair enough. I spoke more from having had a spate of Mavic rim failures
and having sworn off the brand as a result, except for my collection of
MA-2 rims which have been excellent. The only trouble I have had with
the MA-2 rims is that the joint often results in a high or low spot,
suggesting that quality assurance was not what it ought to have been in
that manufacturing step.
Michael Press
Gary Young <garyy...@gmail.com> wrote:
..or they make shoddy rims and publish limits
to evade warranty claims.
jobst....@stanfordalumni.org
>>>>>> Here's a lurid picture of what happened when 275-lb rider put
>>>>>> 500 miles on cxp33 rim with a too-wide tire and what he
>>>>>> mistakenly thought was an acceptable pressure:
http://members.cox.net/younggg/Wheel1.jpg
>>>>> Another reason to not use current Mavic products. The company
>>>>> seems intent on going from strength to weakness.
>>>> Do you know of any manufacturers who post maximum recommended rim
>>>> widths and pressures for their rims that are higher?
>>> It's hard to draw any conclusions from Mavic's recommendations
>>> without further information. Such recommendations are sometimes a
>>> sign of fragility, not strength -- for instance, titanium-spindled
>>> pedals typically carry a maximum weight recommendation, whereas
>>> steel spindles usually don't.
>>> Mavic may have more concern for safety than velocity, or it may
>>> push the envelope more than velocity, or it may just have more
>>> nervous lawyers than velocity. Not to mention the fact that we
>>> don't seem to know anything about how Mavic derived its
>>> recommendations.
>> No offense, but I draw the conclusion that Mavic is saying that
>> those are the maximum recommended pressures for tires of those
>> widths on those rims.
> I have no quarrel with that, but you seemed to be drawing the
> conclusion that Mavic's recommendations speak to the robustness of
> its rims. Otherwise why bring it up in reply to Tim's comment? For
> what it's worth, though I avoid Mavic rims, I think Tim's
> to-hell-in-a-handbasket comment was likewise under-determined by his
> evidence.
>> If other manufacturers say nothing, they say less than Mavic.
> And that says what about the quality of their rims?
>> If they say more, I'd love to add the link to my list.
>> Here's Sheldon's edited table of a German table for safe tire
>> widths versus rim widths, with this comment from Sheldon:
>> If you use a very wide tire on a narrow rim, you risk sidewall or
>> rim failure.
http://www.sheldonbrown.com/tire_sizing.html#width
>> Here's the original table:
>> http://tandem-fahren.de/Technik/Reifentips/index.html
> Unfortunately, my high-school German has all but evaporated, but if
> Google translate is any good, then the table is derived from
> recommendations by the European Tire and Rim Technical Organisation
> (and was made a standard in DIN7800?).
> The only factors in that table are the width of the rim bed and of
> the tire. In other words, all it seems to say is that a tire of a
> certain width will work with a rim of a certain width regardless of
> whether the rim is made by Mavic or Velocity or whomever.
> If Mavic's recommendations are drawn from ERTRO, then they don't
> tell us anything about the quality of Mavic's rims in
> particular. I'll have to see if I can track down the standard.
Hold the phone! As we have discussed here before, these
recommendations are not for rim strength but rather for tire blow-off
which is dependent on the lateral angle of the tire casing from the
bead. I don't believe these have anything to do with rim failures,
knowing how high some tires are inflated.
>> True, we don't know the details of how the table was devised, but a
>> picture like this after 500 miles suggests that a combination of
>> too much pressure, load, and tire width is indeed a bad idea:
http://members.cox.net/younggg/Wheel1.jpg
> I'm not disputing that certain combinations are bad (though was a
> rim defect ever ruled out in that failure?). What I dispute is the
> idea that publishing a table of recommendations is very probative
> evidence of quality, especially since such recommendations are often
> given when a less-than-robust part is put on the market (as with
> titanium pedal spindles).
I think we are way off base with this matter. The picture of the
split rim does not explain how that failure came to be or what the
tire was inflated. You'll notice this was not a "jersey-pro" with
16-spoke wheels and high pressure racing tires. It is a mundane,
transportation bicycle with no step-in pedals or toe clips, not one to
run excessively high pressure.
Jobst Brandt
Gary Young
Do you know why Mavic publishes maximum recommended tire pressures for its
rims or how it derives its figures? I suppose it's possible that
high-pressures lead to tire blow-offs, which lead to damaged rims (during
the resulting crash, not as a direct result of excessive pressure), which
lead to warranty claims that Mavic doesn't want to deal with (with good
reason). Or maybe Mavic doesn't have a particularly good understanding of
what leads to rim failure?
jim beam
give us a break - they have the minerals to publish tire pressure
recommendations [among other things]. where do you think they get those
numbers from? tarot?
and while you're thinking about that, here's your homework assignment
for the weekend...
"anisotropy: discuss"
HarryB
<spamv...@bad.example.net> wrote:
>HarryB wrote:
>> On Fri, 06 Apr 2007 10:58:39 -0700, jim beam
>> <spamv...@bad.example.net> wrote:
>>
>>> HarryB wrote:
>> [snip]
>>>> My choice of words may have been poor. What I meant is that I agreed
>>>> that I did not run 60psi - I ran 85-95psi.
>>> that's high for a 20" wheel.
>> The tire that was on the rim is a Primo Comet 20x1.5 which is rated at
>> 100psi max.
>
>ok, that's the tire. now let's look at the rim. a 1.5" tire is ~43mm.
> using a linear model on the mavic numbers, they recommend a 3.22psi
>drop per mm increase in tire width. that would give ~70psi max for your
>tire width. unless you /know/ the velocity to be stronger with respect
>to its extrusion axis, you should regard the mavic numbers as a max for
>your rim too.
>
I have not given any thought to the relationship between tire pressure
and rim strength. None of the discussions I remember reading dealing
with tire pressures on tandems have discussed this. And I'm not
familiar with the "mavic numbers" to which you refer. However, doing a
little googling I came across the following pertinent information at
Sheldon Brown's site:
http://www.sheldonbrown.com/tire_sizing.html
http://www.sheldonbrown.com/tires.html
Recommended tire widths for this rim (18mm wide) are about 27-42mm.
The tire that came with the bike is a 20x1.5", so its 38mm width falls
within these guidelines. Sheldon has another chart which he claims is
helpful for getting a rough idea for a starting tire pressure. For a
37mm tire he recommends that the tire be inflated to about 60psi for
each 100# of weight that it carries. Our combined weight (2 riders
plus tandem) is somewhere around 360#. Extrapolating from his chart I
find that his starting recommendation is inflating our front tire to a
little over 100psi - which just happens to be the "recommended"
maximum pressure for this tire. So, when I have inflated this tire to
85-95psi, I certainly haven't been overinflating it based on Sheldon's
recommendation. (I suspect that inflating this tire to your suggested
60psi would greatly increase the likelihood of pinch flats on our
tandem.)
You suggested that these types of pressures are too great for this
DeepV rim. Maybe so, but I have read nothing but good things about
Velocity's rims on the tandem lists. Since Velocity no longer makes
the DeepV in a 20" size they recommended that I consider their Aero
Heat. And once again, Peter White comments that this is an incredibly
strong rim. Sounds good enough for me.
Harry
[snip]
Sandy
Gary Young <garyy...@gmail.com> a réfléchi, et puis a déclaré :
> ... maybe Mavic doesn't have a
> particularly good understanding of what leads to rim failure?
>
Well, of course, Gary. What would a little manufacturing company know
compared to the extensive wisdom and engineering expertise you and others
offer, especially here, where it's about chest-thumping, not actual
fabrication or business?!
So I, and a lot of other future customers, look forward to your new
enterprise, where you lay it all on the line, fearing nothing, as you
demolish that ratty gang over there (oops!, over here, I mean) and save the
cycling world. That must be the positive contribution you had in mind, when
you write, yes?
--
Sandy
--
Il n'est aucune sorte de sensation qui soit plus vive
que celle de la douleur ; ses impressions sont sûres,
elles ne trompent point comme celles du plaisir.
- de Sade.
Gary Young
> Dans le message de news:a7mdnXWC4fN1ioXb...@giganews.com,
> Gary Young <garyy...@gmail.com> a réfléchi, et puis a déclaré :
>
>> ... maybe Mavic doesn't have a
>> particularly good understanding of what leads to rim failure?
>>
> Well, of course, Gary. What would a little manufacturing company know
> compared to the extensive wisdom and engineering expertise you and
> others offer, especially here, where it's about chest-thumping, not
> actual fabrication or business?!
I asked a question (note the squiggly mark at the end of my sentence). I
don't expect anyone to judge Mavic wrong based solely on my say-so. That's
why I directed my question at someone (Jobst) who is an engineer, who has
decades worth of experience working for companies engaged in "actual
fabrication or business," who has designed well-regarded tires that are
fabricated by an actual business, and who has made a lifelong study of
the bicycle wheel. Do you have a problem with that?
As it happens, the question arose not simply because I decided to pose it.
In part, this thread has been concerned with why Mavic publishes
recommendations but other manufacturers like Velocity do not. In fact, the
OP has said that Velocity told him it has no recommendations. In essence,
the question was posed by the practice of one company (or set of companies
-- as far as I can tell, no rim manufacturer other than Mavic makes such
recommendations) as against another similar company. Both companies are
engaged in "actual fabrication or business."
Even if that weren't the case, I still wouldn't feel presumptuous in
asking whether Mavic understands the problem. One need only read the
cycling press to see that a lot of silly products are put on the market.
Mavic certainly seems no exception, what with some of its gimmicky "high
performance" wheels that do badly on aerodynamic tests.
Furthermore, someone who has mastered the practical aspects of a task does
not necessarily have a theoretical understanding of the subject. For proof
of that, I suggest you read what successful makers of bicycles and bicycle
frames say on a whole host of questions like ride quality. At the very
least, you will be perplexed by how they contradict each other.
In any event, though I directed my question at Jobst, I would be glad to
hear your thoughts. Do you know why Mavic publishes recommended tire
pressures but other rim makers don't? Do you know the method Mavic uses to
arrive at its figures? Do you have anything to contribute but a lot of hot
air?
> So I, and a lot of other future customers, look forward to your new
> enterprise, where you lay it all on the line, fearing nothing, as you
> demolish that ratty gang over there (oops!, over here, I mean) and save
> the cycling world. That must be the positive contribution you had in
> mind, when you write, yes?
> --
Sorry, I can't take this any more seriously than when I'm accused of being
anti-American for questioning the judgment of Detroit automakers or the
morality of Halliburton.
Sandy
Gary Young <garyy...@gmail.com> a réfléchi, et puis a déclaré :
> On Sun, 08 Apr 2007 09:24:16 +0200, Sandy wrote:
>
>> Dans le message de
>> news:a7mdnXWC4fN1ioXb...@giganews.com, Gary Young
>> <garyy...@gmail.com> a réfléchi, et puis a déclaré :
>>
>>> ... maybe Mavic doesn't have a
>>> particularly good understanding of what leads to rim failure?
>>>
>> Well, of course, Gary. What would a little manufacturing company
>> know compared to the extensive wisdom and engineering expertise you
>> and others offer, especially here, where it's about chest-thumping,
>> not actual fabrication or business?!
>
> I asked a question (note the squiggly mark at the end of my
> sentence). I don't expect anyone to judge Mavic wrong based solely on
> my say-so. That's why I directed my question at someone (Jobst) who
> is an engineer, who has decades worth of experience working for
> companies engaged in "actual fabrication or business," who has
> designed well-regarded tires that are fabricated by an actual
> business, and who has made a lifelong study of the bicycle wheel. Do
> you have a problem with that?
Everyone knows that I do. Tire design of a full generation ago, and not
design, exactly, does not qualify a person to comment on today's tires.
Even though I have sent him some rather recent test information, which he
does not comment on. Not to mention, that tires and rims are rather
different technologies, though interdependent. I also think that market
pressures would have eliminated a rotten organization long ago, were it
producing such inferior products.
>
> As it happens, the question arose not simply because I decided to
> pose it. In part, this thread has been concerned with why Mavic
> publishes recommendations but other manufacturers like Velocity do
> not. In fact, the OP has said that Velocity told him it has no
> recommendations. In essence, the question was posed by the practice
> of one company (or set of companies -- as far as I can tell, no rim
> manufacturer other than Mavic makes such recommendations) as against
> another similar company. Both companies are engaged in "actual
> fabrication or business."
Posing an insincere question to a group of conversationalists is fine. It
will beget the usual.
>
> Even if that weren't the case, I still wouldn't feel presumptuous in
> asking whether Mavic understands the problem. One need only read the
> cycling press to see that a lot of silly products are put on the
> market. Mavic certainly seems no exception, what with some of its
> gimmicky "high performance" wheels that do badly on aerodynamic tests.
Reading the cycling press does not lead to the conclusion that there are
silly products on the market. Evaluating the press reports may do so, but
that it yet another step forward in thinking, not instantly apparent. Your
idea that Mavic is not an exception, with reference to wheels that "do badly
on aerodynamic tests" is not founded on anything I seem to have read. I'd
be glad of a reference. Presuming, of course, that the wheel was made to
offer exceptional aero benefits.
>
> Furthermore, someone who has mastered the practical aspects of a task
> does not necessarily have a theoretical understanding of the subject.
> For proof of that, I suggest you read what successful makers of
> bicycles and bicycle frames say on a whole host of questions like
> ride quality. At the very least, you will be perplexed by how they
> contradict each other.
So, rather than try to evaluate the manufacturers' presentations, it is
wiser to accept the word of those who lack the detailed knowledge of the
different fabrication methodologies and specific underlying science ? I am
not of that opinion.
>
> In any event, though I directed my question at Jobst, I would be glad
> to hear your thoughts. Do you know why Mavic publishes recommended
> tire pressures but other rim makers don't? Do you know the method
> Mavic uses to arrive at its figures?
No.
> Do you have anything to
> contribute but a lot of hot air?
Hot air ? It was criticism of your commentary. A question mark does not a
question make.
>
>> So I, and a lot of other future customers, look forward to your new
>> enterprise, where you lay it all on the line, fearing nothing, as you
>> demolish that ratty gang over there (oops!, over here, I mean) and
>> save the cycling world. That must be the positive contribution you
>> had in mind, when you write, yes?
>> --
>
> Sorry, I can't take this any more seriously than when I'm accused of
> being anti-American for questioning the judgment of Detroit
> automakers or the morality of Halliburton.
Were you less vague, perhaps I could comment. Are you a fan of Halliburton
or Detroit ?
--
Sandy
The above is guaranteed 100% free of sarcasm,
denigration, snotty remarks, indifference, platitudes, fuming demands that
"you do the math", conceited visions of a better world on wheels according
to [insert NAME here].
Gary Young
> Dans le message de news:s8WdnTzY_Kj1VIXb...@giganews.com,
> Gary Young <garyy...@gmail.com> a réfléchi, et puis a déclaré :
>> On Sun, 08 Apr 2007 09:24:16 +0200, Sandy wrote:
>>
>>> Dans le message de
>>> news:a7mdnXWC4fN1ioXb...@giganews.com, Gary Young
>>> <garyy...@gmail.com> a réfléchi, et puis a déclaré :
>>>
>>>> ... maybe Mavic doesn't have a
>>>> particularly good understanding of what leads to rim failure?
>>>>
>>> Well, of course, Gary. What would a little manufacturing company know
>>> compared to the extensive wisdom and engineering expertise you and
>>> others offer, especially here, where it's about chest-thumping, not
>>> actual fabrication or business?!
>>
>> I asked a question (note the squiggly mark at the end of my sentence).
>> I don't expect anyone to judge Mavic wrong based solely on my say-so.
>> That's why I directed my question at someone (Jobst) who is an
>> engineer, who has decades worth of experience working for companies
>> engaged in "actual fabrication or business," who has designed
>> well-regarded tires that are fabricated by an actual business, and who
>> has made a lifelong study of the bicycle wheel. Do you have a problem
>> with that?
>
> Everyone knows that I do.
Sorry, I'm not familiar with your earlier postings.
> Tire design of a full generation ago, and not
> design, exactly, does not qualify a person to comment on today's tires.
> Even though I have sent him some rather recent test information, which
> he does not comment on. Not to mention, that tires and rims are rather
> different technologies, though interdependent.
What are your qualifications to make these assessments? Without knowing
that, I have no way of evaluating your claims.
> I also think that market
> pressures would have eliminated a rotten organization long ago, were it
> producing such inferior products.
>>
>>
>>
In a market driven in large part by fashion, I'm not so confident that
technical merit will be rewarded.
But I do want to clarify something. I've argued in this thread that the
fact that Mavic publishes recommended tire pressures is not a reliable
sign of quality. But I've never argued that it proves that Mavic's
products are inferior.
Furthermore, even if Mavic's recommendations are based on a
misunderstanding of theory, that doesn't, by itself, mean that their
products are inferior. To take another example, DT, Wheelsmith and Sapim
make questionable technical claims about spokes (with one manufacturer
sometimes contradicting another), but everyone seems to agree that all
three make high quality products.
>> As it happens, the question arose not simply because I decided to pose
>> it. In part, this thread has been concerned with why Mavic publishes
>> recommendations but other manufacturers like Velocity do not. In fact,
>> the OP has said that Velocity told him it has no recommendations. In
>> essence, the question was posed by the practice of one company (or set
>> of companies -- as far as I can tell, no rim manufacturer other than
>> Mavic makes such recommendations) as against another similar company.
>> Both companies are engaged in "actual fabrication or business."
>
> Posing an insincere question to a group of conversationalists is fine.
> It will beget the usual.
Q: Why does Mavic recommend maximum tire pressures when other rim makers
do not? How do they arrive at their recommendations?
A: You're insincere.
Is that really an answer you want to stick with? Who cares if I'm
insincere? If it's a question that some sincere person might want to have
answered, then it's a good question. Would it help if I could get a
sincere person to endorse my question?
>> Even if that weren't the case, I still wouldn't feel presumptuous in
>> asking whether Mavic understands the problem. One need only read the
>> cycling press to see that a lot of silly products are put on the
>> market. Mavic certainly seems no exception, what with some of its
>> gimmicky "high performance" wheels that do badly on aerodynamic tests.
>
> Reading the cycling press does not lead to the conclusion that there are
> silly products on the market. Evaluating the press reports may do so,
> but that it yet another step forward in thinking, not instantly
> apparent. Your idea that Mavic is not an exception, with reference to
> wheels that "do badly on aerodynamic tests" is not founded on anything I
> seem to have read. I'd be glad of a reference. Presuming, of course,
> that the wheel was made to offer exceptional aero benefits.
The results have been discussed here. If no one chimes in, I'll search the
archives. In any event, it's not essential to my point, which is simply
that there are enough silly products in the market that I feel justified
in denying a presumption of correctness to manufacturer claims.
>> Furthermore, someone who has mastered the practical aspects of a task
>> does not necessarily have a theoretical understanding of the subject.
>> For proof of that, I suggest you read what successful makers of
>> bicycles and bicycle frames say on a whole host of questions like ride
>> quality. At the very least, you will be perplexed by how they
>> contradict each other.
>
> So, rather than try to evaluate the manufacturers' presentations, it is
> wiser to accept the word of those who lack the detailed knowledge of the
> different fabrication methodologies and specific underlying science ? I
> am not of that opinion.
>>
>>
I don't know how to evaluate manufacturers' presentations other than by
posing questions to the most qualified people I know, especially when the
manufacturer gives no supporting evidence for its presentation.
>> In any event, though I directed my question at Jobst, I would be glad
>> to hear your thoughts. Do you know why Mavic publishes recommended tire
>> pressures but other rim makers don't? Do you know the method Mavic uses
>> to arrive at its figures?
>
> No.
>
>
Then I guess we'll be having a short conversation.
>> Do you have anything to
>> contribute but a lot of hot air?
>
> Hot air ? It was criticism of your commentary. A question mark does
> not a question make.
>>
>>
>>
When you're angry that a question is being asked, but can't close the
matter with an answer, and instead have to resort to questioning the
motives of the person who asked the question, that's hot air in my book.
>>> So I, and a lot of other future customers, look forward to your new
>>> enterprise, where you lay it all on the line, fearing nothing, as you
>>> demolish that ratty gang over there (oops!, over here, I mean) and
>>> save the cycling world. That must be the positive contribution you
>>> had in mind, when you write, yes?
>>> --
>>
>> Sorry, I can't take this any more seriously than when I'm accused of
>> being anti-American for questioning the judgment of Detroit automakers
>> or the morality of Halliburton.
>
> Were you less vague, perhaps I could comment. Are you a fan of
> Halliburton or Detroit ?
The point is that it doesn't matter whether I'm a fan of Haliburton or
Detroit.
Gary Young
> HarryB wrote:
>> On Fri, 06 Apr 2007 10:58:39 -0700, jim beam
>> <spamv...@bad.example.net> wrote:
>>
>>> HarryB wrote:
>> [snip]
>>>> My choice of words may have been poor. What I meant is that I agreed
>>>> that I did not run 60psi - I ran 85-95psi.
>>> that's high for a 20" wheel.
>> The tire that was on the rim is a Primo Comet 20x1.5 which is rated at
>> 100psi max.
>
> ok, that's the tire. now let's look at the rim. a 1.5" tire is ~43mm.
> using a linear model on the mavic numbers, they recommend a 3.22psi
> drop per mm increase in tire width. that would give ~70psi max for your
> tire width.
Does this mean you're abandoning the claim that rim diameter plays a part?
After all, there exist 20" rims (the Rhinolite, for instance) that are
wide enough to make a 1.5" tire acceptable under the Mavic guidelines.
Also, why are you using a linear model of Mavic's numbers when the Mavic
numbers seem decidedly non-linear? It's not as if you're averaging out
random variations. Instead, you're obscuring what Mavic seems to think
happens -- that adding a millimeter to the width of a tire requires a
greater drop in pressure when its an already wide tire than
when its a narrow tire. Do you have an explanation for why
Mavic's recommendations have that nonlinear form?
> unless you /know/ the velocity to be stronger with respect
> to its extrusion axis, you should regard the mavic numbers as a max for
> your rim too.
>
Without knowing the method Mavic used to reach its recommendations and
the validity of the method, I would disagree. The results seem
somewhat formulaic (for instance, they don't distinguish between disk and
non-disk versions of rims) and thus it's not clear to what extent they're
even based on testing.
Ben C
> On Sun, 08 Apr 2007 13:08:49 +0200, Sandy wrote:
>> I also think that market
>> pressures would have eliminated a rotten organization long ago, were it
>> producing such inferior products.
>>>
>>>
>>>
>
> In a market driven in large part by fashion, I'm not so confident that
> technical merit will be rewarded.
>
> But I do want to clarify something. I've argued in this thread that the
> fact that Mavic publishes recommended tire pressures is not a reliable
> sign of quality. But I've never argued that it proves that Mavic's
> products are inferior.
>
> Furthermore, even if Mavic's recommendations are based on a
> misunderstanding of theory, that doesn't, by itself, mean that their
> products are inferior. To take another example, DT, Wheelsmith and Sapim
> make questionable technical claims about spokes (with one manufacturer
> sometimes contradicting another), but everyone seems to agree that all
> three make high quality products.
The "technical claims" are often just marketing BS anyway. If you spoke
to the engineers who work at these places, I'm sure they'd know what
they were talking about. It seems unlikely that the people who design
Mavic (or any other successful brand of) rim wouldn't understand the
theory.
Ben C
>
>> HarryB wrote:
>>> On Fri, 06 Apr 2007 10:58:39 -0700, jim beam
>>> <spamv...@bad.example.net> wrote:
>>>
>>>> HarryB wrote:
>>> [snip]
>>>>> My choice of words may have been poor. What I meant is that I agreed
>>>>> that I did not run 60psi - I ran 85-95psi.
>>>> that's high for a 20" wheel.
>>> The tire that was on the rim is a Primo Comet 20x1.5 which is rated at
>>> 100psi max.
>>
>> ok, that's the tire. now let's look at the rim. a 1.5" tire is ~43mm.
>> using a linear model on the mavic numbers, they recommend a 3.22psi
>> drop per mm increase in tire width. that would give ~70psi max for your
>> tire width.
>
> Does this mean you're abandoning the claim that rim diameter plays a part?
> After all, there exist 20" rims (the Rhinolite, for instance) that are
> wide enough to make a 1.5" tire acceptable under the Mavic guidelines.
>
> Also, why are you using a linear model of Mavic's numbers when the Mavic
> numbers seem decidedly non-linear?
You might expect it be linear since casing tension (or "hoop stress")
is proportional both to pressure and to tyre minor diameter.
> It's not as if you're averaging out
> random variations. Instead, you're obscuring what Mavic seems to think
> happens -- that adding a millimeter to the width of a tire requires a
> greater drop in pressure when its an already wide tire than
> when its a narrow tire. Do you have an explanation for why
> Mavic's recommendations have that nonlinear form?
Good question.
Sandy
>> Tire design of a full generation ago, and not
>> design, exactly, does not qualify a person to comment on today's
>> tires. Even though I have sent him some rather recent test
>> information, which he does not comment on. Not to mention, that
>> tires and rims are rather different technologies, though
>> interdependent.
>
> What are your qualifications to make these assessments? Without
> knowing that, I have no way of evaluating your claims.
To one item, having sent physically the test results from a magazine, and
receiving confirmation of reception, I _know_ that there was never a public
acknowledgement of them, here. Nor am I aware of any writing by the bard
(of RBT) to indicate he has reviewed the most recent (February) tests.
Experts try to stay current, examine confounding information, and try to
address it all intelligently. Having read the forgoing, and having read no
commentary, it seems that the currency of knowledge of that author is
lacking a bit.
I didn't suggest you question /my/ qualifications, but rather, be more
judicious in accepting the "authorities" who resort to looming over a forum,
repeating knowledge of tests from 25 years ago.
>> I also think that market
>> pressures would have eliminated a rotten organization long ago, were
>> it producing such inferior products.
>>>
>
> In a market driven in large part by fashion, I'm not so confident that
> technical merit will be rewarded.
Fair point, yet the "large part" is, to my mind, a big overstatement as to
longevity of a fabricator. All markets are partially driven by fashion,
which in some cases is actual fruitful innovation. I am not endorsing any
particular product with that statement.
>
> But I do want to clarify something. I've argued in this thread that
> the fact that Mavic publishes recommended tire pressures is not a
> reliable sign of quality. But I've never argued that it proves that
> Mavic's products are inferior.
Nothing is capable of actual proof, here, in RBT. But you know that.
>
> Furthermore, even if Mavic's recommendations are based on a
> misunderstanding of theory, that doesn't, by itself, mean that their
> products are inferior. To take another example, DT, Wheelsmith and
> Sapim make questionable technical claims about spokes (with one
> manufacturer sometimes contradicting another), but everyone seems to
> agree that all three make high quality products.
While each seller is entitled to boast having a great product (true or not),
it does nothing to reflect on your contention (just above) that Mavic
misunderstands theory. I see absolutely no evidence of that. They make
rims and wheels for sale to suit applications, I suspect, not to win
scientific awards.
>>> As it happens, the question arose not simply because I decided to
>>> pose it. In part, this thread has been concerned with why Mavic
>>> publishes recommendations but other manufacturers like Velocity do
>>> not. In fact, the OP has said that Velocity told him it has no
>>> recommendations. In essence, the question was posed by the practice
>>> of one company (or set of companies -- as far as I can tell, no rim
>>> manufacturer other than Mavic makes such recommendations) as
>>> against another similar company. Both companies are engaged in
>>> "actual fabrication or business."
>>
>> Posing an insincere question to a group of conversationalists is
>> fine. It will beget the usual.
> Q: Why does Mavic recommend maximum tire pressures when other rim
> makers do not? How do they arrive at their recommendations?
>
> A: You're insincere.
>
> Is that really an answer you want to stick with? Who cares if I'm
> insincere? If it's a question that some sincere person might want to
> have answered, then it's a good question. Would it help if I could
> get a sincere person to endorse my question?
No. You're insincere, and the question is rhetorical footsie.
>>> Even if that weren't the case, I still wouldn't feel presumptuous in
>>> asking whether Mavic understands the problem. One need only read the
>>> cycling press to see that a lot of silly products are put on the
>>> market. Mavic certainly seems no exception, what with some of its
>>> gimmicky "high performance" wheels that do badly on aerodynamic
>>> tests.
>>
>> Reading the cycling press does not lead to the conclusion that there
>> are silly products on the market. Evaluating the press reports may
>> do so, but that it yet another step forward in thinking, not
>> instantly apparent. Your idea that Mavic is not an exception, with
>> reference to wheels that "do badly on aerodynamic tests" is not
>> founded on anything I seem to have read. I'd be glad of a
>> reference. Presuming, of course, that the wheel was made to offer
>> exceptional aero benefits.
>
> The results have been discussed here. If no one chimes in, I'll
> search the archives. In any event, it's not essential to my point,
> which is simply that there are enough silly products in the market
> that I feel justified in denying a presumption of correctness to
> manufacturer claims.
Something being discussed here is a giant leap downwards from Wikipedia,
which itself is the distance of a great chasm from quality research
material. Ask the Guru, if you don't like my answer.
Archives to prove that the aero effect was Mavic's aim, and that they failed
? I'll be waiting.
>> So, rather than try to evaluate the manufacturers' presentations, it
>> is wiser to accept the word of those who lack the detailed knowledge
>> of the different fabrication methodologies and specific underlying
>> science ? I am not of that opinion.
>>>
>>>
> I don't know how to evaluate manufacturers' presentations other than
> by posing questions to the most qualified people I know, especially
> when the manufacturer gives no supporting evidence for its
> presentation.
How are you evaluating these presentations, then ? You actually are using
the opinions here ?Again, the manufacturer did not do its thing to win a
science fair. Try to be realistic.
>>> In any event, though I directed my question at Jobst, I would be
>>> glad to hear your thoughts. Do you know why Mavic publishes
>>> recommended tire pressures but other rim makers don't? Do you know
>>> the method Mavic uses to arrive at its figures?
>>
>> No.
>>
>>
> Then I guess we'll be having a short conversation.
Depends on your intellectual honesty. I will be waiting for the proofs you
will search in the archives. (Spokes, aero effects...)
>>> Do you have anything to
>>> contribute but a lot of hot air?
>>
>> Hot air ? It was criticism of your commentary. A question mark does
>> not a question make.
>>>
> When you're angry that a question is being asked, but can't close the
> matter with an answer, and instead have to resort to questioning the
> motives of the person who asked the question, that's hot air in my
> book.
--
Sandy
Verneuil-sur-Seine FR
The above is guaranteed 100% free of sarcasm,
denigration, snotty remarks, indifference, platitudes, fuming demands that
"you do the math", conceited visions of a better world on wheels according
to [insert NAME here].
OK - your book is your book. But I wasn't angry. No need to misconstrue
criticism as anger.
Gary Young
I've never found the possession of "minerals" to be a very reliable
predictor of whether someone is in possession of the truth.
I don't know where they got the numbers from. And, quite clearly, neither
do you.
>
> and while you're thinking about that, here's your homework assignment
> for the weekend...
>
> "anisotropy: discuss"
>
When entering a debate, it's usually a good practice to try to offer
information that's somehow relevant to the issue at hand. For instance, if
two people were arguing about whether a whale is a mammal or a fish, it
wouldn't be very helpful to interject that it's a vertebrate.
Similarly, in a discussion in which neither side has asserted, either
implicitly or explicitly, that rims are equally strong in every direction,
it seems rather odd to be offering lessens on anisotropy.
Unless of course I'm missing some subtlety here. Is there any? If not, I'm
afraid that all I've gotten is a review of a very old lesson -- that you
have a good memory for jargon and bits of materials-science fact, but
not much aptitude for using logic to make extrapolations from those facts
or to judge their relevance to debates here on rbt.
Tim McNamara
jim beam <spamv...@bad.example.net> wrote:
> Gary Young wrote:
> > Do you know why Mavic publishes maximum recommended tire pressures
> > for its rims or how it derives its figures? I suppose it's possible
> > that high-pressures lead to tire blow-offs, which lead to damaged
> > rims (during the resulting crash, not as a direct result of
> > excessive pressure), which lead to warranty claims that Mavic
> > doesn't want to deal with (with good reason). Or maybe Mavic
> > doesn't have a particularly good understanding of what leads to rim
> > failure?
>
> give us a break - they have the minerals to publish tire pressure
> recommendations [among other things]. where do you think they get
> those numbers from? tarot?
That's as likely an answer as any.
> and while you're thinking about that, here's your homework assignment
> for the weekend...
>
> "anisotropy: discuss"
Thanks, perfessor. Nice to see that your arrogance hasn't gone to your
head.
jim beam
> On Sat, 07 Apr 2007 09:10:43 -0700, jim beam wrote:
>
>> HarryB wrote:
>>> On Fri, 06 Apr 2007 10:58:39 -0700, jim beam
>>> <spamv...@bad.example.net> wrote:
>>>
>>>> HarryB wrote:
>>> [snip]
>>>>> My choice of words may have been poor. What I meant is that I agreed
>>>>> that I did not run 60psi - I ran 85-95psi.
>>>> that's high for a 20" wheel.
>>> The tire that was on the rim is a Primo Comet 20x1.5 which is rated at
>>> 100psi max.
>> ok, that's the tire. now let's look at the rim. a 1.5" tire is ~43mm.
>> using a linear model on the mavic numbers, they recommend a 3.22psi
>> drop per mm increase in tire width. that would give ~70psi max for your
>> tire width.
>
> Does this mean you're abandoning the claim that rim diameter plays a part?
i never said it did gary - you said that. /i/ was questioning rim
diameter as a function of typical tire size - smaller rims typically use
fatter tires, and fatter tires should run lower pressures. that's not
hard now is it?
> After all, there exist 20" rims (the Rhinolite, for instance) that are
> wide enough to make a 1.5" tire acceptable under the Mavic guidelines.
>
> Also, why are you using a linear model of Mavic's numbers when the Mavic
> numbers seem decidedly non-linear? It's not as if you're averaging out
> random variations. Instead, you're obscuring what Mavic seems to think
> happens -- that adding a millimeter to the width of a tire requires a
> greater drop in pressure when its an already wide tire than
> when its a narrow tire. Do you have an explanation for why
> Mavic's recommendations have that nonlinear form?
yes - it's a non-linear function!!! /i/ couldn't be bothered to do a
curve fit. /you/ can do that if you want - all i did was illustrate the
principle.
>
>> unless you /know/ the velocity to be stronger with respect
>> to its extrusion axis, you should regard the mavic numbers as a max for
>> your rim too.
>>
>
> Without knowing the method Mavic used to reach its recommendations and
> the validity of the method, I would disagree.
of course you would. that's why i suggested you look into anisotropy.
> The results seem
> somewhat formulaic (for instance, they don't distinguish between disk and
> non-disk versions of rims) and thus it's not clear to what extent they're
> even based on testing.
so where do you think they got the numbers from? if they have an
accurate predictive model, that's /way/ more impressive than lab work.
<snip remainder>
jim beam
if you don't understand the principle, you won't follow the logic. read
up on anisotropy. the principal strength requirement for a rim is
axial, which is convenient since that is the result of extrusion, the
method by which rim sections are most easily formed. secondary is
transverse strength, which is also convenient since under normal
conditions, transverse loading is relatively minor. excess spoke
tension and excess tire pressure can exceed transverse loading limits
however, hence cracking.
M-gineering
>
> Also, why are you using a linear model of Mavic's numbers when the Mavic
> numbers seem decidedly non-linear? It's not as if you're averaging out
> random variations. Instead, you're obscuring what Mavic seems to think
> happens -- that adding a millimeter to the width of a tire requires a
> greater drop in pressure when its an already wide tire than
> when its a narrow tire. Do you have an explanation for why
> Mavic's recommendations have that nonlinear form?
The force on the rim might be linear with tyrediameter, but I would
expect that Mavic assumes the force of the wide tyre acts higher up the
rimwall, so with a longer lever.
--
---
Marten Gerritsen
INFOapestaartjeM-GINEERINGpuntNL
www.m-gineering.nl
Gary Young
> Gary Young wrote:
>> On Sat, 07 Apr 2007 09:10:43 -0700, jim beam wrote:
>>
>>> HarryB wrote:
>>>> On Fri, 06 Apr 2007 10:58:39 -0700, jim beam
>>>> <spamv...@bad.example.net> wrote:
>>>>
>>>>> HarryB wrote:
>>>> [snip]
>>>>>> My choice of words may have been poor. What I meant is that I agreed
>>>>>> that I did not run 60psi - I ran 85-95psi.
>>>>> that's high for a 20" wheel.
>>>> The tire that was on the rim is a Primo Comet 20x1.5 which is rated at
>>>> 100psi max.
>>> ok, that's the tire. now let's look at the rim. a 1.5" tire is ~43mm.
>>> using a linear model on the mavic numbers, they recommend a 3.22psi
>>> drop per mm increase in tire width. that would give ~70psi max for your
>>> tire width.
>>
>> Does this mean you're abandoning the claim that rim diameter plays a part?
>
> i never said it did gary - you said that. /i/ was questioning rim
> diameter as a function of typical tire size - smaller rims typically use
> fatter tires, and fatter tires should run lower pressures. that's not
> hard now is it?
>
Any sensible reader can scroll up and see what you said, which was
ambiguous at best.
>> After all, there exist 20" rims (the Rhinolite, for instance) that are
>> wide enough to make a 1.5" tire acceptable under the Mavic guidelines.
>>
>> Also, why are you using a linear model of Mavic's numbers when the Mavic
>> numbers seem decidedly non-linear? It's not as if you're averaging out
>> random variations. Instead, you're obscuring what Mavic seems to think
>> happens -- that adding a millimeter to the width of a tire requires a
>> greater drop in pressure when its an already wide tire than
>> when its a narrow tire. Do you have an explanation for why
>> Mavic's recommendations have that nonlinear form?
>
> yes - it's a non-linear function!!!
I'm not satisfied with that answer because it is unsatisfactory! I was
hoping for less of a tautology and more in the way of an explanation that
ties the numbers to some physical phenomenon that behaves in a nonlinear
fashion. It may be that Marten Garretsen has supplied the explanation
elsewhere in the thread.
> /i/ couldn't be bothered to do a
> curve fit. /you/ can do that if you want - all i did was illustrate the
> principle.
>
Actually that's not the case. You were making specific
recommendations to the OP about whether his tire was the right
size.
>>
>>> unless you /know/ the velocity to be stronger with respect
>>> to its extrusion axis, you should regard the mavic numbers as a max
>>> for your rim too.
>>>
>>>
>> Without knowing the method Mavic used to reach its recommendations and
>> the validity of the method, I would disagree.
>
> of course you would. that's why i suggested you look into anisotropy.
>
>> The results seem
>> somewhat formulaic (for instance, they don't distinguish between disk
>> and non-disk versions of rims) and thus it's not clear to what extent
>> they're even based on testing.
>
> so where do you think they got the numbers from?
I'm not sure why you keep asking me this silly question, since I've said
repeatedly that I don't know and would like to know. It is a pertinent
question to ask you, however, since you've come to the defense of the
recommendations, but oddly don't have anything substantive to say about
them.
> if they have an
> accurate predictive model, that's /way/ more impressive than lab work.
>
Sure, if it's accurate. But that leaves us with the same questions --
what is their model and do they have good evidence that it's accurate?
> <snip remainder>
jim beam
<snip crap>
>
> Sure, if it's accurate. But that leaves us with the same questions --
> what is their model and do they have good evidence that it's accurate?
that you can write that raises /so/ many questions of logic, intellect
and even philosophy, it negates my ability to have any further
discussion. i'm sorry i wasted my time.
carl...@comcast.net
wrote:
[snip]
Dear Gary,
I've been browsing some rim sites listed here:
http://www.mikebentley.com/bike/wheels.htm
Only Campagnolo and Mavic seem to have any tables for pressures for
their rims.
Campagnolo seems to use this table, but it's described as "operating
pressures," without any explicit maxium stated:
rim_mm max_psi
19 137
20 130
23 113
25 104
You can see some or all of the table on the Neutron, Zonda, Shamal,
and Vento pdf manuals. Here's alink to the Neutron Ultra pdf, which
has the table on page 5:
http://www.campagnolo.com/pdf/NeutronUltra_UK_1006.pdf
The Campagnolo table seems more conservative than the Mavic explicit
maximum recommendations, with only 137 psi instead of 146 psi for 19
mm rims, and only 104 psi for a 25 mm rim.
max__psi tire_mm
track/triathlon
cxp33 117..146 28..19
open pro 117..146 28..19
reflex 117..146 28..19
road
kys es 103..146 32..19
cosmic e 103..146 32..19
road
a719 103...66 50..28
a119 103...66 50..28
a319 103...66 50..28
mtb
xc717 113...59 53..25
xm317 69...49 58..48
ex721 49...32 76..58
http://www.mavic.com/ewb_pages/p/produit_jante_cxp33.php?onglet=3&gamme=route
Cheers,
Carl Fogel
Gary Young
I doubt that there's anyone on this newsgroup who needs a lecture on
principles so general. We all know that rims have weaknesses, that the
weaknesses are greater in some directions than in others, and that those
weaknesses can lead to failure in certain conditions. The question is a
specific one -- do rim-tire-pressure combinations outside of Mavic's
recommendations (but within the range of actual practice) lead to failures?
Your platitudes do nothing to answer that specific question.
Michael Press
"Sandy" <leu...@frree.fr> wrote:
> Everyone knows that I do. Tire design of a full generation ago, and not
> design, exactly, does not qualify a person to comment on today's tires.
> Even though I have sent him some rather recent test information, which he
> does not comment on. Not to mention, that tires and rims are rather
> different technologies, though interdependent. I also think that market
> pressures would have eliminated a rotten organization long ago, were it
> producing such inferior products.
That is simply not so. Large organizations get that way through
acquisition of and exercising of raw power. Mavic is not the same
organization that designed, manufactured, and distributed the MA2
rim. Mavic is an acquisition of a larger organization in the
marketplace. Mavic charges $60 US for a rim that is equaled for
quality by rims costing half that. Mavic introduce thick layers of
anodizing that actually weakens rims. Mavic introduced machining
of rim brake surfaces that reduces the rims usable lifetime. They
have power and use it; this is the meaning of market forces. That
college level malarky dries up and blows away in the real
marketplace.
jim beam
<snip for brevity>
> I doubt that there's anyone on this newsgroup who needs a lecture on
> principles so general. We all know that rims have weaknesses, that the
> weaknesses are greater in some directions than in others, and that those
> weaknesses can lead to failure in certain conditions. The question is a
> specific one -- do rim-tire-pressure combinations outside of Mavic's
> recommendations (but within the range of actual practice) lead to failures?
yes!!! jeepers.
the whole point of publishing data is to help users to limit their
"actual practice" to something that will not cause failure. when a car
manufacturer puts a red line on the tachometer at 6krpm, what does that
mean? that the motor's safe for 16krpm?
> Your platitudes do nothing to answer that specific question.
no, very little i say does anything for your comprehension. but that's
not an engineering issue.
i'm done. enjoy the rest of your weekend.
Michael Press
"Sandy" <leu...@frree.fr> wrote:
> Nothing is capable of actual proof, here, in RBT. But you know that.
Therefore, all the assertions you have made here, technical and
personal, are insupportable.
Sandy
news:rubrum-F620DB....@newsclstr02.news.prodigy.com,
Michael Press <rub...@pacbell.net> a réfléchi, et puis a déclaré :
Your wonderful explanation needs to be rushed to Chrysler-Daimler. I think
they are in need of your skillful business strategic planning. Maybe they
are just too timid to acquire, grow or exercise their power. Market forces
will move anything, when the market is relatively free, and even in non-free
markets, demand modifies market profiles.
You don't know the cost, I will bet.
You don't know the quality, same.
You don't know the design rim life, ditto.
But you do seem to want to irk me, and there, also, you are not on the mark.
--
Sandy
Verneuil-sur-Seine
*******
La vie, c'est comme une bicyclette,
il faut avancer pour ne pas perdre l'équilibre.
-- Einstein, A.
jim beam
> In article <4618cd41$0$28887$426a...@news.free.fr>,
> "Sandy" <leu...@frree.fr> wrote:
>
>> Everyone knows that I do. Tire design of a full generation ago, and not
>> design, exactly, does not qualify a person to comment on today's tires.
>> Even though I have sent him some rather recent test information, which he
>> does not comment on. Not to mention, that tires and rims are rather
>> different technologies, though interdependent. I also think that market
>> pressures would have eliminated a rotten organization long ago, were it
>> producing such inferior products.
>
> That is simply not so. Large organizations get that way through
> acquisition of and exercising of raw power.
really? a french company exercises "raw power" in the united states?
remarkable! don't let the taiwanese or chinese know - we could have
real trouble on our hands.
> Mavic is not the same
> organization that designed, manufactured, and distributed the MA2
> rim.
that's /so/ troubling.
> Mavic is an acquisition of a larger organization in the
> marketplace.
that's /so/ troubling too.
> Mavic charges $60 US for a rim that is equaled for
> quality by rims costing half that.
so don't buy them!!!
> Mavic introduce thick layers of
> anodizing that actually weakens rims.
not true. prevention of corrosion extends rim life considerably.
unless you live in palo alto of course.
> Mavic introduced machining
> of rim brake surfaces that reduces the rims usable lifetime.
not true. see:
http://flickr.com/photos/38636024@N00/121453841/
the machined section is /thicker/ than the rest. it's a /real/ simple
matter to extrude according to the intended machining operation.
> They
> have power and use it; this is the meaning of market forces.
how do you intend to counter that, comrade? communism? protectionism
for all the american rim manufacturers?
> That
> college level malarky dries up and blows away in the real
> marketplace.
no, ability to cope does not continue to mature past college level in
some individuals.
data...@yahoo.com
mavic exists, obviuosly. therefore due to market forces in the bicycle
market which are knidawierd given the latest 3500 wheel
set...butbutbut ignoring that
mavic mass produces these rims (specialized does not mass produce,
haso i hear) for the market and the market repsonds buying mavic rims
so mavic makes more rims
you see the point?
that's one reason why russia's economy never developed
Sandy
carl...@comcast.net <carl...@comcast.net> a réfléchi, et puis a déclaré
:
> On Sat, 07 Apr 2007 03:09:43 -0500, Gary Young <garyy...@gmail.com>
> wrote:
>
> [snip]
>
> Dear Gary,
>
> I've been browsing some rim sites listed here:
>
> http://www.mikebentley.com/bike/wheels.htm
>
> Only Campagnolo and Mavic seem to have any tables for pressures for
> their rims.
>
it was there; I did not search for others.
http://www.amclassic.com/faq.html
Near the bottom of the page ...
Perhaps other manufacturers also do this?
--
Sandy
--
C'est le contraire du vélo, la bicyclette.
Une silhouette profilée mauve fluo dévale
à soixante-dix à l'heure : c'est du vélo.
Deux lycéennes côte à côte traversent
un pont à Bruges : c'est de la bicyclette.
-Delerm, P.
Ben C
>> if you don't understand the principle, you won't follow the logic. read
>> up on anisotropy. the principal strength requirement for a rim is
>> axial, which is convenient since that is the result of extrusion, the
>> method by which rim sections are most easily formed. secondary is
>> transverse strength, which is also convenient since under normal
>> conditions, transverse loading is relatively minor. excess spoke
>> tension and excess tire pressure can exceed transverse loading limits
>> however, hence cracking.
>>
>
> I doubt that there's anyone on this newsgroup who needs a lecture on
> principles so general.
I didn't know rims had this anisotropy of being stronger axially but
prone to cracking when pulled apart sideways as a result of being
extruded.
jobst....@stanfordalumni.org
>> Everyone knows that I do. Tire design of a full generation ago,
>> and not design, exactly, does not qualify a person to comment on
>> today's tires. Even though I have sent him some rather recent test
>> information, which he does not comment on. Not to mention, that
>> tires and rims are rather different technologies, though
>> interdependent. I also think that market pressures would have
>> eliminated a rotten organization long ago, were it producing such
>> inferior products.
> That is simply not so. Large organizations get that way through
> acquisition of and exercising of raw power. Mavic is not the same
> organization that designed, manufactured, and distributed the MA2
> rim. Mavic is an acquisition of a larger organization in the
> marketplace. Mavic charges $60 US for a rim that is equaled for
> quality by rims costing half that. Mavic introduce thick layers of
> anodizing that actually weakens rims. Mavic introduced machining of
> rim brake surfaces that reduces the rims usable lifetime. They have
> power and use it; this is the meaning of market forces. That college
> level malarkey dries up and blows away in the real marketplace.
I am amazed how the effect of marketing passes unnoticed in most
matters. That is shown best by the current political campaign where
only money (advertising) is the measure of a candidate's chances. As
should be apparent, the current Washington administration was brought
into office and re-elected that way.
Jobst Brandt
jobst....@stanfordalumni.org
> [...]
>>> if you don't understand the principle, you won't follow the logic.
>>> read up on anisotropy. the principal strength requirement for a
>>> rim is axial, which is convenient since that is the result of
>>> extrusion, the method by which rim sections are most easily
>>> formed. secondary is transverse strength, which is also
>>> convenient since under normal conditions, transverse loading is
>>> relatively minor. excess spoke tension and excess tire pressure
>>> can exceed transverse loading limits however, hence cracking.
>> I doubt that there's anyone on this newsgroup who needs a lecture
>> on principles so general.
> I didn't know rims had this anisotropy of being stronger axially but
> prone to cracking when pulled apart sideways as a result of being
> extruded.
If you haven't had the experience than you might believe these claims
but it isn't true. I have ridden MA-2 rims until the sidewall had
less than 0.5mm thickness (1/3 its original wall) from braking in the
rain on long descents. The rim did not burst.
The pressure ratings for rims are for tire lift-off and as was
analyzed here in this forum, that force is dependent on the angle at
which the casing departs from the rim. That is why fat tires blow-off
at lower pressure than skinny ones. The separation force is the same
regardless of tire width, but the angle of pull of the casing is not.
Separation force depends on the width between sidewall beads only but
the force on the casing is dependent on cross section. The angle of
departure affects retention as well.
Jobst Brandt
Sandy
news:rubrum-E3AB1D....@newsclstr02.news.prodigy.com,
Michael Press <rub...@pacbell.net> a réfléchi, et puis a déclaré :
In this strange and unreal context you are right. That is probably a fair
generalization, of course, limiting it to "here".
Sandy
jobst....@stanfordalumni.org <jobst....@stanfordalumni.org> a
"'Marketing" is not a ubiquitous replacement for "power". Marketing,
however, is ubiquitous in selling. Whether it is the charming claim of
"These wheels were assembled and finished by the magical elves of a tiny,
dedicated atelier," or "These wheels are made by the most comprehensive
manufacturing company ever to exist," they are both inside the brackets of
Marketing 101.
I imagine you are also contemptuous of the plain folk who believe all that
rot about their favorite politicians. They have no hope, I understand from
your text.
--
Sandy
--
S'endormir au volant, c'est très dangereux.
S'endormir à vélo, c'est très rare.
S'endormir à pied, c'est très con.
- Geluck, P.
M-gineering
> really? a french company exercises "raw power" in the united states?
> remarkable! don't let the taiwanese or chinese know - we could have
> real trouble on our hands.
>
Finnish owned actually
---
Marten
Gary Young
> On Sat, 07 Apr 2007 03:09:43 -0500, Gary Young <garyy...@gmail.com>
> wrote:
>
> [snip]
>
> Dear Gary,
>
> I've been browsing some rim sites listed here:
>
> http://www.mikebentley.com/bike/wheels.htm
>
> Only Campagnolo and Mavic seem to have any tables for pressures for
> their rims.
>
> Campagnolo seems to use this table, but it's described as "operating
> pressures," without any explicit maxium stated:
>
> rim_mm max_psi
> 19 137
> 20 130
> 23 113
> 25 104
>
> You can see some or all of the table on the Neutron, Zonda, Shamal,
> and Vento pdf manuals. Here's alink to the Neutron Ultra pdf, which
> has the table on page 5:
>
> http://www.campagnolo.com/pdf/NeutronUltra_UK_1006.pdf
The accompanying text (under Caution!) doesn't show any concern about
damage to the rim from over-inflation:
"Excessive tire pressure reduces grip on the road and increases the risk
that the tire will unexpectedly burst."
That doesn't seem to be because the possibility of rim damage didn't occur
to them. After all, rim damage is listed as a possible problem with
under-inflation.
On the face of things, Campagnolo would seem to agree with
Jobst that blow-off is the risk to worry about over-inflation.
I suppose the question arises why Campagnolo is giving warnings about a
product they don't make. Human kindness might be one explanation; a more
hardheaded one -- which might also apply in the case of Mavic -- is the
desire not to be saddled with warranty claims for which one bears no
responsibility.
Ben C
> Ben C? writes:
>
>> [...]
>
>>>> if you don't understand the principle, you won't follow the logic.
>>>> read up on anisotropy. the principal strength requirement for a
>>>> rim is axial, which is convenient since that is the result of
>>>> extrusion, the method by which rim sections are most easily
>>>> formed. secondary is transverse strength, which is also
>>>> convenient since under normal conditions, transverse loading is
>>>> relatively minor. excess spoke tension and excess tire pressure
>>>> can exceed transverse loading limits however, hence cracking.
>
>>> I doubt that there's anyone on this newsgroup who needs a lecture
>>> on principles so general.
>
>> I didn't know rims had this anisotropy of being stronger axially but
>> prone to cracking when pulled apart sideways as a result of being
>> extruded.
>
> If you haven't had the experience than you might believe these claims
> but it isn't true. I have ridden MA-2 rims until the sidewall had
> less than 0.5mm thickness (1/3 its original wall) from braking in the
> rain on long descents. The rim did not burst.
>
> The pressure ratings for rims are for tire lift-off and as was
> analyzed here in this forum, that force is dependent on the angle at
> which the casing departs from the rim. That is why fat tires blow-off
> at lower pressure than skinny ones.
Suppose hypothetically I had a Mavic XM317 rim and a 47mm tyre of
standard geometry but made out of super-adamantium or something so
neither will fail during this experiment. Are you suggesting that if I
keep pumping up the tyre, at some pressure it will eventually blow off
the rim?
jobst....@stanfordalumni.org
>>> [...]
I don't see where yo find that in the paragraph above, but yes, the
tire will separate from the rim as many riders have found
unexpectedly. How much of that is caused by brake heating and how
much by increased pressure is not yet clear, but it occurs often
enough.
What I said was that under conventional inflation pressure (100psi for
a 25mm tire) on an MA-2 the rim does not crack. I do not recommend
the limit of the example I cite, but mention it just to make the point
that rims do not readily crack and that inflation limits are mainly
for the safety of tire retention. Typically, on some steep roads in
Austria bicycles are not permitted to descend for that reason,
although riding up is permitted (Zirlerberg: http://tinyurl.com/jhiu)
with six run-away escape exits for failed auto brakes.
Jobst Brandt