Cracking rims

On Sat, 06 Dec 2008 11:33:30 -0600, Tom Sherman
may have said:

Does my wheel have enough spokes?
http://farm3.static.flickr.com/2249/2163925995_f7a5dd2a3b.jpg?v=0

Well, maybe, I mean there's still room to drill more holes, so you
*could* add some, but mostly you forgot to chrome it.

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
Words processed in a facility that contains nuts.

Mike Jacoubowsky wrote:

someone was bound to figure it out some time - shallow =
dentable, deep and stiff = round and reliable.

There's more to it than that. Early Rigida 1320 rims had
approximately the same cross section as many Mavic rims, and yet
they dented far more easily. But all things being equal (same
material used), it's absolutely correct that a deeper cross
section is more resistant to denting. Actually, I should say more
resistant to becoming out of round, not denting.

I don't know what type of "dents" you mean, but most dents that I
see are sidewall "dings" in the bead, ones that often can be
corrected with a large Crescent wrench by bending the bead back
where it belongs, the roundness of the wheel not having been
affected.

Dent is perhaps the wrong word. Bulge might be better. And yes, I
used to use crescent wrenches frequently, to good effect. But
again, not anymore. It just doesn't come up nearly as often, and
when it does, the rim is as likely to crack as bend.

The reason it doesn't occur often anymore is that most riders that go
off pavement use fat tired MTB's. In the days of yore, we rode 23 &
25mm cross section tubulars and after that 25mm clinchers. It was
with these off road clincher rims that rim sidewall dings occurred. I
don't recall getting flat spots except in crashes and those needed
pretzel straightening and that caused flat zones that could
occasionally be pulled out.

Jobst Brandt

Dent is perhaps the wrong word. Bulge might be better. And yes, I
used to use crescent wrenches frequently, to good effect. But
again, not anymore. It just doesn't come up nearly as often, and
when it does, the rim is as likely to crack as bend.

The reason it doesn't occur often anymore is that most riders that go
off pavement use fat tired MTB's. In the days of yore, we rode 23 &
25mm cross section tubulars and after that 25mm clinchers. It was
with these off road clincher rims that rim sidewall dings occurred. I
don't recall getting flat spots except in crashes and those needed
pretzel straightening and that caused flat zones that could
occasionally be pulled out.

Jobst Brandt

Jobst: The rides we did in the days of yore were not typical of all
riders. Those whose bikes I worked on were, for the most part, just like
the serious recreational riders today. I don't think most people had a
need to explore the world to the extent we did/do. Not then, not now.

"Normal" people don't ride the dirt trails on the back side of Loma
Prieta on road bikes. Nor do normal people do the San Gregorio/Tunitas
loop in pouring rain (thus I feel I still don't qualify as normal). In
other words, you and I aren't normal. But those "normal" folk still put
in a lot of miles on the road. They did then, they do now. And those are
the people I have the most experience with, in terms of what goes on
with their bikes.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com

On Tue, 09 Dec 2008 18:31:36 -0800, Mike Jacoubowsky wrote:

"jim beam" wrote in message
...
Mike Jacoubowsky wrote:
someone was bound to figure it out some time - shallow = dentable,
deep
and stiff = round and reliable.

There's more to it than that. Early Rigida 1320 rims had approximately
the same cross section as many Mavic rims, and yet they dented far
more easily.

but but but, evil mavic choose their diabolous materials so they crack
and can thus rip customers off, not because of desire to achieve better
mechanical performance...

Jim: We've traded one type of failure for another. Simple as that.

don't agree. there is no technical reason to over-tension a wheel.
zero. so there's no reason to waste material resources on trying to make
everything idiot-proof.


The
problem, from my end (retail & repair) is that the customer looks at a
dent and understand how they caused the problem. Not so for cracks at
the spoke/rim interface. So even if we have a "stronger" wheel, we
increase the likelihood of warranty claims and customer unhappiness.

"increase"??? how? the only rims i've ever seen crack are ones that have
been over-tensioned. and that goes for pre-builts as well as hand-
builts. jobst-inspired lbs over-tensioning of wheels is absolutely rife
in the industry - of course such rims are going to crack.





--Mike Jacoubowsky
Chain Reaction Bicycles
www.ChainReaction.com
Redwood City & Los Altos, CA USA

"jim beam" wrote in message
. ..
On Tue, 09 Dec 2008 18:31:36 -0800, Mike Jacoubowsky wrote:

"jim beam" wrote in message
...
Mike Jacoubowsky wrote:
someone was bound to figure it out some time - shallow = dentable,
deep
and stiff = round and reliable.

There's more to it than that. Early Rigida 1320 rims had
approximately
the same cross section as many Mavic rims, and yet they dented far
more easily.

but but but, evil mavic choose their diabolous materials so they
crack
and can thus rip customers off, not because of desire to achieve
better
mechanical performance...

Jim: We've traded one type of failure for another. Simple as that.

don't agree. there is no technical reason to over-tension a wheel.
zero. so there's no reason to waste material resources on trying to
make
everything idiot-proof.

It takes a certain amount of overall tension to hold a rim in place
under load. More spokes and the average tension required decreases.
Fewer spokes requires more tension per spoke. To suggest that all rim
failures (due to cracking) are from over-tensioning doesn't wash. It's
proper tensioning with a rim that isn't adequately designed to carry the
load. A rim that will work fine for 32 spokes may be a very poor choice
for 20.

It's not about making something idiot-proof. It's about reasonable life
expectancy.

The
problem, from my end (retail & repair) is that the customer looks at
a
dent and understand how they caused the problem. Not so for cracks at
the spoke/rim interface. So even if we have a "stronger" wheel, we
increase the likelihood of warranty claims and customer unhappiness.

"increase"??? how? the only rims i've ever seen crack are ones that
have
been over-tensioned. and that goes for pre-builts as well as hand-
builts. jobst-inspired lbs over-tensioning of wheels is absolutely
rife
in the industry - of course such rims are going to crack.

I cannot get around the fact that overall life expectancy of a wheel is
probably not much different (maybe even better) today than 20 years ago,
despite the prevalence of rims cracking at the nipple/rim interface.
Back in the day, the wheels would be damaged from riding (dented,
flat-spotted, whatever) before you would get to the mileage we see today
with cracked rims. The point I was trying to make is that a customer
will see a cracked rim and think bad design, even though it went through
the same set of roads & potholes as the rim of yesteryear, which would
have dented without the customer questioning the wheel's design.

The customer who dented the older wheel is probably blaming him or
herself for the wheel's damage, while the customer with the cracked rim
blames the manufacturer. In all likelihood, the customer with the
cracked rim is less happy with the product than the customer with the
dented rim.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com

In article ,
"Mike Jacoubowsky" wrote:

I cannot get around the fact that overall life expectancy of a wheel
is probably not much different (maybe even better) today than 20
years ago, despite the prevalence of rims cracking at the nipple/rim
interface.

Ummm.... In the old days- e.g., before the mid 80s- people usually rode
the OEM wheels that came with their bikes for the entire service life of
the bike- decades, sometimes. I've got several sets of wheels with rims
like those that have seen over 20,000 miles without a problem. By
comparison, every recent Mavic rim I have used (X222, Open Pro, Cosmic
Expert) cracked in under 3000 miles- in the case of the Cosmic Expert,
cracked two rear rims in under 1000 miles; the first was built by Mavic
and the second was built by me to the same tension that Mavic used.

Basically I find the opposite of your observation- that modern Mavic
rims (specifically) have a dramatically shorter life expectancy than
used to be the case compared to 20 years ago. You can still ride a
dinged wheel or a wheel with a flat spot. A broken rim is no longer
usable.

Back in the day, the wheels would be damaged from riding (dented,
flat-spotted, whatever) before you would get to the mileage we see
today with cracked rims. The point I was trying to make is that a
customer will see a cracked rim and think bad design, even though it
went through the same set of roads & potholes as the rim of
yesteryear, which would have dented without the customer questioning
the wheel's design.

Because the customer generally understood that this was the consequence
of riding too-skinny and/or underinflated tires, bottoming out the rim
when they hit those things. I think we see less of this because most
people ride tires pumped to 110-120 psi instead of tires pumped to 70
psi as was often the case 30 years ago.

On Dec 13, 7:39*am, Tim McNamara wrote:
In article ,
*"Mike Jacoubowsky" wrote:

I cannot get around the fact that overall life expectancy of a wheel
is probably not much different (maybe even better) today than 20
years ago, despite the prevalence of rims cracking at the nipple/rim
interface.

Ummm.... In the old days- e.g., before the mid 80s- people usually rode
the OEM wheels that came with their bikes for the entire service life of
the bike- decades, sometimes. *I've got several sets of wheels with rims
like those that have seen over 20,000 miles without a problem. *By
comparison, every recent Mavic rim I have used (X222, Open Pro, Cosmic
Expert) cracked in under 3000 miles- in the case of the Cosmic Expert,
cracked two rear rims in under 1000 miles; the first was built by Mavic
and the second was built by me to the same tension that Mavic used.

Basically I find the opposite of your observation- that modern Mavic
rims (specifically) have a dramatically shorter life expectancy than
used to be the case compared to 20 years ago. *You can still ride a
dinged wheel or a wheel with a flat spot. *A broken rim is no longer
usable.

Back in the day, the wheels would be damaged from riding (dented,
flat-spotted, whatever) before you would get to the mileage we see
today with cracked rims. The point I was trying to make is that a
customer will see a cracked rim and think bad design, even though it
went through the same set of roads & potholes as the rim of
yesteryear, which would have dented without the customer questioning
the wheel's design.

Because the customer generally understood that this was the consequence
of riding too-skinny and/or underinflated tires, bottoming out the rim
when they hit those things. *I think we see less of this because most
people ride tires pumped to 110-120 psi instead of tires pumped to 70
psi as was often the case 30 years ago.

Mike:

I had a wheelset that was mavic cxp 21 32 holes. They came in a new
bike. After a bout 3000 miles the rear rim cracked evenly around the
spokes. I bought one of the new dt rims and replaced. The dt rim is
holding great after around 10,000 miles. I weigh between 190 and 200
and have a heavy legged riding style not much spinning but rather more
torque. In other words rough on components.

What makes the dt rim better than the cxp 21or than the crappy mavic
reflex that also cracked the same way after 3000 miles or so?

On Fri, 12 Dec 2008 21:51:41 -0800, Mike Jacoubowsky wrote:

"jim beam" wrote in message
. ..
On Tue, 09 Dec 2008 18:31:36 -0800, Mike Jacoubowsky wrote:

"jim beam" wrote in message
...
Mike Jacoubowsky wrote:
someone was bound to figure it out some time - shallow = dentable,
deep
and stiff = round and reliable.

There's more to it than that. Early Rigida 1320 rims had
approximately
the same cross section as many Mavic rims, and yet they dented far
more easily.

but but but, evil mavic choose their diabolous materials so they
crack
and can thus rip customers off, not because of desire to achieve
better
mechanical performance...

Jim: We've traded one type of failure for another. Simple as that.

don't agree. there is no technical reason to over-tension a wheel.
zero. so there's no reason to waste material resources on trying to
make
everything idiot-proof.

It takes a certain amount of overall tension to hold a rim in place
under load. More spokes and the average tension required decreases.
Fewer spokes requires more tension per spoke.

not true - that's a fundamental jobstian mistake. wheel strength is /not/
a function of tension, it's a function of rim stiffness.




To suggest that all rim
failures (due to cracking) are from over-tensioning doesn't wash.

it's the /only/ explanation because it's the /only/ loading point.



It's
proper tensioning with a rim that isn't adequately designed to carry the
load. A rim that will work fine for 32 spokes may be a very poor choice
for 20.

a rim available for both 20 and 32 is overbuilt for the 32.





It's not about making something idiot-proof. It's about reasonable life
expectancy.

The
problem, from my end (retail & repair) is that the customer looks at a
dent and understand how they caused the problem. Not so for cracks at
the spoke/rim interface. So even if we have a "stronger" wheel, we
increase the likelihood of warranty claims and customer unhappiness.

"increase"??? how? the only rims i've ever seen crack are ones that
have
been over-tensioned. and that goes for pre-builts as well as hand-
builts. jobst-inspired lbs over-tensioning of wheels is absolutely
rife
in the industry - of course such rims are going to crack.

I cannot get around the fact that overall life expectancy of a wheel is
probably not much different (maybe even better) today than 20 years ago,
despite the prevalence of rims cracking at the nipple/rim interface.
Back in the day, the wheels would be damaged from riding (dented,
flat-spotted, whatever) before you would get to the mileage we see today
with cracked rims. The point I was trying to make is that a customer
will see a cracked rim and think bad design, even though it went through
the same set of roads & potholes as the rim of yesteryear, which would
have dented without the customer questioning the wheel's design.

they'd only think that if they were under some false impressions having
read jobstian drivel about anodizing or some such. /i/ look at cracked
rims and immediately think of anisotropy and spoke tension.




The customer who dented the older wheel is probably blaming him or
herself for the wheel's damage, while the customer with the cracked rim
blames the manufacturer.

again, i blame the lbs. when i've tried to buy boxed wheels locally,
they've invariably been opened and "helped". this is completely
unacceptable in my view - unless they're somehow el-cheapo crap that's not
true out of the box.



In all likelihood, the customer with the
cracked rim is less happy with the product than the customer with the
dented rim.

unless these are truly awful cheapo wheels, only ignorance causes a
cracked rim.

On Sat, 13 Dec 2008 08:01:04 -0800, wrote:

On Dec 13, 7:39Â*am, Tim McNamara wrote:
In article ,
Â*"Mike Jacoubowsky" wrote:

I cannot get around the fact that overall life expectancy of a wheel
is probably not much different (maybe even better) today than 20
years ago, despite the prevalence of rims cracking at the nipple/rim
interface.

Ummm.... In the old days- e.g., before the mid 80s- people usually rode
the OEM wheels that came with their bikes for the entire service life
of the bike- decades, sometimes. Â*I've got several sets of wheels with
rims like those that have seen over 20,000 miles without a problem. Â*By
comparison, every recent Mavic rim I have used (X222, Open Pro, Cosmic
Expert) cracked in under 3000 miles- in the case of the Cosmic Expert,
cracked two rear rims in under 1000 miles; the first was built by Mavic
and the second was built by me to the same tension that Mavic used.

Basically I find the opposite of your observation- that modern Mavic
rims (specifically) have a dramatically shorter life expectancy than
used to be the case compared to 20 years ago. Â*You can still ride a
dinged wheel or a wheel with a flat spot. Â*A broken rim is no longer
usable.

Back in the day, the wheels would be damaged from riding (dented,
flat-spotted, whatever) before you would get to the mileage we see
today with cracked rims. The point I was trying to make is that a
customer will see a cracked rim and think bad design, even though it
went through the same set of roads & potholes as the rim of
yesteryear, which would have dented without the customer questioning
the wheel's design.

Because the customer generally understood that this was the consequence
of riding too-skinny and/or underinflated tires, bottoming out the rim
when they hit those things. Â*I think we see less of this because most
people ride tires pumped to 110-120 psi instead of tires pumped to 70
psi as was often the case 30 years ago.

Mike:

I had a wheelset that was mavic cxp 21 32 holes. They came in a new
bike. After a bout 3000 miles the rear rim cracked evenly around the
spokes. I bought one of the new dt rims and replaced. The dt rim is
holding great after around 10,000 miles. I weigh between 190 and 200 and
have a heavy legged riding style not much spinning but rather more
torque. In other words rough on components.

What makes the dt rim better than the cxp 21or than the crappy mavic
reflex that also cracked the same way after 3000 miles or so?

easy, the d.t. rim was built right, the cxp21 wasn't. i've got cxp22's on
my fixie, no eyelets just like the cxp21, and they haven't cracked in 4
years. oh, and i made sure all spokes were correctly tensioned to
manufacturer spec. coincidence?

On Dec 14, 1:42*pm, jim beam wrote:
On Sat, 13 Dec 2008 08:01:04 -0800, wrote:
On Dec 13, 7:39*am, Tim McNamara wrote:
In article ,
*"Mike Jacoubowsky" wrote:

I cannot get around the fact that overall life expectancy of a wheel
is probably not much different (maybe even better) today than 20
years ago, despite the prevalence of rims cracking at the nipple/rim
interface.

Ummm.... In the old days- e.g., before the mid 80s- people usually rode
the OEM wheels that came with their bikes for the entire service life
of the bike- decades, sometimes. *I've got several sets of wheels with
rims like those that have seen over 20,000 miles without a problem. *By
comparison, every recent Mavic rim I have used (X222, Open Pro, Cosmic
Expert) cracked in under 3000 miles- in the case of the Cosmic Expert,
cracked two rear rims in under 1000 miles; the first was built by Mavic
and the second was built by me to the same tension that Mavic used.

Basically I find the opposite of your observation- that modern Mavic
rims (specifically) have a dramatically shorter life expectancy than
used to be the case compared to 20 years ago. *You can still ride a
dinged wheel or a wheel with a flat spot. *A broken rim is no longer
usable.

Back in the day, the wheels would be damaged from riding (dented,
flat-spotted, whatever) before you would get to the mileage we see
today with cracked rims. The point I was trying to make is that a
customer will see a cracked rim and think bad design, even though it
went through the same set of roads & potholes as the rim of
yesteryear, which would have dented without the customer questioning
the wheel's design.

Because the customer generally understood that this was the consequence
of riding too-skinny and/or underinflated tires, bottoming out the rim
when they hit those things. *I think we see less of this because most
people ride tires pumped to 110-120 psi instead of tires pumped to 70
psi as was often the case 30 years ago.

Mike:

I had a wheelset that was mavic cxp 21 32 holes. They came in a new
bike. After a bout 3000 miles the rear rim cracked evenly around the
spokes. I bought one of the new dt rims and replaced. The dt rim is
holding great after around 10,000 miles. I weigh between 190 and 200 and
have a heavy legged riding style not much spinning but rather more
torque. In other words rough on components.

What makes the dt rim better than the cxp 21or than the crappy mavic
reflex that also cracked the same way after 3000 miles or so?

easy, the d.t. rim was built right, the cxp21 wasn't. *i've got cxp22's on
my fixie, no eyelets just like the cxp21, and they haven't cracked in 4
years. *oh, and i made sure all spokes were correctly tensioned to
manufacturer spec. *coincidence?

I was looking for a rational answer from a friendly person with
extensive practical experience. That is why I prefaced my question
with "Mike". Had I been looking for illogical responses from an
unknown nutjob with zero proven experience who tends to cuss at those
who don't agree with him/her(?), I may have summoned jb. And while jb
certainly provides amusement with his diatribes and his references to
his knowledge of secret experiments, in this case, I was looking for
information and that is the reason I summoned Mike.

So, please remain at post until I ask for the jester.