Cracking rims

In article ,
Carl Sundquist wrote:

Michael Press wrote:


Lest we forget:
bicycles are ridden by brandy swilling,
cigarette smoking,
pot belge using reprobates.


If one swills brandy and smokes cigarettes, by what means does one use
pot belge?

Intravenous drip.
I should have said "pot belge shooting";
then again somebody would have taken me
to be condoning forcible elimination of
cycling marshals.

--
Michael Press

"Practical" and "well engineered" have never been enduring buzzwords in
this industyry, Jobst. You should know that by now.

- -
Compliments of:
"Your Friendly Neighborhood Wheelman"

If you want to E-mail me use:
ChrisZCorner "at" webtv "dot" net

My website:
http://geocities.com/czcorner

On Sun, 07 Dec 2008 19:28:01 +0000, jobst.brandt wrote:

Chalo Colina wrote:

OK, here is a view of the whole bike:

http://farm3.static.flickr.com/2314/...0222bf.jpg?v=0


What is the disc on the right side of the front wheel?

If one chooses to run the "return" side of the chain off the idler for
less drive train friction, the disc will keep the chain out of the
spokes:

http://farm3.static.flickr.com/2340/...2e0173.jpg?v=0

Oh.

Why not just use tungsten carbide spokes and a sacrificial brass chain?
The wheel would be stiffer (even with smaller-gauge and thus more
aerodynamic spokes) and the chain more lubricious. Faster! Also you
could use PTFE boxer shorts for higher speeds "draggin' ass" through
corners.

Don't say that or someone will get the bright idea of making yet stiffer
spokes whereas 2mm diameter cross section steel spokes are already
stiffer than needed, to make a durable wheels with extruded aluminum
rims. Back in the days when the bicycle was the state of the art in
mechanical design, the ancients did not use many thin spokes for naught.

Not to mention that aluminum rims are what enables good braking on
mountain descents because aluminum conducts well and has a reasonable
heat capacity. Those of us who rode wood rims are well aware of this
from hot brake pad debris hitting the legs... ouch!

When engineering went on to motorized vehicles and aircraft, bicycle
mechanics took over to invent a bunch of less reliable components as
roads became progressively smoother. What was overlooked is that
failure stresses are from fatigue rather than forced rupture, as most
people assume... even today: "I hit a bump that broke a spoke." The
bump having little to do with cause of failure other than to expose it.

anecdotes are not analysis jobst.

On Sun, 07 Dec 2008 11:51:02 -0800, Mike Jacoubowsky wrote:

But Fiamme Reds and Martanos and other rims of that era were
notoriously soft and "squished" (I won't even say "dented" because
they were so soft it was more like a "squish" where the rim would
visibly bow out at the point of impact). Modern rims are far less
prone to denting or squishing.

I think there are issues with modern rims that go more to the
materials used than wheel design. We've traded softer, squishier, more
dent-prone versions for rims that are now considerably less likely to
dent, but considerably more likely to crack (with your choice of
either a much higher impact required to make modern rims fail or a
much shorter period of actual use resulting in the infamous cracks at
the spoke/nipple interface).

I don't know what you were doing on all those Sunday rides in the Santa
Cruz mountains but I and those who attended my tubular patch sessions
had no dents or cracks in our rims other than from a crash. I rode the
Alps on unpaved or cobblestone roads for many years with tubulars
before rim cracking and clincher rim dents became common.

I am not convinces this is a materials problem, but rather the deep
dish and low spoke count with fatter and fewer spokes. Just consider
the repetitive stress cycles from that.

Jobst Brandt

I was working in the trade even back then, so I got a pretty wide sample
of wheels coming my way. Unless you believe that roads are built a lot
better then than now, or that tubulars are more likely to cause rim
damage than clinchers, I will state categorically that the evidence
shows rims were more prone to denting/squishing then (apparently from
being softer) than they are now.

Now I'm just waiting for someone to come to the defense of the Martano
rim. You only need be in the vicinity of a pothole to get one of those
to dent.

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


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

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.

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


"jim beam" wrote in message
. ..
On Sun, 07 Dec 2008 11:51:02 -0800, Mike Jacoubowsky wrote:

But Fiamme Reds and Martanos and other rims of that era were
notoriously soft and "squished" (I won't even say "dented" because
they were so soft it was more like a "squish" where the rim would
visibly bow out at the point of impact). Modern rims are far less
prone to denting or squishing.

I think there are issues with modern rims that go more to the
materials used than wheel design. We've traded softer, squishier,
more
dent-prone versions for rims that are now considerably less likely
to
dent, but considerably more likely to crack (with your choice of
either a much higher impact required to make modern rims fail or a
much shorter period of actual use resulting in the infamous cracks
at
the spoke/nipple interface).

I don't know what you were doing on all those Sunday rides in the
Santa
Cruz mountains but I and those who attended my tubular patch
sessions
had no dents or cracks in our rims other than from a crash. I rode
the
Alps on unpaved or cobblestone roads for many years with tubulars
before rim cracking and clincher rim dents became common.

I am not convinces this is a materials problem, but rather the deep
dish and low spoke count with fatter and fewer spokes. Just
consider
the repetitive stress cycles from that.

Jobst Brandt

I was working in the trade even back then, so I got a pretty wide
sample
of wheels coming my way. Unless you believe that roads are built a
lot
better then than now, or that tubulars are more likely to cause rim
damage than clinchers, I will state categorically that the evidence
shows rims were more prone to denting/squishing then (apparently from
being softer) than they are now.

Now I'm just waiting for someone to come to the defense of the
Martano
rim. You only need be in the vicinity of a pothole to get one of
those
to dent.

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


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

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...




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.

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


"jim beam" wrote in message
. ..
On Sun, 07 Dec 2008 11:51:02 -0800, Mike Jacoubowsky wrote:

But Fiamme Reds and Martanos and other rims of that era were
notoriously soft and "squished" (I won't even say "dented" because
they were so soft it was more like a "squish" where the rim would
visibly bow out at the point of impact). Modern rims are far less
prone to denting or squishing.
I think there are issues with modern rims that go more to the
materials used than wheel design. We've traded softer, squishier,
more
dent-prone versions for rims that are now considerably less likely
to
dent, but considerably more likely to crack (with your choice of
either a much higher impact required to make modern rims fail or a
much shorter period of actual use resulting in the infamous cracks
at
the spoke/nipple interface).
I don't know what you were doing on all those Sunday rides in the
Santa
Cruz mountains but I and those who attended my tubular patch
sessions
had no dents or cracks in our rims other than from a crash. I rode
the
Alps on unpaved or cobblestone roads for many years with tubulars
before rim cracking and clincher rim dents became common.

I am not convinces this is a materials problem, but rather the deep
dish and low spoke count with fatter and fewer spokes. Just
consider
the repetitive stress cycles from that.

Jobst Brandt
I was working in the trade even back then, so I got a pretty wide
sample
of wheels coming my way. Unless you believe that roads are built a
lot
better then than now, or that tubulars are more likely to cause rim
damage than clinchers, I will state categorically that the evidence
shows rims were more prone to denting/squishing then (apparently from
being softer) than they are now.

Now I'm just waiting for someone to come to the defense of the
Martano
rim. You only need be in the vicinity of a pothole to get one of
those
to dent.

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

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

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.

Jobst Brandt

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 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.

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.

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

"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. 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.

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

On 06 Dec 2008 16:50:25 GMT, may have
said:

The cracked rim is a child of "modern" bicycle components trend to be
lighter and more aerodynamic with each "improvement". It may be
apparent that the 36-spoke wheel on 1.8_1.6_1.8mm butted spokes is
passé. Today, with fewer and thicker spokes, stress cycles are
proportionally greater by spoke thickness divided by number of spokes.

Eveen paired spokes add to the cracking syndrome, because nearly all
wheel load is carried by tension change in only two spokes.

Bicycle technology today is primarily fashion as I see it. The myriad
vendors at InterBike showed that in recent years. Some positive
features have been produces but their reliability has not come along
for the ride.

Fortunately, there are still components available to build
unfashionably durable wheels.

Of course, barring accidental damage, it takes a long time to wear the
rim flanges down to the point where replacement is mandated when
riding on relatively flat terrain such as we have around here...so I
build wheels in double sets just in case. I have had too much
experience with the phenomenon of the component that's no longer
available when a replacement is finally required.

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