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Maybe I figured out the open pro rim problem?(6 posts)

Maybe I figured out the open pro rim problem?rwbadley
Feb 18, 2003 11:13 AM
Previous post a few days ago about a shuddering I was getting from the op/record wheelset. Thanks for all of your suggestions for cause and fix.

I put the main offender (the front) on my truing stand and spun and watched. It spins pretty true so I grabbed a felt tip marker and set against the brake surface to mark the problem.

What I found was indeed an irregularity that appears to be in about ten spots or so on the rim. It seemed to be mirrored on the other side in the same locations. The thing was, most of the rim was 'high' with the offending spots being 'low' or indented. The low spots were all about 1" or so long and at various (not even ) places of the circumference on the braking surface.

So, here's my thinking... is it possible that with the strength of the dual pivot brake calipers that if you were stopped after a high speed descent with heated rims, if high brake pressure were applied to the motionless rim the rim could be damaged by this pressure? I see not much else that explains what I am seeing here...

Anyway the end result is the same, toasted rims.

re: Maybe I figured out the open pro rim problem?Spunout
Feb 18, 2003 12:06 PM
Do these OPs have alot of miles on them? Do you run very high pressure (like Vredsteins at 145 psi)? Sounds like they are very close to failure! Heat changes the shape of aluminum, so maybe over-heating on a descent would warp things a bit.

I have OPs, use michelins at around 105-115 and hope to get a good life out of them.

BTW, the old GP4s did swell at the spoke nippes, just from the tension.
re: Maybe I figured out the open pro rim problem?rwbadley
Feb 18, 2003 12:32 PM
They appear not to have high miles. They were not new when I aquired them so I have no idea on their previous life.

I run 105-115 psi also. Anyway I will probably get a couple of cxp 33 and relace these hubs. The cxp is a little heavier, but I have had good luck with them in the past. I have hit some pretty big holes at high speed (not my fault!?) and they have never failed nor given concern.
re: Maybe I figured out the open pro rim problem?Ambishawn
Feb 19, 2003 7:09 PM
How about Ceramic Open pros? They dissapate heat better. The ceramic are almost as heavy as CXP33 though. If people think ceramic taking heat well is a bunch of bunk, talk to any mechanical engineer about the use of ceramic on pistion tops on future engines. Joe Young highly recommends CXP33. I may go with them Myself.
Some actual data on heat dissipationKerry
Feb 20, 2003 5:13 PM
So, the thermal conductivity of aluminum oxide (the "ceramic" coating on these rims) is about 50, and the conductivity of aluminum is 235. The ceramic is about 20% the thermal conductivity of a plain Al rim. So how do they dissipate heat better? Some law of thermodynamics that isn't normally studied in engineering?
they don'tDougSloan
Feb 20, 2003 5:44 PM
They don't dissipate heat better; they retain their braking ability at higher temperatures (of the rim and the pad), though; isn't that the idea?