Bicycle Mechanics - Cracked Wheel
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05-27-05, 08:32 AM
While putting air in the rear tire of my 6 year old Bianchi, I noticed two hairline cracks radiating out from a spoke hole several spokes away from the valve stem. On close examination, I also found another crack at a spoke hole four spoke away. While the wheel still spins true with no hops, my LBS advised me that the wheel was unsafe to ride (I figured this was the case).
I find this to be very odd. Has anyone else seen this before? The wheels are 32-hole Mavic CXP21s laced to Veloce hubs with straight guage spokes. The bike has a little over 10k miles on it.
Anyway, I just ordered a new wheelset from Performance since my shop didn't have ANY Campy compatible wheels and no CXP21s to lace onto my old hub. The wheels I ordered are Mavic Open Pros in silver, laced with butted DT spokes to 32-hole Record hubs. I know it probably sounds silly to put such nice wheels on a mid-level Bianchi (celeste Veloce) but the bike is nearly perfect and still rides like a dream.
The shop was at a loss to explain the wheel cracks. Does anyone have any idea what caused them? Any comments good or bad on my new wheels? John
05-27-05, 08:45 AM
The shop was at a loss to explain the wheel cracks. Does anyone have any idea what caused them?
Either from impact or from the repeated (cycling) stress of riding (fatigue).
The rim may have had small stress risers around the machined areas (holes were not de-burred).
Replace the wheel and be happy you caught it before the wheel collapsed.
05-27-05, 09:17 AM
!! Jeez, I've got the exact same rims. Just went out to inspect them very closely, because I've been having issues with spokes breaking on the drive side, and I've been wondering if the entire wheelbuild is squirrelly. I don't have any cracking in the rims, but I've got very low mileage on the wheels. At least I think I do -- they came on a used bike.
I might just trash the entire set and buy new.
I have Mavic SSC SL. Rear wheel cracked the same way as you explained, but 3 spoke holes - all next to each other - were cracked both sides. A friend on the Simple Green team has broken 2 Mavic SSC SL rear wheels. It cost $75 to ship the wheel (both ways). Mavic put on a new rim, but used the same spokes and hub. I understand that this is caused by the type of Aluminum Mavic uses. Anyway, I sold them on ebay and bought a pair of Topolini's - best clinchers I have ever ridden.
05-27-05, 10:19 AM
Make sure you have the spoke tension checked after a few rides. I bought some open-pros on ultegra hubs from Performance and the rear spokes loosened up on me. I was looking at the Record-open pro wheelset for my Campy road bike but I am not sure about Performance's wheel builds. I weigh about 225lbs so it might have just been my fat ass.
05-27-05, 10:25 AM
Yes, this is not an unusual occurrence. Typically, its from the spokes being over tensioned, but its hard to say. 6 years and 10k miles is alot for a mid-level rim like the CXP21 (not that its not a nice rim, its pretty good).
I agree with Cerberusql. Get the spoke tension checked on those new wheels. Machine built wheels are notorious for being a little undertensioned.
This is the typically the way rims fail, not unusual at all. According to Jobst Brandt rim cracks are caused by stresses related to riding rough roads or impacting chug holes etc., rarely due to excess spoke tension. If you have good hubs and spokes simply rebuild the wheels with new rims. CXP 21 rims are often used as OEM on moderately priced bikes. Replacing them with Open Pros or similar light weight rims can make an immediate improvement to the bike's performance without sacrificing strength or durability.
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