"From personal experience, the stresses on the drivetrain while touring far exceed the stresses while racing. " ---- I believe this can be explained by gearing. Take a 170-pound cat 2 rider & 30-pound bike (200 lb together), charging up an 8% grade at 10.5mph. Then the rider is expending about 354 Watts. A 42/26 gear gives a cadence of 82rpm, an average force on the pedals of about 52lb, tension on the chain is 108lb, the radius of the rear cog is about 1.5 inch, and the rider is exerting a torque of about 19 ft-lb on the rear wheel. Now take the same rider expending 354 Watts up a hill, but increase the total weight from 200 lb to 400lb to represent a heavy touring load. The rider can now only go 5.7mph, and for a cadence of 80rpm a gear of 32/36 (!) is appropriate. Now the average pedal force is still 53lb, but the chain tension has increased to 145lb, the cog radius has increased to 2.86 inch, and the torque on the rear wheel is now 34.5 ft-lb. So: when a cat-2 racer went touring with a heavy load the torque applied to the rear wheel doubled, the force on the chainring increased by 50% and the applied force on the pedal eye was the same. But let's go back and check on Mr. Cipollini: rolling at 40mph on the flat in a 53/11 gear with a cadence of 104 and a power output of 1292 Watts, the pedal force is now 152lb, the chain tension is 248lb, the cog radius is only .87inch and the torque on the wheel is 'only' 18.1 ft-lb. (this is just an example, I hear he maxes out at 2000Watts) So in a finishing sprint in a high gear, Mario is much less likely to pull the wheel out of the dropout, but substantially more likely to break a crank or chain. Brad Stockwell Palo Alto
Jan Heine wrote:From personal experience, the stresses on the drivetrain while touring far exceed the stresses while racing. Recently, we went for a weekend trip, and my Mercian was loaded with camping gear for three, a trailer and a 30-lb. 2-year-old. The Mercian has horizontal dropouts and Campy C-Record hubs. (I had replaced the broken axle prior to the trip.)
Several times when starting from a light, the rear wheel pulled out of the dropouts. I tightened the QR as much as reasonable, but to no avail. I finally "learned" to start using a very light touch, and that helped.
In all my years of racing (up to a Cat. 2), using Campy NR hubs and horizontal dropouts, I never had a wheel pull out during a sprint (fortunately, I might add - I might not be around to tell the tale).
Why? I don't know, but I suspect the reason is simple: When Cipollini pushes on the cranks, the bike has the option of going forward to alleviate the stress. A loaded touring bike puts up much more resistance... and thus stresses the entire drivetrain much more.
But we are getting away from classic bikes here.
Jan Heine, Seattle
>
>From: Tom Dalton
>Subject: Re: [CR]Predicting/preventing NR/SR crank breakage
>To: classicrendezvous@bikelist.org
>
>
>Jerry & Liz Moos wrote:
>I suspect that laboring up a mountain pass with 50 lbs of gear
>stresses a crank as much as a Cippolini sprint.
>
>Sure, and the crankshaft in my Chevy Nova gets just as much stress
>as the crank in Michael Schumacher's Ferrari... Ugh!
>
>
_______________________________________________
---------------------------------
Do You Yahoo!?
Yahoo! Finance - Get real-time stock quotes