Bicycle Mechanics - excessive drivetrain friction?

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otoman
10-25-04, 06:59 PM
Is this a valid test for drivetrain friction?
With the bike on a repair stand, move the pedals forwad fast enough to get the rear wheel moving at a decent clip, then backpedal OR carry the pedals forward but slow enough so that you still hear the pawls in the freehub clicking.
When I do this, my pedals stop almost instantly. I have even tested it when I have gotten the rear wheel moving very fast in a big gear, then dropped to the small chainring so that I could turn the pedals over relatively quickly without engaging the freehub. Even then, my pedals stop almost instantly. Is this normal? How often should the chain and/or rear derailleur pulleys be replaced?

FYI: Ultegra 9 speed with about 2000 miles on all of the parts; chain cleaned, lubed pretty regularly. No bottom bracket symptoms whatsoever (crank play, thunking/clicking).

I appreciate everyone's input.

John E
10-25-04, 07:19 PM
Make sure your crank turns freely with the chain removed. Your BB bearings may be overtightened or otherwise in need or service or adjustment.
boyze
10-25-04, 07:30 PM
Your approach is probably a first order indictor on bottom bracket bearing resistance and freewheel bearings and maybe a crude check on when these bearings need attention. It doesn't check the wheel bearings at all unless the freewheel is locked up. I suspect your crank stops because of the derailleur pulleys umless the bottom bracket has problems.

For the full drive train I would rank the order of bearing importance as 1) rear wheel, 2) front wheel, 3) chain, 4) derailleur pulleys, 5) bottom bracket and 6) freewheel. The wheel bearings can be checked crudely with a coast test on your favorite hill or do a wheel spin test on a stand and measure the spin time. The caveats to the spin time method is 1) the unknown intial speed although a speedometer could be used and 2) the missing load on the bearings . The chain is a tough one because it's resistance to flex will be dependent on the chain load. Derailleur pulleys can be checked by spinning the pedals backwards. Bottom bracket bearings can be checked by slipping the chain off the chain rings and spin the pedals. However, this can be deceiving because the rolling resistance will be influenced by the pedal force on the bearings. Freewheel bearings - who cares unless they freeze up :D