Bicycle Mechanics - Gear changing.

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Bokkie
07-12-02, 01:48 AM
I was reading a magazine recently and it made the sensible comment that you should try to keep the chain running straight. That is, don't select gears where the chain is on, say, the inner chain ring while it's running on the outer rear cog. Chains are quite flexible so is it the chain they are more concerned about, or possibly the potential damage it might do to the gear teeth? I ask this because on my Cannondale road bike, I have 2 up front and 7 behind and some of the rear cog teeth look a little rounder than normal. Is that because I've been inadvertently running the chain on the 'wrong' gear selections? The gear ratios are such that I don't have too many duplicated, so they are mostly 'valid' selections as it were.

MichaelW
07-12-02, 04:25 AM
cross-gears are mostly bad for your chain.
chewa
07-12-02, 06:10 AM
Cross gears increase wear on your chain and presumably would also cause uneven wear on your rear block. It might be however that the shapes you noticed are modified teeth to "ramp " the chain when changing.

On both my road bikes the middle rear cog wears before any of the rest (I can feel it through the pedals) because that's the gear I use most with my 52 front

RainmanP
07-12-02, 06:17 AM
Generally it is recommended to avoid the extreme combinations - big front/largest rear, small front/smallest rear. On 9sp some even recommend avoiding two, ie, big front/largest rear, 2nd largest rear. I generally abide by this, but if I need one more gear on a short climb I will go to the big/big without hesitation since it is quicker and easier than shifting the front.

Cogs, especially the 1-2 you use most, do wear out in a 2,000-4,000 miles or so though some people report getting many more than that regardless. Although cross chaining can accelerate wear, you would have to do it a lot for it to really make a difference. If, for instance, you ride your small front/small rear all the time, I'm sure you would experience significantly accelerated wear. This is probably the worst combination since small cogs wear faster (fewer teeth=more contacts per tooth per mile) and it seems like the smaller diameters would exacerbate the angle of the chain.
FWIW,
Raymond