Gearing questions: 46 x 16 vs 40 x 14
07-13-13, 11:44 PM
#1
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Thread Starter
Gearing questions: 46 x 16 vs 40 x 14
I am currently running 46 x 16 which I like.
I just got some vintage cranks that I want to use and I wanted to use the same gear ration. Unfortunately the bcd on these cranks are 118 (old SR size) and rings are hard to come by. The bike came with a 40t ring that's in good shape. My LBS has a 42t ring also. I ran the numbers through Sheldon Brown's gear calculator and came up with (for 165mm crankset):
46 x 16 = 75.8
40 x 14 = 75.4
42 x 14 = 79.1
If I use 40 x 14, I assume that everything should feel the same. Also, I get that since the chain and rings are smaller, everything will work harder and wear out sooner. Are there other considerations I should consider? (It seems that the 40t chainrings were one of the most popular sizes and are easy to come by). BTW, I will be using 3/32 if that makes a difference.
I just got some vintage cranks that I want to use and I wanted to use the same gear ration. Unfortunately the bcd on these cranks are 118 (old SR size) and rings are hard to come by. The bike came with a 40t ring that's in good shape. My LBS has a 42t ring also. I ran the numbers through Sheldon Brown's gear calculator and came up with (for 165mm crankset):
46 x 16 = 75.8
40 x 14 = 75.4
42 x 14 = 79.1
If I use 40 x 14, I assume that everything should feel the same. Also, I get that since the chain and rings are smaller, everything will work harder and wear out sooner. Are there other considerations I should consider? (It seems that the 40t chainrings were one of the most popular sizes and are easy to come by). BTW, I will be using 3/32 if that makes a difference.
07-14-13, 01:06 AM
#2
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You're good. Wear will probably be negligible. Only thing to worry about is shortening your chain.
07-14-13, 01:46 PM
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Also, smaller chainrings are a lil more uncool looking, unless you're on dirtjumper or CX. 
07-14-13, 04:06 PM
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First, the crank arm length has nothing to do with the gear ratio, only the gain ratio. Second, those numbers are the "gear inches", not "gear ratio." Third, those numbers are dependent on tire diameter, which based on those values appear to be 700 x 25c. Fourth, personally I prefer lower gearing, and would choose 42 x 15 = 73.9 gi, which will also reduce the wear and drag on the rear cog, particularly with a 3/32" cog.
