Bicycle Mechanics - gear ratios, what's the difference
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07-17-11, 05:30 AM
Quick question, as I'm quite numerically challenged, is there much difference between a 40:28 gearing which gives a ratio of 1:43 (10:7) and a 34:25 gearing which gives a ratio of 1:36 (34:35) in real terms when climbing. Any thoughts?
07-17-11, 06:34 AM
The 34x25 gear is 5% lower than the 40x28 (1.36/1.43=0.95) so it will require 5% less pedal pressure but 5% higher cadence to maintain the same climbing speed. I think it would be a slight but noticable difference.
A 5% or so difference at the low end isn't that noticeable if the higher one is low enough, but will give you a bit more breathing room when you need it.
Most road bikes are set up with 5-7% jumps toward the high end giving you the ability to fine tune your cadence and pedal effort where you do most of the riding. But as we move toward the low end the jumps are usually closer to 10%, since in those gears cadence isn't the issue, just leverage and torque.
So figure the 5% difference as being about 1/2 of a typical low end gear step.
07-17-11, 12:34 PM
Yea, you want to use the 34/28, rather than the 40/28..
easier to compare things that only have 1 variable.
rather than 2 ..
07-17-11, 03:16 PM
Many thanks. Makes much more sense.
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