Gearing Changes, What mph?

Gearing on my bike is currently 26 x 22.

If I move to 31 x 22, and my engine can keep the same RPM, what mph increase would I see? What about 31 x 20?

I've tried to find a calculator or something on google, but I figure you guys probably have this stuff memorized or something.

Re: Gearing Changes, What mph?

You can figure by % increase of the front sprocket diff. Your change would be 19% in the first case and an additional 9% on top of the 19% for the second case. I can't remember the formula I used for bicycles so I just do it this way

Re: Gearing Changes, What mph?

negating increased HP requirements to go faster...

new speed = old speed (new front #/old front #) (old rear #/new rear #)

Re: Gearing Changes, What mph?

Thanks matt.

So with the 31 front I should see

45mph 1.192 = 53.64mph

and with he 20 rear as well I would have

45 1.192 * 1.1 = 59mph

Guess I'll just have to get the speedo, do it, and see if I've got enough HP to pull those sprockets.

Re: Gearing Changes, What mph?

There are a lot of ways to do this, the easiest way I've found is as follow.

First divide your front gear (lets say 14)t by the rear gear (lets say 45t) to come up with a ratio.

14/45 = 0.31

Then take the known top speed at that gear ratio(lets say 30)and divide it by that ratio to come up with a Kfactor (constant) for your engine set-up.

30/0.31 = 96.43

Now you can figure out what top speed are achievable with different gear ratios.

First figure out the new ratio, lets say you want to switch to a 40t rear.

14/40 = 0.35

So then you take that new ratio and multiple it by the Kfactor for your engine.

0.35*96.43 = 33.8

So in theory a bike that did 30 with 14/45 gearing will be able to do 33.8 with 14/40 gearing.

Hope that helps.

Re: Gearing Changes, What mph?

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