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Old 12-06-2008, 12:37 AM
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conradcliff conradcliff is offline
Motorized Bicycle Senior Member
Join Date: Oct 2008
Location: Tampa, Fla.
Posts: 67
Default Re: Need mental and ratio help! Please!

Originally Posted by 5-7HEAVEN View Post
A gear ratio of 11.41:1 would spin an engine at 6,000rpm to reach 40mph.

You would need 6t/32t sprockets(5.33333:1), then

8t/44t sprockets(5.5:1), then

36t/14t final drive(.389:1).

5.33333 X 5.5 = 29.33333

29.333333 x .389 = 11.41

I might be wrong, so someone else can doublecheck.
Following your procedure above I get:

6t/40t sprockets(6.67:1), then

10t/44t sprockets(4.4:1), then

36t/14t final drive(.389:1).

6.67 X 4.4 = 29.33333

29.333333 x .389 = 11.41

Originally Posted by 5-7HEAVEN View Post
Your present calculation gives you 6.87:1., and you need 11.41:1.

An easier resolution is to calculate gear ratio with the next-to-last(larger) sprocket on the rear hub.

Tell me what it is, and we can do more easily attainable calculations.
I trust that I'm doing something wrong as I haven't had any experience with this but I just can't see where..could you point out my error?

Thank you so much for all the help you've provided.

When he mentions 58t sprocket and 5.8:1, you must multiply this by 4.15 internal gear reduction to calculate to 24.07:1.

Multiply 2.7 by 4.15) internal gear reduction to get 11.21:1 top speed gearing.

The ratios are so different because he is using all the gears in the cassette.

His ratios may be lower because the china engine produces its hp and torque at a lower rpm.
Yeah, I figured that the change in ratio was due to the cassette I just didn't think about the internal gear reduction at first which was throwing me off.

Last edited by conradcliff; 12-06-2008 at 12:41 AM.
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