I am currently running 48 pitch gears and I know the tooth sizes that perform well in 48 pitch, but I want to change to 64 pitch. How do I convert the the number of teeth on gears from 48 pitch to 64 pitch?

-The short answer is: take the number of teeth on the 48 pitch gear and divide that number by 1.5 and then muliply that answer by 2. Here's and example:

(81 tooth 48 pitch) 81 ÷ 1.5 = 54 x 2 = 108

The answer of 108 will be the tooth size to use in 64 pitch. In that example we get a whole number after converting, 108. Not all of the numbers will work out this cleanly, lets take an 86 tooth gear for example:

86 ÷ 1.5 = 57.333 x 2 = 114.666.

We need to round this number off to the nearest whole number, 115 (a common 64 pitch spur gear size).

Just reverse the equation to convert 64 pitch to 48 pitch. 108 ÷ 2 x 1.5 = 81.

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!!! Will converting the number of teeth from 48 pitch to 64 pitch ( or vice a versa ) change my gear ratio ???

-Hmmm... good question. The answer is no. Lets take a look with an example using a 21T pinion and an 81T spur. The gear ratio is found by dividing the spur by the pinion,

81 ÷ 21 = 3.857

a gear ratio of 3.857 to 1. ( for every 3.857 revolutions of the pinion the spur gear makes 1 revolution ). After converting the 21T and 81T 48 pitch gears to 64 pitch as shown above we come up with 28T pinion and 108T spur 64 pitch. So when we divide the spur by the pinion, 108 ÷ 28 we get 3.857 again. The same gear ratio.

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What is the advantage of 64 pitch over 48 pitch?

-Finer gear ratio changes. Here are some examples with 64, 48 and 32 pitch:

64 pitch

28T by 108T = 3.857

27T by 108T = 4.000

a difference of .143

48 pitch

21T by 81T = 3.857

20T by 81T = 4.050

a difference of .193

32 pitch

14T by 54T = 3.857

13T by 54T = 4.153

a difference of .296

It's useful to note that in the three above sets of examples, that you could take the gears of the first example in each set, set the gear mesh, and then interchange them with the other two examples without readjusting the gear mesh.

Information was taken from

http://www.robinsonracing.com/tips.html very help full when going through a Gear Conversion !!!