I was wondering if anyone knows how much the size of the rear tire throws the gear ratio off. For example I have a 39 tooth rear sprocket and a 14 tooth front sprocket which equals 2.785 gear ratio. Now, I have a 22" rear tire which is actually 21.9". What will my gear ratio be now and how do I add the rear tire into the equation?

 

From what i have gone through with all my gearing issues and 22 inch rear tires i have found that to get back to stock gearing with 22 inch rears it would be like going down about 1.3. So down a tooth on the front to a 15 tooth and up 3 on the rear.

 

This might help.
http://www.ljsoftware.com/DS/GearSpeedCalculator.html