Front / Rear Sprocket Equivalents

For the 6th Gen, the stock gearing is 16/43. If I go -1 on the front, what is the positive equivalent for the rear to maintain the same gear ratio? As a general rule, I always thought that -1 on the front was equivalent to +3 on the rear, but does anyone know the exact math?

 

43/16=2.6875 final drive ratio.

So multiply the new 15 tooth front sprocket by 2.6875 to get the equivalent rear sprocket size, maintaining the stock ratio.

15x2.6875=40.31 teeth.



And going to smaller sprockets will make your chain wear out faster, all else being equal.

You'd be better off with 17/46, assuming you can get a steel rear sprocket with 46 teeth.

That would give 2.705:1 which is within 0.7% of stock gearing.