one in the front is not the same at 3 in the rear.
ie: stock is 14/36 for a ratio of 2.571
dropping to 13/36 yields a ratio of 2.769 the ratio difference in dropping one tooth is .198
now look at adding 3 teeth in rear to stock to stock
14/39 = 2.786. That changed ratio .214. So 3 teeth in rear to one in front is much more of a change. now add 2 teeth to rear 14/38 = 2.714 ratio change of .143
so, adding teeth in the rear as compared to dropping one in the front is in between 2 and 3. Looks like 2.5 teeth without going any further with it.
Best thing to do is simply lay out a table in excell. Internal gearing stays same, primary drive stays same. So all that's left is finding the right ratio. Here is an example.
If you use the calculator Shady posted. Gear Ratio Calculator
Then the ratio is the number you put in the calculator for ring and pinion. If all you want is to see top speed vs torque, put 2.602 in the 4'th gear column (which is really 5'th gear on your quad) and input the different ratios from gearing combo's into ring/pinion. The more top speed you have, the less torque you have througout the band.. the lower the top speeed you have, the more torque you will have within the power band. I used it for what i'm considering this year at the dunes. 15/40. that is a 2.667 ratio which is close to 13/35 I ran last year but it takes stress off the primary drive.
Hope that helps
2007 LT-R450 -
500cc BB kit @ 12.5:1 - CP Piston
+2 Ti Valves w/Newen Countour Valve Job
Williams Performance custom grind race Cams (both)
Port/Polish by Williams Performance
HMF Full Exhaust
FCR-41 Carb with Dial-A-Jat and Innovate LM-2 Tuner.
1995 RM 250
Rips like a chainsaw