I was just googling around and found some information and I put together a working formula. It just basically tells you the affect a bigger tire does, and what ratio the tire wants. I dunno if it's been mentioned or put up before but here we go...



Using stock Blazer 3.42 gears and 235/75/15 tires we will see how 31x10.5x15 tires affect it...

power ratio = gear ratio / (new tire diameter / old tire diameter)

3.18 = 3.42 / ( 30.97 / 28.87)

Meaning with 31"s, your car will feel as though it has 3.18 gears.


To find the ratio the tire would like...

wanted ratio = gear ratio * (new tire diameter / old tire diameter)

3.66 = 3.42 * ( 30.97 / 28.87)

Meaning with 31"s and the new gears, your car will feel like stock.

 

Mine tows and drives perfectly without regearing. I don't feel like the benefits would outway the costs of replacing gears. I have plenty of power when towing or offroading, and I still get 21 mpg hw. Granted I have a few mods, but nothing crazy.