i was wondering if a a 3.55 gear ratio would be find to replace my broken gear. 235/75/R15and most likely go up to 30s with 2" lift.

 

I think I know what your asking. stock tooth count with 3.55 is 35, going up in tire size from stock you should probably replace with a 36/37. the number is usually cast into the gear. each tooth changes speedo by about 2mph.

 

36 or 37 tooth count would be good?

 

you actually will be just fine with the tires your thinking about.. you really won't notice much in speedo difference until your into the tires that are over 31"

 

This may relate to the question. My Cherokee has wires coming from the speed sensor on the back of the transfer case. When changing tires sizes and gear ratios, do we need to change the speedo gear or is there a way to do it electronically?

 

It's still controlled by the speedo gear system.

 

I have 355 gears with 31" tires and the gear is a 32 tooth gear
First link to determine which tooth count you need,
Second link from Quadratech for the gear

http://liftyourxj.com/tweaks.html#Speedo

http://www.quadratec.com/products/pr...ears&submit=Go

 

for 30" tires and 355 gears you would need a 33 tooth gear to correct the speedo