OK - so I am a Novice - I can handle that. I am totally confused about where to get the information to recalibrate my speedo with a new gear. I have seen the sights, but must be missing something. I have 12.5/35 tires - I know the speedo is 10 MPH slow at 65 MPH (speedo shows 55). I know I have a 30 tooth gear(electronic hook-up). Can somebody help me figure out what gear to change to to get the speed accurate. I am no math major.

welcome to rockcrawler
To figure up what tooth gear you need I need a little more info (im not math guy either). What type of gearing in axles do u have, also what kind of vehicle im assuming wrangler maybe tj but not sure. Also If you should post in a different place like if you have a tj in the tj section or if you have a yj in yj section youll get more responses.

This message has been edited. Last edited by: wile e coyote,

Thanks for the "starter info". It's a YJ. This is gonna sound real dumb, but I can't find a location of the ratio on the axle tag - maybe I am not looking in the right place or reading the tag right. What I found was a metal strip on the left side of the rear axle with some numbers on it. I really expected to find a ratio there - 4:1, 3:1, or something like that. But instead, if I read it right, it's a string of numbers. I may have to write back tommorrow after I crawl under again to get the tag numbers - I don't have them with me.