What is the proper tire measurement to use in calculating RPM’s and evaluating which gears to upgrade to? We say we have 35’s or 33’s based on our sidewall size but that does not necessarily mean that is the tire size. The stock Rubicon 255/75R17 is listed as 32” but the tire rolls out to 31” on the ground. My 35” ProComp Xtreme AT’s roll out on the ground to 105.5”, which equals 33.5” diameter. If I jack the tire off the ground and measure the circumference at the center of the tire treads it is 109” or 35” diameter. If I calculate using 33.5” then it seems 4.88 gears are best as the RPM’s are almost identical to those of a 35” tire with 5.13 gears. I am trying to decide the right gears for my JK automatic. I have read the numerous posts on the 4.88 vs. 5.13 debates, but it seems the actual tire diameter versus the sidewall listing would have some bearing on the selection? In my case it is a difference of 1.5” in diameter. Any thoughts are appreciated.

Johnny

07 Flame Red Rubicon, 2 door, automatic
Full-Traction 3" Ultimate
ProComp 17" wheels
ProComp Xtreme AT's

 

I gotta admit I've had close to that same thought in my head for the last 8 weeks.
My JK has MT 33's on it, and I think in the end after reading a lot of useful information on here that the best way to go in my situation is 4.88.
And they are being installed as we speak, Superior finally shipped them out to the vendors about a week ago, and I got that magical call....