In my opinion, yes.

 

There is a very simple way to enter the correct tire size. The speedo sensor counts revolutions of the wheel so the computer needs to know the "ROLLING" diameter and not the stated diameter or the standing diameter. The "CORRECT" rolling diameter is arrived at by measuring the distance from the road up to the center of the hub and multiplying that by 2. Diameter=2 times the Radius. Any number other than the ROLLING diameter will give incorrect info to the computer and affect shift points and mpg indicated.

 

I've seen so much debate over the correct way to measure tire size (measure side to side, measure the spare, use a straight edge on the top, etc, etc.) but this idea makes sense. I just tried it and my speedo was right on the money when compared to my GPS. Thanks Crasher!!!

 

Or if you want to get real precise with it you can measure the circumference (in inches) and divide it by pi (3.14) and you will have the actual rolling diameter.

Just put a white chalk mark on your tire sidewall at the bottom where it's in the center of the contact patch. Also make a chalk mark on you driveway right next to the chalk mark on the sidewall (make sure to leave enough room to pull forward one tire revolution.) Then have a buddy slowly pull forward while you watch the chalk mark on the sidewall. When it gets to the bottom again (making one complete revolution) stop and make another chalk mark on the concrete. Now measure the distance between the two chalk marks on the concrete (that number will be the circumference of the tire) and divide that number by 3.14 and you will have the actual rolling diameter of the tire.

 

Thanks for the info

 

Thanks 'jdubb75' that makes complete sense and the math was great too, I think 5 out of 4 readers are bad with fractions, but will be able to follow your logic.

 

So i put my lift on this past weekend and 35s. I know I need the superchip but what will be able to do besides recalibrate my speedo?

 

Superchips allows you to program for power, economy, towing modes; it also has the ability to change rev limiter, max speed for high speed (not rec. for Jeeps) and change the fan on temp settings for crawling - I'm sure if you visit the Superchips website you will find all the possibilities avail.