Ok just recently added the cs edge programmer and went through and changed tire size and gear ratio but my programmer is reading around 10-12 mph slower at 45+ mph(ex. I will be going 75 by GPS but the programmer reads 64).... is there something I have missed here?

 

Sounds as if your gears are inaccurate. As I recall, after you enter s value in gears or tired, you can go back and check your entry as it erases what has been entered. Could that be happening?

 

No I can go back in and it shows what the changes. I have 3.55 rear end and I have 38 in tires. And I have checked them both on quote a few occations. It has the stock tranny. Just not sure what I can do to fix the probably.

 

Did you use their formula to calculate the tire entry?

 

Yes. They are military tires. Now will it hurt if I change the gear ratio up and see if it will bring it all into sync?

 

Can you adjust your tire revs per mile? My new MPT tunes were made for 275/70/18 but speedo was 4mph too slow. Adjusted for revs and I'm right on.

 

You can adjust gears and/or tire sizes - doesn't matter which - just adjust till it's right.