I have to write a new tune for my new tires. The new tires are pretty close, with in about an 1" of the one I had tuned around. Size doesn't appear to be important, because I had 35s but my tune was closest with 36.5" diameter.

Is there an easy way to calculate roll out or do I have to trial and error it?

Right now, 25 on speedo is 29 and 52 is 55, I am comparing it off my GPS. I am going to figure
52/36.5 = 55/x for about 38.5 to get my top end right.

 

What software do you use and what does it give you as far as Tire Size adjustments? Is it inches, mm, revs per mile?

Normally, I'd say use the three-roll method to get your rolling circumference and use that for your setting.

One thing to remember, the speedometer nearly always read 2 MPH faster than what the ECM is actually sending. I don't know for sure why this is, but if you were to get your needle dead-on then the ECM would actually be 2 MPH slow and your odometer would be off a small percentage.

Let me know...

Bill

 

I am using Sniper Special Forces, I have adjustment from the mid-20s to 42" I think.

That's odd about the speedo, so how do LE agencies get the speedos certified/calibrated?

 

Dunno... I guess you could always make sure your ECM is corrected and then adjust the needle on the speedo to match.