Ill i be messing with my custom tune too much if i change the tire size?...i heard the dealerships can adjust this for you is that true?

 

Nope, it's made to be messed with. Just figure your tire size and about 3-5% "squish" factor on the tire and input the number. The dealers can do it, but it'll only be for the stock tune and cost about $80 to do. Really no point since you have a programmer to go that way.

 

Preciate it i just didnt know if this could result in messing with shift points and stuff since i figured bill set everything up to work best together

 

How large of change from the original tune did you make in tire size? Even so with the change (keeping the same line pressures as are written in the tune), it shouldn't affect the shifting too much if any. If they are vastly different tire/wheel sizes the changes would mostly be felt in changing the final gearing.

 

I havent changed sizes since ordering the tune but my speedo was off some and i wanted to tinker with it but i think ill leave it be im sure its the best thing to do

 

If it's off by 1 or 2 mph compared to a GPS I wouldn't worry about it. If it's more than that then I'd be worried.

 

I messed with it and the custom tune left alone made the truck drive better and its only off 5 at the most when up past 70 so i can live with that just fine the truck performs too good to mess with ha preciate the help sir

 

After I changed my tire size mine is off about 2mph. When I put in my tire size the tuner rounded up for some reason so I knew it would be a little off any way. Also when I changed the size the shift points changed a little. Noticed it mainly in shifting to overdrive, used to shift when speedo got to 40 mph and now shifts at 45mph.