Bigger Tires = New Tunes?

[pohlmeyr]

I just put some 295/75/18 tires on my truck and wasn't sure if needed to get new tunes?
I feel the shift points might need to be adjusted

[Longshot270]

No you can adjust the tire size through the custom options menu when ever you reprogram. Try entering 2750 as your tire size and see how close that gets you.

Or the best thing to do is to program a value you know is incorrect like 2600. Then if you have a GPS going clear both it and your odometer and drive at least 15 miles. Then do this little formula:

GPS odometer/truck odometer x the tire size you just entered (2600). The number you get is your actual tire size.

[88Racing]

Use the custom options menu to change also double check the gear ratio...

[bikerfuzz]

so would the same apply if it was a 295/65/18? Its still an 18? Thats cause I just out my new tires on too. So under greate custom option hit yes? and just fix the tire size to ??? and hit yes thats it.?

[Jackpine]

Originally Posted by bikerfuzz

so would the same apply if it was a 295/65/18? Its still an 18? Thats cause I just out my new tires on too. So under greate custom option hit yes? and just fix the tire size to ??? and hit yes thats it.?

No, a 65 series tire has a much different diameter and circumference than a 75 series tire. Longshot gave you 2750 for the 75's, I would have suggested 2730, but that's a small difference that might be good "boundaries" on the values to try. If you've installed a 75 series tire, start with a value between 2750 and 2730.

If you are using 65 series tires, they are not nearly as tall (but they're "fatter"). Try something between 2580 and 2560mm.

You would enter these values in the Custom Options Menu - Tire Size.

- Jack

[bikerfuzz]

Ok. I'm going to try. But why the range ? Is it to get as close to actually displayed speed?