For the track I got a set of 255/50/16 Mickey Thompson DR's with 16" CVPI steel rims. Considering these are much shorter than stock I knew they would change my effective rear-gear ratio. I want to get a second tune to account for that, so I calculated my new rear ratio with the MT's...
The stock tire diameter for the KDWS is 28.6"
The stock diameter for the MT DR's I have is 26"
I used this equation:
(Orig Diamter * Gear ratio) / New Diamter = effective gear ratio
So... (28.6*4.10)/26 = 4.51
Sound good? So that's pretty close to 4.56, which probably makes things easier, can I just get a second tune with a 4.56 transmission shift schedule/speedo adjustment then.
Sounds close enough to me!