Why do you have to supply your tire roll-out for a custom tune?(TTS Xtreme) It is really no big deal, but I am planning on changing tire diameter fairly soon. I was wondering if I will have to send my ECM back when I change tire size.

Steve uses the tire roll out to correct the speedo. Tuners like the Preator and Hypertech also ask for your tire diameter to correct the speedo. Two different measurements that accomplish the same thing.

Thanks Sp33d.