If you want to adjust for tire size, I'd just get something like BD's Speed eliminator with RAD. I put one on my truck and I can adjust tire size, It also serves as a speed eliminator, but I'd think most chips would do the same. I have one as well as the drag comp, and I'm really happy, I couldn't tell ya how much it cost cause my friend gave it to me, but I think he only paid like 200 or something. RAD is nice if you want to race too,