i have a 3.8L mustang. i just purchased a sct x3 tuner. i just put on new 18" inch rims and tires. So i plugged in my tuner and was trying to change the tire size on the computer so that my spedometer becomes correct and the option on the computer to do so says "tires revs/mile" i do not understand what that means at all. When changin it from stock it gives me the options of 500, 505, 510, 515...and so on in increments of 5. Can anyone explain all this to me? thanks

 

You would get that specific info from the tire manufacturer. What brand tire and size are you running? Just shoot an email over to the tire company and they'll send you the number.