Board Thread:Game Discussion/@comment-31526827-20200207093248/@comment-29898480-20200207221201

Amrosa wrote: Actually it seems that only off-track driving further reduces service life. Damage does not affect it, I've tested this.
 * In Race damage and running off track will further reduce the amount of Service. Run a perfectly clean race and you should only be effected by the distance run.

Important to note that "off-track" in this context means any part of the tire touching an off-track area, so anything other than all 4 wheels solidly on-track results in the accelerated service life reduction, which is quite steep (5x-6x the reduction per unit distance)