adjust the motor's timing so it's 3mm from zero.
have a look at www.gearchart.com
on that web page you can create gearing charts, telling you the number of mm the car travels when the motor turns 1 time.
You can adjust this number by gear selection, and rear tire diameter.
Normally you start with a full size tire (diameter around 63 mm) and a certain rollout that suits your motor, the motor's timing, the track you run on and your driving style.
When your tires wear down, the rollout number changes.
By adjsuting your gearing, you can keep the same rollout and motor performance.
just have a try, and report back if you can't get it figured out.