does a dt3 work better on an 18'' rr or 17'' rr

Several drivers feel the 17" works better because of the width of the tire and side wall construction.

Either, have ran both, and cant tell a ton of difference

In my opinion it really depends on the track conditions. If the track is smooth and getting dry then break out the 17" and go to town with the added sidebite. If the track is heavy or choppy the 18" will be much more forgiving.