Grip of a tire (8)
I believe the answer is:
traction
(Other definitions for traction that I've seen before include "Medical stretching" , "Pulling - into cart (anag)" , "The action of drawing or pulling over a road or track" , "(In orthopaedics) the pulling on a bone or limb to relieve pressure during healing" , "Grip - rat in cot (anag)" .)