Toe-in is the amount in fractions of an inch that the wheels are closer together at the front compared to the back of the tire as viewed from the top of the vehicle. Toe in is necessary because the natural action of the tires against the road tend to make the wheels toe-out.

Too much toe-in will cause the tires to scuff and wear in a "feather-edge" pattern on the inner edge of the tread.

Toe-out will cause a similar wear pattern on the outer edge of the tire.