Toe is the inclination of the wheel front and rear as seen from above the vehicle. The wheel installation angle is called the toe angle. When the front of the wheels are closer than the rear of the wheels, this is called “toe-in”. The opposite arrangement is called “toe-out”. Roll of toe angle Conventionally, the primary purpose of toe angle has been to cancel out the camber thrust generated when camber is applied. Toe angle therefore prevented the front of the wheel from opening to the out side when toe-in was applied for positive camber. As a result of an increasing use of negative camber and improved performance of the tires and suspension in recent years, however, the need to cancel camber thrust has diminished. Thus, the primary purpose of toe angle has changed to ensuring straight-line stability. When a vehicle rides up on an incline on the road surface, the body tilts to one side. The vehicle feels as if it is about to turn in the direction in which the body is tilted. If the front of each wheel is turned to the inside (toe-in), however, the vehicle will try to move in the direction opposite that in which the body is tilting. As a result, straight-line stability is maintained.
If toe-in is excessive, the side slip force causes uneven wear of the tires. If toe-out is excessive, it is difficult to secure straight-line stability.
Side slip is the total distance that the left and right tires slip to the side while the vehicle is running. Both in the case of toe-in and negative camber, side slip occurs towards the outside.