Toe - Out

Lesson 1/Learning Event 2

That is, the left wheel tries to pivot to the left and the right wheel to

the right. The wheels are able to pivot out to some extent because the

steering knuckles and tie rod ends must have a slight amount of clearance to

permit easy steering. To offset this, the wheels are aligned with a slight

amount of toein.

Toedin wheels are closer together at the front than at the rear. Toein is

measured in inches. The amount is found by measuring the distance between

the front wheels, first at the front outer edges of the tires and then at

their rear outer edges. The amount of toein is the difference in the two

measurements, which is usually about 1/32 inch to 1/8 inch. If the wheels

are closer together in the rear than in the front, they are said to be toed

out. The amount of toein can be adjusted by shortening or lengthening the

adjustable tie rod.

Ideally, the toein, measured with the vehicle standing still, should

exactly equal the amount the wheels pivot outward when the vehicle runs at

cruising speed. Then, the wheels will roll perfectly straight ahead at

cruising speed with no side slippage.

Toe-out

Side slippage of the tires must also be considered when turning a corner, to

ensure positive steering control and to prevent excessive tire wear. Each

wheel must be at a 90 angle to the center of rotation if it is to roll

easily and not scuff the tread of the tire.

This is no problem forfifth wheel steering. Pivoting the axle assembly

moves the front wheel at the outer edge of the turning radius ahead of the

inner wheel, and the 90 angle is obtained. With Ackerman steering,

however, the wheels must toeout on a turn.

With Ackerman steering, when turning a corner, one straight line cannot be

extended from the center of both front wheels. Instead, two lines must be

extended at different angles in order to pass through the center of the

wheels. For both wheels to be at a 90 angle to the center of rotation, the

inner wheel must pivot more than the outer wheel. (The exact difference in

the amount that the wheels should pivot is the value of the angle formed by

the lines extended from the center of rotation through the center of the

front wheels. For instance, if the lines form a 3 angle, the inner wheel

must pivot 3 more than the outer wheel.)