Caster, Camber, and Toe-In

PROPER ALIGNMENT
Front wheel alignment refers to the angular relationship between the suspension attaching parts, the wheels, and the ground. Proper alignment is considered essential for efficient steering, good directional stability, and to prevent abnormal tire wear. The most important factors of front wheel alignment are caster, camber and toe-in.





CASTER
Caster is the tilting of the front steering axis either forward or backward from the (1) vertical. It is measured in degrees. A rearward tilt is positive and a forward tilt is negative (Figure 1) On the short and long arm type suspension you cannot see a caster angle without a special instrument. However if you look straight down from the top of the upper control arm to the ground, the ball joints do not line up (fore and aft) when a caster angle other than 0 degrees is present. With a positive angle, the lower ball joint would be slightly ahead (toward the front of the vehicle) of the upper ball joint center line. Incorrect caster may result from damaged control arms and other related front suspension parts.





CAMBER
Camber is the inward or outward tilting of the front wheel from the vertical. When the wheels tilt outward at the top, the camber is positive. When the wheels tilt inward at the top, the camber is negative. The amount of tilt measured in degrees from the vertical is called the (1) camber angle. If the camber is extreme or unequal between the wheels, improper steering and excessive tire wear will result. Negative camber causes wear on the inboard side of the tire, while positive camber causes wear to the outboard side.





TOE-IN
Linear sum toe-in exists when the distance between the front wheels is less at the front of the axle than at the rear of the axle. Angular toe-in is the angle of the front wheel centerline, relative to the intersection of the forward projected vehicle center line.The actual amount of toe-in is normally a fraction of a degree. Toe-in is measured from the center of the tire treads or from the inboard side of the tires. The purpose of toe-in is to assure parallel rolling of the front wheels and to offset any small deflections of the wheel support system which occurs when the vehicle is rolling forward. Incorrect toe-in results in excessive tire wear and unstable steering. Toe-in is the last angle to be set in the front wheel alignment procedure.