What is wheel alignment?
Wheel alignment is the correct relative position of the four wheels to obtain a true, free-rolling movement over the road without scuffing, dragging or slipping. Five different angles determine wheel alignment: camber; caster, toe-in; turning radius (toe-out on turns); and steering axis inclination. These angles are purposely designed into your car to properly distribute weight on moving parts and to facilitate steering. Remember:
Properly aligned front wheels are never straight; they’re at a slight angle top-to-bottom. Now let’s take a look at each of these five critical angles and discuss, briefly, how they should be checked Camber. This refers to the outward (or inward) tilt of a wheel at the top. It is measured in degrees which represent the amount the center line of the wheel is tilted from true vertical. If wheels tilt outward at the top, that’s positive camber. Inward tilt at the top is negative camber. Manufacturer’s specifications denote whether the wheels of a particular car should be set for positive or negative camber by the letters P or N, or by the symbols + or -. Where neither letter nor symbol is indicated in the specs, positive camber is called for. This specification usually provides two figures: a desired camber and a limit. For example, camber specifications for the 1965 Corvair call for a desired angle of +1°. However, any angle between +10/2 and +110/2 is acceptable; this means +1/20 to +11/2 from true vertical. With your car’s camber correctly set, the road contact of the tire is brought more nearly under the point of load. Thus easier steering results because the weight of the car is borne by the inner wheel bearing and spindle. Also, tire wear is held to a minimum. When camber is incorrectly set, excessive load is put on ball joints and wheel bearings, the vehicle will pull to one side and there will be excessive wear on one or the other side of the tire tread, depending on whether the camber is thrown out of kilter negatively or positively. If there’s too much negative camber, tire tread will wear on the inside; too much positive camber will wear down the tread on the outside. Depending on the car you have, adjusting camber is done by adding or subtracting shims or by turning self-contained eccentric bolts. The same type of procedure applies to caster adjustment. To adjust caster and camber on a 1961-through-1965 Olds F-85, for example, you shim at the upper control-arm shaft attaching points. Adding (or subtracting) shims at the front location changes caster toward negative (or positive) with practically no change to camber. Adding (or subtracting) shims at the rear location changes caster toward positive (or negative) and camber toward negative (or positive). Adding (or subtracting) equal shims at both front and rear locations won’t change caster, but will change camber toward negative (or positive). On the other hand, in changing caster and camber on 1958-through-1965 Ply-mouths and Valiants you adjust the upper control-arm attaching bolt and cam assemblies.
Caster. Caster refers to the backward or forward tilt of the kingpin or spindle support arm at the top of the wheel. It is a directional control angle that is measured in degrees and indicates to what ex-tent the center line of the spindle support arm is tilted from true vertical. Backward tilt of the spindle support arm at the top is positive caster. Forward tilt of the spindle support arm at the top is negative caster. Manufacturer’s specifications designate negative or positive caster in the same way they do negative or positive camber; that is, with letters or symbols. Caster determines directional control of the car by causing the front wheels to maintain a straight-ahead position, or to return to a straight position from a turn. Caster also helps to offset the natural crown of the road. The car’s straight-ahead position is maintained by tilting the spindle support arm so that it projects the center line of the support arm ahead and establishes a lead point ahead of the point of contact of the wheel. This compares to the ability of kids to ride their bikes straight and true without touching the handlebars. The Bear Manufacturing Co., one of the leading producers of wheel-alignment equipment, emphasizes that caster must stay within the range of the carmaker’s specifications. However, the company does recommend that about 1/2° more positive caster be provided the right front wheel than the left front wheel to compensate for the effects of road crown. Excessive caster will cause a car to pull toward the side having the least amount of caster; it can also cause hard steering, road shock and shimmy. Too little caster will cause the car to wander and weave. Toe-in and toe-out. Toe-in describes the shorter distance between the front of the front wheels and that distance separating the rear of the front wheels. Conversely, toe-out (not to be confused with turning radius — i.e., toe-out on turns) describes the greater distance between the front of the front wheels and the rear of the front wheels. Got it? By the way, toe-in and toe-out apply to the rear wheels as well; they should be checked also. Usually excessive toe-in or toe-out of the rear wheels indicates a bent rear housing, though in some cars with independent suspension it could just indicate the need for adjustment. Toe-in is the most critical angle affecting tire wear. It is measured in inches. Its purpose is to compensate for widened tolerances in the steering linkage. If the car is toeing-in, tire wear starts to show up as a feather-edged scuff across the face of both front tires. Too much toe-in can also result in wear appearing on the outside of the right front tire only. On the other hand, too much toe-out will result in wear appearing on the inside of the left front tire only. Toe-in and toe-out are adjusted by turning the tie-rod adjusting sleeves until the measurement taken at the front of the wheels falls within manufacturer’s specifications. The trouble chart at the top of this page lists some of the problems created by faulty camber, caster and toe-in. At this point, let’s leave the rest of the discussion of wheel alignment (specifically, turning radius and steering axis inclination) until next month when we’ll wrap up the package with a good look-see at wheel balance.