Automotive Wheel Alignment

Most alloy wheels differ from normal steel wheels because of their lighter weight, which improves the steering and the speed of the car. Alloy wheels are also better heat conductors than steel wheels, which reduces the chance of brake failure.

A big advantage of alloy wheels is that balancing them is easy. The balancing weights are attached in the centre unlike steel wheels where they are attached at the edge of the rim.

Magnesium Alloy Wheels (Mag Wheels) - are sometimes used in place of heavier steel or aluminum wheels, which allows for better performance. Magnesium wheels are flammable and have been known to catch fire after prolonged exposure to the ground, as in a flat tire.

Steel Wheel - a basic automobile wheel, which is made from steel.

Spare Wheel (Donut) - is an additional wheel and tire carried as a replacement for one that goes flat and is not meant to be driven long distances and has a maximum speed 50 MPH.

Chrome Wheel - highly polished wheels are plated with a chrome mirror finish that shines in sunlight or streetlight.

Wheel size

13" - 24"

The wheel size is the diameter of the wheel in inches where the beads of the tire seat on the wheel. This measurement does not include the rim flange.

Load capacity

Load capacity is the amount of weight a wheel will carry. This number will vary depending on the number of lugs, the PCD, the material used and the type of axle the wheel is used on. All wheels will have the load capacity stamped on the back of the wheel.

An important part of vehicle ride control is directional control.

Wheel alignment is the adjustment of angles made by the front wheels in relation to:

The vehicle's suspension (caster)
The road (camber)
Each other (toe)

The alignment of one of these angles affects the other two. All three angles are adjustable on coil spring and torsion bar suspension systems.

On strut systems, there may or may not be provisions for the caster and camber adjustments. Toe is adjustable on all systems.

If caster or camber is not within specifications on a strut system where those angles are not adjustable. Do not attempt to make adjustment by bending parts.

A weak strut may cause a car to sag, which affects the caster and camber angles. In such a case, the spring may need to be replaced.

When checking or adjusting alignment, tire pressure should be up to manufacturer specifications. Low tire pressure may affect alignment.



	CASTER



	CAMBER



	TOE



	POSITIVE AND NEGATIVE CAMBER

Camber is the inward or outward tilt of the wheels, as seen from the front. Camber is positive when the top of the wheel tilts outward, and negative when the top of the wheel tilts inward. Camber is zero when the wheel is perfectly vertical.

The camber angle is measured between the center line of the wheel (as seen from the front) and a true vertical line, which intersects the center line at the point of tire contact to the road.

The purpose of camber is to uniformly distribute vehicle load across the tire face to minimize tire wear. Excessive positive or negative camber, however, will increase tire wear dramatically on one side of the tread -- the side toward which the top of the wheel is leaning.

Incorrect camber can also cause steering problems.

Caster is the backward or forward tilt of the wheel spindle support. On a strut system, the strut itself, along with a lower ball joint, supports the wheel spindle. On a conventional suspension system, the upper and lower ball joints form the wheel spindle support. A line drawn through the centers of the two ball joints, as seen from the side of vehicle, illustrates the tilt of the wheel spindle support: the wheel's caster.

The caster angle is measured between the center line of the wheel spindle support and a vertical line through the center of the wheel. The caster angle is positive when the center line of the spindle support intersects the road in front of the tire's point of contact with the road. Caster is negative when the spindle support center line meets the road behind the tire's point of contact. Zero caster occurs when the spindle support center line is vertical, meeting the road at the tire's point of contact.



	FRONT CASTER

Most cars are designed with positive caster. Positive caster provides good directional stability by tending to return toe front wheels to the straight-ahead position -- which is why too much positive caster causes hard steering.



	POSITIVE AND NEGATIVE CASTER

Toe is the difference in the distance between the front of the front wheels and the distance between the rear of the front wheels. If the front of the wheels are closer together than the rear of the wheels, the difference in the distance is called "toe-in". If the front of the wheels are farther apart than the rear, the distance is called "toe-out". Almost all vehicles are designed with a certain amount of "toe-in", measured in inches or millimeters.

Toe is the most critical tire wearing angle. The purpose of toe is to ensure parallel rolling of the front wheels; but if either wheel has too much toe-in or toe-out, the tires will sideslip. This results in a feather-edged scuff across the face of the tire.



	TOE IN AND TOE OUT

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