Camber, Caster, and Toe
by Jim Kerr Camber, Caster, and Toe. No, it's not the latest craze in square dancing. These three terms refer to the angles of the tires on your vehicle. When you take your vehicle in for a wheel alignment, these are the angles a technician checks and sometimes adjusts.

Correct camber, caster, and toe angles are important for maximum tire life and safe vehicle handling. Even a small error can make a dramatic difference to the way a vehicle drives. Getting a wheel alignment for your vehicle should put everything back into the correct relationship, but why do they change?

Normal wear in suspension parts may cause the angles to change slightly, but major changes are usually caused by impacts or parts failure. Let's look at Camber first. Camber is the tilt of the wheel in or out. Positive camber readings show the top of the wheel is tilted out, while negative readings show the top of the wheel is tilted in. Theoretically, you want the wheel to be at 0 degrees or straight up and down, and most vehicles are close to this, but suspension design or handling demands may require negative caster settings.

Negative camber is usually used on performance cars. During hard cornering, the body rolls to the outside of the turn. If camber settings were 0 degrees, or vertical, the wheel and tire would roll as well, tilting the top out. The tire tread would lift on the inside of the tire, giving less traction and less cornering force. Negative camber settings will move the tire towards the vertical as the body rolls, keeping all the tread on the ground.

Most passenger cars will have camber settings of 0 degrees to about ¾ positive camber. This keeps the tire vertical during most driving, and the slight positive camber causes the load of the car to be supported better by the wheel bearings. High performance cars often have camber settings of 0 degrees to minus 1½ degrees. The settings are determined by suspension design and the amount of body roll. MacPherson strut suspensions tilt the tire out as the body rolls on corners, so a higher negative camber setting is used than unequal A arms, which tend to tilt the tire in as the body rolls. Solid rear axles used on trucks and some cars should have 0 camber. A negative camber angle usually indicates a bent axle housing and possible bearing failure in the future.

Vehicle engineers and racecar teams will measure the temperature of the tire tread at several points across the tread face to determine if camber settings are correct. Higher heat on one edge of the tire indicates that part has the most grip. Settings are adjusted so the tire grips evenly. The most common causes of camber settings being out are bent suspension parts, or sagging or broken springs. Even a slight impact with a curb (other than parking) can bend suspension parts. Everything may look fine, but if the angles are out, something has moved. Many vehicles on the road today have non-adjustable camber from the factory. Most front wheel drive cars have the angle set at the factory and the body must be modified or aftermarket parts installed to change the camber. If no parts are bent, then the body is probably sitting at an angle or too low because of sagging springs. Many times, replacing the springs will bring camber angles right back to factory specifications.

Don't worry if camber is different from one side of the vehicle to the other. Vehicles pull towards the side with the most positive camber and sometimes a slight difference of ½ degree or less is used to compensate for the crown of the road, which makes the vehicle pull towards the right.

Caster has no effect on tire wear. Caster is used for vehicle stability. Too much caster and the wheels can begin to shimmy like the front wheels on a grocery cart when you go too fast. To little caster and the wheels don't follow the path well. Typically, caster settings will be from + ½ degree to + 4 degrees, but I have seen Mercedes cars with up to +10 degrees specified. Higher caster settings give a little more straight-line stability, while lower settings make the steering lighter and the car tend to turn easier. Caster settings that are incorrect by a few degrees from one side of the vehicle to the other usually indicate bent parts.

Last comes toe. This refers to the in or out turn of the wheels from a straight-ahead position. In the past, most vehicles would have "toe in"; the front of the wheels were turned slightly inwards. This gave good vehicle stability, and as vehicle speed increased, the tire resistance would cause the toe to change to the straight-ahead position. Now, some front wheel drive cars use offset wheels (the bolt flange is not positioned in the center of the width of the wheel) and different wheel bearing positions that require toe settings to be "out". As the vehicle drives, the loads placed on the tires cause the wheels to turn in to the straight-ahead position. Toe-in or toe-out, the factory specifications should be followed closely. Toe out on a rear axle can cause unpleasant spins during braking or on corners, especially on wet or icy roads. Again, solid rear axles should have a 0 toe reading or the axle is bent or out of position in the vehicle.

Incorrect toe settings caused by wear or impacts can wear tires quickly. I have seen a new tire worn out in only a few hundred kilometres because the toe setting was out dramatically. Even if it is out a little, tire life is shortened, and tires are expensive. Toe is checked during a wheel alignment and should be adjusted if it is out of specifications.

Camber, caster, and toe settings are all checked during a wheel alignment. Having and alignment done once or twice a year will prolong your tire life and prevent your vehicle from "dancing" all over the road.

Jim Kerr is a master automotive mechanic and teaches automotive technology. He has been writing automotive articles for fifteen years for newspapers and magazines in Canada and the United States, and is a member of the Automotive Journalist's Association of Canada (AJAC).

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