Camber Caster Toe Adjustment
Lining up suspension technology
A suspension alignment is one of those automotive maintenance chores that most of us put off until a set of tires worn to unusable tells us it's already too late. Bringing the three key alignment measurements into the numbers specified by the manufacturer can prevent expensive tire replacement bills, and vastly improve vehicle handling, braking, and safety.
The best time to have the alignment checked is when the car is getting a new set of tires. Those familiar with the experience will remember reading a year old magazine and listening to canned music for an hour, then being presented with a bill. On the bill is usually a bunch of plus or minus signs and numbers with odd words next to them like caster, camber and toe. While alignment adjustment is a job best left to the pros, knowing how camber, caster and toe affect suspension and handling can help you sort out the numbers.
Camber—The Leaning Tower of Tire
Camber as it applies to a wheel and tire is a measure of vertical lean. With the wheels pointed straight ahead look down the length of the car. The measure of the vertical axis of a wheel and tire as it relates to the body of the car is the measure of camber. Negative camber has the top of the tire leaning into the car. Positive camber has the top of the tire leaning away from the car. Zero camber will have the wheel and tire straight up and down.
Look to the front wheels of an open wheel racecar for an obvious example of camber. Large degrees of negative camber point the tops of the tires together when the racecar is traveling in a straight line. When the racecar dives into a corner, the outside wheel will go to zero camber and be flat with the track for traction. Too much positive camber and the tire will fold over on to its sidewall and lose traction. Passenger cars usually come with a small amount of negative camber to prevent excessive tire wear, but still help with cornering. Camber has to be equal on all sides or the car can pull one way or the other.
Caster—Putting It Out Ahead
The easiest way to think about caster is with a chopper and a shopping cart. A chopper riding on long forks places the wheel far in front of the handlebars. The handlebars steer the chopper like the front suspension of a car. The angle away from this vertical axis of steering is the measure of caster. The huge amount of positive caster in the chopper helps the motorcycle to cruise effortlessly in a straight line, but hinders the choppers ability to corner.
Positive caster in cars helps with stability, and also brings the steering wheel back to center when the turn is completed. No car runs with negative caster, for a reason. Shopping cart front wheels are an example of negative caster, which is why shopping carts handle negatively. Out of whack caster won't cause tires to wear, but can cause a drifting effect—or a steering wheel that likes to stay turned instead of returning to center.
Figuring out what toe is all about as it applies to cars is as easy as gazing down at your feet. Point your toes inward. That's toe-in. Turning your feet out is toe-out. If your feet, or the tires on your car, are parallel to each other they have zero toe. Incorrect toe angle can not only cause the car to pull left or right, but can also wear out tires quicker than you can say 500 bucks.
Imagine walking about soley on the insides or outsides of your feet and the picture of tire wear is clear. While toe is the easiest to understand, it is also the most important when it comes to handling and tires. Rear-wheel drive, front-wheel drive, and all-wheel-drive vehicles all have unique toe adjustment requirements. Discussion of each type of suspension and drivetrain gets into Ackerman steering geometry and linkages, which is the subject of many books. Neglecting alignment can be dangerous at worst, and can surely tie you up in tire bills. (A special thanks to Hotchkis Sport Suspension, www.hotchkis.net.)
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