A Tires 101 lesson on
... Tire Alignment
Tire alignment is critical if you want to receive the best
wear and performance from your tires. Incorrect alignment settings will usually
result in abnormal treadwear. Poor alignment is usually the result of poorly adjusted
suspension and steering systems. Any unusual tread wear pattern is a clue to
alignment problems and should be checked by an alignment specialist, but
before you do, make sure tire inflation pressures are correct, as incorrect inflation can
also cause uneven wear.
The different types of wheel alignments are front-end alignment, thrust angle alignment,
and four wheel alignment.
In a front-end alignment, the front only is checked. This is
fine in some cases, but problems can occur if the front tires are not properly
positioned in front of the rear tires.
With the thrust angle alignment, front to rear positioning is
checked so that the wheels are "squared" to each other. This will eliminate the
"dog tracking" that you may have seen on a car that appears to be going down the
road with the rear end a foot over from the front.
The best way to align the car is a four wheel alignment. This
goes beyond the thrust angle alignment to include adjusting the settings on the rear of
the car as well as the front. Not all cars are fully adjustable, but most are. The
measurements that need to be checked are caster, camber and toe.
Toe refers to the difference in distance between the front and the rear of the tires. If
the distance between the tires is less in the front than it is in the rear, it is referred
to as "toe-in". It would be what could be commonly called "pigeon
toed". If the distance is greater between the front than it is in the rear, it is
called "toe-out".
Camber refers to the angle the tire is tilted away from vertical. A tire has negative
camber when the top of the tire leans inward toward the center of the vehicle. Positive
camber is when the top of the tire leans outward from the center of the vehicle. The
camber angle should be adjusted so that the tire is vertical under cornering load.
Properly set
camber will allow the tire to work at its best, but not have the tire putting too much of
its force on the inner edge while moving in a straight line. Tire wear and handling become
a compromise. Less negative camber typically will reduce the cornering ability, but give
very even wear. The next time you see a photo of an Indy Car, notice how much camber
there is. That is certainly an example of tire wear not being as important as
cornering ability.
Caster is the most difficult of the three measurements to
describe. If you think back to your bicycle and remember how the tire tilted slightly when
turned, that was caster causing the tilt. If you drew an imaginary line through the upper
and lower ball joints and compared the angle of difference to a line drawn perpendicular
to the ground, the resulting difference is the caster angle. Caster settings allow the
manufacturer to balance low speed steering effort and high speed stability. Increasing the
amount of positive caster will increase low speed steering effort. Caster also tends
to cause an increase in the amount of negative camber as the steering angle is increased.
Regular wheel alignments will usually save you as much in tire wear as they cost. It
should be considered routine, preventative maintenance.
Return to Tires 101 Page
|
