Most people can tell when their car pulls to the right or left. What they can’t tell is whether it’s due to alignment issues, worn tires or a combination. Wheels require proper alignment on the X, Y and Z axis for the tires to wear properly. If the alignment is off, it can destroy the tires. The three axis are called Camber, Caster and Toe-in.
The camber can be seen when looking at the front of the vehicle. The ideal camber is at 0° or straight up. If the camber is positive the top of the tire is angled away from the car. If the camber is negative the tire is angled toward the car. When the camber is off, the tire shows an angle of wear or a slope across the top of the tire to one side or the other. This uneven wear will cause the car to pull.
Like a shopping cart on a pivotal wheel, front tires require the ability to turn on a pivot while staying connected to the suspension system. Caster is the angle of that pivot. If the top of the pivot leans toward the back of the car it is a positive pivot. Leaning toward the front of the car is considered negative.
The ideal is not straight up at 0°, as most would suppose. A positive caster of 2°-5° helps non-professional drivers by returning the steering wheel back to center after the turn. Racecars use a negative caster to make sure the wheel doesn’t return until the driver manually moves it back.
The distance between the front and back of two parallel tires is the Toe-in measurement. If the front of the tires point inward like a person standing pigeon-toed instead of in parallel, its called a toe-in. If the front of the tires point outward, it’s called toe-out. Again, the ideal is 0° or parallel tires.
One additional consideration is the Thrust Angle or the position of the front tire relative to its back tire. This measurement became significant with the evolution of four-wheel drive vehicles. The alignment keeps the front and associated rear tire in parallel.
All alignments start and end with a test drive. The front end and steering linkage is checked for wear before any alignment work can be done. Tires in good shape simplify the alignment work.
If alignments were put off and the tires are now excessively worn, the process will correct the alignment, but in the case of a camber worn tire, the tire will now only partially touch the street.
Some people get concerned when their alignment job didn’t turn out “perfect,” when it actually did. Consideration must be given to the effects of tires with unequal air pressure, pre-worn tires, power steering problems, and brake issues. All of the mentioned parts can give the illusion that the wheels are out of alignment when they are spot on.
But, sometimes it’s not an illusion. There are standards in how roads are built that most municipalities and states follow. This includes what’s known as the road crown, which is up to a 7° curvature in the road for drainage purposes. When a car is aligned, it’s not typically aligned to a flat surface, but to the average degree of road crown in the area.
Without that consideration, “perfectly” aligned cars in the right lane would always pull to the left. When in the left lane of a four-lane highway, the car would pull in the opposite direction. On a six-lane highway, the driver will always feel some tension on the steering wheel regardless of the lane due to the crowning affect.
Trusting the technician to mechanically align the wheels according to best practices is important. The standards allow each wheel to be “within tolerance” up to 3/16th from center. That allows the tires to be off halfway between a ¼ inch and a ½ inch, which can cause excessive wear of the tires and the hardware that holds everything in place. Sharp mechanics use a zero tolerance to make sure the tires are spot on.
Making sure wheel alignments become a part of regular maintenance is critical to a healthy car. How often an alignment is necessary comes from the manufacturer’s recommendations and the number of curbs and potholes the driver tends to hit. The key is making sure the alignment happens often enough that the tires wear evenly.