Here's the alignment specs.
You're probably aware of this, but for the benefit of others researching this issue, tire wear on the outer edge can be caused by too much positive camber, meaning the top of the wheel is tipped out too far, as viewed from in front looking back at the vehicle. It can also be caused by too much "total toe-in".
One clue that camber is out of specs is a tire wants to pull in the direction it's leaning. The goal is to have both front wheels tipped an equal amount, then we add a little more positive camber to the left wheel to create a slight left-hand pull to offset "road crown". That's the tilt of the road surface to the right that makes water run off.
There's a few clues that toe is off. That's the direction the wheels are steering when the steering wheel is straight. Both front wheels must be adjusted so total toe is in specs to prevent tire wear, but both wheels can be off in opposite directions an equal amount. That will still give good tire wear but the steering wheel will be off-center. One confusing item is when all of the other adjustments are perfect except toe is out of specs on just one wheel, it still affects tire wear on both front tires equally, (plus the steering wheel will be off-center). You always have to turn the steering wheel until that incorrect toe is equal on both wheels to make the vehicle go straight. When you have outer edge wear on just the one tire, it is usually not due to incorrect total toe.
When that outer edge wear is seen on just one tire, it's usually due to too much positive camber on that wheel, but that should be accompanied by a pull in that direction.
Notice I covered myself by including a number of "shoulds" and "usuallies". Some vehicles are very forgiving for unequal camber settings and will still tend to go straight, so it can be easy to overlook one of those clues. Unequal camber is rather consistent when driving, meaning any pull will usually remain constant. Total toe, on the other hand, makes the vehicle somewhat unstable or it tends to wander a lot and need constant steering correction. Crosswinds have a big affect too. If total toe is toed out, the two front wheels are steering away from the center of the vehicle. A crosswind from left to right will blow the vehicle to the right, plus it pushes more of the vehicle's weight onto the right tire. Vehicles want to follow the tire with the most weight on it, and the other one walks away until the sidewall can't flex any further, then it snaps back and starts that all over. That creates a choppy pattern, but usually on both tires. Because of the reaction to the crosswind, the pull to the right is much stronger than normal. It makes for a very tiring vehicle to drive.
Camber out of specs results in a smooth wear pattern on one edge of that tire. Total toe that's out of specs results in a choppy pattern. That can be over the entire tread surface or just on one edge.
I haven't mentioned "caster" yet. That's the rearward tilt of the steering knuckle, similar to the rearward tilt of the front fork on a bicycle. Caster is a result of the position of the upper ball joint or upper strut mount in relation to the lower ball joint. As the upper moves further rearward, "positive caster" increases. In the past with heavy rear-wheel-drive vehicles, caster causes a pull toward the side with the lower value. (One degree of caster pull one way can be offset by half a degree of camber pull the other way, to a point). The universe doesn't know why, but on almost all front-wheel-drive vehicles, unequal caster seems to have no effect on pulling and can't be adjusted to correct a pull. In fact, very few models even provide a means of adjusting caster. We use it more as an indicator of proper crash repair.
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Monday, December 4th, 2023 AT 3:57 PM
