Where have you been for the last 25 years? There is no such thing any longer as a "front end alignment". All alignment computers since the mid 1980s perform 4 wheel alignments. Not all cars can have the rear wheels aligned but that is mostly a Ford problem. They are famous for building cars that have the front tires tipped way out on top and way in on the back. That makes them ride real smooth compared to other car brands so they sell a pile of them, but what they don't want you to know is 15,000 miles is about the best you can hope for on a set of tires.
Toe and camber are the two important settings on your rear tires. Camber is how much they are leaning in or out on the top. If that is wrong for either or both tires it will cause excessive wear on the inner or outer edge of that tire. Toe is the direction the tires are steering. Common sense says the two tires should be perfectly parallel but that is not the case. Road forces pull the tires back and out a little so most manufacturers specify to set them a little closer together on the fronts compared to the rear of the tires. The same is true usually of the front tires.
When you look at the printout from the alignment, it is typical to find that both rear tires are not perfectly parallel with the car body. They can be hard to set precisely so most mechanics are satisfied that "total toe" is correct. That just means both rear tires are steering a little to the left or a little to the right. All alignment computers look at which way the rear wheels are steering to determine where to set the two front wheels so the steering wheel will be straight when you go down a straight road.
Even though individual toe on either rear wheel can be wrong, it's the total toe that affects tire wear. When that is wrong, the tires are steering away from or toward each other. That makes them skid going down the road. What you will FEEL for tire wear is a rough tread pattern when you rub your hand across the tread one way and much smoother the other way. Each block of rubber on the tread will have a raised side and a worn down side. Think of holding a pencil straight up with the eraser on a table. As you drag the pencil sideways, the leading edge of the eraser will wear down and make eraser crumbs, but the trailing edge will bend and lift up so there is no wear on that part. Each block of rubber on the tire tread is like an eraser. When you feel those high and low spots, the total toe is not set to specs.
Saturday, April 16th, 2011 AT 11:39 PM