Tires and alignment

  • 3 CYL
  • 4WD
  • 190,000,000 MILES
I had driven my car for about six months after getting new tires and a new alignment, after about six months of driving I was having a family member change the back breaks when he noticed the tired in the back were wearing out as if I was driving them in the angleague of "/". This of course made the inner half of the tires lose all traction while the outer half remains untouched. Would this have been an issue of the realignment done by the mechanic I brought it to or is this another issue? We have never had an issue with the tires wearing out like this until the new tires and realignment were done. Please assist, I am not very formidable with cars. Thanks!
Do you
have the same problem?
Sunday, May 22nd, 2016 AT 7:18 PM

1 Reply

To start with, you have a dandy way of showing the leaning tire, but is that the left or right tire? Next, " half of the tires lose all traction", and "outer half remains untouched" both imply that part of the tire isn't touching the ground. I cannot tell if it is the inner or outer part of the tread that is wearing faster.

There are a couple of things that must be explained first. If "camber" is out-of-adjustment, that wheel is leaning in or out on top as viewed from in front of the car. When the wheel is leaning in on top, the inner part of the tread has the most weight on it and will wear out faster than the outer part. The important thing to note is that affects only that tire; none of the others. Both wheels can be tipped in or out, and both tires on the same axle can have the same wear patterns, but each tire is affected by the angle it is leaning at.

The second alignment angle is "toe". That is the direction the wheel is steering. Most alignment specs take into account the wheels are going to be tugged rearward from road forces and from braking forces, so to make them perfectly parallel to each other, they start out with a little "toe-in", meaning the fronts of the wheels are slightly closer together than the rears of those wheels. If that toe-in is severe, like the "V" of a snowplow, the outer edges of the tires will scrub off. Those are the leading edges. If you exaggerate this for clarity, think of the fronts of the wheels getting closer and closer together until the left tire is pointing almost perfectly to the right, and the right tire is steering totally to the left. Now it is easy to visualize that the outer edges of both tires are closer to the front of the car, hence, "leading edge". Next, think of holding a pencil upright with the eraser pointing down. Place the eraser on a table, press down, then drag the pencil across the table. The leading edge will scrub off, and the "trailing edge" will bend and lift up. The leading edge makes eraser crumbs and the trailing edge sees no wear at all. THAT is what causes tire wear due to toe problems. There's two important things to consider with toe wear. Most importantly, toe wear always affects both tires equally. Second, there will be a choppy pattern to the tread caused by the tire steering off-center as far as possible, then the sidewall can't flex any more and the tread skids back, then starts again.

The point to remember is if you see excessive wear on the inner or outer edge of only one tire, it has to be a camber issue. If the wear is on both tires, it could be a total toe issue OR it could be two separate camber issues.

Another place where people get confused is when toe is off on just one wheel. Think of the left front wheel being adjusted too far to the right so it is steering that way. Overall, even though the two front tires are steering in different directions, on average the car is going to steer to the right. You counteract that by turning the steering wheel to the left to make the car go straight. The bad tire wear will, again, affect both tires since now they're steering off-center by the same amount. You will, however, have an off-center steering wheel.

The rear wheels get a little trickier. First, on a lot of older cars that had adjustable rear wheels, they were adjusted by installing a shim to turn that wheel. There are only a few sizes of shims made for some cars so we had to select the one that brought the alignment as close as possible to perfect. Usually "close enough" was more than good enough for good tire wear. However, that almost always left the two wheels not exactly equal, so the rear of the car would steer a little to the left or right. You might be talking an eighth inch, so it was not noticeable, but then we use those rear wheels as an index point to know where to set the front wheels. That makes all four wheels steer the same way so what you see is a straight steering wheel. Think of having four perfectly parallel wheels in perfect alignment, then lift the body off the frame, turn it a little, then set it back down on the frame. The car will go down the road turned slightly, but tire wear will be perfect.

Hopefully that will help you determine which alignment angle is not correct, but there's still more to the story. One of the issues has to do with the wheel bearings. On many cars there's a larger bearing on the inside that is supposed to carry the car's weight, and a smaller bearing on the outside that is only there to hold the wheel straight. Alignment specs are concerned with tilting the wheel to where the weight will be placed right over that larger bearing, AND with good tire wear. Sometimes that is a compromise. That tilt is also a contributor to comfort. The engineers at Ford chose comfort over tire wear on their 1980's Escorts and Tempos. As a result, they sold a pile of them because they road better than all other brands of small cars. What the salespeople did not want you to know though was the tires wore out in about 15,000 miles. There was no means of adjustment on the front. The aftermarket industry came up with corrective parts that allowed us to fix the rear wheels. Those cars were easy to spot on the road. The front tires were tipped out so far it looked they were about to fall off. The rear tires were tipped in just as far, but we could correct those.

The point of that part of my story is the mechanic might have set your wheels correctly, but the specs put more importance on comfort or on reliability of the wheel bearings than on tire wear. That is why tire rotations are recommended. You might have accelerated wear, but it will be spread across all four tires evenly so you do not notice the few miles you get from the set.

Now that I have shared all of that wondrous story, there is a much more important thing to look at. That is ride height, especially given the age of the car. All of the car's control arms and spindles makes up a carefully-designed geometry, like a big rectangle. Based on that geometry, the wheels will tilt in and out on top as the car body goes up and down over bumps in the road. Think of the pendulum in a grandfather's clock. It swings equally both sides of center. As the car ages, the springs sag and the car sits lower to the ground. That rectangle isn't any more. That's like tilting the clock. The pendulum might still swing the same total distance, but not equally in both directions. On a sagged car, the wheels usually tip in on top, then they tip even more as the car goes down after hitting a bump. The problem here is even if the wheels are set to perfect alignment, they are going to tip in more than normal just from normal driving. To say that more clearly, you will have poor tire wear, even with perfect alignment, if the suspension has sagged. There is really nothing we can tweak to the specs to prevent that. The only cure is new coil springs, unless you have a Chrysler or GM vehicle with torsion bar suspension, which is adjustable.

We have a saying for ride height problems. "With sagged ride height, we are aligning to the rack, (hoist), not the road". What that means is on the alignment rack, the numbers on the computer's display can show everything is in perfect specs, but on the road you are going to have unacceptable tire wear. Ride height is the most often overlooked criteria when explaining alignment problems.

Every alignment shop has a small book that lists every make, year, and model, and shows where to take those measurements and what they should be. The acceptable range is usually about an inch, but very few ten-year-old cars will be in that range.

The first thing I would do is return to the shop that did the last alignment and have them perform an inspection. Worn parts cause more tire wear problems than simple misalignment. They should measure ride height too and give you those numbers. If misalignment appears to be the cause of the bad tire wear, they might offer to align it again for free, but a lot can happen in six months so don't hold them to that. Some shops will realign a car for free if parts are needed and you let them do the work.

If no worn parts are found and you have the car aligned again, be sure to get a printout so you can share the numbers with me. All alignment computers have that capability. The printouts show the "before" numbers, meaning what the car had when it came in, and the "after" numbers meaning what each adjustment was set to at the end of the alignment. I can tell from those what to expect for tire wear, pulling, and centered steering wheel, but I cannot tell what sagged ride height will cause.
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Sunday, May 22nd, 2016 AT 8:34 PM

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