In the beginning of this series on irregular wear prevention, we said irregular wear is the result of irregular abrasion. And irregular abrasion is the result of irregularity (or non-uniformity) in the way tires roll down the road. Correct, uniform inflation pressures are a great start, but there are lots of other things that should be uniform too. 

Let's start with mounting. We might assume that there's only one way to mount a tire on a wheel, but nothing could be further from the truth.

If a wheel is dirty, rusty or corroded, and especially if the wheel and tire haven't been properly lubricated, a tire can actually be mounted slightly off-center or crooked on the wheel. This "non-concentric" mounting can produce symptoms similar to those you'd find if the axle were off-center or bent.

A tire mounted off-center or crooked can cause ride disturbances, rapid wear, irregular wear ­ or all three.

Either can cause ride disturbance (non-uniform ride), rapid wear, irregular wear ­ or all three. We've dealt with mounting uniformity in Real Answers before (see Vol. 1, Issue 3, pp. 26-29), so we won't go into it in depth here.

Are there other sources of non-uniformity?

Today's tires and wheels are manufactured to very tight tolerances, but there's really no such thing as "perfect." There are usually high points, resulting in "runout" (both radial and lateral), in both tires and wheels.

There's no way to make the tire or wheel perfect. What you can do is to try to minimize variations by making them cancel each other.

On some original equipment Bridgestone tires, the high point of radial runout is marked with a red dot.

Likewise, original equipment steel wheels often have a dimple, marking their low point. If the red dot on the tire is matched with the dimple on the wheel, the forces should partially cancel each other, helping minimize ride disturbance and irregular wear potential. 

Because aluminum wheels are machined uniformly, even OE wheels are not marked with a low-point dimple. And, many steel wheels aren't marked either. In that case, match the dot with the valve stem.

Because that's usually the heavy static balance point of the wheel, the point where the wheel is a bit heavier. A hole has been drilled through the wheel and a tiny bit of metal has been removed, but that small amount of metal has been replaced with a fairly large, heavy valve stem.

On a dual assembly, put the dots 180 degrees apart. This will minimize forces, and keep valve stems from interfering with each other during maintenance.

Bridgestone radials have a yellow dot. This marks the light static balance point. Match this with the valve stem (the heavy spot), regardless of whether the wheel is aluminum or steel, and you'll help achieve a better initial static balance. Again, put dots 180 degrees apart.

Yes it does. And, in a previous issue of Real Answers (Volume 2, Issue 1, pp. 26-29) we dealt with balancing tires in some detail.

A tire and wheel assembly that is out of balance behaves a bit like an assembly where the tire is crooked or off-center ­ with similar results. Balancing, especially full dynamic balancing, can help a great deal in preventing ride disturbance and wear.

On drives and steers, ride disturbance is the usual
complaint. But the fact is, an assembly may be out of balance, even if there's no ride disturbance. On trailers, even a severe imbalance may not be noticeable. Some drivers say they can't feel an imbalance of less than 10 ounces, but it may still cause irregular wear. So ride disturbance is not a very reliable way to determine imbalance.

The way to be sure is to use a good off-vehicle dynamic balancing unit, a good precaution if there's an otherwise unexplainable irregular wear condition.

The Maintenance Council (TMC) recommends no more than 18 ounces on steers and no more than 22 ounces on drives. If the tire and wheel assembly can't be brought into balance with that much weight, you probably have a different problem, like a non-concentric mount, a bent wheel or some other non-concentric or out of balance component, like a hub or drum.

Every part that interacts with the axle, wheel and tire ­ from the differential to the hub ­ can have an effect on how evenly tires wear. That includes shocks, air bags, bearings, springs, shackles, brake drums, even lug nuts.

The contribution of each may be small, but there are so many components that neglect can add up to a big effect. As we said before, the key to uniform wear is uniformity in the tire's interaction with the road.

And don't forget proper maintenance of that other wheel.

The "Fifth" wheel. Proper lubrication here is critical. If you imagine the worst case, no lube at all, the result would be almost like driving a very, very long straight truck. Huge forces would be fighting you during turns, and these could cause severe tire wear problems.

Follow manufacturer's recommendations on the type and amount of lubrication to use. And be sure to lubricate converter dollies and pintle hook mechanisms, too.

Fifth wheel position is also important. Too far forward, and you may exceed the limit of 12,000 pounds, overloading the steer tires, which can lead to premature replacement of tires and steering components.

Too far back, and you may "unload" steer tires, which can also cause irregular wear. And, it is possible to overload your drive tires, causing wear problems there.

As an ancient philosopher said, "Virtue lies in the middle way." You want straight wheels with tires properly centered on them, with the whole assembly in good balance for best results. You want inflation pressure that's not too high, not too low. And every component should be in good condition ­ and properly lubricated. Only good maintenance can give you all of that.

Proper fifth wheel lubrication can reduce forces during turns that can contribute to irregular wear.

Next time, we'll move on to the next letter of our "S.M.A.R.T." acronym, "A" for "Align your vehicles on a regular basis."