Bridgestone South Africa

How Can Uniformity Help Us Get Even Wear?

After inflation, then what?

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 tyres roll down the road. Correct, uniform inflation pressures are a great start, but there are lots of other things that should be uniform too.

For example?

Let’s start with mounting. We might assume that there’s only one way to mount a tyre 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 tyre haven’t been properly lubricated, a tyre can actually be mounted slightly off-centre or crooked on the wheel. This “non-concentric” mounting can produce symptoms similar to those you’d find if the axle were off-centre or bent. Either can cause ride disturbance (non-uniform ride), rapid wear, irregular wear – or all three.

Are there other sources of non-uniformity?

Today’s tyres 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 tyres and rims.

Atyre mounted off-centre or crooked can cause ride disturbances, rapid wear, irregular wear - or all three

Because no tyre is ever perfectly round, there are usually high and low points around a tyres circumference

What can we do about that?

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

On some original equipment Bridgestone tyres, 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 tyre is matched with the dimple on the wheel, the forces should partially cancel each other, helping minimise ride disturbance and irregular wear potential.

And with aluminium wheels?

Because aluminium wheels are machined uniformly, even O.E. 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.

Why at 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 minimise forces, and keep valve stems from interfering with each other during maintenance.

What if there’s no red dot?

Bridgestone S.A. 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 aluminium or steel, and you’ll help achieve a better initial static balance. Again, put dots 180 degrees apart.  

Bridgestone radials have a yellow dot marking the light static balance point. Match the yellow dot with the valve stem for best initial static balance.

That brings up balancing, doesn’t it?

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

How do we know we have a balance problem?

On drives and steers, ride disturbance is the usual complaint. But the fact is, an assembly may be out of balance even it there’s no ride disturbance. On trailers, even severe imbalance may not be noticeable. Some drivers say they can’t feel an imbalance of less than 300 grams, 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 unexplained irregular wear condition.

Is there a maximum allowable weight for balancing?

The Maintenance Council (TMC) recommends no more than 500 grams on steers and no more than 620 grams on drivers. If the tyre 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. 

Can other parts affect wear?

Every pan that interacts with the axle, wheel and tyre – from the differential to the hub – can have an effect on how evenly tyres 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 tyre’s interaction with the road. And don’t forget proper maintenance of that other wheel.

What “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 tyre 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 5.5 tons, overloading the steer tyres, which can lead to premature replacement of tyres and steering components. Too far back, and you may “unload” steer tyres, which can also cause irregular wear. And, it is possible to overload your drive tyres, causing wear problems there.

Sounds like the middle’s the best place to be

As an ancient philosopher said, “Virtue lies in the middle way.” You want straight wheels with tyres properly centred 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!

Bridgestone South Africa

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