Bridgestone Commercial Truck Tires

B y P O P U L A R D e m a n d

popular1.gif (11448 bytes) Real Answers readers tell us that one of the biggest challenges they face is fighting premature tire removal due to irregular wear. In this issue, we look at the first letter of our irregular wear prevention acronym “S.M.A.R.T.” As we’ll see, “S” stands for “Select the right tire for the job,” the first step in saving money by reducing irregular wear.

Which tire design wears most evenly?

It all depends. No two situations are absolutely identical, and no one tire will wear evenly everywhere you use it. For example, a tire with a tread compounded for on-highway use may not perform as well off the road. And vice versa.

In fact, irregular wear is often a sign that you’re using the wrong tire for the job.

What causes irregular wear?

If you already have the Bridgestone video Saving Through Reducing Irregular Wear, you should also have what we call the "S.M.A.R.T." card.

On the back of that card, you’ll find a "fishbone" chart, listing 6 different categories and some 36 different causes of irregular tire wear. And those are just common ones! There are many others, and they all can act together in different combinations. That’s why no single tire is best for every application.

How can I narrow my selection?

One good way is to start by looking at axle position and type of hauling. In this article, we’ll focus on steer axles. Just about everybody uses rib tires on steers, but even within that category, there are many to choose from.

Knowing your type of hauling can help. For example, here are some characteristics of long distance line hauling:

Very slow tread wear
Minimal scrubbing
Relatively high speeds

Why is tread wear slow for long distance haulers?

Tires are designed to roll in a straight line. And long distance line haulers tend to drive in nearly straight lines – most of the time. Since wear is caused by abrasion, and since there’s very little scrubbing, slipping and dragging in line haul operations, overall tire wear tends to be slow.

How does that affect tire choice?

For steer axles, tires with straight (or nearly straight) grooves should perform well. When the grooves between ribs are straight, the tire naturally tends to roll in a straight line, requiring little steering input to keep it that way. That means very little steering-related scrub, and long, slow wear.

But don’t zig-zag grooves produce better traction?

Not necessarily. Zig-zag grooves provide "biting" edges that can be helpful in slicing through water and road films, but there are other ways to accomplish that.

Besides, one of the functions of a groove is to provide a channel for removing water from the tire footprint. As you might expect, especially at higher speeds, it’s harder to push water through a zig-zag groove than through a straight groove.

So how do you get high traction with straight grooves?

Early in tire history, John Sipe found a real answer for increasing traction.

He cut thin slits into the tread surface. Today, those slits bear his name. Sometimes, these "sipes" go all the way across a rib from groove to groove. Sometimes they are tiny s-shaped cuts in the middle of a rib. Or they may look like tiny notches or nicks along a rib edge. Sipes can improve wet traction on tires with straight groove designs.

Not only that, but sipes can also improve a tire’s wear characteristics.

How do they do that?

A tire’s normal shape is round. But as it rolls through its footprint, this round shape is temporarily flattened — over and over again. This creates tremendous stresses in the tread that can cause it to run hot, wear quickly or wear in an irregular pattern.

Sipes break the large shape into hundreds of smaller shapes, greatly relieving these stresses. The result is fewer places for irregular wear to start and spread.

Then why make a tread with zig-zag grooves?

For one thing, you can use fewer sipes with a zig-zag design. That can mean a simpler, less expensive mold and lower cost tire. In addition, even though sipes tend to be very thin, hundreds and hundreds of them add up to a significant amount of rubber that is not there to make contact with the road.

In high scrub situations, with more rubber in the footprint, abrasive forces are distributed over a wider area, weakening them.

Couple that with tread compounds designed to resist scrub, and you can experience greatly enhanced tread life in severe wear situations.

But wouldn’t a scrub-resistant compound be good for long distance line haul treads too?

Not necessarily. It might generate too much heat at prolonged highway speeds. That could accelerate tread wear and even reduce retreadability.

So what’s the conclusion?

On steer axles, if you’re a long distance line hauler, you’ll probably have good luck with a tire with straight grooves, extensive siping and a tread compound designed to run cool — like the Bridgestone R227.

For shorter hauls and pickup and delivery work, a tire with a large tread area and very tough compound, like the R250F or R250 may provide better service.

Next time, we’ll talk about some of the latest tread design innovations for preventing and reducing irregular wear on tires designed for steer axles.

Radials with straight grooves, like the Bridgestone R227, often perform well in long distance line hauling. Extensive unidirectional siping removes water efficiently for high wet traction.

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The Bridgestone R187F uses zig-zag grooves, rather than extensive siping to enhance traction. This design tends to perform best in regional or urban hauling where turns are frequent.

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Shoulder edge sipes on the Bridgestone R196 help relieve stress buildup as the tire rolls through its footprint, while the rib sipes provide edges to enhance wet road traction.

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To receive a copy of the "S.M.A.R.T." card, just check the box on the reply card bound into this issue of Real Answers.

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