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ONE . Making Tires Last
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What FACTORS should drive my choice of DRIVE radials?

Last month, we looked at how choosing the right steer radial can prevent premature removal due to irregular wear. As we continue looking at the first letter in the irregular wear reducing acronym, “S.M.A.R.T.,” we’ll try to get a grip on “Selecting” the right drive.


On good pavement, rib radials provide powerful traction and fight irregular wear, while effectively cutting through water and films.

The Bridgestone M711 features an aggresive traction pattern and open shoulder deisng for a powerful soft surface grip, and a deep tread for long wear.

 

 



The Bridgestone M726 EL drive axle radial offers an ultra-deep (32/32") tread, with continuous contact shoulders to combat tread element squirm and resulting irregular wear.

 

What’s the secret to long drive tire life?

Part of it is selecting the right tire for your drive axles.  Notice, we didn’t say “selecting the right drive tire.”  Because sometimes the right tire for your drives isn’t a “drive” tire at all.

Why is that?

Most drive tires are designed to dig into soft, wet surfaces, trying to grab, so that the torque of the engine can be transferred to the road. You’re taking upwards of 80,000 pounds of vehicle at rest, and trying to get it into motion.

But what if the road surface is neither wet nor soft?  All those aggressive lugs and blocks that characterize most drive tires may be unnecessary.

How can that be?

For best traction and torque transfer, Indy racers use “slicks.”  The pavement has to be hard and dry, but slicks maximize the amount of rubber in contact with the road – and the traction that results.

So why does everybody use aggressive lug and block patterns?

Actually, not everybody does. Some fleets that operate in the southern part of the country, or that run routes where they never encounter snow, have had good luck running rib radials in drive positions.

Dry traction is a function of the amount of contact between tire and road. “Slicks” actually produce the highest possible traction on clean, dry pavement.

Why use rib radials on drives?

If you don’t have to deal with snow, rib radials can be an excellent choice for drive axles. Even on wet pavement, the traction can be superb. And typically, rib radials have shallower tread depths than lug or block patterns. There’s less tire weight to put into motion. 

In addition, contact with the road is more or less continuous throughout the tread face. That means less noise and vibration. And generally, there is less tendency for irregular wear, especially of the “heel and toe” variety.

For some fleets, ribs are just more practical. Especially if they can standardize on a single size and pattern for all axle positions. That can greatly reduce tire inventory.

Finally, rib radials usually have far less rolling resistance than drive radials. That can mean superior fuel economy.

Cross-rotation of drive tires can help scrub out heel and toe wear patterns. It also can help equalize wear if the tires on one tandem wear faster than those on the other.

Will any rib radial work?

Not necessarily. You’ll want to test it, on your own vehicles and over your own routes, before making a commitment to rib radials on drive axle positions. Remember that unlike steer and trailer positions, tires on drives are subjected to very high torque. That can cause tires to wear rapidly.

And, you’ll also want to consider the fact that many drivers don’t believe rib radials will give them the traction they want.

We encounter plenty of mud and snow. What should we do?

You probably should choose a drive radial with a traction pattern. Depending on your situation, either the Bridgestone M711 or the M726 EL should perform well for you.

How do we decide which to use?

The M711 has a very aggressive block tread pattern, with open shoulders for extraordinarily high soft surface traction.  If your average annual tractor mileage is less than 90,000 miles, and if most of your drive tires are removed because of wear out rather than irregular wear, the M711 can be an excellent choice.

What kind of irregular wear occurs on drive tires?

Pretty much any kind, but one of the most troublesome is “heel and toe” wear. As the name implies, individual tread blocks are worn unevenly, with more wear on the “toe” of the block (the last part to leave the road as the tire turns) than on the “heel.”

This wear is caused by slipping and “snapping” of the toe of the block edge as it loses contact with the road.

What can we do about that?

If heel and toe wear is the only irregular wear you have, cross-rotating your drive tires, to reverse their direction of rotation, can help equalize wear patterns, by transferring wear forces to the other side of the blocks. Nevertheless, you’ve added a lot of extra tire handling.

(If you’re experiencing alternate shoulder lug wear on open-shoulder drive radials it may be due to a mismatch of inflation pressure in dual assemblies.)

You can also switch to a shallower tread drive radial with shorter blocks that squirm less. But, you must sacrifice original tread depth – and mileage – to combat the irregular wear. Fortunately, there’s another choice.

What is that?

The M726 EL radial has continuous contact shoulder ribs, together with one of the deepest treads in the industry. The deep tread produces very long original life, and the continuous shoulders help stabilize the tread against squirm and side forces that can cause irregular wear.

Why not simply go with the M726 EL?

You could. Many fleets do. But if you prefer a more aggressive pattern, the M711 may be better for your needs. Your best bet is to try them for yourself, and see which delivers the least irregular wear and lowest cost per mile in your operation.

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