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Published on August 16, 1999

PROPER MATING VITAL TO TIRE PERFORMANCE

Tire mating, also known as tire matching, is probably the sexiest term we have in the tire business. So if sex sells and people are so focused on it, how come so few follow this when it comes to tire mating in the truck tire world? Perhaps it's like safe sex: Many people talk about it, but how many are actually doing it?

Tire mating is vital to the life, performance and well-being of truck tires. But a lot of people don't think this practice applies to them.

It's impossible, for example, to mate tires when making a service call on the side of the road. Heck, you're lucky if you've brought the right tire size, never mind mating the tire by dimensions to the other tire on the axle.

And that's OK. Most fleets have policies that call for removing the new tire installed on the road and replacing it with one that is more suited for the position from a tread and mating standpoint.

The main goal here is for you to get the vehicle back on the road as quickly as possible.

But today, as more commercial tire dealers take on more responsibility for tire maintenance—including installing tire and wheel assemblies on vehicles for fleets—tire mating does apply to you.

If you are running tires in a fleet and wonder why they aren't performing as well as they should, or wonder why they exhibit some weird irregular wear patterns, you should be concerned about the fleet's tire-mating practices. And you should advise the fleet of the importance of proper tire mating, too.

Mismatched duals have the same effect on tire life as low inflation or overloading. An underinflated tire in a dual assembly shifts its share of the load to its mate, which then becomes overloaded, and frequently fails prematurely.

A similar situation occurs when a tire's diameter is smaller than that of its mate. A difference of 1/4 inch in diameter may result in the larger tire carrying up to 600 pounds more than the smaller tire.

This shift in load becomes worse as the difference in diameters becomes greater. Since the larger tire has to flex severely to carry more than its share, heat builds up within the tire, which leads to reduced strength and breakdown of the rubber components.

Improperly matched duals also will wear poorly. Because the larger tire carries more load, the footprint changes and it will wear unevenly. The smaller tire, which must rotate at the same speed as the larger tire, is forced to scuff as it runs over the road to keep up, and it, too, develops irregular wear that never evens out. The overall result is abnormal and unequal treadwear for both tires.

The same thing occurs if inflation pressures of duals are different.

This makes it critical that tires in dual positions are matched by size and diameter, and that their inflation pressures are the same (preferably within 2 psi). Most people think 5 psi is OK, but that is probably too much.

Matching tires on drive axles is doubly important.

Since tire diameter controls the revolutions per mile, the drive differentials may fail if the tires are fighting with each other to run at different rpms.

Unless the vehicle is equipped with an inter-axle differential, the tires on both of the tandem drive axles must be closely matched to safeguard the differential and prevent excessive slip, loss of traction and uneven wear.

Inter-differential fight due to mismatched tire diameters also will lead to premature component failure.

The four drive tires on a single-axle-drive application should be matched within 1/4-inch across the axle.

Twin-screw or tandem-drive axles require that all eight tires be matched so that the average diameter on one axle is no more than 1/4-inch different than the average diameter on the other.

Since a typical drive tire may lose as much as 4 1/2 inches in circumference due to normal wear and still be serviceable, it is apparent that a wide difference in tire circumference may exist on the vehicle.

Thus, it is important that the tires on tandem-driving axles be inspected and matched at regular intervals to ensure the tires remain matched within 1/4 inch in diameter.

Tire rotations between the rear and forward drive axles are extremely valuable to extend tire life and ensure these tires wear evenly.

It also is important to match tires on free-rolling axles.

Although a differential is not a consideration on trailers and dollies, maximizing tire life and extending tread wear is. Tires on these axles should be mated within 1/4-inch side by side and 1/2-inch across the axle.

Tires on both tandem-axle tractors as well as trailers can benefit by rotations since the tires on the rearward axle will wear faster than those on the forward axle.

During turning, the truck or trailer tends to pivot on the forward-axle tires and drag the rearward-axle tires around the turn, resulting in a faster wear rate for the rear-most tires.

Tire diameter can be measured in several ways. A stationary tire meter mounted on the wall can be used to quickly measure the overall diameter of tires off the vehicle. This is a good tool to use in the tire shop or service area where all tires that have just been mounted can be measured and marked with their diameters.

This practice is important when new tires of different manufacturers or models may be mixed on the same axle, or when retreaded tires are used.

Due to prior service, the method of retreading used and the techniques used during the retread process, newly retreaded tires with the same make, model casing and tread may have different overall diameters.

Marking the diameter on the tire immediately after it is mounted saves the technician time during installation on the vehicle.

Tire calipers and dual-tire maters measure the diameter of tires on the vehicle. Once the tire changer knows the diameter of the tires remaining on the unit, he then can select an appropriate replacement tire from the stock that has the diameters already marked.

Another fast but not always accurate way is to take tread-depth measurements. Generally, if tires are within 4/32nds inch in tread depth, they are within about 1/4 inch in diameter. This quick means of measuring diameter differences can vary, however, due to variations in casing dimensions.

In addition to matching tire diameters and inflation pressures on dual applications, it is very important to mate tires on the basis of construction. Do not mix radials and bias-ply tires on the same axle due to their different load/deflection characteristics.

Since radial tires deflect more under a given load than bias tires, the bias tires will carry a greater share of the axle load and may operate in an overloaded condition that will result in reduced mileage and early tire failure.

It is acceptable (but rarely done) to mix tube-type and tubeless tires of the same physical size on the same axle as long as they all are radials or all bias plies. Inflation pressures must still be the same in both of these tires to ensure each carries its share of the load.

Employing proper tire mating practices is not difficult, but like safe sex, it requires planning ahead and taking a few precautionary steps to avoid problems down the road.

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