Some nuances of proper commercial tire maintenance

I recently talked with a commercial truck tire dealer who was complaining that the trucking industry seems to be changing.

When his technicians are called to replace a tire on the road, they have to put on a new tire. But if the tire is on a dual position, it won't properly match dimensionally with its worn mate.

In the past, he would advise his fleet customers that both tires should be replaced, but now-a-days more and more carriers are telling him to replace just one tire, forget about the other, and get the vehicle back on the road as fast as possible.

With the summer heat upon us, tire-related en-route breakdowns are spiking, and he was wondering what is going on that is making fleets forget about proper tire matching and what information can he supply to these customers to convince them that both tires must be replaced.

There are several things happening in the trucking industry that are affecting how truckers maintain their tires.

Driver hours-of-service regulations require that time for en-route breakdowns be deducted from drivers' available driving time, and e-commerce has put pressure on all fleets to deliver their goods quicker.

Today freight haulers have no time for en-route delays but when they happen, they want quick fixes that get the trucks back on the road as soon as possible. So their mindset is to just slap a new tire on and "let 'er roll!"

Many small fleet operators that make up the majority of the trucking industry do not have people on staff who know the nuances of proper tire maintenance.

This is especially true for the growing number of third-party logistics companies (3PLs), which provide one or many of a variety of logistics-related services that include public warehousing, contract warehousing, transportation management, distribution management and freight consolidation.

Many do not own a truck, and some that do may not have a maintenance department or vehicle maintenance personnel.

In many instances you are talking with a person in dispatch or operations whose only knowledge of tires is that they are black and round and flat on the bottom.

Many cognitive fleets require that any tire they buy on the road be a steer tire. That way when a vehicle comes back to the yard with a steer tire in the wrong place like on a drive or trailing axle, they can readily see it and replace it with the correct type of tire and properly match it to its dual mate.

However, that still does not address the situation in which a new steer tire with 19/32nds-inch tread depth is matched with a worn trailer tire that has 2/32nds of tread.

The worst case is when a truck has a new drive tire with a tread depth of 30/32nds installed on the road that is mated with a worn tire that has 2/32nds of tread.

In this case you might find that the worn tire does not touch the ground at all, and since all of the weight on that end of the axle is carried by the new drive tire — which is overloaded on a fully loaded axle — it's bound to fail.

What can you do? Education is the answer but, as with anything, you have to have patience and understanding when dealing with commercial accounts, especially those that don't know very much but think they do.

Below are a few facts about tire matching that you might find helpful.

• Mismatched duals have the same effect on the life of tires as underinflation or overload.

When a tire's diameter is smaller than its mate's, it becomes overloaded and frequently fails prematurely.

A difference of ¼-inch in diameter may result in the larger tire carrying up to 600 pounds more than the smaller tire. This shift in load worsens as the difference in diameters increases.

Two tires with different diameters cannot cover the same distance in the same number of revolutions unless they are bolted together.

In that case, this condition can lead to both rapid and irregular wear. Since the larger tire has to flex severely to carry more than its share of the load, heat builds up within the tire, which leads to fatigue, breaking down the rubber components and eventual destruction of the tire.

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 develops irregular wear that never evens out.

In the best scenario, both tires develop irregular wear. In the worse scenario, the larger one fails due to overload first, and the smaller tire fails for the same reason soon after.

• Matching tires on drive axles is doubly important.

Since tire diameter determines the revolutions per mile (rpm), 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 interaxle differential, the tires on both of the tandem drive axles must be matched closely 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, which is far more expensive and time consuming than just replacing two tires.

The four drive tires on a single-axle drive application should be matched within 1/4-inch diameter (1/8-inch radius) or less across the axle.

Twin-screw or tandem drive axles require that all eight tires be matched so that the average diameter of the tires on one axle is no more than 1/4 inch (1/8-inch radius) different from the average tire diameter on the other axle. (When measuring dual matching on the vehicle with a tire square, radius is being measured.)

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 still are.

Therefore, tires on these axles should be mated within 1/4 inch side by side and 1/2 inch across the axle.

I once visited a fleet that ran three or four brands of tires and went to the trouble of matching duals not only by size but by make and model.

This degree of effort is not necessary. It is acceptable to have multiple tread designs and brands across an axle as long as the dual matching tolerance is 1/4-inch in diameter.

• Many people think that if they mount a set of radial retreads with the same tread design on a vehicle, that they will be matched properly. Not true.

Just because the retreads are all on the same type and size casing does not mean they all have the same overall diameter.

Due to the tires' prior service, the method of retreading used and the techniques employed during the retread process, newly retreaded tires with the same make, model casing and tread may have different overall diameters. Always check the dimensions of new retreads to ensure they are properly matched.

When servicing a tire on the road, the odds of having the exact diameter size tire to mate with an existing tire in a dual position are usually not good.

Therefore first measure the tire radius with a tire square to determine the tire diameter. Don't go by tread depth since this is not an accurate measurement for comparing two different tires.

• If the truck operator will not replace both tires in a dual set as he should, place the larger tire on the outside. Since the outside tire wears faster than the inside tire, as it wears its diameter will approach that of the inside tire.

Also, if the smaller tire is on the inside, the crown of the road (if there is one) will help make up the size difference between the two tires as they run.

Technology, e-commerce, government regulations and the Internet of Things (IoT) are changing trucks and trucking operations. However, the basic best practices for operating and maintaining truck tires have not.

As long as the basic laws of physics apply, tires must be matched properly to ensure they deliver optimum performance and in many cases just survive.

Let your customers in on this little piece of knowledge. It could save a tire or two's life.

Peggy can be reached via e-mail at [email protected].