What techniques do you suggest?

First, let's do something basic, and look at the mathematics of "cost per mile."

It's an equation. We divide costs by the miles we travel.

Sounds simple, and in the "miles" part, it usually is.

Costs are another matter. Some fleets include labor costs for their maintenance department, some don't. Some create a value for new tires that were supplied as original equipment on new trucks and trailers, some don't.

And, are we talking about total fleet costs, or just tire costs? It can get complicated, and it depends on how you do your accounting. For our purposes, we'll limit ourselves to tire-related costs.

What will reduce the value of the equation?

Two things: We can decrease costs, but we can also increase the number of miles. We ought to try to do both.

How can we reduce the cost factor?

As we pointed out in the last Real Answers, if you really want to reduce tire life cycle costs, you have to consider both costs associated with tire wear and costs of fuel consumed by the tires. Fortunately, there are ways to reduce both.

What are these?

Number one is, as always, maintaining correct inflation pressure. Correct inflation optimizes tire fuel economy, while minimizing wear and maximizing retreadability. No wonder we consider it such an important way to prevent tire ills.

INFLATION PRESSURE vs. FUEL ECONOMY

Regardless of the type of tires you use, maintaining correct inflation pressure for the load will optimize tire performance and fuel economy.

Regardless of the type of tires you use, maintaining correct inflation pressure for the load will optimize tire performance and fuel economy.

How much effect will it have?

While inflation doesn't have a huge effect on fuel economy, it does have a positive effect, and it is something you can start benefiting from right now, with no change in equipment.

As to wear, based on TMC figures, tire tread life decreases about one percent for one percent of underinflation. Faster tire wear means fewer miles, and, it also means higher tire and tire maintenance costs, because you'll be servicing and replacing tires more often.

And, underinflated tires tend to run hotter, diminishing retreadability. So, you could get fewer total miles per casing and fewer salable casings, leading to a decrease in miles and an increase in tire costs, and increased cost per mile.

How else can we reduce costs?

Consider regulating your speed. Speed has a negative effect on fuel economy, as well as on tire wear and casing life. It's a rule of thumb, but you will lose about two percent on your miles per gallon for every mile per hour you increase speed between 55 and 65 miles per hour.

THE EFFECT OF SPEED ON FUEL ECONOMY

Speed reduces fuel economy and retreadability, while increasing tire wear, all of which tend to increase cost per mile.

How can maintenance help?

As Steve Maxson of Averitt Express points out, a good, regular inspection of tires can often detect things that might not yet be problems, but that could become problems.

What are some examples?

Underinflation is one. You cannot simply inflate your tires, then forget them. Just through diffusion of air molecules through the rubber, tires can lose two psi per month.

With no attention to inflation, at the end of the month, if your normal inflation is 100 psi, that 2 psi loss would be 2 percent, and according to TMC, you'll start losing about 2 percent in tread life. And it just gets worse with time.

A good inspection can also tell you if you have irregular wear that you might be able to scrub out with tire rotation. Remember, when any part of a tire's tread is worn beyond the legal limit, you must remove the tire. So, you always want to equalize wear if you can.

Inspections cost money, though. Still, a good inspection may help you avoid a breakdown, including emergency road service costs and downtime losses, either of which is usually far greater than the cost of inspecting and maintaining tires.

Besides, TMC estimates that inflation pressures on an 18-wheeler can be checked and adjusted in 20 minutes or less. And, many tire suppliers are willing to perform regular tire inspections for you at a very nominal cost.

They may even suggest you pull tires a bit earlier, or rotate them, not so much to equalize wear, as to extend wear.

Why would we pull tires earlier?

First, to enhance their retreadability. The shallower the tread gets, the more vulnerable the tire is to road hazards and punctures. These can render it unretreadable. Second, as Averitt Express has learned, if your trailers don't come into the shop all that often, it's possible you may have some with tires worn close to the legal limit. A DOT inspector could force your driver to replace them on the road, an expensive and time- consuming process.

By moving drive tires back to trailer positions at about 10-12 32nds remaining tread depth, you can greatly increase the useful life of their treads, reducing cost per mile.

And how can rotation extend wear?

With deep tread drive tires, like the M726, when remaining tread depth gets down to about 12/32nds, drivers may complain that the tires no longer look aggressive. Rather than send these tires to the retread shop, where all that remaining tread will be buffed away, you can move them back to trailer positions.

Since many trailer tires start out at just 12/32nds, it's like getting a new set of trailer tires, and typically, you'll find these partially used drives wear very slowly and evenly, giving you a huge increase in overall tire mileage.

The best way to reduce cost per mile is BOTH to reduce costs and increase miles. Maintaining proper inflation and reducing excessive speed, together with an effective tire inspection and maintenance program, can control and reduce cost per mile.