Heavy Duty: In the Groove

Okay, everyone in the fleet transportation industry understands how important it is to hang onto good drivers. Some experts estimate that it costs a company in excess of $10,000 to get a driver behind the wheel of a truck, so it makes sense that fleets would want to do anything they can to pamper their drivers and get maximum return out of that investment. They might even start to swap tires out before their time, just so drivers don’t complain about a loss of traction.

They might, but according to industry experts, they’d be making a costly mistake.

According to Doug Jones, customer engineering support manager, Michelin North America, the lowest tread depth allowable on heavy-duty steer tires by the Federal government is 4/32nd of an inch, while 2/32nds of an inch is allowable on heavy-duty drive tires.

“But what we find is that most fleets will pull their tires for retreading at about 8/32nds to 10/32nds,” he says. “That means that you’ve got about 6/32nds to 8/32nds of inch of useful tread that is buffed off when the tire goes to the retreader.”

In other words, fleets are losing tire life, and losing money in the process. “How much money they’re losing depends on driving habits and applications,” Jones explains, “but if a new tire comes with 30/32nds of tread depth, and they’re taking them off for retreading at 10/32nds, they’re losing about a third of their usable tread.”


First off, Jones recommends that all fleets have a tire management program. As part of that program, he says, the fleet maintenance manager should decide on a casing policy. “How they want to use that casing after its first life determines when they pull it,” he says, but it’s easy to make an error in judgement. “Their thinking is that they’re protecting the casing (in setting short periods for retreading), but, over the years, casing endurance has increased.”

It’s common practice, of course, for fleets to buy new steer tires, then retread them and move them to a drive or trailer position. Many of those fleets will then retread the casings a second time, and return them once again to a drive or trailer position.

“Some will retread the casing for as many times as they think they can get useful life out of it,” Jones observes. “Some will only retread the casing once, and they may be short-changing themselves there, too. But one of the reasons they’ve done this in the past is that when you get a casing that gets down to about 4/32nds tread depth, they become more susceptible to stone drilling.”


Unfortunately, few drivers are as knowledgeable about tires and casings as Jones is, and that’s where problems can arise.
Perception, as they say, is reality, and if a driver perceives that a tire is lacking traction, he or she is likely to make an issue of it.

“A lot of fleets develop their practices based on driver satisfaction,” Jones says. “The drivers, when they do their pre- and post-trip inspections, they see the tires wearing down, and they become concerned.

“That’s one of the main reasons tires are pulled early,” he explains. “The driver is saying, ‘This tire doesn’t have any traction; it broke loose, and it’s getting down to a point where I don’t think it’s safe.’”

Again, the legal standard for a roadworthy tire is 4/32nd-inch of tread on the steers and 2/32nd-inch of tread on the drives, but when the tread is that shallow, looks can be deceiving, and unsettling.

“When traditional tires start to wear down, a lot of the sipes will disappear,” Jones explains. “If there’s an open shoulder, the appearance of the open shoulder will disappear and it will appear to have a solid shoulder. The appearance of a loss of traction is there, but it’s not necessarily true that a visible groove means better traction.

“Now, in the case of wet traction, which is what most people have to deal with, the traction comes from the grooves in the tread and their ability to evacuate water,” Jones continues. “In the snow, the drivers perceive that the deeper the groove, the greater the snow traction they’ll have, but snow traction is a combination of things, not only the surface-to-void ratio but the tread pattern itself.”

That may not matter to an upset driver, however, and in Jones’ experience fleet management may not be willing to argue the point with the driver. “In fact,” he says, “in some fleets the drivers are unionized, then you’ve got an additional situation to deal with. If you refuse the driver he can take it to the shop steward, and then you’ve got a big hassle. So a lot of times it’s misunderstanding of how the tires work, and the management trying to appease the drivers.”


There may not be much you can do about drivers misunderstanding how a tire wears, but there’s no excuse for misunderstanding among your technicians. According to Jones, every fleet maintenance shop should have a tire management program, and that program should be written down, should be communicated to the technicians, and should be followed up on. “If you don’t communicate it across the board, and you never follow up to see that people are following it, then you’ll have problems,” he says.

That tire management program should tell your technicians at what tread depth they should be pulling tires for retreading. And if there is any question about whether that number is too high or two small, Jones has a suggestion: Test it.

“If they’re pulling at 8/32nds and they want to see what happens if they went down to 4/32nds, if they can control that they should run them down to that depth and then see if the amount of casing rejects increases or not,” he says. “If their rejected casings increase, they might want to move back up towards 8/32nds. That’s what I tell fleets; they should always be willing to test.”

What Jones doesn’t necessarily recommend is regrooving old tires, a practice he sometime sees in transit fleet maintenance garages.

“They’ll take the existing tread rubber, and cut additional grooves in it as it wears down,” he explains. “It’s not something we recommend for over-the-road fleets, because you run the risk of cutting the grooves too deep and allowing moisture to get into it, and you end up with the tire throwing the tread.”


Bill Sweatman, president and CEO of tread manufacturer Marangoni Tread North America, says that fleet maintenance managers may sometimes err on the side of maintaining proper balance between dual tires.

“There are a lot of things that cause tire wear,” he says, “and if (drive or trailer tires) are mismatched and some need to be pulled (for retreading) and some don’t, then I can see where maybe they’d pull them all, send them all in for retreading, where maybe three or four of them hadn’t reached that pull point.”

Sweatman points out that as tires wear down they wear at a slower rate, making those last few 32nds of an inch very valuable. New tires with a lot of tread tend to scrub more than worn tires, and so the first few 32nds will wear at a faster rate than those further down in the tread.

“By the time you get down to the last few 32nds, they’re wearing at many more miles per 32nd, because you just don’t have the tread blocks scrubbing; you don’t have any movement, and that’s really critical,” he says. “On the other hand, you get better fuel economy, because the less tread you have, the less resistance to rolling you have. But if you run them too long and they get down into the steel, then they’re not repairable or retreadable.”

Different tire brands wear at different rates, according to Sweatman, and within a particular brand you might have different compounds. “A guy may buy fuel economy tires which wear at a different rate than the tires that were on that truck before, that were higher mileage tires,” he says. “If he thinks he should get 15,000 or 20,000 miles of wear per 32nd, and 250,000 miles out of his drive treads, it might be a wrong assumption, because there are so many different variables and tires wear at different rates.

“You have to watch them, you have to have a visual inspection, you need to measure your tread depth and understand if you’re in compliance with your own program,” he says.

“Some guys find that balanced tires wear a lot better in their application than tires that aren’t balanced,” says Sweatman. “Matching, rotation, there are just so many things that you have to watch to establish these pull points. As long as you’re still getting the performance characteristics that you’re looking for. You don’t want to sacrifice traction for fuel economy by running tires down too far.”


Eugene Johnston, manager of business development for retreader Bandag, Incorporated, suggests that tire dealers may be better judges of when tires are ready to be retreaded.

“Most fleet managers think about their trucks in terms of PM schedules, and most of their PM work is focused around the engine, and engine PMs are generally handled by mileage,” he says. “How many miles do you have on the truck? Every 15,000 miles you might get an oil change, for example; they don’t have an indicator like tread depth on an engine that tells you when it’s time to get an oil change or it’s time to flush the radiator, so they’re used to using mileage and/or time periods. In fact, much of the software fleets use to schedule maintenance intervals is based on mileage or calendar time.

“If you have a tire dealer doing that work for you, they’re going to base it on tire-related criteria,” he says.

But for fleet maintenance managers who prefer to do their own tire work in-house, Johnston has this advice: “If he has the capabilities—and this does depend on the people and the systems he has available to him—he should be using tire inspection criteria from the TMC (Technology & Maintenance Council). They have Recommended Practices; they can go there to see what conditions would justify removing a tire from service because of damage or weather cracking or whatever other conditions there may be.

“But when it comes to tread depth and wear, ideally they would look at tread depth rather than mileage or months in service,” he says. “You want to make sure that the next time that truck comes in for maintenance, the tread is still well within the legal limit for tread depth.

“At the bare minimum, you want to make sure that you’re not going to be taken out of service by a DOT inspector or a CVSA guy for being too thin on the tread,” he says.


In the end, it’s up to you to decide the proper tread depth at which your technicians should be pulling tires for retreading.

Equally important, Johnston stresses, is deciding how many times you want to retread your casings: once? twice? three times? “My advice is to take all your tires that are in reasonable condition, send them to your retreader and let him decide which ones are retreadable,” he says.

If you “judge each tire on its own merits,” as Johnston says, you should never have to worry whether you’re retreading too late, or too soon.