“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.