Light Duty: Maintaining All-Wheel and Four-Wheel Drive

Whether your fleet is built for rocky off-roads or slick winter highways, AWDs and 4WDs both need TLC.


Not every light-duty fleet vehicle needs all-wheel or four-wheel drive, but depending on what conditions your drivers are moving through, they could be an absolute must.

While 4WD systems generally call for the driver to manually switch between two-wheel mode for street and highway driving and four-wheel mode in low-traction conditions like ice, mud or gravel, AWD systems are sometimes called “full-time 4WD.”

The difference is AWD can be used on dry pavement because it uses a center differential, which allows each tire to rotate at a different speed, eliminating driveline binding, wheel hop and other related issues associated with the use of 4WD on dry pavement. AWD systems are more sophisticated, and the computer will transfer grip to the tires with the best traction, diverting power where necessary

Dave Williams, fleet operations area manager for Verizon Communications, is responsible for maintaining around 100 four-wheel drive vehicles that go through some of the most snowy, mountainous terrain in the country—upstate New York. He said while the fleet has no AWD vehicles, the four-wheelers are a necessity—typically GM or Chrysler pick-up trucks and SUVs.

“Most of the (trucks) that service the cell towers have four-wheel drive because they’re typically on a higher elevation, and these four-wheel drives help them get up the hills, which are roads but are not typically paved,” he says.

When trying to figure out whether to equip your vehicles with AWD or 4WD, Williams says the first, and most important step, is justification.

“If most fleets are like we are, if you ask them they all need four-wheel drives, so you really have to look at the job requirement—does (the job) really need it?” he says. “Typically we replace like for like—if the job requirements are the same, then we give them the same kind of vehicle back—but when they’re asking for it initially, we look to qualify it to what they really need it for.”

FLEET NEEDS

Picking the optimal truck for the job is a crucial first step, says Chrysler, LLC product engineer Frank Thompson.

“Down South, maybe they just pick the two-wheel drive because there isn’t the need for four wheel, but in the Midwest, especially, there are days where you would not have been able to get through with a two-wheel drive, but you don’t necessarily want the mileage hit of a full-time four-wheel drive truck.”

Toyota spokesperson Bill Kwong says cost-wise, since it’s cheaper for fleets to own a part-time four-wheel drive system versus a full-time system, four-wheel drives should only be used if needed.

“Maintenance-wise, that’s one less differential to service, and you don’t have to service the transfer case,” he says. “You’re not dragging around all those extra components. Even when you’re in two-wheel drive mode with a part-time four-wheel drive, you’re still dragging all that weight—any little edge you can get.”

Tim Cavanaugh, marketing product manager for GM’s fleet and commercial operations, says fleet officials have varied opinions on choosing 4WD or AWD for their needs.

“People that are picking the four-wheel drive are usually picking it because of the payload and what they’re hauling, and also your four-wheel drive, because it’s in trucks or utilities, would give you a lot more clearance up off the road,” he says. “I know in cases where we have long linemen that have to go out and check lines where they have to drive up to a major power pole—they might have to drive up the side of the mountain, and literally the rocks that are there, because it’s not generally a road that gets you there, it’s driving off-road.

“They need to be a lot higher up, they need on/off road tires so they have puncture-resistance sidewalls, and it’s got to be a really robust suspension to keep them above the rocks so they don’t poke a hole in the gas tank or oil pan, to make it to the top of the hill,” he says. “Your all-wheel drive would be good to some extent, until it comes to the bigger rocks, where it doesn’t have the clearance off the bottom of the vehicle.”

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