Light Duty: Staying in Control

Fleets are gaining more safety options with ride stability systems.

“Essentially there is no friction or wear on the air spring if they’re properly installed, because they’re not rubbing the road like a tire is,” Gibson says. “We build millions of air springs for the big over-the road-trucks, and (fleets) look at a million miles on a pair of air springs as not unusual.”


Charlotte, NC-based Roadmaster Active Suspension has a ride stability system designed for any vehicle with a rear leaf spring suspension with up to one ton carrying capacity. Owner/CEO Clive Schewitz says it makes vehicles with a higher center of gravity considerably more stable and less prone to rollover. The key is keeping the natural arch in the springs, he says.

“When a vehicle is not loaded the leaf springs are in the optimum working position, which is an arch,” Schewitz says. “The greater the load, the less arch you get in your springs, and it starts flattening out and magically, you start losing your suspension, or the full effect of your suspension.”

Once you lose suspension, the vehicle is more difficult to control.

“What you’ll find is when a vehicle is heavily loaded, you’ve virtually lost your suspension,” Schewitz says. “The back of the vehicle sits down, the front of the vehicle goes up, and you lose your contact with the front wheels, as they should be sitting firmly on the actual road surface.

“So when you go around the corner, because it’s a rear-wheel drive vehicle, it’s actually trying to push the vehicle in a straight line, and when you try to turn your wheel, it doesn’t respond nearly as well as it would if the vehicle was level.”

The system can also keep wear and tear to the rest of the vehicle at a minimum, particularly the tires, which can save fleets some serious cash.

“A lot of people say, ‘How can a suspension product save fuel?’ but if you drive behind any vehicle that is loaded to what the manufacturer would recommend, or in some cases maybe more, you’ll find that any road surface, no matter how smooth you think it may be, has got undulations and bumps,” Schewitz says. “As the vehicle moves along, you’ll find that because your leaf spring now is virtually completely flat, you’ve lost the arch in the spring, and the weight of the load is now transferred right through the suspension right through to the tires, which are continually bulging and flexing.

“That happens continually and the footprint increases, (so) you’ve got the additional drag and larger footprint—that tire is continually bulging, and as the tire bulges, not only are you getting additional heat buildup in the tire, the roll resistance becomes greater, and the vehicle has to burn more fuel. And there are a lot of vehicles on the road that are grossly overloaded.”

Keeping an even load will also help save tire wear when cornering.

“The reason why tire wear savings are so high is not only are you eliminating that terrific flexing of the tire, but when you’re going around a corner, all four wheels are (level) to the ground, and you don’t get any tire skidding,” Schewitz says. “So it’s not wearing down the tread.”

The system is available as an aftermarket add-on, though Schewitz says the company is working with an OEM to possibly sell the systems on new vehicles. He says fleets can get a return on their investment in a matter of months, on tire wear and fuel savings alone.

“We have to get the message out to as many fleets as possible,” Schewitz says. “You don’t have to have traction bars or torsion bars, or beef up your leaf springs.”

Installation of the system should take no more than an hour for technicians unfamiliar with it; Schewitz says well-practiced technicians can get it done in just over a half-hour.

“It’s a very simple installation, and once it’s installed, no maintenance is required.,” Schewitz says. “We’ve got vehicles running around 11-and-a-half years old and they’ve never had to touch the Roadmaster.”


General Motors’ ESC system is the StabiliTrak Control System, which will be standard on all retail GM cars and trucks in the U.S. and Canada by the end of 2010. Nearly 50 of GM’s 2007 models feature the system, including such fleet stalwarts as the Sierra, Silverado, Suburban, Tahoe, Yukon, and Savannah and Express passenger vans.”

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