Light Duty: Staying in Control

Whether it’s a glass company delivering an expensive new display or a snowplow keeping your grocery store parking lot clear, maintaining a stable load on the road is the name of the game.

And while today’s ride stability systems may not be as complex as those serving the big rigs, they are every bit as important at keeping accidents and costs down and keeping things moving smoothly and safely.

Here are a few of the more popular ride stability systems on the market that can improve suspension and handling, reduce wear of parts and help prevent accidents.


Available on the Mercedes Sprinter for years in Europe for recreational and utility purposes, Firestone’s Ride-Rites have found their way to many hard-working light duty fleets here in the states to help manage loads.

“Most of the trucks today are outfitted for commercial usage,” says Firestone Ride-Rite product manager Paul Gibson. “They end up having a load on them all the time.”

To Gibson, ride stability is simple: Maintain vehicle height and position in the face of heavy, non-centered loads.

”If it’s a glass truck or plumbers’ truck or a van, most for years have had a right-hand sliding door,” Gibson says. “So people put their racks and things on the other side, so depending on the industry it was being used in, all of a sudden you had 500, 600 or 1,000 pounds of pipe fittings on one side, and maybe a 250-pound driver, and they can’t figure out why the vehicle kind of leans.”

The same can be said for the thousands of snowplows trudging across North America these days. But variable or off-set loads are no problem, Gibson says, because you can keep the air springs separate and inflate or deflate to keep proper vehicle balance.

“You take a 600 to 700-pound plow and stick on a three-foot lever arm and now the front axle is seeing close to 1,000 or more pounds,” Gibson says. “So we’ve developed kits for most of those vehicles so they can support the load of the plow, so when the plow is on, the truck still maintains ride and handling characteristics that were intended by the manufacturer, and when the plow is taken off, you can reduce the pressure and still keep the front end in alignment.”

Gibson said one reason pick-up trucks ride much better than in the past is because they are now so commonly used purely as passenger vehicles.

“They just kept softening them up so they would be acceptable,” he says. “That’s where air really comes into play, because you can inflate or deflate, depending on what the load is, and keep the vehicle square and maintain the ride and handling characteristics the (OEM) intended.”

Gibson says the bottom line is that stability systems ensure that vehicles handle and perform the way the manufacturer intended, even when loaded past capacity.

”No one tells you what that vehicle is going to look like or handle at maximum (load-carrying capacity) without any additional support,” Gibson says. “So suddenly the back’s down, the front’s up, braking is not as effective, steering is affected. (You want) the headlights pointing in the right direction, and not hunting ‘coons. It makes it a lot safer and handle better and corner better.”

The more a fleet uses its vehicles, the more these systems can provide a benefit, Gibson says.

”A guy who’s got a load in there, day after day after day—those steel springs start to lose their supporting ability as time goes on,” Gibson says. “It may have started out life two or three inches high on the rear end, but after 75,000 miles on it, it’s level or something below that, especially if a utility body or power tailgate is installed on the back end.”

Short of making sure that the installation is done correctly and the system has full pressure, Gibson says there’s really very little for technicians do, as far as troubleshooting and maintenance.

“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.”

It works by recognizing wheel skid—sensors detect the difference between the steering wheel angle and the direction the driver is actually turning by “reading” the steering wheel position 25 times a second and factoring in the amount of sideways force in play, vehicle speed and the vehicle’s response to steering wheel input.

Integrated with ABS and traction control, the system uses the brakes to enhance control of the vehicle’s direction and reduces engine torque while applying precise amounts of pressure to individual brakes to help keep the vehicle on track. These brake and engine interventions help realign the vehicle’s path with that being steered by the driver.

GM technical fellow Mike Rizzo says that, much like the other systems, StabiliTrak lays dormant until it is needed.

“It’s waiting for the vehicle to get to an evasive handling situation, then it’s providing assistance through intelligently applying brake forces independent of the driver’s foot being on the brake, to stabilize the vehicle,” Rizzo says. “(It’s) not trying to do something to the vehicle until the control algorithm determines that a wheel is skidding or the vehicle is skidding due to an evasive handling maneuver.

“Then, the system is coming on and providing assistance to regain control of the vehicle or a wheel skidding. In normal driving, you won’t even know it’s there,” he says.

Typically, StabiliTrak includes a yaw rate sensor, lateral accelerometer, steering wheel angle sensor, master cylinder pressure sensor, wheel speed sensors, and interfaces with the engine control module to control engine torque.

Systems with all-wheel drive may have a longitudinal accelerometer due to the fact you can spin all four wheels at the same time, Rizzo says, and that sensor is necessary to detect those kinds of situations.

Rizzo says the system is essentially designed to be maintenance-free, though he says issues with malfunctioning sensors can crop up on occasion. In that case, your technicians can use software to detect problems and can make repairs by reading the malfunctioning code stored in the control module.

Other than that, Rizzo says the only real maintenance is determining now long to go before changing your brake fluid. When this is the case, some care is needed.

“It’s crucial for the system, since it’s applying brakes, that when you change the brake fluid or you open up the brake system, that you use the diagnostic Tech II procedure for getting the air out of the brakes lines,” Rizzo says. “Sometimes you have that modulator sitting there, and if you open up the brake system and any air works its way back into the air modulator, doing a base brake bleed might not get rid of that air. We have a routine in our Tech II that exercises the control modules, all the valves and stuff, and pushes fluid through that, so if there’s any air in that module, it will exit and come through the bleeder screw.”

Also, Rizzo says the StabiliTrak sensors should not be moved, because they are finely tuned to respond from fixed locations.

“Relocating them, for whatever reason, would be an area of concern,” Rizzo says. “The algorithm is tuned based on where the sensors are in the van as we sell it. You definitely want to keep those sensors where they’re located and make sure they’re oriented the according to what the service manual specifies.”

According to GM, the next generation of StabiliTrak will assess the vehicle response to driver steering, acceleration and braking inputs and help steer the vehicle as necessary to maintain vehicle stability.


Many vans and light duty trucks are built for work purposes these days, with safety features already standard. Whether spec’ed out from your favorite OEM or added on afterwards, these ride stability systems are relatively easy for your technicians to install and maintain.

More importantly, they can help avoid accidents and keep your vehicles in better shape—saving on parts, repairs and (most importantly these days) fuel, providing an added layer of security for both your fleet and your bottom line.