Electronic stability control is a generic name for a suite of active safety systems that aim to prevent loss of vehicle control, including reducing rollover risk. They work by selectively braking certain wheels and controlling engine output in order to mitigate driver error or slick road conditions.
Stability control is scheduled to become mandatory safety equipment on all vehicles by the 2012 model year, and while it certainly improves safety, it could also create problems for those who modify their pickups — particularly with upgrades like lift kits and suspension modifications.
Stability control is an antilock-braking-based safety system. On trucks, when they’re driven too hard through a corner, the system’s yaw sensors can recognize that the truck is likely to tip over. At that point, it checks inputs like steering-wheel direction, individual wheel speed sensors and what the driver is doing with the brakes and throttle to assess the driver’s intentions. If the driver’s interpreted intentions don’t fall within the systems acceptable operating parameters, it intervenes.
The system could help bring a swerving truck under control by cutting throttle and individually braking wheels, which would scrub off speed and whip the front end back in line, averting disaster. If this happens, a small icon usually flashes in the instrument panel, or a warning tone may sound, and the driver will notice a brief moment of hesitation while driving through the corner. Should the yaw detector see more-than-acceptable tilt, it will interpret that as an unsuccessful intervention. Airbags could even deploy beyond the point of recovery but before the vehicle has rolled completely, to protect occupants.
As America’s most customized vehicles, pickup trucks are often fitted with specialized aftermarket equipment. However, when an owner alters a vehicle’s wheels, tires, suspension, steering or anything that affects the center of gravity, the stability system could be compromised. This could theoretically include putting a roof rack with a spare tire on top, adding larger tires or an off-road suspension, or even changing to a different-size steering wheel.
Adding complexity: pickup truck stability control systems require special calibration settings that can exceed that of cars and crossovers because most trucks are rear-wheel drive and ESC response has to account for when a truck is hauling a load over those wheels in the cargo box and when it’s empty.
So far, nobody really knows exactly which alterations can be tolerated without compromising a stability system, but it’s clear the arrival of these systems will be a game-changing event for both owners and the aftermarket.
To get a sense of what would happen if modifications were indiscriminately made to a new pickup with stability control, we asked GM’s full-size truck vehicle line director Mike Tulumello.
“Systems integrated to compliance [with mandatory stability control] could be harder to monkey with,“ Tulumello said.
He explained that the electronic systems are so interwoven, it’s hard not to affect some aspect of stability control when you change the handling charateristics of the truck by adding or replacing driveline or suspension hardware.
“Everything has to talk,” Tulumello said. “It’s all integrated. They’re not independent systems.”
Customizing a pickup truck could be risky, he said, “depending on how you do it. More and more, as you alter center of gravity, you’ll get yaw sensors that predict rollover and you’ll get false airbag deployments, things like that.”
Nick Cappa, spokesman for Chrysler, agreed that modifications could be problematic.
“Engineers design, test and optimize performance on factory tires and suspension,” he said. “Modifications, tampering with safety devices and the installation of some aftermarket parts can create unforeseen issues with stability and safety systems.”
The widespread use of stability control technology has prompted manufacturers of suspensions, wheels and tires to begin to study stability systems and what can be done to allow owners to continue to confidently install specialty equipment.
Legally, should an accident occur, the aftermarket parts manufacturer and installer could be targeted, whether the accident was caused by the alterations or not. Once the safety equipment becomes government-mandated, altering a vehicle’s dynamics might even be considered tampering — a federal offense. The worst-case concern is that aftermarket modifications for pickup trucks could be legislated out of existence.
The Specialty Equipment Market Association is already well aware of the issue. John Waraniak, SEMA’s vice-president of OEM relations in Detroit, is leading a team that’s been working with computerized simulations that OEMs use to predict stability in vehicles they design. The simulations can make predictions about what happens when specific changes are made.
“I can tell you that we have been working on this for the last two years,” Waraniak said, adding that he is not ready to roll out specific information on what may or may not constitute a problem. Waraniak did say that SEMA is planning seminars on active and passive safety systems for SEMA members attending the show next November.
Some manufacturers have already begun stability testing on their own.
Explorer Pro Comp, a manufacturer of wheels, tires and suspension systems, based in Compton, Calif., recently announced it had completed a round of stability control compliance testing, successfully passing what’s known as FMVS Test 126, as described by the National Highway Traffic Safety Administration.
So far as we know, Pro Comp is the first suspension manufacturer to report significant progress in this area. Its test vehicle was a 2008 Chevrolet Silverado equipped with a six-inch lift, 35-inch A/T tires and 18-inch alloy wheels. For each test, the vehicle performs maneuvers at various steering-wheel angles. Because the test involves the possibility of rollover, a robotic steering-wheel controller is used. While driving at 50 mph, the robotic steering wheel, when activated, rotates the steering wheel up to 300 degrees to the left and 300 degrees to the right in less than half a second.
The Silverado was instrumented with a multi-axis inertia-sensing system to measure roll, pitch and yaw. It also included ultrasonic distance-measuring sensors to measure ride height and calculate vehicle-roll angle; a radar speed sensor to measure vehicle speed; and a data acquisition system to record the test data.
According to the Explorer Pro Comp announcement, the test results demonstrated that this combination of wheel, tire and suspension system didn’t alter vehicle dynamics to a degree that the stability system would be significantly degraded.
“The results are not blanket results,” said Mark Mathews, marketing manager at Explorer Pro Comp. “This is just a first step, but it demonstrates our commitment to offer a high-quality product and respond to the changing demands of the market. This is the future; it’s what it’s going to take in order to be successful in this business.”
While Pro Comp’s testing showed that a Chevy pickup truck with a well-engineered, moderately tall lift can comply with government standards, each truck chassis is different. There are also differences in stability systems themselves from manufacturer to manufacturer, so much more testing will be needed. Mathews said the company would be doing more testing in the future using different platforms.
“The complexity of the systems and how they are engineered varies a bit between Ford, Chevy and so on,” Mathews said.
The question will be, how much added time, complexity and money will this testing add to the development of new suspension components for trucks? Have we approached the point where giant or moderate-sized lift kits will no longer be feasible for either consumers’ or manufacturers’ wallets? If that’s the case, the number of customization options available to truck owners will have shrunk as government-mandated safety regulations have grown.