Auto Tech: Roll stability control

May 6, 2009

Now the computer has all the information and can start to control the vehicle to make it safer. Roll stability is very different at high speeds, compared with low speeds or even off-road speeds. During a high-speed corner, the body might not seem to lean very much, but because of the vehicle speed, it could be enough to cause the vehicle to roll. When the computer program determines there is the possibility of a roll situation, it operates the individual wheel brakes selectively to minimize the roll. Braking slows the vehicle so there is less potential energy to cause a roll. By braking only the front outside wheel, the system makes the vehicle turn away from the corner. Because the vehicle is now travelling in a straighter path, there is less chance of it rolling.

During slow speed operation, such as when off-roading, the sensors are still sending the same information, but now the computer knows the vehicle is travelling slowly. There is less potential energy in the body and less possibility of the vehicle rolling, even though it could be turning the same arc as it was during high speed operation. The system doesn’t have to intervene as quickly, or perhaps not at all, to prevent a roll.

Even though roll stability control will help minimize the possibility of a vehicle rollover, the electronics can’t overcome all the laws of physics. If you are off-roading and the body angle is too high, the vehicle can still roll over sideways. If the shock absorbers are worn or the springs are broken, the body can roll too far, and the roll control system may not be able to keep the body under control.

Finally, tire pressures are still critical to proper vehicle handling. If they are too low, the sidewalls flex, allowing the body to roll more. As good as the roll control systems are, there are some things for which electronics can’t compensate, so check those tire pressures regularly.

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