A Guide to … Vehicle Stability Control

A Guide to … Vehicle Stability Control

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Stability Control has been touted as the most important automotive safety device since the seatbelt.

Governments in North America, Europe and Australia have plans to make the technology compulsory on all new vehicles because studies have shown it can reduce the likelihood of single-vehicle crashes and prevent roll-overs.

It is designed to prevent cars from an unintended skid in a bend. In most cases the technology works without the driver knowing that he or she has had a brush with danger. In essence, Stability Control protects drivers from minor indiscretions, such as when suddenly finding themselves on wet or slippery pavement, or in an unexpectedly tight corner.

However, Stability Control does not (and nor does it promise to) over-rule the laws of physics. If you’re travelling way too fast for a corner or for the conditions, you may still run off the road. Stability Control is an extremely worthwhile technology, but it is important to note that some systems are more effective than others.

Car makers use different names to describe the technology; there are more than 20 acronyms across the industry. Stability Control was originally called ESP, for Electronic Stability Program, a deliberate pun on Extra Sensory Perception because the technology uses sensors to monitor driving conditions and driver behaviour.

Stability Control first appeared on a production car in 1995, on the luxury flagship sedan, the Mercedes-Benz S Class, although the technology was developed on its behalf by electronics company Bosch and appeared on other vehicles soon after. Today, the technology is most commonly called ESC, for Electronic Stability Control, although in recent times it has simply been called Stability Control.

To understand in the simplest terms how Stability Control works we need a brief history lesson. The roots of Stability Control started with anti-lock brakes, or ABS (Anti-lock Braking System). In an emergency stop, ABS systems automatically clamp and release the brakes up to 20 times per second while the driver is applying full brake pedal pressure.

Once again, this often occurs without the driver necessarily knowing that the technology is at work.

The benefit is straightforward: ABS prevents the brakes (and therefore the tyres) from ‘locking’ and gives the driver the ability to steer around an obstacle. It is especially helpful in wet weather braking.

For ABS to work, cars had to be fitted with extra sensors to monitor the speed of each of the four wheels. Engineers eventually found a new use for these sensors and created what became known as Traction Control. This is where the speed of the driven wheels is constantly compared to the speed of the other two wheels.

When one pair of wheels is travelling faster than the other, the system intervenes and applies the brakes and/or automatically cuts engine power until the vehicle’s speed is reduced, and all four wheels are again travelling at the same speed.

For example, in a rear-drive car, if the rear wheels started to spin at a faster rate than the front wheels (which indicate the real speed the vehicle is travelling), then traction control would be activated in milliseconds. The same thing happens if the front wheels spin faster than the rear wheels in a front-drive car (when equipped with Traction Control).

Traction Control is typically most useful at detecting unintended wheelspin when accelerating from a standstill, such as when trying to drive up a steep wet slope, or when accelerating aggressively out of a corner. ABS and Traction Control then became the building blocks for Stability Control. Once these sensors were in place, it was simply a matter of adding a steering wheel sensor, a throttle sensor and a sensor which detects how much pitch or lean the car is experiencing in a corner.

Engineers also found a way to apply the brakes to each individual wheel, to help bring the car under control in the safest and most effective manner possible.

Modern versions of the technology is so good, a race driver in a car without Stability Control would unlikely out-manoeuvre the same car with a well-calibrated Stability Control system, because the system can do what the driver can’t: brake individual wheels. All this requires an incredible amount of computer power.

Stability Control systems constantly monitor and process hundreds of times per second the following information:

  • Vehicle speed (wheel sensors)
  • Steering input (steering wheel sensor)
  • Acceleration (throttle sensor)
  • Braking (brake sensor)
  • Pitch or ‘lean’ of the car (yaw sensor)
Thanks to complex algorithms and thousands of hours of tests and calibrations, engineers develop Stability Control systems to suit each vehicle’s characteristics, such as weight, mass, engine power and tyre grip.

Some cars are programmed for conservative drivers and so the Stability Control system is prone to intervene at the earliest hint of a skid. Some cars, particularly performance vehicles, often have a slightly higher threshold because they have a higher level of grip. Despite the varying levels of effectiveness, Stability Control is still proven to be a life-saver.

Overseas studies of crashes involving cars equipped with Stability Control claim there have been reductions of between 35 and 50 per cent in serious injury single-vehicle collisions.

This is one of the reasons that the European New Car Assessment Program (ENCAP) and the Australian New Car Assessment Program (ANCAP) recently decided that only vehicles with Stability Control could be awarded a Five Star safety rating.

As with its European affiliate, ANCAP is an independent body that crash tests vehicles to higher standards than those imposed by Governments. It is intended to be a consumer guide to car safety and most top-selling models are tested.

ANCAP is supported by Australian and New Zealand automobile clubs, the State government road and transport authorities of NSW, Victoria, South Australia, Queensland, Tasmania, Western Australia, the New Zealand Government, the Victorian TAC, NRMA Insurance and the FIA Foundation.

When checking the safety rating of a new vehicle on the ANCAP website be sure to check if a vehicle has Stability Control (some older Five Star ratings didn’t require the technology).

Most importantly, though, when you’re looking to buy your next car, check with the vehicle manufacturer that the exact model you are buying has Stability Control.

If you're in the market to rent a car in Australia or New Zealand DriveNow provides the most comprehensive breakdown of features for Car Rental fleets to ensure you have all the information required when selecting a vehicle.

Today Stability Control is rapildy becoming a standard across mid-range as well as luxury cars, but on more affordable vehicles the technology may be standard on some variants and optional or not available on others.

About NRMA Insurance NRMA Insurance is a provider of insurance products, including car insurance and home insurance in NSW, ACT & TAS.

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