Reader question: Is electronic stability control for emergency purposes or sporting support?
We’ve been asked whether systems like electronic stability control (ESC) there to add “sportiness” or for emergency purposes?
Hi Practical Motoring,
I have a slightly random question for you. Just read a review of SUVs where they talk about electronic stability control activating in on the corners. I was under the impression that the ESC was there for emergency purposes rather than for sporting support. Am I right?
D.
Hi there and thanks for your email,
A very interesting question. Let’s start with a definition.
Electronic Stability Control (ESC) is a system to keep a vehicle going in the direction the driver wants it to go, which is usually on the road and rubber side down. ESC can be thought of as anti-skid control, and it primarily corrects understeer and oversteer. Understeer is when you run wide around a corner, needing to wind on more and more steering lock to no or little effect. Oversteer is when the back of the car wants to overtake the front.
ESC uses wheel speed sensors to determine how fast each wheel is travelling, then a lot more sensors such as roll, yaw, throttle position, steering wheel angle and more to figure out whether the car is going where the driver wants. The on-board computers then apply the brakes to one or more of the four wheels to correct the vehicle’s direction.
For example, if you’re understeering it may apply the brakes on the inside wheels and release those on the outside slightly, thereby tightening the vehicle’s turning radius. In an oversteer situation it will brake one or more of the outside wheels. Generally, if the steering wheel is turned the car will try and respond to that direction, so here’s some advice – look where you want to go, and keep the steering wheel turned where you want to go.
In extreme cases stability control can also cut the throttle, despite the accelerator being floored. It also uses traction control to help it do the job where appropriate, for example to prevent fishtailing in powerful rear-wheel-drive cars.
So to answer your question – yes ESC is there only for emergency purposes. If it does activate on public roads then one of the following must be true:
- you’re driving very badly, for example jumping off the brakes then steering, accelerating out of a corner while winding on steering lock
- something is wrong with the car, for example the tyre pressures are too low, the steering alignment is badly out or you have a major suspension fault such as a blown damper
- you’re driving too fast for public roads
or a combination of all three. Either way, something needs to be fixed.
Now in the case of modern vehicles, including SUVs, the ESC is well-calibrated enough that it won’t kick in unless it really needs do. In fact, with modern vehicles you can get to the point where all four tyres are screaming and the car is slightly sliding yet the ESC still hasn’t kicked in…provided you’re smooth enough with the controls. So I don’t understand why anyone would get to the point where it activates on public bitumen roads. However, sometimes stability control is confused with traction control – we’ve got an explanation of the difference here.
Some advanced vehicles have a variant of stability control that activates well before a car begins to slide out of control and is designed to help the car corner. This might be called corner brake control (CBC), or torque vectoring (often misnamed, but anyway). Those systems are to improve cornering ability, or you could say sporting intent. They are very subtle and you don’t notice them activating, unlike stability control which is often quite noticeable, as it should be; there’s usually a warning light, sometimes an audible warning and you can feel the brakes being applied to the specific wheels.
So yes, you’re right. ESC is a safety aid, not for sporting support. There is also no need to switch it off on public roads and doing so is a safety risk. Nobody is that good a driver that ESC can’t help save them and you won’t go any faster with it off.
I used my manual ND MX5 recently at a hill climb. 8 runs no traction control and 6 runs with traction control. I managed a quickest of 45.6 (traction control off) and a 45.7 (on) ( the time keepers were on using basic stop watches). My observation was that the traction control was superb at individual corner braking as I explored different apexes in the corners but would cut the power (quickly but also re-apply the power quickly as well) at the slightest sign of traction loss accelerating out of a corner. In my opinion the traction control was superb at assisting in braking into corners but not so great at controlling wheel slip on acceleration. It was confidence inspiring in aggressive cornering but at the cost of power loss at the slightest sign of wheel slip in acceleration.
Hi Andrew. Thanks for the post, good information. The ND is a very new car so its stability control (not just traction control) is well calibrated. With sports cars at higher speed events if you are sliding enough for the electronics to activate then you’re slow anyway. Hillclimbs are a different matter as they are slower speed and often have tight corners, and this is where you might need to slide the car a bit for a quick time, more than stability control would let you. Regardless, stability control is a great safety net…if people left it on then there would be fewer crashes at motorsport events. But with motorsports it’s mostly your car, your choice…on public roads that does not apply.