Reaction to skids in an ESP-equipped car

[triquet]

Indeed. I think that as the coefficient of friction approaches zero all the bets are off and the most sophisticated of algorithms are not going to help.

Well, that much is obvious!

Not altogether. When the icy weather sets in there are a surprising number of 4WD people who think otherwise.

[Tosh]

This video adds an interesting slant to the effectiveness of ESP on sheet ice at 70mph. (02:00 onwards)

[Astraist]

Do keep in mind that sheet ice is less slippery (particularly compared to what TripleS Dave described) and the snow layer acts as a brake along the sidewall of a slipping tyre. The car is also fitted with tyres suitable to ice driving.

Not to mention that it is in the hands of Tiff Needel. Put another driver in his stead and he or she might make it a lot harder to ESP to cope with the situation. Relative to the situation he really rocks the car as little as needed.

[waremark]

The Tiff demo says it was uploaded in 2007. He thinks all cars should be fitted with ESP. Now they are, and now doubt the systems are further improved since then.

To what extent will the amazing potential safety benefits be offset by drivers driving faster in slippery conditions?

What does the ADUK collective think of Tiff's steering at 5.00?

[Astraist]

I am personally happy with the safety benefits of ESP, as I find that drivers' confidence to brave the car's limits with it are not proportional to it's abilites. Statistics seem to back this up, unlike with the initial application of ABS on road cars.

ESP has improved over time and instead of relying only on ABS sensors for detecting a skid, now relying on several other inputs like comparing yaw and steering angle. Generally, ESP can tuck a car in if it's driven within about 30% past the critical speed of the car for the bend.

As for Tiff's steering. Could you steer as quickly like that (lock to lock) in any other way?

[Astraist]

A lot of the statistics around ABS came about not because people relied on the system to stop them but on the fact that ABS allowed you to steer. In the US the edges of the road are less, shall we say, kind to vehicles leaving the carriageway. When you didn't have ABS you slide in a serence straight line into the impact rather than barrel rolling in the countryside...

Indeed. The freedom to steer can therefore be seen as a dual-edged knife. It could help avoid an obstacle (or being hit from behind) but it can also send you off of the road.

Strictly speaking, most ESP systems are designed to cut in before then at the end of the linear range of the tyres. Some of the more 'hero' systems allow a little more leeway.

"Strickly" as far as the physics of tyre behavior is concerned. From a driver's point of view, entering a bend at a speed of some 30% excess of the critical speed usually means going off of the road, with or without ESP.

You could try letting go of the steering wheel and letting the tyres do it for you...

If the car is oversteering (as it is after the second weight transfer in the video) it can help, but I have found that in extreme situations (like this) turning the steering on it's own isn't quick enough. The driver need to help it get some momentum.

[TripleS]

A lot of the statistics around ABS came about not because people relied on the system to stop them but on the fact that ABS allowed you to steer. In the US the edges of the road are less, shall we say, kind to vehicles leaving the carriageway. When you didn't have ABS you slide in a serence straight line into the impact rather than barrel rolling in the countryside...

Indeed. The freedom to steer can therefore be seen as a dual-edged knife. It could help avoid an obstacle (or being hit from behind) but it can also send you off of the road.

Strictly speaking, most ESP systems are designed to cut in before then at the end of the linear range of the tyres. Some of the more 'hero' systems allow a little more leeway.

"Strickly" as far as the physics of tyre behavior is concerned. From a driver's point of view, entering a bend at a speed of some 30% excess of the critical speed usually means going off of the road, with or without ESP.

You could try letting go of the steering wheel and letting the tyres do it for you...

If the car is oversteering (as it is after the second weight transfer in the video) it can help, but I have found that in extreme situations (like this) turning the steering on it's own isn't quick enough. The driver need to help it get some momentum.

Doesn't that depend on the strength/speed of the castor action on the particular car?

This might (once again) sound like a ridiculous attitude to take, but if I were to be acquiring another car, and ESP and ABS were optional extras, I wouldn't bother with them. My current car does not have ESP, though it does have ABS, but the latter has never felt to be of benefit, and in winter conditions I have felt to be a hindrance to optimum stopping. I would prefer to avoid these systems, not only due to cost at purchase time, but certainly on account of their potential for generating large bills should they fail later in the life of the car.

[fungus]

At one of my IAM groups monthly talks, the guest speaker, who was a superintendant in the Dorset Police traffic devision, implied that the Northern Constabulary have stopped using skid pans after three BMWs were written off when the drivers reacted in the conventional manner, confusing the cars computor system, and that in cars fitted with ESP the driver should let the car sort itself out.

[triquet]

How does ESP actually handle things after breakaway and tyres are actually going sideways? I need a bit of explanation on this one.

[TripleS]

How does ESP actually handle things after breakaway and tyres are actually going sideways? I need a bit of explanation on this one.

Me too. If the tyres are truly travelling sideways, I guess it's all in the lap of the gods and it's time to brace yourself for the impact.

[Astraist]

It senses the difference in wheel speed and the differences between steering and yaw angle and than it (usually) cuts off power and applies mild braking to one of the tyres to allow the car to yaw around it.

If the car oversteers it retardates the inside front tyre to stop the rotation of the car, whereas in understeer it brakes the rear-inside wheel. In this case the problem is that this tyre is the least loaded one, and it's often swung in the air by dint of anti-roll bars.

In heavier vehicles (like lorries) it might brake trailer tyre too, in order to prevent it swinging or ploughing forward (resulting in a jackknife) and/or brake the outside wheels to prevent roll-over.

[Ancient]

The first time I drove a car with 'automatic' skid control was back in 2000, in California. It was a hired 4x4 and we were in Death Valley: Not insured for off-road, but some of the tourist attractions are accessed over dirt tracks.

The car had automatic selection/deselection of 4-wheel drive, anti-skid control (whatever it was called) and I drove it for a total of two weeks. At one point we were going down a wash-boarded dirt slope, with a sharp right bend at the bottom (complete with hard earth/rock bank ahead). The car started to slip slightly sideways and in kicked the 4-wheel drive and presumably its skid control; at the same time I steered into the slide, at which the light telling me I had 4-wheel drive went off. Presumably the car was satisfied that it was heading in the desired direction (it wasn't)! I managed to straighten out and it happened again, every time I corrected for the skid, the car cut back into 2-wheel drive mode and started sliding again. In the end I just let it slide and miraculously we made it to the flat road around the bend . For someone then used to driving an MGA (or occasional hire cars on good roads) it was ... disconcerting!

[triquet]

Thanks Dave. I feared as much.

[jont]

How does ESP actually handle things after breakaway and tyres are actually going sideways? I need a bit of explanation on this one.

I used to be very cynical about the value of ESP until I had my car on an airfield last year and had the opportunity to practice emergency lane changes at motorway speeds. Quite frankly it was staggering just how hamfisted you could be and it would still keep everything under control. On the other hand, don't talk to me about overly nannying traction control

[Tosh]

How does ESP actually handle things after breakaway and tyres are actually going sideways? I need a bit of explanation on this one.

I used to be very cynical about the value of ESP until I had my car on an airfield last year and had the opportunity to practice emergency lane changes at motorway speeds. Quite frankly it was staggering just how hamfisted you could be and it would still keep everything under control. On the other hand, don't talk to me about overly nannying traction control

Yep! These stability systems turns the track day idiot into a driving God just like this chap...