Can electronic stability control outperform me?

Factual Questions
1

A skilled driver, operating in predictable traction conditions (e.g. on a track), can outperform ABS by staying just on this side of the traction limit (whereas ABS repeatedly crosses back and forth between static/sliding friction). However, ABS works well for the rest of us, who operate on a huge array of public roads with highly variable traction conditions and far less (if any) practice with threshold braking.

So what’s the deal with electronic stability control? It recovers from skid conditions by using 4-wheel independent braking and throttle control. If I’m in a car without ESC, my tools for skid recovery are steering, throttle and one single brake pedal for all four wheels.

So assuming I’m familiar with recovering from a skid, are there driving situations where ESC is able to use its toolbag to recover from a skid, but I, with my toolbag, can’t?

2

You will NEVER be able to outperform the computer. The reason they include these things is for exactly that reason. It’s well documented during tests that when you turn the ESC off on cars that have it the cars become wildly unpredictable.

ESC is not intended to rescue you once you’ve exceeded the limits of the car. If you’re there it’s far too late for you or any stability control to save you. It will bring you back from certain uncontrolled situations which you almost certainly cannot recover from yourself. Here’s an example.

Also, studies have shown that it is quite effective. You cannot hope to match that.

3

You are kind of begging the question here, are you not? If you are an ideal driver, then of course you drive ideally and could of course outperform a system that by its very nature is less ideal. But, you are not an ideal driver. You get distracted, you overreact, you stress out, you get fatigued, and all sorts of other things. The ESC system is always going to perform at its just less than perfect level, but your performance will vary quite a bit depending on conditions.

4

I’m not sure if you are conflating anti-lock braking systems and electronic stability control, but it simply isn’t true that “a skilled driver…can outperform ABS,” and I don’t know of a single automotive authority who would presently claim this. ABS detects the presence of a skid (e.g. the wheel is not turning but the car is in motion) and pumps the brakes faster than any driver possibly could (~100 ms) to regain control. If the driver is able to maintain traction and no forward skidding, ABS will never be activated. Some trick cars have ABS disabled in order to better instigate forward skidding, but it is entirely possible to perform a controlled lateral skid (or as the kids call it these days, “drift”) with ABS functioning. ABS is only concerned with maintaining a rolling friction condition regardless of any other factors.

Electronic stability control is a little different. It is basically an expert system which senses when the vehicle is at or beyond a threshold and applies an algorithm to reverse the condition. ECS isn’t designed to maximize performance or allow the driver to take the vehicle to the edge of its stability envelope, and so it will limit what a professional driver can do with a car, hence why most cars allow for ECS to be disabled by a switch. However, unless you’ve had professional training and a couple hundred hours of track time under inclement conditions, you are probably not going to be able to significantly improve upon what a good system can do, and such a system will help prevent inattentive or incautious drivers from getting too far beyond their aptitude. That being said, there are a lot of vehicles that have very mediocre or overly active ECS which are scarcely better than no system at all.

Stranger

5

The car has precise information about wheel RPM, engine RPM, transmission state, and speed you can only guess at. Like it or not, some things a computer will respond more quickly and accurately than any human being. I would be willing to bet ESC will outperform 90%+ of all drivers.

I use my ESC without a second thought and I have been through EVOC (emergency vehicle operations course) where they dump a couple tons of crushed ice in a parking lot and make us learn to control skids through it.

6

I suspect that manufacturers assume that the driver will always leave stability control on, and don’t spend as much effort as they used to on the dynamics of the unassisted vehicle. It also lets them cut costs - for example, most BMWs no longer have a limited-slip differential, instead using the ABS system to “fake it”.

I have one car which is full of nannies (the aforementioned BMW) and one with none whatsoever (an Ariel Atom). They’re very different cars (obviously), but each fun in their own ways. It was an interesting experience driving nothing but the Atom every day for over a month and then getting back into the BMW land barge…

I agree. But there’s a big difference between competing on the track, where everybody is giving it 100% concentration, and normal driving on public roads.

7

I beleive that ESC can do things that a driver with only one brake pedal cannot do (e.g., apply braking to one wheel but not another). If so, even an ideal driver might not be able to outperform it, simply because it has tools that are not in the driver’s toolkit.

8

I suspect that they engineer the cars to be unstable to get more performance out of them and then put the nannies on so that the average driver doesn’t turn themselves into road pizza. Think about it: if you engineer a car to be stable at 9/10ths you’ve created a grandpamobile. People who buy performance cars want to be able to hang it out a little bit without getting killed. They’ve done the same with aircraft for decades.

I doubt it’s about costs, either. People who buy things like an M5 aren’t going to be dissuaded by price. Like you, for instance. Can you credibly say you’re price-conscious when you drive both a BMW and an expensive toy like an Ariel Atom?

9

It is true that ESC has a tool not available to the driver (4-wheel-indie braking). But the driver has a tool not available to ESC (steering inputs). So while it may be possible for ESC to respond to a skid condition more rapidly than a driver, the two are using different tools to effect corrective action.

And so the question is perhaps better restated thus:

Given that the driver and the ESC are using different tools for skid recovery, are there situations where one can effect recovery and the other cannot?

10

Back in late 2009, I was helping my cousin deal with her parents’ estate after her father died. She lives in L.A. and would fly back to Georgia for 7-10 days every month or so and I spent a lot of that time with her.

I live in a semi-rural area about 50 miles away from her parents’ home. The majority of the drive is rural two-lane roads. Some nights I wouldn’t head home until 11pm or later.

One Saturday night, it was around 1am when I finally started out for home. About 10-12 miles of the trip is a very curvy, winding two-lane highway (55mph drops to 35mph for some of the curves). I was driving my 2007 Ford Explorer (with Roll-Stability-Control, Anti-lock brakes, Traction Control and other safety features). As I exited one of those curves, I met a large SUV (a Tahoe or Suburban, I think) and it was at least 4-5 feet across the center line and in my lane. There was less than a few hundred feet between us and I was going at least 50mph and so were they.

Instinctively, I veered off the edge of the road into the grass/dirt and avoided a head-on collision. I also stood on the brake pedal and let the ABS do its thing. I knew that I needed to reduce my speed and ease back onto the road, but then I realized I was closing in on a utility pole! I freaked and tried to steer back onto the road too quickly. When the left front wheel touched the pavement, I thought I was going to die!

I have over-steered and the vehicle was heading into a spin. But SUVs have a high center gravity and rather than spin, they tend to roll over. I felt the left rear corner of my SUV start to lift off the pavement when both front wheels (steered hard to the left) were back on the road. I knew that I was about start rolling and I prayed that roof was strong enough to hold up. I had slowed to at least 35mph or so by this point, so with the dozen or so airbags, maybe I’d survive….

Just as I sensed that the car was going to roll, lights started flashing, I heard tires squealing and all sorts of clicks, pops and other unusual sounds. The ‘Roll Stability Control’ had kicked in and used the ABS, Traction Control and Yaw Control to selectively modify braking force and engine power on each wheel to keep (or return) all four wheels to the ground).

At the time, Ford featured an exclusive ‘Vehicle Roll Motion Sensor’ in the form of a gyroscopic sensor that monitored vehicle roll motion approximately 150 times per second. According to the folks I spoke with at Ford and at the NHTSA afterward that was probably the only reason the system reacted in just the nick of time to prevent a rollover!

I came to a complete stop in a fully upright position on all four wheels (although three tires were flat and two wheels were bent all to hell). There was suspension damage and some body damage to left side of the vehicle as well as some undercarriage damage. My insurance company ended up paying $6800 in repairs and I actually hated driving it after that…it never felt right again.
I kept it for three more years and it had over $7000 of freakish problems/failures that were very likely a result from the ‘incident’ but came out of my pocket. Finally, on 11/30/2012, I got rid of it and bought a new Mazda CX-9. I despised the Explorer by that point, but it did kinda save my ass once upon a time.

11

By controlled braking of the wheels independently, the ECS also has steering (or in the case of a situation in which the driver overcorrects fora skid such as that storied by Beelzebuba, counter-steering) which is more responsive and has higher fidelity of control than the front steering input, especially in an incipient slip/skid condition. The reason that professional drivers deactivate the ECS isn’t because they can perform a controlled recovery of the vehicle better in normal driving but so that they can put the car into a dynamically stable state (such as a controlled slide) that the ECS would ordinarily compensate for because it cannot interpret the driver’s intent.

A modern, well designed ECS is so much faster than a person can possibly respond (and has so many better quantified inputs from slip rate indicators, accelometers, throttle feedback, et cetera) that even an expert driver with hundreds of driving hours in adverse conditions can barely even compare, and as systems become even more mature they will be incomparably better than the best human driver.

Stranger

12

So 'splain how that works. If I’m in a non-ESC car in a left-hand turn (maybe it’s the second half of the infamous right-then-left swerve maneuver that is used for ESC demonstrations), and the back end starts to break loose and step out to the right, I will crank the steering wheel to the right, minimizing the resistance of the front end to movement in the direction of the skid. The rear tires, which are in a skid condition, are resisting movement in the direction of the skid, causing drag; the front end wins the race, and the rear end falls in line behind the front end, terminating the skid.

Now suppose I do the same maneuver in a car with ESC, and I neglect to provide any corrective steering inputs when the skid starts. What will ESC do with the brakes and throttle to effect skid recovery?

13

I also feel the need to share the importance of Traction Control, which is part of most Stability Control systems, or sometimes featured on cars without Stability Control. On my new vehicle, a 2012 Mazda CX-9 (which is classified as a Large CUV or Crossover Utililty Vehicle rather than an SUV because it is built using unibody construction, rather than body-on-frame like trucks and true SUVs) would be very difficult to drive in rain without Traction Control.

The CX-9 was designed to be the best handling and most driver-oriented vehicle of its type. It has a 273hp 3.7L V6, which is pretty average for the class, but the ratios for the lower gears (especially 1st gear) of the 6-speed automatic are geared for improved acceleration. In the Front-Wheel-Drive versions of the CX-9, it’s very difficult to start from a stop on a wet road surface without slight wheel spin which triggers the Traction Control to kick in. On the upside, it’s a 7-seater CUV/SUV that will do 0-60mph in 7.3 seconds and will kick down multiple gears for passing when needed.

14

[Hijack] Here is a somewhat related case in which I know that a human cannot outperform a computer. Can two helicopters list a long beam between them? Not if they are under human control. If one gets even a bit higher than the other, it begins to carry less weight and rises even higher, while the other one begins to carry more weight and sinks a bit. Positive feedback. But if the copters are under computer control, the computers can adjust fast enough, adding bit of power to the lower one and powering slightly down the upper one and can overcome the positive feedback.

15

Goose the front wheels, selectively brake the rear tires, which affects the same result only significantly faster than a driver could turn the front tires. In fact, asserting stability by selectively actuating or braking the tires is superior to turning the front wheels because it maintains the same essential condition of the tires, whereas turning the wheels introduces potentially new conditions, e.g. a tendancy to rotate into the turn.

It is important to understand that under high speed conditions (versus “parking lot” speeds of under 25 mph), the direction in which the wheels are turned is less of an effect on vehicle direction than the rates at which the tires are turning. The car will always steer into the slower front wheel regardless of how the wheel is turned (within reason; obviously a tire turned more than 15 degrees would be significantly skidding which would complicate the dynamics), and it would be entirely possible to design a car that could drive at highway speeds with no controlled articulation of the front tires at all, as long as the suspension were sufficiently compliant, although its turning radius at residential speeds and road conditions would be attrocious.

As with modern aircraft systems, “fly by wire” control via sophisticated microcontrollers allows for maneuvers that would simply be impossible for a human being to perform unaided. In the next twenty years or so, mechanical linkages to vehicle steering will probably disappear to be replaced by pure electromechanical systems which taken input from the steering controls (and synthesize feedback) but prevent the vehicle from entering into an uncontrolled condition.

Stranger

16

How about launch control? Does it perform better than humans?

17

In straight line stopping on packed snow, I can outperform ABS by keeping just above the threshold of where it kicks in. But just barely (I measured).

A friend took a winter driving school a few years ago and said, and was told, the same thing.

18

There are also rare instances in deep snow where you can outperform ABS by just slamming on your brakes, letting them lock, and letting the snow mound up in front of the tires. I don’t have ABS on my car, but I’d opt for it in a heartbeat as the instances where I might possibly be able to outperform it are rare.

19

Have you driven a car with launch control? The primary function of launch control is to precisely balance the throttle and feather the clutch so as to minimize wheel spin and get the quickest possible takeoff. The rate and amount of feedback that a controller gets is far more than the driver in such a circumstance. Only the most experienced drivers with a specific vehicle could hope to even get within a couple tenths of the 0-60 mph time of an automatic launch control system.

It is unclear what you mean by “outperfrom”. If you mean minimizing the stopping distance, than it is true that solid braking is superior to ABS (which releases the brakes on a 50-100 ms interval to prevent loss of traction) in that regard. But if you can brake without causing slippage, ABS isn’t needed to begin with. ABS is not intended to minimize braking distance; it is intended to ensure that the car maintains traction, and can therefore perform other evasive maneuvers while braking which would cause a non-ABS car to go into a skid.

Stranger

20

By ‘outperform’ I mean stop in a little less distance. But that’s under ideal conditions when I am deliberately testing it. Not a panic stop per se. I would never want to get rid of it. And understand that it’s more about maintaining control.

I also have stability control on my Pathfinder. One thing I don’t like is that if it detects ANY slippage during acceleration, it dials back the power for way too long. Now I understand why it does this, but when you drive on snow and ice 6 months out of the year, having a little wheel slip is not at all unusual.

For instance, when I have to power up my driveway in deep snow, I’ll turn ESC off. Just a little slip, and I lose all forward momentum.