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Stability Control and Torque Vectoring Systems - Invasion Of The E-Nannies

Are modern stability control and torque vectoring systems taking too much control away from the driver?

David Pratte
Dec 13, 2013
Scion fr s traction control button Photo 1/3   |   Does pressing the magic “Off” button really put you 100 percent in control of your car? If recent track testing experiences in the Scion FR-S and Ford Focus ST are any indication, then not necessarily.

I do a lot of new car testing at the racetrack, and the more at-the-limit testing I do, the more I’ve come to realize that “Off” rarely means 100 percent off when it comes to electronic stability control (ESC) systems. I completely understand why carmakers don’t see the need to offer a true ESC Off option for their non-sporting models, but it did come as a genuine surprise when I learned that even in the Scion FR-S, a machine designed to go sideways as much as in a straight line, electronic “brake force distribution” (where the computer can apply some rear brake to stabilize and straighten the car’s trajectory if it thinks you’re about to spin off into a ditch) is still active even when you disable both the traction control and stability control systems.

To be honest, I didn’t notice any computer intervention during my first few track tests in a number of different FR-S and BRZ press vehicles, but then I found myself competing in a Time Attack event in a friend’s lightly modified FR-S and noticed some really odd behavior through a particularly tricky hilltop ess-bend where the car got light while drifting sideways toward the corner exit. Clearly, the computers were watching and didn’t approve of this combination of yaw angle, throttle position, and speed, because it felt like power was being cut just as the car was straightening out and settling down. In hindsight, I now believe it was the so-called “brake force distribution” system slowing the car, rather than the engine, though perhaps it was both since there’s also apparently a “panic brake” system for even hairier situations that may cut power as well as apply some rear brake.

Shortly after that event, a friend with an FR-S asked me if I do the “pedal dance” before track testing or racing these cars. I had no idea what he was talking about, so he sent me a link on FT86club.com where the procedure was explained in detail (pull the e-brake three times and hold it up on the third pull, then press the brake pedal three times and hold the pedal down on the third pump, then repeat the e-brake procedure, then press the brake pedal two more times). If the engine is warmed up beforehand and you do the “pedal dance” correctly, you’ll see both of the yellow lights on the dash come on, indicating that the stability and traction control systems are off. But you’ve also disabled the hidden brake force distribution and panic braking features, too, so you should be 100 percent in control at this point. Or so the current line of thinking goes. Who knows what other e-nannies lurk deep within the complex computer systems of these cars.

Another new enthusiast-targeted vehicle, the ’13 Ford Focus ST, displayed some even quirkier behavior during a track test a few months ago. This car has received a lot of love from the automotive press and has generally been declared the new king of the hot hatches. And rightly so, given its impressive turbocharged 2L engine that makes a solid 252 hp and even more torque, though much of the praise has centered on its handling dynamics and willingness to rotate despite its front-wheel-drive powertrain.

I certainly found the ST to be a very willing participant in some tail-out shenanigans, the rear end of the car showing a remarkable ability to change trajectory based on how much throttle and steering angle is dialed in. This type of cornering ability is achieved partly by its base chassis and suspension tuning, but most of the magic seems to stem from its highly sophisticated torque vectoring system. Ford calls its front axle torque vectoring system an “electronic differential,” a term used to explain its primary function of limiting inside wheelspin while cornering and maximizing traction in the process. It does this by applying the inside front brake, rather than reducing torque output to that wheel like traditional torque vectoring systems do, and this does have the added effect of reducing understeer.

Scion fr s brake force distribution Photo 2/3   |   Few cars are as much fun to hoon around a racetrack as a Scion FR-S, but to shut off “brake force distribution,” you need to do the “pedal dance.”

If you’ve spent much time driving FWD cars around racetracks, then you’re no doubt familiar with trail braking, a fairly advanced driving technique in which you gradually trail off the brake pedal as you enter a corner. This technique helps transfer weight to the front tires and off the rear tires, adding grip where it’s needed and in the process reducing understeer or even inducing oversteer. The Focus ST actually does this for you with torque vectoring across the rear axle, where the system will apply some brake force to one or both of the rear calipers as a way of getting the rear end to follow the front. It’s a very clever and very subtle piece of computer-aided intervention, and it works extremely well, at least for a lap or two.

But as I discovered after putting a lot of heat into the ST’s brakes, to the point that they began to fade quite badly (after about three laps around my local test track), all the fancy torque vectoring maths in the world suddenly didn’t amount to much, since the brake system they depend on failed to deliver the required response. With cooked brakes, the ST just wasn’t rotating like it did on the first few laps. In fact, there was an increasing tendency for it to understeer. Plus, it suffered from a prolonged hesitation in power delivery as I came out of a medium-speed left-hander in four-wheel drift. Suddenly, the best handling FWD hot hatch I’ve ever tried was a front tire killer, and its lack of a mechanical limited-slip differential really started to loom large since the brakes were no longer up to the task of pulling double duty as both a torque vectoring tool and a momentum control device.

Simply put, there’s just no substitute for a mechanical limited-slip differential, a truth Mitsubishi has proven with its all-conquering Evolution models. This world-class gravel-chucker employs a torque vectoring system that actively splits torque based on inputs from accelerometers as well as steering angle, brake force, and throttle position sensors. But rather than using the brakes like the ST does, power is split front to rear and from left to right on the rear through an active clutch-type center differential. Plus, the Evo is equipped with a traditional gear-type front LSD, ensuring the kind of at-the-limit consistency and predictability needed during maximum attack rally stages or super lap sessions.

Ford is no stranger to World Rally Championship competition and knows all about the advantages of a mechanical LSD, so why the ST high-performance division chose to go with an open diff on an enthusiast FWD machine like the Focus ST is a bit of a mystery (cost-cutting is the most likely explanation). Don’t let this dissuade you from buying a Focus ST, though, since there’s already an easy fix on the market thanks to Quaife. The company just released a gear-type LSD that is reported to work seamlessly with the ST’s torque vectoring system. I’m curious enough about this upgrade that you’re likely to see a Focus ST Quaife LSD install and track test story in a future issue.

Ford focus front wheel drive track testing Photo 3/3   |   The new Ford Focus ST is as tail-happy an FWD car as we’ve ever track-tested, but because its torque vectoring system uses the front and rear brake system to reduce understeer and induce rotation, when the brakes start to fade, so too does its amazing handling balance.

My track testing experience in the ST, along with the electronic weirdness the FR-S exhibited in that one tricky hilltop corner, further verified (in my mind, at least) the need for a true “Off” button for the endless array of e-nannies even the most driver-focused cars seem to be equipped with these days. Without the ability to fully turn off these so-called driver aids, not only are we being denied the ability to fully control the vehicle we’re attached to, but we’re also being cheated of the opportunity to properly assess its chassis and handling balance and make adjustments to them using tried-and-true mechanical methods like changes to damper rates, spring rates, bar rates, differential lockup characteristics, and so on.

It also highlighted for me that there’s still an important role to be played by the performance aftermarket, since as good as the Scion FR-S and Ford Focus ST are in stock form (and really, they’re both spectacularly good right out of the box), there’s still room for improvement using good old-fashioned tuning techniques as well as some e-nanny interrupters like the “pedal dance.” So don’t let the imperfections and foibles of current electronic control systems discourage you from owning one of these new enthusiast machines. There’s a lot to like about the FR-S and Focus ST, and if I’ve learned anything during my decade or so in this business, it’s that the aftermarket will always come up with a way to make these cars faster, more enjoyable, and more driveable at the limit and around town.

By David Pratte
216 Articles

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