Everyone hates a jerk. They’re unnatural. We’re programmed to avoid them. I’m not talking about obnoxious boors at a party; I’m referring to motions where the rate of change of acceleration (jerk is its official scientific name) is high. Jerky drivers are the ones whose every input to the accelerator, brake, or steering wheel causes your neck to strain and would certainly slosh a martini. Expert drivers manipulate these controls smoothly enough to preserve the liquid in such a glass, and cars that make smooth driving easier are perceived by drivers and passengers to be more comfortable and confidence-inspiring.
Smooth inputs also help race car drivers go faster—just ask the patron saint of smooth driving, the wee Scot Jackie Stewart. He was a maestro of mass management, always shifting his car’s weight smoothly to the axle or corner where it could do the most good. The zoom-zoom team at Mazda has a new trick that helps automate this, called G-Vectoring Control.
Before explaining anything about how GVC works, I was asked to experience it in a Mazda6 test car outfitted with a GVC on-off switch. (Production versions will have no such switch.) I was asked to set the cruise control at 30 mph (48 km/h) and follow an oval course following a line of cones marking the inside of the course as closely as possible. After a couple laps I noticed that I was sawing at the wheel a lot more when the system was off.
Then we learned that the power steering system is not changed at all. GVC primarily involves some powertrain software code that cuts an infinitesimal amount of engine torque when the steering wheel is being turned then restores it when the wheel unwinds. This torque reduction, which typically happens within 30-40 milliseconds of a steering input (as small as one-tenth of a degree!) generates a longitudinal g force of between 0.01 and 0.05 g. That’s far below the threshold that a normal human can perceive, but it’s enough to load the outside front tire with between 2 and 10 pounds of additional force, increasing its cornering force and effectiveness accordingly. Unwind the wheel, and the resumption of full torque transfers weight to the rear, stabilizing the completion of the maneuver.
What this really does is shorten the time it takes for your brain to perceive that your steering request has been implemented. This prevents you from dialing in more steering lock because the first amount didn’t seem to do the trick, only to later have to unwind some lock when the tires start to “bite” and the car overreacts. It is most difficult to discern at normal driving speeds on dry pavement, but its benefits become more noticeable in slipperier conditions or when driving faster on dry pavement.
This is an idea Mazda has been working on for some time, but the processing power to implement the torque reduction quickly enough didn’t exist until the current generation of far more powerful Skyactive powertrain computers arrived. The engine-control unit can implement the requested torque reduction in multiple ways, but under most circumstances it retards the timing slightly.
Some new connections were provided between the chassis CAN bus and the powertrain controller, but virtually nothing in the bill of materials changes, as this is primarily just a software programming feature. Therefore there is little or no added cost attributable to the feature, which will be rolled out as standard equipment. It should also be noted that although this is primarily a chassis dynamics improvement achieved solely via the powertrain, the system will always be developed and optimized to work with the suspension’s bushings, spring and damping rates, steering rack and ratio, etc. That’s why the Mazda6 will get it first—that car’s existing setup works perfectly with GVC, whereas most others will require very minor tuning changes. Mazda envisions proliferating GVC throughout its entire range, as it works equally well with front-, rear-, or all-wheel drive. Cars with a lot of anti-lift geometry baked into the rear suspension present greater tuning challenges, so the MX-5 may take longer to develop.
So to recap: This is NOT “torque-vectoring” or “active yaw control.” In those systems the drivetrain creates a yaw moment on the car by overdriving the wheel(s) on the outside of a turn and/or under-driving the inside wheel(s). This is the engine computer implementing a Bob Bondurant/Skip Barber high-performance driving tip to let your tires deliver faster, crisper turn-in. You should also know that this is an extremely shy technology. If you’re looking for it, you’ll never find it. You’ll just get out of your Mazda thinking, geez, that car feels like an extension of my body. Unless, of course, you drive like a jerk.
Pictured below is the 2016 Mazda6