Ford Engineer Tom Salmon
Ford Engineer Tom Salmon. Click image to enlarge

Review and photos by Justin Pritchard

Originally published March, 2013

I failed calculus.

That’s why Ford Engineer Tom Salmon took me to a whiteboard to draw a diagram explaining what’s called the ‘Bike Model’ by vehicle dynamics experts. The Bike Model is a highly calculus- and physics-based bunch of brackets and lines and symbols and equations next to a simple overhead diagram of a bicycle riding around in a circle.

Salmon is an energetic middle-aged fella’ who gushes happily about traction control and AWD technology using terms like ‘split mu’, ‘yaw rate’ and ‘y-accel’. Or that Bike Model – which illustrates how a vehicle’s front and rear wheels follow each other around a circle in perfect situations. If nothing is wrong, the front and rear wheels follow the same path, and the complicated-looking mathematical formula is happy.

In real life, and especially on snow and ice, wheels don’t always follow the same path. This upsets the math gods and un-balances the Bike Model equation. Oversteer, and the rear wheel goes around the circle faster than the front. Understeer, and the front wheel plows out of the circle, dragging the rear one with it. In either of these cases, the equation behind the Bike Model is all out of whack, and the vehicle in question, and its occupants, are in trouble.

That unsettling of the equation in a newer Ford model (and may other brands, for that matter) instantly sets off a concert of reactions from various systems and modules that set off trying to balance the equation – thereby bringing the front and rear wheels back in line with one another via intervention through the electronic stability control (ESC) system. If the model has AWD, power delivery to the wheels can even be recalibrated to pitch in and help.

Ford AWD and Stability ControlFord AWD and Stability ControlFord AWD and Stability Control
Ford AWD and Stability Control. Click image to enlarge

At the wheel of a Ford Explorer Sport Ecoboost with the traction controls turned down, you can feel it while skidding intentionally, hard on the throttle, around an icy skid pad. Only a moderate drift is allowed. Exceed a few degrees of slip, and you can feel the brakes pulsing and AWD system moving power about to try and keep the skid within preset limits. With the traction controls on fully, it behaves similarly – though with much tighter tolerances for slides.

Last time I saw calculus, it made me toss a high-school textbook across my room, stab a mechanical click pencil into my wall, consider harming myself, and cry loudly into a pillow for the better part of an hour. At my teacher’s, Mr. Fievoli’s, advice, I dropped the course a week later.

Fast forward a decade and a bit, and while watching Salmon and his team drift Fords at alarming speeds around a snow-covered track, I realized Mister Fievoli was right: calculus IS fun. Oh, and it makes vehicles that are safer, more confident and better handling.

Salmon even told me that Ford pays someone, with actual money, to drive a winter-tire equipped Shelby GT500 around a similar test track, to ensure it’ll work in the snow. You know, for those owners that’ll set off in a blizzard with a rear-drive super Stang packing more horses than a truckload of Whoppers.

But drifting and sliding around in the snow is juvenile business that doesn’t fall into the realm of concern for most folks about to shell out hard-earned cash on a new family ride. Drifting is fun, it looks pretty in photographs and makes for sometimes-entertaining YouTube videos. But snow drifting is, largely, a loss of control – and it’s mostly confidence that new car shoppers are after.

Traction. Grip. The sense that their ride has their back if they have a ‘whoopsie’ that’d otherwise jam them a metre and a half into a snowbank.

Whether used for tackling cottage trails in summer, to enhance performance on dry pavement or to dispense quickly with snowstorm conditions, AWD is becoming more and more popular all over the place. It’s a major purchase decision for folks in many Canadian markets, like the East Coast and Great Lakes. Ford says AWD sales are even on the rise in Miami. Ahh, marketing.

Advancements in the technology and mechanical bits behind many of Ford’s AWD and dynamics systems are helping sales, too. Like other carmakers, Ford’s AWD hardware is now lighter, smarter, more effective and more fuel efficient than ever. It’s also even more undetectable in action, and backed by new advanced controls and software programming that can balance that Bike Model equation to regain control faster than ever—or even prevent it from going out of whack in the first place.

Ford AWD and Stability Control
Ford AWD and Stability Control
Ford AWD and Stability Control. Click image to enlarge

Example? Torque vectoring. On a whiteboard, a vector is a line with an arrow on one end and a dot at the other. It’s used to show where something that’s moving wants to go. In vehicular applications on numerous Ford models, that ‘vector’ comes into play when the inside drive wheel in a cornering situation is braked slightly. Decelerating the inside drive wheel automatically accelerates the corresponding outer wheel, helping ‘push’ the car into the corner.

Effectively, Torque Vectoring uses a precisely calculated touch of one-wheel braking to help point the car’s vector into the corner, rather than out of it. Maintaining throttle application through an icy corner in a front-drive Fusion, the nose did a far better job of staying pointed where I asked it to. This car was noticeably faster around a snowy road course with all of the stability aids turned on.

That’s partly because torque vectoring is a way to keep the car going where it’s pointed without tripping the ESC system into intervention. And, on your AWD-equipped Ford, that torque vectoring works on both inside wheels in a corner, not just the front ones. This all works pre-emptively to keep the Bike Model equation happy.

Mind you, not all traction-related issues occur when driving around some portion of a circle—and Salmon’s team has off-the-line traction nailed down with some preemptive thinking, too.

Say you’re in an AWD-equipped Fusion, Escape or Explorer. When you come to a stop, a clutch in an assembly called a ‘Traction Module’ mounted to the rear axle receives an electronic signal to clamp down, mechanically tying the front and rear wheels to one another.

Ford AWD and Stability ControlFord AWD and Stability ControlFord AWD and Stability Control
Ford AWD and Stability Control. Click image to enlarge

So I took an Escape 4WD and parked it with the front wheels on ice and rear wheels on pavement. Then, I stood on the gas. The launch was fuss-free. No drama. No lurching. No shockwave sent through the driveline as the rear wheels are engaged while the front ones are spinning fast. It’s all a significant advancement over what some folks might call a ‘slip-and-grip’ AWD system.

There’s no differential involved here, and thus, no preset front-to-rear torque split. Instead, the traction module takes orders from the vehicle’s main computer brain, which considers dozens of sensor inputs and then works the rear clutch with a specific force at a specific time. This controls, very precisely, how much power is transmitted to the back wheels.

So whether it’s the Bike Model equation in a corner, or more fuss-free off-the-line grip on snow and ice, the effect on the vehicle is virtually imperceptible grip enhancement in any situation.

Related Articles:
Feature: Winter Tires vs. All-Season Tires
Northern Exposure: Best Winter Highway Cars
Comparison Test: AWD vs FWD Family Sedans on Ice
Auto Tech: Ford Driver Assist Technology

Manufacturer’s Website:
Ford Canada

Photo Gallery:
Ford’s AWD and Stability Control

If you’re paying attention, you’ll feel a bit of this. The nose, for instance, snudges tight to the inside of the corner when torque vectoring kicks in, and there’s a ‘tug’ and muted ‘thuck-thuck-thuck’ sound as brakes are pulsed away to help please the Bike Model and math gods when the ESC kicks in.

If you’re cruising along focusing on the road and not the vehicle, you’ll just be happy that the car goes obediently where it was pointed every time.

For decades, cars have gotten around corners and off the line in winter just fine. But, with these latest advances (coupled with your good driving and a set of winter tires), automakers like Ford are using calculus to meet the strong demand for added winter-driving confidence amongst the growing masses considering AWD in their next ride.

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