Roger Diez: Winter + physics = Time for safe-driving tips

Merry Christmas to all the readers of this space! I hope that Santa was good to you and that you found race tickets, certificates for track time, or maybe that new cam you needed for the race engine in your stocking.

In the world of professional racing, several folks got early presents this year. A.J. Allmendinger was rewarded a full-time ride with Kaulig Racing in the Xfinity series after his stellar part-time performance in 2020. Sergio Perez, out of a ride following the Formula 1 season finale in Dubai, has landed a 2021 job with Red Bull, teaming with Max Verstappen. Unfortunately, 2020 Red Bull driver Alex Albon got a lump of coal in the form of a demotion to reserve driver. And Helio Castroneves got a spot in the Penske Hall of Fame after a lengthy career in IndyCar and IMSA with the team. That went along with his first season championship for the Penske Acura DPi team in the Weathertech series.


Winter officially arrived last Monday, and according to the weatherman we’re due for a taste of it tomorrow — up to a foot of snow in the mountains, and maybe a bit down here in the valley as well. So, keeping in mind that very few of us possess the car control abilities of the aforementioned Allmendinger, Castroneves, and Perez, it’s time for my annual winter driving seminar.


First, a few basic physics facts. A 4,000-pound vehicle at 30 mph provides a serious amount of mass and inertia. This collection of steel, aluminum, glass, and plastic is tenuously connected to the road by four small tire contact patches, and any change in speed or direction must be transmitted through those patches. Anything that detracts from the tires’ adhesion to the road (snow or ice for instance) tends to limit their response to your control inputs.

Tires can transmit only three things from the vehicle to the road: acceleration, deceleration, and change of direction. There is a limit (determined by road surface, temperature, tire tread, and other factors) of just how much input the tires can withstand before they lose grip. And when the tire receives multiple inputs, such as braking and steering simultaneously, it creates a vector of the two forces, but reduces the absolute limit of either force.


Thanking Professor Einstein for the above theory, let’s now put it into practice. Say your vehicle can stop from 30 mph in 100 feet on dry asphalt pavement. On snow or ice, that distance is going to be doubled, tripled, or quadrupled. Worst case, it may even approach infinity. So, slow down in slick conditions, and increase your distance to the car in front of you. Otherwise, unintended NASCAR-style bump drafting may occur.

And remember the reference to vectors in our physics lesson? If you try to brake and turn at the same time on a slick surface, you will immediately experience what the race driver calls “push.” That means you will plow straight ahead with your wheels cranked to the right or left. Similarly, if you accelerate too hard while turning, the racers’ term “loose” will become immediately apparent. You will notice this when the rear of your car passes you.


So, remember to use gentle inputs on all the controls. Brake early and progressively; turn the steering wheel slowly and smoothly, and accelerate gently, feathering the throttle. You also need to stay more alert in slick conditions. Get “up on the wheel” as Darrell Waltrip use to say. Keep your level of concentration and situational awareness above the level of most drivers — semi-comatose. In slippery conditions, inattention can lead to a trip to the body shop or worse yet, to the hospital. Don’t be that guy!


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