Roger Diez: Winter driving: Maintain situational awareness

As you’re probably aware, it’s winter here in Northern Nevada, and with winter comes snow and ice and treacherous driving conditions. So, once again I’m here with my winter driving tips, cautions, and advice.

Let’s begin with some basic physics. A 4,000-pound vehicle at 30 mph is a considerable amount of mass and inertia. This collection of steel, aluminum, glass, plastic, and organic material (you) is tenuously connected to the road by four small tire contact patches. 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 ability to respond to your commands.

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, and other factors, of just how much of these inputs the tires can transmit 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.

OK, let’s put theory into practice. Say your vehicle can stop from 30 mph in 100 feet on dry asphalt. On snow or ice, that distance is going to be double, triple, quadruple, or quite possibly infinite. Remember to slow down in slick conditions, and to increase your distance to the car in front of you. Drafting is definitely not recommended. Also remember the reference to vectors in the last paragraph. If you try to brake and turn at the same time on a slick surface, both your braking and turning performance will suffer. You will immediately experience what the racing driver calls “push”, and you will plow straight ahead with your wheels cranked to the right or left. Similarly, if you accelerate too hard while turning, you will be confronted with the condition racers call “loose.” You will notice this when the rear of your own car passes you.

Speaking of racing drivers, I have found driving on snow and ice is great training for driving a race car, which is why Scandinavian drivers excel at racing. Where a race car starts sliding around at 100, 150 mph, the same thing can happen on snow and ice at as little as 5 mph. When driving a race car, the trick is to keep the tires at the limit of adhesion (or very near it) at all times, with speed and cornering forces pushing the tires to that limit. On snow and ice, the limit of adhesion is reached at much lower speeds because the coefficient of friction of the road surface is approaching zero. You can experience the aforementioned “loose” and “push” conditions at very low speeds, giving you more time to react. It’s great training for the aspiring racing driver, but others might want to stay well below that limit of adhesion.

The main thing to remember is to use gentle inputs on all the controls. Brake early and progressively; turn slowly and smoothly, not jerking the steering wheel; brake early and progressively; and accelerate smoothly, feathering the throttle. You should also be more alert in slick conditions. Get “up on the wheel” as NASCAR champion and commentator Darrell Waltrip was fond of saying.

Also, maintain situational awareness of what’s around you at all times. Unfortunately, the level of concentration most people bring to their daily driving is just above comatose. In slippery conditions, that can lead to a trip to the body shop or, worse yet, the hospital. Don’t be that guy.