Slippery Conditions

Ray Johansen - Instructor ADSI

As a follow-up to one of my previous articles, Traction Control, located on our website I wanted to follow up with another article, timely for the season upon us. For drivers in colder climates, driving in snow and slippery conditions can be a combination of apprehension and stress. For drivers who are used to driving in dry conditions, the addition of wet and slick snow can add time and stress to a typically easy commute to the office. In this article, we are going to present how a driver can prepare themselves and their vehicle to conquer the winter months.

To review the previous Traction Control article, let us define what grip or traction is. A vehicle can only do three things, accelerate, brake and steer – “Go, Stop and Turn”, in ADSI parlance. The level of grip or the adhesion of a vehicle’s tires to the road surface dictates how well it can perform those three main functions or more importantly a combination of those three main functions, go and turn or stop and turn. On snow-covered roads, a vehicle may only have 10 to 20 percent traction, as compared to that of a dry road surface. With this reduced level of adhesion a vehicle has a very limited ability to maneuver, whether accelerating, braking or steering.

We are asked quite frequently “how does a driver better their odds driving in the snow”?

One quick answer to that question would be to adjust speed appropriately to the weather conditions as well as leaving enough space and preparing for potential hazards far ahead. Thus giving yourself more time and distance to stop as well as turn your vehicle. However, a more technical answer would be to examine the only part of a vehicle touching the road, the tires. To better take advantage of the amount of traction, or lack thereof, is selecting a set of appropriate tires. Off the showroom floor you will find the most popular design are All Season Tires. All Season Tires are made to do just what they say, work ok in all seasons but do not excel in any one category. Top of the line All Season tires are fine for climates that are always changing such as Southern New England, where you may have a bad snow storm, but the roads are clean a short time after the storm. Where in a northern climate where snow is constant, parts of Canada or Northern New England, snow tires would be a smart choice. In rainy climates the choice would be to purchase an Aqua Tread or tire designed for the rain. It is very important to understand that All Season tires provide a compromise between wet, dry and snow-covered roads. This compromise leads to longer overall tread life, but the tires are not optimized for reduced traction conditions. One of the best investments a driver can do for their vehicle is to purchase a set of specific tires appropriate to the conditions typical to their driving environment. Notice the word “set”. Cars will perform much better in any condition with a matched set of tires on all wheels. Having mismatched tires between front and rear will provide very unpredictable handling behavior.

Tire technology has grown by leaps and bounds over the past few years. Much like performance tires, winter tires are offered in different compounds, tread patterns and sizes for differing conditions. What may be appropriate for a driver who drives in an environment with deep, loose snow may not be appropriate for a driver who has to travel on ice or packed snow-covered roads. If you have questions on what may be the appropriate winter tire for conditions you encounter, there are a number of resources to review prior to purchase and installation. In addition to being one of the largest on-line retailers of tires and related products, Tire Rack (www.tirerack.com) offers reviews of their tires, easy to navigate product selection for tire type and products that will fit your vehicle.

Secondary to tire selection is the driveline layout of a vehicle. Never before has a consumer enjoyed a choice of different driveline configurations. Rear-Wheel Drive (RWD), Front-Wheel Drive (FWD) and All-Wheel/Four-Wheel Drive (AWD/4WD) are available in many manufacturers’ product offerings. Many consumers are making buying decisions based on driveline layout but neglecting the most important selection mentioned in the previous paragraph, tires. No matter the number or location of the drive wheels, if proper tires are not used in inclement weather, the driver will still have a difficult time accelerating, braking and turning. Obviously, with more drive wheels in an AWD configuration, an AWD vehicle will have an easier time accelerating, but when it comes to braking or even turning, the vehicle is going to be limited by the tire’s grip on the road surface.

Taking into consideration and vehicle driveline configuration is the driver’s experience level on slippery surfaces that snow and ice offer. In technical terms, the coefficient of friction is much less in snow and ice-covered roads than that of a dry surface. This means the level of grip afforded to the driver, or more appropriately, the tires; is much less. So, take a hypothetical off-ramp that can be driven safely at 40mph during the summer (dry conditions), may only be negotiated at 15mph before losing grip and going into a slide during a snowstorm. If we review the effects of weight transfer and what the different driver inputs do to the balance of the vehicle when accelerating, braking and turning; we can see that when driving in slippery conditions it is very important to maintain smooth inputs as not to upset the balance of the vehicle. If we take that dry off-ramp above safely at 40mph, we may have plenty of reserve to make throttle, brake or steering adjustments without losing grip and sli ding. If we increase the speed to a hypothetical 58mph and approach the handling limits of the vehicle, it becomes much more important to execute these adjustments smoothly as not to upset the balance of the vehicle and introduce a slide. Now, this same off-ramp is snow covered and we set a limit of 15mph as the limit of a given vehicle’s speed before losing grip. It is equally important to use smooth control adjustments as to maintain the vehicle’s balance and not to introduce a slide. In snow, losing grip will happen at much lower speeds and a driver must be comfortable with their vehicle to make these smooth inputs and also react if and when the tires lose grip and start sliding.

Traction Control devices can help a driver maintain control of their vehicle when the amount of grip is much less. It is important to know that Traction Control cannot defy the laws of physics so it is up to the driver to maintain a safe speed for conditions and realize loss of grip will happen at a much lower speed in snow verse a dry road surface.

Beyond understanding vehicle dynamics, the appropriate tires for the season and the driver aids provided by Traction Control devices; is the importance of driver skill level and experience. Nothing boosts the confidence of the driver than the knowledge and ability of driving a car at or near its limits in a controlled environment. Knowing why and how a vehicle loses traction and recovering from it are skills than can be used during any season. “Perfect practice makes perfect”