Winter driving is all about traction, so increasing available traction and making the most of what you have is key. Loss of traction under acceleration leads to wheelspin, under braking can lead to wheel-lock and hard cornering can lead to sideways sliding. While automatic stability controls in modern vehicles can limit these outcomes to a large extent but they are reactive, they step in when trouble has already started, because of this there is no substitute for driving with safe, precautionary technique.

Quick Tips for Winter Driving

For those of you that don’t have the time or patience to read the whole article here are some quick tips for winter driving.

  • Keep speed low
  • Be aware of changing conditions
  • Top up washer fluid and antifreeze
  • Never brake in a corner
  • Be prepared for understeer and oversteer, and know how to correct them
  • Be prepared to use ABS or avoidance braking techniques
  • Increase the distance between you and the cars around you
  • Slow much more than usual for corners and any other hazards
  • If you have to climb a slippery hill, first look for an alternate route, if not ensure the top is clear before starting the ascent

Winter Tires

winter-tire-construction
Winter Tire Construction

Depending on where you live and the conditions you may experience on the road, it may be worth investing in a set of winter tires. Experiencing an ice covered road in Sport tires vs. dedicated winter tires is like night and day.

Winter tires use several methods to increase friction and help maximize traction in rough conditions. Rubber compounds in winter tires are usually much softer at much lower temperatures which, this allows for optimum friction but also results in faster wear.  Winter tires can also employee ‘sipes’ which provide grippy edges to the tire. Finally, winter tires tend to be wider and deeper with provides more bite when driving on snow or ice.

WHATCAR? magazine tested a selection of winter tires with a braking test from 25mph to a complete stop in a VW Golf. The results were pretty dramatic and really help to illustrate the importance of driving with appropriate rubber beneath you.

Driving on Snow

 

winter-tyre-stopping-distances-ice
Source: http://www.whatcar.com/car-news/winter-tyres-tested/snow-and-ice/259257

Driving on Ice

winter-tyre-stopping-distances-snow
Source: http://www.whatcar.com/car-news/winter-tyres-tested/snow-and-ice/259257

Snow Chains for Winter Driving

In deeper snow, it’s often worth using snow chains. If there’s a chance you might encounter deep snow you should at least have some stored in your car. Chains are fitted to the drive wheels and they can provide very dramatic increases in traction when snow is deep.

Chains are usually sold in pairs and must be purchased to match a particular tire size (tire diameter and tread width). Driving with chains reduces fuel efficiency, and requires a reduction in the speed of the automobile to approximately 30 mph.

Tires come with standardized tire code sizing information, found on the sidewalls of the tires. The first letter(s), indicate the vehicle type (P for passenger, LT for light truck). The next three digits indicate the tire’s width in millimeters. The middle two digit number indicates the tire’s height-to-width ratio. The next character is a letter ‘R,’ which indicates radial ply tires (rather than radius). followed by a final two digit number indicating the rim size for the vehicle’s wheels.

Additionally, the correct Society of Automotive Engineers (SAE) class of snow chains must be installed, based on the wheel clearance of the vehicle.

SAE traction device classMinimum tread-face clearance (A)Minimum side-wall clearance (B)
Class S1.46 in.59 in
Class U1.97 in.91 in
Class W2.50 in1.50 in

The classes are defined as follows:

  • SAE Class S – Regular (non-reinforced) passenger tire traction devices for vehicles with restricted wheel well clearance.
  • SAE Class U – Regular (non-reinforced) and lug-reinforced passenger tire traction devices for vehicles with regular (non-restricted) wheel well clearances.
  • SAE Class W – Passenger tire traction devices that use light truck components, as well as some light truck traction devices.

Recovering from Slides in Winter Conditions

First a couple of definitions. Understeer is when you turn the steering wheel but the car continues straight ahead. Oversteer is when the car tries to spin around due to a lack of traction in the rear.  Both situations are more likely to occur on winter roads.

For both situations, understeer and oversteer, do not try to stomp on the brakes. This will make things worse. Ease off the throttle, keep the steering pointed in the intended direction and stay calm. Getting your wheels turning at road speed again is the key to regaining traction.

If you do find yourself in an understeer or oversteer situation on a very slippery road try not stamp on the brakes in panic as this will make things worse. Ease off the throttle and keep the steering pointing in the direction of intended travel. If you have time and presence of mind you can move the transmission to neutral or press in the clutch to remove engine drive from the wheels which will help them get to natural road speed. Once you regain traction be prepared to make steering correction so you don’t start into a slide in the opposite direction.

Electronic Traction Control Systems & Winter Driving

Most modern cars come with electronic traction control systems. These systems can be very helpful in slippery conditions. Two main methods of intervention are employed by traction control systems:

  • Throttle reduction
  • Brake application to independent wheels

Most traction control systems react very quickly and apply more precise corrections than you can. When traction control kicks in, all the driver is really responsible for it keeping the steering pointed in the intended direction of travel.

Winter Driving Myths

The oft repeated and mostly wrong winter driving myths. ABS is bad, lower gears help you get up hills, you should turn off traction control in the snow, pumping the brakes is the key to stopping in the snow.

ABS is Bad in Winter Conditions

This one likely stems from the fact that your stopping distance may actually increase with ABS active. However, ABS prevents wheel lock-up and allows you to continue to steer your vehicle effectively which is usually more helpful when trying to dodge other cars, people and objects in an emergency stop. It’s also very unlikely that you’ll even have the option to disable ABS in a modern car, so it’s best to learn how to use it effectively.

Always Use Lower Gears for Winter Driving

When starting from a stop, the lowest gear is seldom the best. Lower gears increase torque at the wheels which increases the chance of wheelspin. Selecting the highest practical gear, usually 2nd, to start reduces torque which helps you maintain traction.

When descending a slippery hill, the engine braking generated while in a lower gear can be very helpful. Brake application encourages wheel lock, engine braking helps reduce speed while keeping the wheels rotating.

When cruising along at speed you need to balance the ability engine brake with minimizing wheel-spin. It’s best to find a gear which maintains an engine speed between 2000 and 3000 rpm.

Pumping the Brakes

Pumping the brakes or cadence braking is the process of rhythmically applying and releasing the brakes to strike a compromise between steering and braking performance. This technique is only useful in cars without ABS, as ABS will always outperform a human driver by applying this process in a faster and more accurate fashion.

Turning off Traction Control

Most traction control systems can reduce engine power or apply the brakes in response to spinning wheels. Because of this it is actually especially beneficial to keep traction control systems active in snow and ice. Again, you are a human and you will not outperform a computer based traction control system. There are occasions when a reduction in power can hinder you (i.e. you are stuck in snow and trying to get out), then and only then should you disable a traction control system.

Top Tips for Safe Winter Driving

Accelerate Gently and Progressively

In slippery conditions such as snow and ice, aggressive acceleration will greatly decrease traction at the drive wheels resulting in wheelspin. Wheelspin leads to loss of steering in a FWD car and those “Oh Shit,” my car slid 6ft to the right leaving the stop sign moments. In a RWD wheelspin results in oversteer. Both situations send you in unintended directions and are hard to recover from. Prevention is key.

Recovering from Wheelspin

If you do notice wheelspin or sense the traction control system kicking in back off the gas until you feel your tires reconnect and then reapply power smoothly.

Keep Engine Speed (RPM) Low

A constant low throttle will maximise grip and low RPM means you will be less likely to make a jump in wheel speed rapidly. Most automatic cars will start off the line perfectly fine in drive at idle, in a standard transmission in rough conditions a start from stop in 2nd gear is often a great choice. Change gears much sooner than in normal conditions and make gear changes as smooth as possible.

Avoid Sudden Movement

Don’t make sudden, sharp changes in steering, braking, acceleration or gear changes. Driving smoothly and conservatively will conserve grip, and keep you safe on slippery roads.[

Brake Early and Gently

Winter is not the time to test your 100-0. Because you need to be prepared to ease off the brakes when necessary to steer more effectively, you also need to be sure to predict your stops much sooner. Remember, locked wheels don’t steer!

ABS Is Your Friend

If your vehicle is fitted with an Anti-lock Braking System (ABS), you’ll feel when it has been triggered by feeling a pulsing sensation through the brake pedal. You may be inclined to ease off the brakes or pump them, do not do this, rather keep a firm pressure on the pedal for maximum effectiveness. ABS is designed to help you steer as you come to a stop. Again, front wheels have to be turning for you to steer!

An Ounce of Prevention Beats a Pound of Cure

Despite having ABS, traction control and other systems on board and a great ability to control a car in slippery conditions it’s still best to not have to use them.