Snow Driving

snow-drivingSnow is not a frequent occurrence in Southern Africa. Nevertheless, it does happen, particularly in the mountainous regions of the Western Cape Province, the Drakensberg in Kwa-Zulu Natal, as well as the border region between South Africa and Lesotho, and it was with this in mind that Bud, our aspiring off-road driver, sought the advice of the Instructor at the off-road club training area.
Bud had been doing some 4WD training at the club, and this article finds him in the clubhouse after he had been practicing some sand driving techniques on his own in the sand pit. It had been snowing heavily in the Western Cape and he thought he would pick the Instructor’s brains on snow driving techniques while he had the chance. He had read somewhere that only snow tyres work in snow and ice and he wanted to know more about these off-road tyres and general snow driving as well.

Snow Tyres

snow tyres“Sure Bud, you are right, but chances are you might never have to drive in snow, however, if and when you do, make sure you have proper snow tyres on your 4WD because although you may get through snow on sand or even normal on-road tyres, the chances are just as good you may not.”
“Snow tyres work because they have a lot more edges in the tread than any other type of off-road tyre; because snow is so slippery, you need as many edges to grip the surface of the road as you can get. Traction in snow is always marginal and if you have off-road tyres with large tread blocks, like mud tyres for instance, you end up with large areas of rubber on a slippery surface, where what you want is tyres with lots of edges to grip the surface, much like the over-sized lugs on tractor tyres.”
“The trick for manufacturers of off-road tyres is to get the balance between the number of edges and the rubber contact area right; too much rubber on the road lets you slip, and too few edges between the tread blocks means you cannot grip the surface. But apart from that, the rubber compound of the tread as well as the construction of snow tyres are different from say, sand, or mud off-road tyres.”
“All-terrain tyres are a combination of all the features of all types of off-road tyres, but the problem with that is that they cannot be equally effective in all conditions. The compromises between durability, good high speed handling on tarred and gravel roads, road noise, and fuel economy means that all-terrain tyres are just not as effective in any given situation as an off-road tyre that was made for that purpose or application, and especially in snow because they do not have the tread pattern that snow driving demands. So, if you absolutely must drive through snow, fit the correct tyres or avoid the snow altogether.”

Snow Driving and 4WD

“There is unfortunately no way to simulate snow driving conditions so I will just have to tell you about it: you have seen what 4WD mode can do for you, but there are a few things you must remember about 4WD in snow:

• Traction:

4WD does not give you more traction; all it does is helping you make the best use of the available traction. 4WD is good for taking off from a stationary position but it does not mean you have better cornering ability; nor does 4WD decrease stopping distances. In fact, ABS in snow driving conditions is just as bad as it is on sand or gravel, if not worse, so it is usually better to disable the ABS in snow. However, the corollary of that is that the traction control might not work, since it depends on the ABS to measure wheel speeds on systems that use brake based traction control systems.”
“Disabling the ABS to be able to stop on sand is not so much of a problem because traction is so much better on sand than on snow, even with proper snow tyres. So, the best way to maintain traction when snow driving is to use the highest gear at which the 4×4 will get through the snow without labouring or stalling, irrespective of whether you are in 4WD mode or not. The reduced torque acting on the driving wheels in higher gears reduces the chances of wheel spin, but it is also very easy to use the higher speeds that go with using higher gears, so watch out for that.”
“Use the lowest speed at the highest gear the 4×4 will allow you to, because you have virtually no traction and if you need to take sudden evasive action for whatever reason, you might find yourself unable to steer, or to stop in time to avoid an accident. So, keep a sharp lookout for obstacles, but even more importantly, plan your route by deciding on a line to take through the obstacle before you enter it, or the stretch of road with which you are unfamiliar. If there are other 4×4 tracks through the snow, follow them and avoid the areas where the snow is obviously deeper than anywhere else.”

• Traction Control:

“The traction control on your particular 4×4 does not depend on the ABS to work, since it works on the principle of torque distribution, so you may want to disable the ABS to enable you to stop. However, snow is so slippery that all four wheels might start spinning and confuse the system, so the thing to do is to use the minimum amount of torque to give you the maximum momentum at the slowest practicable speed.”
“This takes some practice and you have to know your 4×4 very well to be able to do this, but if you get it right, you minimise the load on the traction control system. Traction control systems are not perfect; although some systems have dedicated snow-driving settings that change the way they work, because the manufacturers have designed and programmed them to work under high load conditions, meaning they prevent wheel spin under conditions of high torque. Snow and ice do not like high torque conditions, so avoid any sudden control inputs such as steering, braking, or acceleration. Sudden acceleration, even just small amounts, could cause all the driving wheels to lose traction in snow, which means that you lose all control.”

• Snow Chains:

piranha-snow-chains“If you have snow chains, use them because snow driving demands all the traction you can get, especially off-road. Snow does not melt at the same rate in all places and if you are on snow tyres and you run into a patch of partially melted snow, you may have to negotiate mud with snow tyres, which is never a good idea. The effect of mud on snow tyres is the same as using bald tyres on a wet paved road: the narrow grooves in the snow tyres will immediately clog up, which will leave you with absolutely no traction, in the same way that a bald on-road tyre will not be able to channel away water.”
“Snow chains will of course not give you perfect traction but they will dig into the mud, in the way that the lugs on a tractor tyre dig into soft soil, but remember that snow chains can damage your snow tyres if you spin your wheels. The principle of maintaining the most momentum at the slowest practical speed applies to snow chains as much as it does to anything else, so be careful when using them. As I said, snow chains will not give you perfect traction but they will get you through a muddy patch if you are on snow tyres, so use common sense and always keep in mind that you need your tyres to get you home. They will look after you if you look after them.”

• Hill Descents in Snow:

“Another very important thing to remember is the fact that it is very difficult, if not impossible, to reduce speed when you are going downhill in snow. HDC, or Hill Descent Control systems work by maintaining braking forces to individual wheels to keep the 4×4 at a pre-set speed, however, this generally only works where the tyres can maintain enough traction to keep the 4×4 at that speed without locking up.”
“With that said, an HDC system becomes useless when it has to keep releasing the brakes to keep the wheels turning, so you may as well not have an HDC system. So, if you have to get down from a steep hill in snow driving conditions, the thing to do is to control your speed right from the top of the descent, but this is sometimes easier said than done, since no two hills are alike and what got you down one safely, might not work on another.”
“The main issue is the marginal traction you have in snow: an HDC system might be completely useless, and engine braking in the wrong gear could cause your wheels to lock up. You need to be able to maintain directional control so you cannot use engine braking in 4WD mode, since your front wheels might lock up, so the best thing to do is to use engine braking in a high gear in high range 2WD mode. This will allow the front wheels to rotate freely, and you will have a measure of engine braking force available. The trick is in using the correct gear though; using one that is too low might have the same effect as pulling up the hand brake, and using too high a gear may not give you enough braking force. So it really comes down to how well you know your 4×4 on the one hand, and the risks you are willing to take on the other.”
“My advice to you would be to avoid snow driving altogether until you are more experienced; you still need to learn how your 4×4 behaves right at the limits of available traction, especially with a few hundred kilograms of weight on the back. You still need to practice slides and how best to recover from them. Slides can be very tricky in snow driving conditions, but the trick is of course not to get into a slide, but it is sometimes unavoidable and it happens to even the most experienced off-road drivers. So, be safe, and avoid snow driving until you know your 4×4 a great deal better than you do now.”

Bud’s Thoughts on Snow Driving

Bud had never done any snow driving, not even in his top-of-the-range German SUV, and since he had begun to trust the judgement of the Instructor, he thought he had been given excellent advice and tips on snow driving. Left to his own devices, he would never have thought of all the issues that were involved; he would never have thought of the inadequacies of his traction control system, or the ineffectiveness of his HDC system, and much less about the fact that 4WD does not decrease stopping distances.
He thought it was good thing that it did not snow more often in South Africa, or the rest of Southern Africa for that matter. He was definitely not yet qualified to do any sort of snow driving but that was not going to stop him from getting another set of rims with snow tyres and a set of snow chains.
Who knows, it might just start snowing all over South Africa this winter.

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