Driving on snow and ice

Driving during winter is much more difficult than driving during summer, as there are more things to consider. Three things that changed during winter is the braking distance, the acceleration and the steering. As it is the tire that is in contact with the road that can be covered by snow and ice, it’s important to have good winter tires to enable better accessibility during difficult road conditions. The tires can either be friction tires, where up in the north or Scandinavia should be Nordic friction tires or studded tires. If the road is covered with ice and snow the tire to road friction will decrease. The friction is a number that describes the contact between two surfaces.

In this case, the road and the tire and how they can move against each other. Friction is often a number between zero and one, where zero friction means that the surface completely slide against each other, and one is that there is very good grip between the two surfaces. When you drive a new car they have systems that will decrease the effects of crashes and help you as a driver. So when a vehicle is driven against another vehicle, the vehicle that you are sitting in will brake by itself when it gets too close. But all of these systems are created on dry asphalt and then the crash will be really small.

But what happens if we do the same test on snow? Then the crash become much larger and it’s because the snow will make the braking distance much longer as the friction actually has decreased. So now I will go through how you can calculate the braking distance, depending on the friction. For that you need three things if you make the assumptions that the final speed will be zero meters per second. The first thing you need is the initial speed of the vehicle, as in this example, it could be 50 kilometers per hour, but this number you need to make into meters per second. So you divide it by 3.6 giving you a speed of 13.9 meters per second.

The second thing you need is the friction that for snow in this example usually is around 0.3 µ. Third, you need a constant of gravity. In this example, up here in Luleå we calculate it by 9.82 meters per square second. Then to calculate the braking distance, d you take the initial speed and you take that squared and then you divide it by 2 times the gravity constant, times the friction, which will give you the braking distance, in this case thirty three metres. But what happens if the friction actually is up to 0.8 µ, instead? Well, then you take the same calculations, you take the initial speed, the constant of gravity, but you change the friction to 0.8 instead.

And then you get the distance of 12 meters. This is actually a 21 meter difference, which is really important to know that the braking distance actually changed that much. If you have low friction caused by snow and ice. And also important is to remember that of course, if it’s taken longer braking distance, you will have more problems to accelerate as well. So that’s something that is really important to know when you drive on snow.