Maybe you’ve been there? The road is becoming icy and slippery and you know it's time to get out there and put on your tire chains. As usual, you’re in a hurry, so the mounting time would cost you another hour of delay. And besides, you don’t feel like leaving your warm cab for the freezing cold roadside… So, is there a trick to get traction anyway? Actually, there is a trick that many experienced drivers know of. Yet, it’s a controversial trick. Here’s why!
The vehicle’s road grip is a result of friction, which in turn depends on the contacting materials – in this case tire rubber and icy road surface – and the applied pressure from the vehicle’s weight. Well, you can’t increase the weight of your vehicle, but still it’s possible to increase the pressure on the tires. But, before sharing how, we need some basic insights.
Load and pressure must be distributed
The reason for having double (or more) axles on the truck is to distribute the heavy payload pressure more evenly. Why? Simply because putting full weight on one single axle would put immense strain on that axle, with unacceptable wear as a result.However, it’s not only about the truck, but also the road is strained. Being stepped on by a woman’s high heel (total pressure is concentrated to a small contact area) will hurt much more than if she wears sneakers (total pressure is distributed over a larger contact area) although her body weight remains the same. It’s the same with roads. Pressure must be distributed to a larger contact area to reduce road wear. This is one reason why there are rules and regulations for vehicle total weights and maximum axle loads.
The trick is to put all eggs in one basket
Now, we’re back in the cab on that icy road and mounting tire chains in the cold is not a very pleasant option. A common trick here is to simply to lift one axle. All experienced drivers know that this improves road grip when slippery. What actually happens when you put all the load on one axle is that you concentrate it to a smaller road contact area (as there are fewer tires in contact with the road), which increases the pressure in the remaining contact area and traction is increased accordingly. For basic knowledge about this, read the blog post: What is traction, friction and road grip?Even if this may seem to be a quick and convenient solution, there are drawbacks:
- Manufacturers strongly advice against this, as the truck isn’t designed to withstand it
- Excessive road wear results in unnecessary costs for society
- In most areas it’s illegal and you’re at the risk of being fined when exceeding maximum axle load
- This is why the “axle trick” is a controversial shortcut.
