What is traction coefficient?

Written by Eric Jones,

In a tyre-surface system, the coefficient of friction is called ‘traction coefficient’. It’s as simple as that. But, what’s more important is to know why the traction coefficient is fundamental to road safety – and peace of mind.

In a scientific report, Analysis Of Tire-road Contact Under Winter Conditions (ISSN: 2078-0966), K. J. Waluś and Z. Olszewski studied different factors affecting traction – and road safety accordingly. In the report, they deep dive into the molecular world of physics. But, for the not so scientifically minded, here is a brief summary.

Safety relies on a very small spot

Imagine a huge heavy loaded truck rushing on the road. Yet, all the forces and moments responsible for safety, directional stability and vehicle dynamics are generated in quite a small road contact area – the tyre footprint. Furthermore, frictional forces and material qualities involved are crucial for the vehicle behaviour, especially in changing weather conditions. Let’s have a look at some of the frictional forces involved.


Friction forces in a tyre-surface system

In a tyre-surface system, friction forces are caused by two main mechanisms – adhesion and hysteresis.


Elastic rubber tyres, under the pressure of many tonnes of vehicle load, adhere to the rugged road surface. The rubber actually penetrates into the ruggedness of the road, resulting in a high traction coefficient. However, this is on a dry road. When roads are icy this adhesive friction will be considerably reduced, and the driver without traction aid should be quite nervous.


Hysteresis is about the rubber being compressed when in the tyre footprint, and expanding when it leaves the footprint, i.e. it depends on material elasticity. To really simplify, you could say that the forces involved in compressing the rubber differ from those when it’s decompressed again, and this is the primary cause of the tyre’s rolling resistance. And yes, also this resisting force is considerably reduced on ice…

Traction coefficient in winter conditions

As you may have guessed, the traction coefficient deteriorates in winter conditions. On icy roads, the friction heat from the tyre melts the ice and a thin layer of water is introduced into the tyre-surface system bringing matters to a head; the adhesion between rubber and asphalt is reduced which impairs the rubber’s ability to ‘capture and grip’ the surface inequality structures. And also, it extends the duration of rubber deformation and thus reduces the hysteresis. This situation is commonly called slipping and requires attentive and careful driving.

On the other hand, the traction coefficient could be substantially improved by introducing an assistive device into the tyre-surface system. That is exactly what Onspot does!


In the report, Waluś and Olszewski conclude that for road safety, ‘it is necessary to determine the effect of the tyres and used assistive devices such as chains or spikes on the characteristics of vehicle traction in winter conditions.’

Actually, without extensive laboratory research on a molecular level, we already know what effect Onspot has on vehicle traction in winter conditions. Thousands and thousands of drivers together with numerous field tests and reports confirm that Onspot automatic snow chains really do the job. Increasing the traction coefficient and road safety accordingly. Improving safety and convenience for the driver and possibly passengers.

Knowing that all this is achievable by just pressing a button should bring peace of mind to any professional truck or bus driver.


Learn about different ways to get traction

Automatic Snow Chains Engineering

Eric Jones

About Eric Jones

Eric is the Global Sales Director for the Onspot brand. He has over 15 years of industry experience and received an MBA from Ball State University. Eric enjoys spending time with his wife and two children and being active outdoors. On the weekend, you can normally find Eric enjoying a craft beer with food sizzling on the grill.


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