Tyres are subject to different forces and loads such as gravity, air resistance, surface adhesion, vehicle weight and many others. A car which is pulling away needs to overcome these forces. Rolling resistance affects the performance of your car and, as a result, your wallet as well. Find out how you can benefit from optimising rolling resistance.
What is tyre rolling resistance?
Ideally, a tyre rolling on a perfectly level surface would not be slowed by any external factors. Unfortunately, the reality is quite different. Your car is subject to physical forces that resist its movement. All the factors acting against this motion are called rolling resistance, which is the optimised ratio between the energy input for the movement and the forces of external factors acting against it.
How does rolling resistance impact fuel consumption?
While driving, the tyre cyclically flexes in contact with the road and after that it returns to its original shape. The resulting momentary deformations are the cause of energy loss; regaining this energy generates additional costs.
Rolling resistance accounts for 70% of the forces acting on the tyres. Inhibited aerodynamics requires more fuel to drive the same distance.
Low rolling resistance may reduce fuel consumption even by 0.25 litre per 100 km, which may not matter at the end of the day, but definitely will in the long run.
Watch our video and see how tyres affect fuel economy.
Good to know!
Low rolling resistance does not only mean lower fuel consumption.
Properly optimised rolling resistance also reduces the consumption of operating fluids. What’s more, it has a positive impact on the environment by reducing CO2 emissions.
What affects the level of rolling resistance?
There are a few key factors that affect rolling resistance. The most important include:
Aerodynamic resistance — the resistance of the surrounding air. The value of the aerodynamic resistance of the tyre increases with increasing car speed and may represent 0% to 15% of the total rolling resistance value.
Weight — the lower weight of the vehicle with tyres, the lower rolling resistance. In general, narrow low profile tyres are lighter. The height of the tyre also influences its rigidity (lower tyres have lower rolling resistance).
Construction and shape of the tread — the rubber compound and optimised tread pattern may reduce the rolling resistance even by 60%.
Micro-skidding — it is a loss of grip caused by deformations occurring within the tyre. Individual parts of the tyre are subject to minimal skidding, which causes energy loss. The share of this factor in rolling resistance is relatively small. When driving straight, its value is below 5%. It may increase during sudden acceleration, braking, or sudden changes of driving direction.
Tyre pressure — insufficient tyre pressure increases the contact of the tyre with the road. When the pressure level is too low, rolling resistance may increase even by 30%.
The influence of various factors on rolling resistance is shown in the diagram below.
Rolling resistance diagram.
Does reduced rolling resistance mean decreased tyre grip?
It is generally thought that by reducing rolling resistance, the grip of the tyre is also reduced. This is not the case anymore - this was true for older models. Modern technologies and the advanced rubber compounds used in low rolling resistance tyres compensate for those negative effects providing a stronger grip and increased durability of the tyre.
The following graph shows the relationship between grip and rolling resistance for different types of rubber compounds.
How to read rolling resistance markings
Until 2012, checking the rolling resistance of a tyre model required reading product descriptions, driver opinions and the results of tests organised by ADAC or automotive magazines. The situation changed after the introduction of obligatory labelling which provide information about fuel efficiency, grip and noise emission.
Now you can easily check the level of rolling resistance of a new tyre (marked with a red box in the illustration). The higher the fuel efficiency class of a tyre, the lower the Rolling Resistance Coefficient.
Fuel efficiency is determined on the basis of the Rolling Resistance Coefficient — RRC. The higher the coefficient, the lower the fuel efficiency class and higher fuel consumption. Determinants for each category are shown in the following tables.
RRC in kg/t:
RRC ≤ 6.5
RRC ≤ 5.5
6.6 ≤ RRC ≤ 7.7
5.6 ≤ RRC 6.7
7.8 ≤ RRC ≤ 9.0
6.8 ≤ RRC ≤ 8.0
9.1 ≤ RRC ≤ 10.5
8.1 ≤ RRC ≤ 9.2
10.6 ≤ RRC ≤ 12.0
9.3 ≤ RRC ≤ 10.5
RRC ≥ 12.1
RRC ≥ 10.6