How to measure Rolling Resistance?: As global warming topics heats up the news circle, people has been paying more attention to sustainability topics and in particular rolling resistance for tires. So what is actually rolling resistance?
The rolling resistance is defined as the energy loss per distance
Source
traveled by the vehicle due to nonelastic deformations of the tires
and losses in the wheel suspension system
The tire rolling resistance is primary caused by hysteresis –> a fancy word describing an energy loss due to loading and unloading of rubber due to its viscoelasticity nature. The main parameter which is measured for tires is called the rolling resistance coefficient define as below
Rolling resistance coefficient, Cr = Resistance force, Fr / Normal load, N)
The most common used unit is N/kN whereby the resistance force is usually expressed in Newtons while the normal load is express in kilo Newton making this coefficient dimensionless. The values given in the EU label tables are also express in this same unit. The table below shows the current rolling resistance coefficient values corresponding to its grade.
| Rolling Resistance Coefficient (N/kN) | EU | Korea | Japan |
| RRC ≤ 6,5 | A | 1 | AAA |
| 6,6 ≤ RRC ≤ 7,7 | B | 2 | AA |
| 7,8 ≤ RRC ≤ 9,0 | C | 3 | A |
| 9,1 ≤ RRC ≤ 10,5 | D | 4 | B |
| RRC ≥ 10,6 | E | 5 | C |
How to measure a tire’s rolling resistance?
There are many known method’s in measuring rolling resistance but in this article we will focus on the most common way which is done through a drum test. The picture shows a drum setup from one of the biggest supplier MTS. The big drum in the middle is used to drive the tires while the force sensors are placed in the center of the tire.
The underlying is quite simple. The machine will apply a load on the tire while it is being forced to turn by the drum. With a force sensor placed on the tire, you will be able to deduce the resistance force which the tire generates to prevent it from turning. The image below shows a clear force diagram to indicate the forces acting on the tire. As the tire reaches a steady state, the acceleration forces turns to 0 allowing a good accuracy of the rolling resistance to be achieved.
So why should we care?
As mentioned in the start, the lower your tires rolling resistance, the less fuel you burn to reach your destination. Hence having a low rolling resistance tire in good for your money and also the environment. Let’s take a look on how much would CO2 less and money you would save when you make the switch to a better rolling resistance tire.
- Switching from Michelin XM2+ (label E) to Michelin e.Primacy (label A)
- Numbers based on your whole tire life of 60,000 km with a Myvi fuel consumption of 6 l/100km.
- Money saved RM 410
- Average fuel consumption with the new tires 5.7 l/100km
- Fuel saved 200 l
- CO2 emissions reduction 527 kg CO2
*Feel free to download the fuel savings calculator to adjust for your own preference.
Summary
Rolling resistance is something you should consider when purchasing your next set of tires. It comes with the benefit of saving the world and also it might spare you some money.