Q. What is rolling resistance and what is its relation to fuel efficency?
A. Rolling resistance is the resistance that occurs when a tyre rolls on a flat surface. As the tyre rotates under the weight of a vehicle, it experiences cycles of deformation and recovery, loosing energy as heat. Low rolling resistance tyres are designed to minimise this heat loss, thus reducing the amount of energy needed to drive a vehicle forward.
Rolling resistance can be expressed with the rolling resistance coefficient (RRC), which is the value of the rolling resistance force divided by the wheel load. A lower coefficient means the tyres will use less energy to travel a certain distance.
Materials which flex more and bounce back more slowly exhibit greater rolling resistance than materials which flex less, such as steel, or materials which bounce back more quickly, such as silica. Low rolling resistance tyres often incorporate silica in their tyre tread compounds to reduce energy loss without compromising traction. Other factors which affect the amount of rolling resistance generated by a tyre include tyre inflation pressure, tread compound, tread design and temperature.
Tyre rolling resistance determines 20-30% of a vehicle’s total fuel consumption, so lowering the rolling resistance of tyres can lead to significant fuel savings and reductions in CO2 emissions. There is currently a 10% fuel consumption difference between the best and worst performing tyres on the market.
Q. What are safer tyres?
A. The safety of tyres is generally measured by their wet grip performance, which reflects the capacity of a tyre to brake on a wet road. There are other parameters which are relevant to the safety of a tyre (road holding ability, directional control, deceleration ability on wet and dry surfaces at high speeds and aquaplaning behaviour) but existing testing methods make it possible only to measure wet grip.
Q. Are there any tradeoffs between rolling resistance, safety and noise?
A. Not necessarily. Advances in tyre technology mean that there are now many premium tyres on the market which achieve low rolling resistance and low noise as well as good wet braking and aquaplaning performance.
The introduction of silica to a tyre’s tread compound, for example, reduces tyre rolling resistance whilst at the same time improving a tyre’s handling and steering capability. Silica has been shown to offer a 15% increase in wet grip, as well as improving traction on icy roads.
Whilst premium tyres can achieve energy efficiency and low noise while remaining safe, tests have shown that some budget tyres compromise on safety. In tests carried out by What Car? Magazine, budget tyres took an average of 14 metres – the length of an articulated lorry – longer than premium tyres to pull up from 100 kph. In the dry the worst budget tyre still took up to five metres longer to stop then the top premium brand.
Q. Are there energy efficent, safe, low noise tyres on sale already?
A. Yes. There are already tyres on the market which set new standards for rolling resistance, noise and wet grip. Tyre manufacturers are also working hard in terms of providing information about their tyres, and many are already in the process of preparing databases with information on the rolling resistance, noise and wet grip values of their products.
Q. Do bettertyres always cost more?
A. There is some evidence that fuel efficient tyres sometimes come at a small price premium. However, this will be paid back by the fuels savings achieved. Also, new Eco Tyre products like Linglong’s “Green Max” have introduced high quality Eco tyres to the New Zealand market at very low prices. The payback period for switching to the most fuel efficient tyres from average tyres is currently estimated at around 6-8 months for car tyres, 2.5 months for van tyres and 5 months for truck tyres; and much less for “green Max”products. The price premium for fuel efficient tyres is likely to reduce as tyre technology develops and demand for low rolling resistance tyres increases. There is no evidence that low noise tyres come at a price premium.
Q. Are Eco tyres as durable as standard tyres?
A. Tyre manufacturers claim that the most energy efficient, low noise and safe car tyres can also achieve long wear life. There is some evidence that some energy efficient tyres have slightly reduced durability, but in-use tests have concluded that the fuel cost savings achieved through switching to these tyres more than outweigh the tyre replacement costs.
Q. Can I buy fuel saving, low noise retreads and secondhand tyres?
A. Not really. At times there are secondhand Eco Tyres on sale, so presumably they would offer the benefits associated with Eco Tyres. But the supply is poor and the price quite high. Car tyre retreads tend to be poor quality, noisey, have high rolling resistance and wear out quickly. Basically they are the direct opposiote of an Eco Tyre.
Q. Are Eco Tyres good for our environment.
A. YES! Eco Tyres reduce fuel consumption and therefore engine emissions and are made with less toxic materials; they are a very green product.