Green tyres, fuel savings, CO2 emission - How far can reduce rolling resistance be reduced?

How far can reduce rolling resistance be reduced?

Environment Published the 18/05/2011

In fifteen years, manufacturers have reduced rolling resistance by one third. Now, gains will be far more difficult to obtain if the balance of performances is not to be compromised.

Rolling resistance diagram Copyright © : rezulteo

Tyre makers can be proud of themselves because from 1995 to 2009, they have managed to reduce rolling resistance by 30%, lowering it from 11 kg/t on average to 8 kg/t. This represents significant progress in fuel savings and CO2 emissions when it is known that a gain of 1 kg/t is equivalent to savings of 0.08 l/100 km at 80 kph (or 24 litres after 30 000 km driven). Now, they are aiming for the 6 kg/t threshold.

Increasingly difficult to lower further

This will not be an easy goal to achieve. "Whatever the dimension of the tyre, its pattern or application, getting to this level of rolling resistance while maintaining the performance on wet or dry surfaces is a huge challenge", says Jean-Pierre Jeusette, director of Goodyear research center for Europe, the Middle East and Africa. We will only be aiming for these figures if we are satisfied with the overall result." In other words, compromising on braking performance is out of the question.

Avenues of research

Today, green tyre is synonymous with sport tyre. The ContiSportContact 5P is a good example. It was approved by AMG, tuner for Mercedes (models C 63, E 63, SL 63 and SLS), and for Audi (R8, RS3). Its tread offers the grip of an ultra-sports tyre, whereas its underlay ensures as low a rolling resistance as possible, by limiting deformation under load. The combination of these two compounds is known as Black Chilli. It is based on a highly structured carbon black, mixed with special polymers and resins.

A similar policy exists at Goodyear with the EfficientGrip, which has a reinforcing high molecular weight polyethylene (in royal blue). Moreover, to reduce weight, the sidewall stiffener (in light blue) has been thinned. In both cases, the operation consists of stiffening the tread to prevent handling problems in turns.

Tyre makers are also working on belt plies, by using lighter-weight threads, and on the sidewalls. Their profile can be different, so as to enhance air penetration, at the same time with thinner protection which remains effective against impacts.

Thinner tyres for the roads of tomorrow?

The latest point of research: dimensions. The principle consists of increasing diameters and reducing widths. "The future roads will possibly have narrower tyres, such as 195/55 R 21", says Pascal Couasnon, director technical information at the Michelin. This manufacturer is also interested at small diameter tyres (10 inches), which could enable significant weight savings for urban vehicles.