Energy tires : How to improve tire design for rolling resistance

Energy tires has become very important becuase with the goverment requirements for better fuel consumtion. The rolling resistance is performance charactoristic and energy tires have be low rolling resistance. The general ideas change to improve tires to energy tires but will certainly affect other properties as well , for better or for worse.

Effect of Rubber Material

ranked various rubber material regarding their effect on energy tire (low rolling resistance) . The rolling resistance index was as the table

Rubber material	rolling resistance index
Natural Rubber	100
Hight cis-BR	94
Solution SBR	93
Emulsion SBR	90
IIR	73

* high rolling resistance index indicated that low rolling resistance coefficient.

Energy Tires Design

Energy tires can be radial construction that it have better rolling resistance than bias construction becouase the radial carcass is more flexible. Energy tires can reduces the gauge thickness of tread to reduce energy dissipation to lead to poorer rolling resistance.

Loading

Energy tires rolling resistance improves when tire’s load is decreased

Inflation Pressure high or low?

To design energy tires to operate with a higher air pressure.

Vihicle Speed.

Energy tires rolling resistance improves when vehicle speed is decreased.

Running Temperature.

Tire’s running temperature has effect on impart rolling resistance. Lower running

temperature may impart more rolling resistance.

Energy Tires : Rolling Resistance

During the tire motion new rubber material enter continously into the contact zone and is deformed,to spring back to its initial shape when leaving it .To produce this deformation it is necessary to spend some energy which is not completely recovered at the end of contact zone due to the internal damping of the rubber material .

This energy dissipation is what causes rolling resistance. It is then clear that it increases with increasing deformation and mainly with decreasing elastic return.The distribution of contact pressure which at standstill was symmetrical with respect to the centre of the contact zone , become unsymmetrical when the tire is rolling and the resultant Fz move forword (Pic.1) producing a torque My = –Fz*dx whith respect to the rotation axis. Rolling resistance is due to this torque . For practical purposes , rolling resistance is usually expressed as

Fr = f*Fz

where the rolling resistance coefficient f must be determined experimentally. Coefficient f depends on many parameter as the tire travelling speed V , inflation pressure p , vertical force Fz ,the size of tire and contact zone ,the structure and rubber material of tire,working temperature and road conditions .(see to energy tire)

Pic. 1 Force in rolling tire