Green car technologiesGearbox and aero tweaks

Small add-on tweaks have aerodynamic benefits

The idea here is to ‘tweak’ conventional cars to be as green as possible, without the high cost of futuristic technology.

Longer gearing is the most obvious trick. Volkswagen, for example, stretches the ratios on third, fourth and fifth gears in its BlueMotion models, meaning their engines are spinning more slowly at a given speed than similar cars’.

Lower engine speed translates directly into lower emissions. A Renault engineer told us that, even if there is no load on the engine, ‘less rpm always means better fuel consumption.’ 

The engine calibration is usually modified, too, so the car runs better with these altered gear ratios.

'Intelligent' gearchange indicators

Also, many companies fit a gearchange indicator to encourage early upshifts. Such devices, a Ford engineer told us, are ‘intelligent’, responding to engine load, rather than being rev-based indicators. So they are well worth adhering to.

The car’s aerodynamics are massaged as well, creating a more ‘slippery’ shape that takes less effort – and therefore less fuel – to push through the air. 

Many cars have special flat underbodies, like a race car, to ensure the airflow is not disturbed, and the suspension is often lowered to reduce drag. 

Rear spoilers also help smooth the flow, while tiny add-on tweaks here and there have subtle, but tangible, benefits in the wind tunnel.

Other detail changes, such as closing up the front grille (on some BMWs, this is done electronically, according to how hot the engine is) and fitting flush aerodynamic wheel trims, mean the car passes along the road with the minimum of air resistance.

For similar reasons, low-rolling resistance tyres can be fitted, and these are often specified with a higher pressure, to further cut down friction. 

Many cars even use low-friction oils, to ensure the mechanical parts encounter as little resistance as possible, too.