Automatic coasting could be the next fuel-saving technology

Angel gear was a big deal when I first hit the road.

Back in the day, my fuel budget never came close to my driving ambitions. So coasting down hills in my ancient VW Beetle, with the gear lever knocked into neutral, was a convenient way to save some fuel. It was hardly the safest thing to do, with no engine braking for coming corners, so it also kept me focused on the job of driving.

I had forgotten those early days until I attended an Audi technology forum a few years ago and sampled a number of ideas to improve economy and reduce the impact of cars on the world's megacities.

Angel gear was back and, this time around, the Audi didn't even need a hill to trigger the switch into neutral in its double-clutch automatic gearbox. It was surprising to feel the lack of drag and see the tachometer needle sitting at idle as the car rolled across the German countryside.

Now I've felt the same thing again in Audi's latest A4 and I can see freewheeling — or angel gear — catching on as rapidly as stop-start tech. It's already becoming a big deal at the VW Group.

The principle of the tech is that the car's kinetic energy is used to overcome road and aerodynamic drag instead of using fuel in the engine.

It's triggered when various sensors detect available energy and zero load as the driver's foot comes off the accelerator.

The clutch is disengaged and the engine drops back to idle, about 800rpm, instead of turning at a road speed equivalent to, say, 110km/h.

Audi reckons the fuel saving can be at least 0.5L/100km, a worthwhile improvement for any car these days.

Would you welcome automatic cruising in your car? Tell us what you think in the comments below.