Free wheeling in your car

April 28, 2008

I’m a fan of getting that extra mile out of a tank of petrol (well diesel… but ya know), and as such have been known to allow my car to freewheel up to lights… I mean come on… surely freewheeling (despite the illegalness) has to be the most efficient… right?

Well it turns out… NO…

If you take the car out of gear, the engine needs a little fuel so it doesn’t conk out. If you leave it in fuel the idea is that the engine is kept going by the inertia, and so doesn’t need fuel.

So its like this, if you are going to free wheel for a very long way… then it will make sense. If it’s a shorter distance like up to the lights, then leave the car in gear. The engine will actually take energy out of the wheels to keep going, and so use less fuel. It will also slow the car a bit, and so you’ll need less breaks… do the savings ever end?