Question on fuel efficiency

rstoday

Hiya

I'm trying to work out if it is more fuel efficient to do a journey which takes around 50 minutes using local A roads covering 17 miles, or to take the M25 which takes the same amount of time but covers well over 30 miles.

My guess is that as the engine is running for 50 minutes either way and the journey via A roads is pretty stop-start, it may be better to take the motorway for fuel efficiency.... but I'm confused by the science! Any clarification much appreciated!

Thanks!

maninthestreet

30/17 = 1.76. Assume 35 mpg on the M25, if the mpg via the A roads is better than 20mpg, you will use less petrol.

Mark_Hewitt

17 vs 30 miles is quite a difference, I'd be surprised if the 30 mile version used less fuel, of course it depends how aggressive you are at driving on the A-road part.
As long as you accelerate gently and don't use the brakes too much then the 17 mile journey should use less fuel.