Didn't Clarkson test this
and found that because he got there quicker, had the engine/aircon/radio etc on for less time that he used less fuel going faster?
( Peej, Tue 9 Mar 2010, 9:48, 1 reply, 16 years ago)

Probably
It depends on the car, the gearing, the road conditions, etc.

Were it possible to do a constant speed, then 50mph will almost certainly use less fuel than 70mph, simply because of air resistance. But we live in the real world, and depending on the thermal efficiency characteristics of your engine, it may well be that it's just as economical to be doing 70 where you can. Especially if you need the aircon.

And doing only 50mph on a motorway is bloody ignorant anyway, because it causes lorries to pull out and overtake, which holds up other traffic.
( K2k6 has a proper job these days, Tue 9 Mar 2010, 9:52, Reply)

That,
and I wouldn't trust Clarkson to test anything properly in a scientific fashion.
(LongJohnBaldry, Tue 9 Mar 2010, 10:06, Reply)

Yes he is a complete cunt
and if he doesn't have his own agenda it will simply be to disprove a theory and look smart/smug.
( whenanimalsattackhumans clad in global hypercolour, Tue 9 Mar 2010, 10:17, Reply)