[liuleichan]

>I personally think that driving style is the most important
>factor when considering mpg.

Agreed - given the done deal of what you've got, I suspect the best can be achieved by altering / improving your driving.

>I can only take my mpg from the
>trip computer. When in neutral coasting downhill (not
>something I do often) I get 99.9mpg,

Just a comment on that: when you're coasting, in neutral, in most ECU controlled cars, you'll probably be using ever-so-slightly more fuel, than you would from being in gear. When you're in neutral, but coasting at speed, there will be no direct relation between road speed and revs, however, the revs will be at least at idle, and probably at quite a high idle, as the ECU detects you're moving at speed. Some - albeit not a lot - but some fuel is used to maintain this.

However, if driving downhill, in gear, with your foot off the throttle, sort of coasting, if you will, but in-gear, with the engine controlling your speed, the car will be in overrun - very little if any fuel will be supplied to the engine, merely air. With some turbo charged cars, there may be a slight amount of fuel still provided, almost used as a cooling effect for the cylinders - but in most cars, on overrun, no fuel is used.

So in these scenarios, it's probably better to be in gear (from a fuel economy perspective), with the gear chosen, correct to maintain the road speed. Plus you get all the advantages of not having the disadvantages of coasting in neutral ;-)

Lei Chan