"scott" wrote in message ...
Redonda wrote:
Gawnsoft wrote:
On Wed, 31 Mar 2004 19:59:08 +0100, "Redonda"
wrote (more or less):

scott wrote:
Redonda wrote:
It's odd that many people
equate exhaust emissions with road speed rather than engine
revs.

Care to explain?

The lower the gear ratio used for a given road speed the faster
the engine is turning, although I do realise that a poorly set up
engine using more torque in a high gear at low speed *will* spew
out more unburnt fuel particles.

The specific fuel consumption of an engine is lowest when revving at
the torque peak.

If an engine is revving at the torque peak in a high gear, going
quickly, the throttle depression will be higher (i.e. more fuel
being fed into each rev of the engine) than when travelling at a
lower speed, in a lower gear, but with the revs at the same level
as before.

snip

Again, it's not the use of lower gears or accelerating hard that trashes the
fuel consumption, it is braking. Try to keep a good gap infront and try to
anticipate having to slow down and ease off the accelerator. (I guess this
might be hard in London!!!) This is the best way to increase fuel economy.
Every time you brake, think to yourself all the fuel you've just wasted by
accelerating up to that speed.

Or to simplify, aim to maximize your minimum speed, rather than minimizing
your maximum speed. In other words everytime you have to slow to a halt, that
fuel wasted having to get back up to speed after. You might find you make
better progress too, by passing transistion points like traffic lights
turning green at 15mph, rather than from zero.