"W K" wrote in message
...

I don't actually know.

YOU made an assertion that pollution would be greater at 20 than at 40 or
50.
If that assertion has any basis of truth, you could do with telling us.

http://www.naei.org.uk/other/vehicle_emissions_v2.xls

ought to be the place to look, but it is not as extensive, nor
clear as the london-research speed data used to be, which
showed pollution per km is best around 45mph (except NOx)

"Nick Finnigan" wrote in message
...
"W K" wrote in message
...

I don't actually know.

YOU made an assertion that pollution would be greater at 20 than at 40
or
50.
If that assertion has any basis of truth, you could do with telling us.

http://www.naei.org.uk/other/vehicle_emissions_v2.xls

ought to be the place to look, but it is not as extensive, nor
clear as the

I presume thats from the TRL.
Rather a complex thing to trawl through, I'll get my calculator out, or ask
my mate Paul.

london-research speed data used to be, which
showed pollution per km is best around 45mph (except NOx)

Perhaps because in london, any road where you are going less than 40 is
horrendously stop start.

W K ) gurgled happily, sounding much like they were
saying :

What is the fuel consumption of a modern, standard CAR at 20, 30 and
40?

Enlighten me.

I don't actually know.

YOU made an assertion that pollution would be greater at 20 than at 40 or
50.
If that assertion has any basis of truth, you could do with telling us.

The easiest way to get an approximation would be to look at the old-style
fuel economy figures - urban, constant 56 are probably close enough to what
we want for this.

The constant 56 figures were always WAY better than the urban ones. That's
a good indication that there's a lot less pollution at free-moving speed.

scott ) gurgled happily, sounding much like they were
saying :

Try this for a laugh, swim 10 lengths as fast as you can, then 10
lengths quite slowly. Which one do you think you've used most energy
for?

I know cars are very different

Erm, yes.

but you still have the basic mechanics of pushing an object
through a fluid at speed.

I don't often drive through "fluid", and my car has more than one gear.

A fairer example would be cycling.

Cycle ten miles, on the flat, at a certain pedal cadence (engine rpm) in
a low gear.

Now cycle ten miles, on the flat, at the same pedal cadence (engine rpm)
in a higher but still comfortable gear.

See the point yet?

If you're cruising (low throttle opening) in a car in a highish gear, at
low revs, that's bound to emit less pollution for a given journey than
similar revs in a lower gear at lower speed - because those revs are
being used for far less time. Assuming the engine's running fairly light
loads, the emissions per minute will be close enough to equal to make no
difference, but if you do the journey in half the time....

"W K" wrote in message
...

london-research speed data used to be, which
showed pollution per km is best around 45mph (except NOx)

Perhaps because in london, any road where you are going less than 40 is
horrendously stop start.

Even supposing that the research was London specific, where
could you average 38mph and be horrendously stop start?

"Adrian" wrote in message
. 1.4...
W K ) gurgled happily, sounding much like they were
saying :

What is the fuel consumption of a modern, standard CAR at 20, 30 and
40?

Enlighten me.

I don't actually know.

YOU made an assertion that pollution would be greater at 20 than at 40
or
50.
If that assertion has any basis of truth, you could do with telling us.

The easiest way to get an approximation would be to look at the old-style
fuel economy figures - urban, constant 56 are probably close enough to
what
we want for this.

The constant 56 figures were always WAY better than the urban ones. That's
a good indication that there's a lot less pollution at free-moving speed.

Complete ********.

The urban figures simulate stop-start driving, the steady 56 _did_ not.

"Adrian" wrote in message
. 1.4...
scott ) gurgled happily, sounding much like they were
saying :

Try this for a laugh, swim 10 lengths as fast as you can, then 10
lengths quite slowly. Which one do you think you've used most energy
for?

I know cars are very different

Erm, yes.

but you still have the basic mechanics of pushing an object
through a fluid at speed.

I don't often drive through "fluid", and my car has more than one gear.

A fairer example would be cycling.

Cycle ten miles, on the flat, at a certain pedal cadence (engine rpm) in
a low gear.

Now cycle ten miles, on the flat, at the same pedal cadence (engine rpm)
in a higher but still comfortable gear.

See the point yet?

Yes, the second is far far better for you.
There will be lower forces on legs and muscles.

If you're cruising (low throttle opening) in a car in a highish gear, at
low revs, that's bound to emit less pollution for a given journey than
similar revs in a lower gear at lower speed - because those revs are
being used for far less time.

This assumes the same throttle position.
In all but the slowest of speeds (see below), this will not be the case.

Assuming the engine's running fairly light
loads, the emissions per minute will be close enough to equal to make no
difference, but if you do the journey in half the time....

The speed where this happens is far from obvious.
As I stated elsewhere, the only place I have seen such things discusses was
by people who loved their monstorous 4x4s

W K ) gurgled happily, sounding much like they were
saying :

As I stated elsewhere, the only place I have seen such things
discusses was by people who loved their monstorous 4x4s

*Bzzzzt*

I can't stand "monstrous 4x4s"

Adrian wrote:
scott ) gurgled happily, sounding much like they were
saying :

Try this for a laugh, swim 10 lengths as fast as you can, then 10
lengths quite slowly. Which one do you think you've used most energy
for?

I know cars are very different

Erm, yes.

but you still have the basic mechanics of pushing an object
through a fluid at speed.

I don't often drive through "fluid",

Really? Mastered the art of driving through solids or in a vacuum have you?
;-)

and my car has more than one
gear.

A fairer example would be cycling.

Cycle ten miles, on the flat, at a certain pedal cadence (engine rpm)
in a low gear.

Now cycle ten miles, on the flat, at the same pedal cadence (engine
rpm) in a higher but still comfortable gear.

See the point yet?

Yes, if I go fast cycling I get hot and knackered. I get there quicker but
I've used more energy. If I take it slowly I don't get hot and hence don't
give off as much "heat" pollution. On my bike I can get to about 20mph for
a few minutes at a time, if I drop that to 15mph I can go for *much* longer.

If you're cruising (low throttle opening) in a car in a highish gear,
at low revs, that's bound to emit less pollution for a given journey
than similar revs in a lower gear at lower speed - because those revs
are being used for far less time.

Yes, but you'll be using less petrol. A lower speed = less power from the
engine. This = less pollution.

Assuming the engine's running
fairly light loads, the emissions per minute will be close enough to
equal to make no difference,

How do you work that one out? If I'm using more power to go faster, surely
I need to be using more petrol? As air resistance increases with speed
squared, the amount of petrol used goes up quite quickly once you get to
higher speeds.

"Nick Finnigan" wrote in message
...
"W K" wrote in message
...

london-research speed data used to be, which
showed pollution per km is best around 45mph (except NOx)

Perhaps because in london, any road where you are going less than 40 is
horrendously stop start.

Even supposing that the research was London specific, where
could you average 38mph and be horrendously stop start?

A580 within the M60 could well fit the bill.
Are there many roads within london where you can do an average 38?

I was going to say 30.
I'd still be interested how they got the information.