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

So. Whose engine is working harder?

Well assuming both drive the same speed, the bigger car is probably
generating more power as it has to shift more weight around.

Yet the bigger engine may well be running at much lower load.

Assuming
both engines are equally efficient, the bigger car is therefore
generating more pollution. At constant speeds the power will be
closer matched, although the bigger car probably has more drag, so
again, bigger car makes more pollution.

Not so. It's far easier to make a large car more aerodynamic than a short
one, both in terms of pure aerodynamics and in terms of packaging. Frontal
area comes into play via CdA, but there's not that huge a difference
between the frontal area of a short car and a long one where both are
required to offer similar interior space, as the long car doesn't have to
be as tall.

In short, it's impossible to say.

On 6 Apr 2004 08:23:45 GMT, Adrian
wrote (more or less):

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

So. Whose engine is working harder?

Well assuming both drive the same speed, the bigger car is probably
generating more power as it has to shift more weight around.

Yet the bigger engine may well be running at much lower load.

Assuming
both engines are equally efficient, the bigger car is therefore
generating more pollution. At constant speeds the power will be
closer matched, although the bigger car probably has more drag, so
again, bigger car makes more pollution.

Not so. It's far easier to make a large car more aerodynamic than a short
one, both in terms of pure aerodynamics and in terms of packaging. Frontal
area comes into play via CdA, but there's not that huge a difference
between the frontal area of a short car and a long one where both are
required to offer similar interior space, as the long car doesn't have to
be as tall.

In short, it's impossible to say.

Of course, aerodynamics don't come into play until high speeds are
reached. (IIRC air resistance dominates over rolling resistance from
about 60mph)

At low and medium speeds, rooling resistance is more significant. In
which weight /does/ play a significant part.


Cheers,
Euan
Gawnsoft: http://www.gawnsoft.co.sr
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Adrian wrote:
scott ) gurgled happily, sounding much like they were
saying :

So. Whose engine is working harder?

Well assuming both drive the same speed, the bigger car is probably
generating more power as it has to shift more weight around.

Yet the bigger engine may well be running at much lower load.

What do you mean by "load"? In absolute terms, the heavier car's engine
will always be developing more power to make it move the same as a lighter
car. If you mean what % of maximum power though, that is going to depend on
the power to weight ratio of the car. I thought this was about pollution
and emissions, in which case I think the raw amount of fuel burnt would be
the main factor. Just look at the fuel economy factors for little cars and
big cars!

Assuming
both engines are equally efficient, the bigger car is therefore
generating more pollution. At constant speeds the power will be
closer matched, although the bigger car probably has more drag, so
again, bigger car makes more pollution.

Not so. It's far easier to make a large car more aerodynamic than a
short one, both in terms of pure aerodynamics and in terms of
packaging. Frontal area comes into play via CdA, but there's not that
huge a difference between the frontal area of a short car and a long
one where both are required to offer similar interior space, as the
long car doesn't have to be as tall.

In short, it's impossible to say.

I agree, you'd have to measure the drag on two cars, you can't say that all
big cars create more drag than smaller cars or vice versa. Longer cars do
tend to have a bigger frontal area though IMO, otherwise they'd look silly
like a stretch-mini or something! More importantly though, anytime you want
to accelerate the lighter car will always use less power.