Yes, a lot of cars seem to get better EPA ratings with bigger engines. BMW
has upped the displacement on almost all of its engines in the past 5 years,
and in more cases than not the EPA ratings have actually gone up. This is
probably due to the fact that they can run taller gears and still get good
acceleration, coupled with other tweaks which make the cars more
efficent/fool the EPA test cycle (like that lovely GM skip-shift feature:).
It makes you wonder how effective the European strategy is, where you can
buy a BMW 716i or a Merc S180 (ok, maybe not, but you get my idea). You'd
think they know something since fuel costs $4.40/gallon there, but maybe
their ideas are just a throwback to the days when cars were much lighter
than they are now. I did notice when I was in Munich that everyone just
guns the living daylights out of their cars from each stop light.
I have always wondered if there is an engine speed below which efficiency
gets worse, and if so, why? If you ever ride a bicycle, you know that the
human body needs a certain cadence for optimum efficiency...
Did anyone see that article in Road&Track (I think) a couple months ago
where they theorized that you could get the best mileage by running wide
open throttle at low revs in high gear? That sounds whack to me (not to
mention bad for the car), but they swore this was the case. The claimed
reason was that while friction goes up as engine speeds increase, pumping
losses are minimized when the throttle is wide open. So you can peel out
with reckless abandon from every stop light as long as you remember to
short-shift before 2000rpm. Uh, ok...
Peter
-----Original Message-----
From: Michael R. Clements [mailto:mrc01@flash.net]
Sent: Friday, February 09, 2001 1:40 PM
To: Phil Esra; ba-autox@autox.team.net
Subject: RE: fuel mileage
It depends on the engine, the gearing and the wind resistance. The latter
tends to dominate since it goes up exponentially with speed. The best engine
speed is usually low RPM but not necessarily the lowest; most (gasoline)
engines run more efficiently around 2000-2500 RPM than they do at 1500. This
"most" excludes Diesels and old fashioned pushrod monster displacement V8s.
You want to drive in your tallest gear, at the lowest speed that enables the
engine to rev into its efficiency range. While it depends greatly on the
car,
the cars I've owned seem to do best from 50 to 70 mph.
Drive up at Tahoe sometime (in the summer, on clean dry roads) and you'll
probably notice that you get better fuel economy up there. The air isn't
that
much thinner, but it's enough to make a difference.
Interestingly, speaking of engine efficiency, you'll find that some cars
actually get better mileage with bigger engines. Compare the Lexus GS300 and
GS430, for example. The only difference is the engine, a V8 vs. a straight
6.
And the V8 gets the same or better fuel economy (not to mention that 300 hp
makes it more fun to drive).
-----Original Message-----
From: owner-ba-autox@autox.team.net
[mailto:owner-ba-autox@autox.team.net]On Behalf Of Phil Esra
Sent: Friday, February 09, 2001 12:59
To: ba-autox@autox.team.net
Subject: fuel mileage
miscellaneous musing:
I was just wondering, and thought maybe someone here would know. What is the
most fuel efficient speed to drive at? My guess is that it would be at
whatever speed you're in your highest gear with the engine turning as slowly
as possible. But is wind resistance great enough that that's not true? Any
thoughts?
phil
(ps--got the bearing replaced, thanks for all the advice--made it home over
the bridge with no drama--had to replace the hub too, $492, ouch...)
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