> If you wanted to design a vehicle to get the best mpg possible on the
freeway,
> you would ideally design a motor with power output about equal to what is
just
> necessary to maintain that speed. Thus the motor runs a WOT all the time
where
> it is most efficient. Unfortunately, this leaves no power left over
passing,
> etc. Again, not very practical.
this is where a hybrid vehicle can deliver good mileage and good power on
demand. one motor to sustain speed and charge battery, another to blast
from the stop lights.
-james c
*** note that my replies are typically not delivered to the list until a few
days after i send them, stupid pacbell ***
----- Original Message -----
From: Andy McKee <andrewmckee@yahoo.com>
To: Giles Douglas <giles@vy.com>; Pat Kelly <lollipop@ricochet.net>
Cc: Phil Esra <philesra@hotmail.com>; <ba-autox@autox.team.net>
Sent: Friday, February 09, 2001 5:18 PM
Subject: Re: fuel mileage
> Gas mileage depends on a whole lot of factors and people often confuse it
with
> efficiency. A gas motor is most efficient, as in you're getting the most
out
> of it for what you put in, at wide open throttle. This seems
counterintuitive
> unless you also take into acount that pretty much every car on the road
has
> plenty of excess power to maintain freeway speeds.
>
> If you've ever followed the Super Mileage competitions, where Universities
from
> around the world go for the highest mileage, you'll realize that they are
> achieving something like 3500mpg (not a typo). Of course, that is with
bicycle
> sized vehicles with aerodynamic bodies running on 1 cylinder motors. They
> achieve the high mileage numbers by employing a "burn and coast" method.
This
> is done by running at WOT (most efficient) up to a certain speed, then
coasting
> down, then WOT throttle again, etc. This averages out to the best
mileage, but
> is not necessarily an approach you want to take on the streets.:-)
>
> If you wanted to design a vehicle to get the best mpg possible on the
freeway,
> you would ideally design a motor with power output about equal to what is
just
> necessary to maintain that speed. Thus the motor runs a WOT all the time
where
> it is most efficient. Unfortunately, this leaves no power left over
passing,
> etc. Again, not very practical.
>
> Your every day car's mileage depends on where in the motor BSFC (brake
specific
> fuel consumption) map it is operating, which takes into acount throttle
> position, RPM, etc. How much throttle is necessary depends on what load
you are
> asking the motor to overcome. Contributors to that load are rolling
resistance
> (can't remember for sure, but I think this goes up linearly with speed)
and air
> resistance. The force of air resistance goes up with the square of speed,
and
> the power required to overcome that force goes up with the cube of speed.
>
> I don't think there is any kind of ideal speed for all cars, with regards
to
> fuel economy. It really depends on each cars motor specs, weight, Cd, and
> other factors. In normal operation, the common sense of keeping RPM's
down,
> easy throttle useage, etc. will probably yield the best results.
>
> -Andy
>
>
>
>
> --- Giles Douglas <giles@vy.com> wrote:
> > Thats a good excuse - rates up there with the "but the dial only says
> > 30mph" (looking at the tach.)
> >
> > My to-be-disposed-of-tomorrow Lexus RX300 seems to purr along nicely at
> > 55mph, but any faster (or slower), and its gas mileage drops off hugely.
> > Very noticable driving I5 to LA. You can either drive 55 and make it to
> > the mountains without stopping, or 85 and fill up at Harris Ranch. I
> > usually take the latter approach.
> >
> > And anyway, I can't autocross a RX300, so what use is it? Now, when my
new
> > audi allroad is broken in.....
> >
> > Which leads to another point. What class would the allroad be in? I'm
> > guessing AS, same as the S4? (It has the 2.7turbo) Hopelessly
uncompetitive
> > of course, due to its weight, but at least it can get across the sand at
> > Marina!
> >
> > Giles
> >
> > On Fri, 9 Feb 2001, Pat Kelly wrote:
> >
> > > I sort of feel like the 55mph deal was an excuse for the govt to rake
> > > in more bucks from tickets. Yes, it was in response to the fuel
problem
> > > (crisis), and the other argument was it made the freeways safer
because
> > > of the lower speeds. Since then, part 2 has been proven incorrect,
since
> > > the deaths per mile have dropped significantly since the speed limits
> > > were raised. As for part 1, since then, the automobiles themselves
have
> > > become far more efficient, and probably burn less gas at 70 mph than
the
> > > 70s cars did at 55.
> > > Remember the cars that were built in the late 70s that had
speedometers
> > > that pegged at 85 mph? So you could be toodling down the freeway at an
> > > indicated 85mph and really be going much faster. :) "Officer, the
speedo
> > > read 85."
> > > --Pat Kelly
> > >
> > > Giles Douglas wrote:
> > > >
> > > > Doesn't it depend on the car (and more importantly, its weight and
drag
> > > > coeffecient?) But in general, I thought it was like 55mph (or used
to
> > be),
> > > > which is why the US speed limits were set at that during the 70s oil
> > > > crisis.
> > > >
> > > > Giles
> > > >
> > > > On Fri, 9 Feb 2001, Phil Esra wrote:
> > > >
> > > > > 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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