There are a lot of factors involved here, not the least of which is the air
resistance increases by the square with speed. At speeds over 65 or so,
this becomes by far the biggest source of drag. I had a Fiesta in the 70s
for my demo while I was working as a salesman for Cal Worthington Ford; neat
car. But its Cs must have been around 1; no amount of gearing would change
the drag over 70! Just a box.
Mike
----- Original Message -----
From: <krazgeo@comcast.net>
To: <shotimes@autox.team.net>; "SHOTimes" <shotimes@autox.team.net>
Sent: Tuesday, August 15, 2006 1:32 AM
Subject: Re: [Shotimes] Speedo Error... was: My MPG Test is Working!!
> -------------- Original message ----------------------
> From: Alan Fanning <Awfanning@earthlink.net>
>
> > If a 5% reduction in final drive ratio nets an improvement of several
mpg's,
> > I question what the manufacturer's were thinking in not taking advantage
of
> > that.
> >
>
> This fact is what brought the whole thing to my attention. We borrowed an
'05 RX330 from the Sac Lexus dealer last summer, while Eva's (now sold)
RX300 got some diagnostics, and drove it over Donner Summit to Reno and
back. While working the tranny manually while using CC, I was able to get
about 25 mpg average while going 65 mph, when her 300 would only get about
18 on that trip. Its engine turned 2900 RPM at 65, while the RX330 turned
2200. With her driving around town, she didn't even get 14. The 300 had
GPS, while the 330 didn't, but had a trip computer. My GS doesn't have
either one.
>
> I discovered on the trip home (I-5, at 70 mph) from Oregon that the GS
still doesn't do as well as I'd like it to above 65 mph. At 70-72, it drops
down to somewhere around 25, while it will get 30+ at between 60 and 65. We
averaged about 27.5 on the I-5 trip home, when I would have expected it to
be at least near 30, after the previous day when it beat 30. The majority
of that earlier trip was at 65 and then 55 in Oregon. It's going to be too
hard to lower the engine speed by another 300 rpm or so, so I'll just live
with it.
>
> I discovered a similar rapid drop in mpg in my '78 Fiesta, which now is
owned by Jim Koper in Ohio. After it got its '98 European engine through
rebuilding, it got REALLY good freeway mileage (32-35) below 70 mph, where
it crossed over the 3000 rpm range. Above that speed the mileage dropped
down to about 25. So that is two vehicles I have seen where an engine speed
change of just a few hundred RPM makes a large difference in mpg.
>
> I'm still keeping the GS till the wheels fall off.
>
> George
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