snyler wrote:
>
> Marc Sayer wrote
>
> >This mixes several data into one pie and obscures the results. With any car,
> >once you get past a certain speed, the cd will have the largest affect on
> >mileage.
> Is that coefficient of drag, or cubic displacement?
>
> At 60 mph, a 1961 Bluebird will probably get better mileage than a 2001 5
> liter mustang, the Bluebird having a much lower engine displacement (and
> weight) but a much higher coefficient of drag.
As I said, mixing a lot of data into one pie obscures the relevance of each
datum. I also said "for any car," which means the data are really only relevant
to one vehicle at a time, and can't effectively be related to similar data from
other vehicles. Above a given speed, for any car (meaning a particular car make
and model with identical specifications) the cd (and not I don't mean a
reflective plastic disc either) is the key factor in fuel consumption at any
steady speed. Compare one car to another and lots of other factors become
relevant and also obscure the data you were looking at. But since those factors
are constant if the car remains constant, they are not relevant for the
discussion we originally headed off on.
>
> If that bluebird were able to (hypothetically) reach 60 in second gear,
> however, it would probably not get the fuel economy of the Mustang in
> high gear also going 60.
Granted, but again this links back to something I said in my original reply,
which was that gearing becomes a major factor at the extreme limits of the bell
curve and 60 in 2nd in a Bluebird is certainly extreme. However, I am sure I
could alter the variables enough to make it possible for the Bluebird to get
better mileage even at 60 in 2nd than a stock Mustang 5.0 liter at 60 in 5th.
For example we could put in a hybrid electric/gas powerplant that can run at
15,000 rpm. Again, the only way any of this means anything is if the variables
are controlled. Throw in enough variables and any test or comparison becomes
meaningless.
The discussion was gearing and specific engine efficiency, and how they relate
to gas mileage. Factor out all the other variables and then test the remaining
variables and you'll have a valid study.
--
Marc Sayer
82 280ZXT
71 FJ510
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