In article <3B929796.6A2E7E1D@brit.ca>, Trevor Boicey <tboicey@brit.ca>
writes
>Michael Hargreave Mawson wrote:
>> The figure of 50.6 mpg at a
>> steady cruising speed of 50 mph was published by "Autocar" shortly after
>> the 1500 was launched.
>
> Ah. Not to diminish the figures, but "steady state" speed
>at 50mph is something else.The figure is useful to know but
>unless you meantion that figure is for "at 50mph" it could
>be quite deceptive.
Most "headline" mileage figures are simply the highest figures that have
been achieved. "Autocar" did its test at 50mph, which is where the
50.6mpg figure comes from; the official tests showed that at 56mph the
figure was 50.2mpg, not too far different. Get on a dual carriageway
and cruise for a while, and you should hit around 50 mpg.
>
>> 4-speed manual gearbox (no O/D)
>> Urban driving 29.4 mpg / 9.6 litres/100km
>>
>> 4-speed manual gearbox & O/D
>> Urban driving 28.7 mpg / 9.8 litres/100km
>
> This seems more inline to what listers are reporting,
>most listers seem to do a little worse but I like to
>think it's because the listers are such "spirited
>drivers". ;>
And the fact that the engines are now 25-30 years old, and most will be
at least slightly worn.
>
>> In other words, an O/D actually costs you more in fuel in urban driving
>
> Does the spitfire of that year come with a different
>axle ratio when you have overdrive?
Not that I'm aware of.
>
> I guess I'm a little surprised that the OD could cost
>that much mileage, considering it's easily spun by
>hand and easily carried.
"That much"? It is a tiny difference really (and might well be down to
experimental error).
>
>> Even basing your calculations on the US gallon, a standard UK-spec
>> Spitfire 1500, straight from the factory or showroom, should give you 42
>> or 44 mpg on the freeway, depending on whether it has an overdrive or
>> not. Pump your tyres up a bit, and you might get even closer to that
>> magical 50 mpg!
>
> A good data point, but I don't think mpg@50mph is the most
>useful figure to state,
This is at 56mph - and the US speed limit on the freeway is 55, is it
not? I'd have thought that this was really quite a useful data point
for US drivers.
> since the rest of the world is thinking
>of combined fuel economy figures, which are obviously much
>lower.
But how do you define them? A driver who only ever drives on open
roads is going to get very different fuel consumption figures to those
of a driver who only ever pootles around town. All you can do is quote
the extremes - stop/start driving; cruising; and high-speed. In other
words, "Urban Cycle;" "steady 56mph;" and "steady 75mph".
>
> At a true 50mpg it would make it sound like the Spit is
>among the most economical cars on the road, when the true
>figure puts it way way way down there. ;>
>
What is the "true figure"? And what are you comparing it to? Bear in
mind that the figures quoted for new cars are all based on the same
tests that the Spitty went through in 1978. "Fuel economy of up to 50
mpg" would still be a proud boast of any modern car manufacturer.
ATB
--
Mike
Michael Hargreave Mawson, author of "Eyewitness in the Crimea"
http://www.greenhillbooks.com/booksheets/eyewitness_in_the_crimea.html
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