Optimum fuel consumption cruising speed

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Robin Smith - 21 Jan 2005 08:28 GMT

Can you determine this by looking at the torque curve, ie sit the speedo on
the point where maximum torque is ?

thx

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Dave Gower - 21 Jan 2005 13:45 GMT

> Can you determine this by looking at the torque curve, ie sit the speedo
> on
> the point where maximum torque is ?

No. The main factor is drag, which goes up much faster than the speed. Being
at the torque peak on any Focus will put you far above the most economical
speed. However, at quite low speeds the engine revs do matter, so there is
an optimum speed, which is generally considered to be in the range of 70kph
(45mph). Anything up to 90kph (55mph) will still be quite economical, but
above that things get thirstier.

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Scott Thomas - 22 Jan 2005 07:16 GMT

>>Can you determine this by looking at the torque curve, ie sit the speedo
>>on the point where maximum torque is ?
[quoted text clipped - 3 lines]
> range of 70kph (45mph). Anything up to 90kph (55mph) will still be quite
> economical, but above that things get thirstier.

Agreed on the drag being a big issue - I have a 2001 SE (four-door)
that makes the long trip to and from Milwaukee (from northern IL, USA)
daily during the week, on a pretty open and straight stretch of road.
Since it's almost all multi-lane freeway, I've gotten a pretty good feel
on where the gas usage goes way up, just from watching the fuel gauge
vs. mileage on the trip odometer.

I notice a slight drop at anything above 65mph, and a significant drop
above 75mph. Cruising at a steady 72 will still get me over 30mpg, so
I'm happy.

Signature

Scott Thomas, thomass@cs.rose-hulman.edu
http://www.cs.rose-hulman.edu/~thomass/

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Freedom55 - 22 Jan 2005 11:21 GMT

>>> Can you determine this by looking at the torque curve, ie sit the
>>> speedo on the point where maximum torque is ?
[quoted text clipped - 15 lines]
> drop above 75mph. Cruising at a steady 72 will still get me over 30mpg,
> so I'm happy.

About 105 (about 65mph) is optimum for me. At 115 (72mph) I start
noticing the difference. It seems that 110 gives me the speed to keep up
to traffic and good (though not excellent!) mileage. 110 appears to be
the best compromise between speed and economy for my 200-ZX3.

Ron

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Robin Smith - 24 Jan 2005 12:34 GMT

Thx gents, good data

rgds

> Can you determine this by looking at the torque curve, ie sit the speedo on
> the point where maximum torque is ?
>
> thx

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