On Oct 8, 12:18*pm, The Natural Philosopher wrote:
Dave Baker wrote:
"Chris" ] wrote in message
]...
I would like to make a graph of car fuel consumption versus speed.
My driving is not smooth enough to gather the raw data myself.
Do you know of any reliable figures, or graphs?
I'm interested in relative values, rather than those for any particular
car.

The equations and sample data are on my website.

http://www.pumaracing.co.uk/TOPSPEED.htm

Excellent site Dave. And it shows that for 100mph about 70bhp/ton is
fairly close. and no more than 35 needed for 70mph.

However it does seem to be a bit conservative - many cars exceed 60mpg
at 56mph, and also the fact of the matter is that so long as the big
heavy cars aero losses are well below the frictional losses it doesn't
matter a damn what speed it goes at. I.e. my old Jaguar would never ever
turn in better than 27mpg no matter how slow it was driven. Typically it
did 19-20mg. To get 27mpgh required it to be trundled at - yas - 56mph
constantly. One stop would ruin it!

It does show that there is plenty of room fr improvement though. Low
friction small turbo charged engine, and lighter more aerodynamic cars
and skinnier tyres could still have the speed. *motorcycle has the speed
but not the fuel consumption, after all.

Hmm!
10 cubed = 1000
20 cubed = 8000
30 cubed = 27000
40 cubed = 64000
50 cubed = 125000*
60 cubed = 216000*
Maybe the fact that it almost doubles between 50 and 60.
And:
63 cubed = 250047 (Hey that's double the number at 50 so anyone going
'just a bit over' not plus ten per cent or anything!
Just a thought anyway.
PS. Seem to remember from wind loading on radio antenna on tall
towers; something about Pressure = 0.003 times the wind velocity
squared????
For example at 30 mph; p = 0.003 x 900 = 2.7 lbs per square foot.
(Roughly say 3)
Whereas at 100 mph p = 0.003 x 10,000 = 30 lbs per sq.ft.
So that's at variance with the cubed theory?