>From: Michael Hargreave Mawson <OC@46thFoot.com>
>Bad form to follow up my own posting, I know, but I have just come
>across a programme on-line which is supposed to calculate this stuff.
>According to this programme (which can be found at
>http://pw1.netcom.com/~sgalaba/mph.htm#GearSpeed), we should be getting
>55.97 mph at 3000 rpm in top (with 155/80R13 tyres). I don't believe
>it!
>
>Somebody, somewhere, must have the official Triumph figures, surely?
>Please? Pretty please?
>
Hi, Mike.
According to a reprint of the March 1975 test by Autocar Magazine:
Mph per 1000 rpm
OD Top 22.6
Direct Top 18.0
OD 3rd 16.2
3rd 12.9
2nd 8.3
1st 5.1
So, 3000 rpm in 4th would be 18 X 3 which equals...uh... 54 Mph? So
the program you've discovered is pretty close.
BTW, there are no frictional or wind resistance losses associated
with engine speed/road speed relationships. If you double engine
speed, you will double road speed (there is a very small factor
associated with the tires ballooning at speed due to centrifugal
force, but this can be ignored).
Another way that may be easier to calculate true speed, is to
put a drop of paint on your tires and roll the car. Measure
how far about the dots are and you can easily calculate how
many times your wheel turns in a mile. Multiply that by 3.63
(your final drive ratio) and that will be engine speed at
60 mph.
Cheers!
Greg Rowe
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