Dear All,
Having recently replaced the gearbox and speedo cable in my non O/D
1500, I have noticed that the readings I am getting on the speedo are
lower for a given engine speed than hitherto. For example, at 3000 rpm
in top gear I used to see 51 mph on the speedo; now I see 46 mph.
I went straight to the Owner's Handbook and whilst it does not give a
table of figures, it does give the following:
Engine rpm at 10 mph in 4th - 555
Road speed at 1000 rpm in 4th - 18.0
If I assume that the relationship between road speed and engine speed is
linear for a given gear (and, ignoring air resistance, I can't think why
it shouldn't be), that means that the car should give 54 mph at 3000
rpm, regardless of which of these figures is used for the calculation.
Of course, it also means that the car should give 108 mph at 6000 rpm,
and we know that the correct figure is actually only a fraction over 100
mph, so there are performance losses of about 7.4% at maximum revs, and
presumably similar or lesser losses at lower revs.
Now, it would be rather handy to know whether I am doing 46 mph, 51 mph
or 54 mph at 3000 rpm (or rather, to know by what percentage my speedo
is reading low at a given speed). Does anyone have a formula to
convert rpm into road speed for a UK-spec 1500?
A corollary to the above question is, "Is there anything I can do to
calibrate my speedo?"
Any help, as always, will be most gratefully received.
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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