On Fri, 8 Oct 1999, Cometman wrote:
> It's not long till my speedometer gear gets here from England, but I
> was told that in top gear, you double the rpms/100 to get the
> approximate speed.
It's not quite that simple with a Spitfire, although it works pretty well
with most GT6s and the big TRs, where each 1000rpm in top gear is worth
approximately 20 mph. On the earlier Spitfires with the 4.11:1 diff, 1000
rpm in top gear is worth 15.7 mph with original size tires; figure 16 mph
as an easier number to work with. Similarly, later Spitfires with the
3.89:1 diff will give around 16.7 (figure 17) mph per 1000 rpm in top gear.
> If you invoke the overdrive how does that affect
> the calculation?
It's a reduction of about 20% (although the later "J" type OD units might
be different? Help me out here).
--Andy
* * * * * * * * * * * * * * * * * * * * * * *
* Andrew Mace, President and *
* 10/Herald/Vitesse (Sports 6) Consultant *
* Vintage Triumph Register <www.vtr.org> *
* amace@unix2.nysed.gov *
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