(I am back from a nice vacation up in the frozen, snow-covered (mostly) New
Hampshire. Spent quite a few days exposed to cold, some warm too, skiing,
and I still haven't gotten Bell's palsy. Maybe x-cntry skiing generates too
much heat...)
About speedometer/tachometer comparisons, a friend who used to have a '69
Spitfire Mk 3 (and his wife who drove a '68 Mk 3) used to tell me how the
Spitfire tach and speedo needles ran parallel when in 3rd gear, which is
decidedly not the same as the implied 4th gear comparison as someone here
described for E-type Jags. So the issue as we saw it was whether that was
intentional, and whether Triumph tried to repeated it on the 1500's. On my
1980 Spitfire 1500, the two needles behave almost the same way, i.e. almost
parallel in third gear, but it can't be quite correct over all speeds since
the resting (zero) points aren't the quite the same. Still, over the useful
rpm/speed range, the two needles are nearly parallel in 3rd gear, as they
were for Rich's and Steph's Mk 3's. It sort of raises the question of what
Triumph (or BL) did during the Mk IV's short life, when the final drive ratio
bounced all over the map while BL tried to decide if people bought it for its
performance (!) or for its gas mileage. Regarding rpm/mph, in 4th gear with
OD engaged, the speedo reads about double the tach, i.e. 3000rpm <=> 60mph.
The theoretical numbers of rpm per mph are close to this too, though not exact.
So if your Spitfire 1500 ever blows its speedometer cable, you can figure your
speed from 3rd gear, or from OD-4th if you have OD.
Jim Muller
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