Tom :
Guess everyone really did go to VTR !
Anyway, both my Haynes and Chilton just give the original tire size as
either 5.20S-13 bias or 145R-13 radial.
The Haynes also gives what you probably want :
3.89 ratio no OD gives 16.7 mph per 1000 rpm
3.89 with OD 20.8 mph per 1000 rpm
4.11 no OD 15.9 mph per 1000 rpm
4.11 with OD 19.9 mph per 1000 rpm
working these backwards, I get an effective aspect ratio of 77 for the
145R-13.
Tire makers were pretty casual about actual size and aspect ratio back
in the '70s, so these are approximations at best.
Randall
Tom Ambrose wrote:
>
> Another slow night. Does someone know if the original tire size on Spit Mark
> IVs were 155/80 or perhaps 155/70? I have the bolt-on wire wheels. They
> currently have 165/80s, a bit tall, but interesting.
>
> I have a busted tach drive on my distributor and I'm trying to figure RPM
> using MPH on my fresh engine among some other projects. A hassle to be sure.
>
> If anybody is out there,
>
> Tom
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