>
>Does anybody know what size tires the TR-6 originally came with?
>I suspect that the tires on my new (?) TR-6 are considerably smaller
>than stock since the speedometer is rather, um, optimistic. It
>appears to be reading 20-25% fast. The tires aren't going to last
>much longer, and I'd like to get replacements which will give me
>reasonable speedometer readings.
>
> Jeff Lo
> jlo@elan.com
I don't have an owners manual in front of me, but near as I can
recall, the original tires were 185-15. You didn't mention
what size tires are on the car now, but if the speedometer is
off by the 20-25% you believe, the tires are not the source of
that much error. Probability is the speedometer itself.
A common problem with the speedometer is that the return spring
may have weakened with age, thereby giving a higher reading
than actual speed. The speedometer works by the cable turning
a wheel with magnets on it. That wheel is adjacent to a wheel which
has the speedometer pointer mounted to it, but with a spring attached
to prevent it from fully turning. The movement of the wheel with the
magnets causes the wheel with the pointer on to move also with the
spring providing resistance.
Calibration of the speedometer is therefore a function of the
spacing of the magnets to the pointer wheel AND the effective
resistance
of the return spring.
Additional external factors are the tires, but not to the amount
of error you believe is occuring in your TR-6.
Bill Sohl
Vintage Triumph Register president
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