<VV> Tires & Speedometers
Chris & Bill Strickland
lechevrier at earthlink.net
Wed Sep 23 15:34:56 EDT 2009
All the tire size for "correct" speedometer readings chat is a bit
bogus, imo. If you want "correct" tires, get some bias-ply 6.00 x 13's
from Coker or somebody -- anything else is something less than
"correct". It may meet some rules at some goat show somewhere, but it is
not "correct". Many people went with 6.50 x 13's the first time they
replaced the factory tires anyway -- they were cheaper and in stock.
Nor did Corvairs did come originally with calibrated or "Certified"
speedometers -- they were just generic, mass produced speedos that
sorta gave you a rough idea of the road speed -- some worked rather
well, and some didn't. Calculated figures here are not real life, unless
you had one of those speedos that didn't come with the car. And because
they were such good winter cars, you put on a new set of sawdust
retreads (when new, they were almost always a much taller tire) at the
start of each winter season, and took them off when they went bald,
generally about August 1st, just in time for that summer trip to
California on the highway tires. Using someone else's tire data for your
speedo head, well, not everyone likes chocolate ice cream ...
*IF* it is important to you, you could probably do better by figuring
out what tire circumference gives your particular speedometer head the
greatest accuracy, and/or by sending your speedo head out to a shop and
get it "Certified" (used to need the whole car to do this - $$$) or at
least calibrated, and/or by having a speedo shop build you up a "ratio
adapter" to give you a correct speed for your speedo and the tires and
gearing that you choose, rather than making tire size choices based on
someone else's idea of how your speedo should read and what your car
should look like. Then when you put on your "winter tires" (for those
that drive year round), you just change the ratio adapter, too.
There are many shops that provide these services -- just one example is
http://www.speedometerservice.com/services.php
OR, you could just figure out that your speedo with those tires reads
about 8.6% fast, and then do the math, which was the "authentic" Sixties
way, for you Pure Stock types.
A college roomie bought a brand new Camaro in '67 and it would just get
us back to our hometown in no time flat, about an hour less than what we
had been driving it, until, smart college students that we were, we did
the math, and figured out the speedo was about 20 mph slow (and we were
driving it a little fast anyway) -- last I knew, he still had the car
with that same uncorrected speedo -- he just drives it accordingly, and
it is still oem as-delivered "stock", except maybe for the tires.
also see
http://www.rodandcustommagazine.com/techarticles/0801rc_mechanica_speedometer_calibration/index.html
Bill Strickland
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