> AFAIK, the 820 is the earliest USA speedo. I think they changed to 805
> during 1982 model production. Why, when same tires were used on both?
> Don't know.

My '81 has an 820.  It was built in January of '81.

Lots of rules changed from '81 to '82--emission standards,
etc.  Maybe the feds changed the rules of speedo tolerances?

My '81 reads X under the true speed, where X is the speedo
tens place.  In the twenties, it is 2 faster than the speedo.
In the thirties, three; forties, four....  So 60 on the
speedo is really 66.  Getting close to ticket tolerance,
or intolerance, eh?  That's not tire circumference, but
the spring the the speedo, I suspect.

Richard