Speedos and MPH

[mit-eddie!cs.utah.edu!mjb%hoosier@EDDIE.MIT.EDU (Mark Bradakis)]

Hopefully your tach is working reasonably well.  For the TR250 and 6 the
relationship is pretty simple.  The speed is roughly twice [*] the tach,
that is, 3,000 rpm means you are going 60 mph.  This assumes tires of
a diameter similar to the 185/15 Michelin.  Around 25.5", I think, I can't
remember offhand.

A jumpy needle may just be poor cable lubrication, or it may be the bearing
in the speedo head itself is getting to the point of failure.  Oil the cable
first, see if that helps.

mjb.