[alga]

In general most speedos are calibrated for 1000 revolutions per mile. The Sierra tyre size is 185/60R14, which gives 887 revs per mile, which means 1.127 revs of the cable per wheel rev.

When I switched from mechanical speedo to digital, I used a Hall speedo sensor that sends 8 pulses per revolution in place of a cable. I calibrated the speedo for 5000 pulses per km (=8046 pulses per mile) and it is dead on.