I did the "old, lift one wheel off the ground, turn the tailshaft" trick.

Here's what i found....just over 1.5 turns of the tailshaft gave a complete revolution of the lifted wheel.

This means (using the doubling required) that the diff ratio is most likely (if not certainly) a 3.08:1
Given i have a 235/60/15 rear tyre, this seems quite odd as to the rpm I'm seeing at 100 km/h....the fuel economy seems to support the rpm ;)

online calculators don't agree with what I'm seeing :(

My math says:
3000 rpm at engine =
3000 rpm tailshaft revolutions =
974 wheel revolutions/min = pi x diameter = 3.1415 x 663mm
2083mm/min =
2.083 m/min =
125 km/h?????


I've got something wrong????