Ford Sierra aficionados and super-geeks on diff ratios

[Richard]

... and the answer was?

[AshleyO]

ok
roll of drums
we rolled both wheels round at the same time and the answer was very quickly 3.38m so that was easy
I am going to do the GPS test as a double-check, once the car is on the road

Meanwhile, now we have the diff ratio, and thus the calibration ratio, I have entered this but no reading on the speedo

[Tony C]

Sounds like you've sorted it now, but if you want a second check I've just done the following using guidance from YouTube

Raise one rear wheel off the ground so the other can't move. Rotate the free wheel ten times while counting the number of times the prop turns. Multiply the number of prop rotations by two, then divide by ten and you have the diff ratio

[DJ.]

Yes Tony, that's correct as Ashley found, if just one wheel is moving, you get half as many turns of the propshaft.
I wasn't talking rubbish after all