as the title reallt tryin to work out final drives and would like a figure for the overal wheel and tyre diameter if a 12" wheel and tyre.

my guess is around 17 - 18inches

cheers Al

Depends on the size & aspect ratio of the tyre

I use this to calculate wheel and tyre sizes.

http://www.mintylamb.co.uk/?page=tyre.htm

145/70R12 and 165/60R12 have a diameter of just under 20 inches.