A 245/75r16 tire is very well matched
with 4-12 Speedo gear and 32-7 differential
245/75 r16 tire is nominally specified at 662 revolutions per mile according to generic tire size specifications
vs the 656.25 revolutions of the ideal diameter tire for the above Speedo and diff ratios
If you have these ratios Your speedometer will be reading very slightly high compared to actual speed.
The math:
1000 revolutions per mile is the speedo input
1000 x 12/4 speedo gears is a drive shaft speed of 3000 rpm
3000rpm into a 32/7 ratio diff is 3000/32x7 rotations per minute or rotations per mile at 60 mph of 656.25
-s
