Tire Height Change From 8" to 10" Wheels

[blackdiamond]

I recently swapped out a set of 35x12.50x15 BFG KM tires with a set of 35x12.50x15 Cooper STT PRO tires.  I can't find the specs for the old KM tires, but the new KM2 is listed as 34.8 inches on a 10 inch rim.  The STT PRO is listed as 34.57 inches on a 10 inch rim.  I was surprised when I pulled my old KM spare out of the 4Runner today and it measured 34-3/4 inches on its 8 inch wheel and the new STT PROs are measuring right at 34 inches installed on 10 inch wheels. 

Anyone have an idea of the expected height difference between a 8 and 10 inch wheels?  Just curious...