tires

i have a few questions. first of all, what is the tire size of the tires on the 4x4 s-10 models. secondly, i have the 15x7 2 wheel drive rims and am wondering if the 4x4 tires would ft on these rims.

also, would the difference in size between the 2 wheel drive tires and 4 wheel drive tires affect my gas milage by that much, or offset my odomoter speedometer?

i have 31-10.50's on my 95 4wd on the newer style rims and i get 19 -20 mile to the gallon94.3 vortec)

i have 31-10.50's on my 95 4wd on the newer style rims and i get 19 -20 mile to the gallon94.3 vortec)
this is the factory size tires