Larger tires will make to go faster than your speedo shows. Think about it this way; speedo is calibrated for original tire size --- let's say 30 inches tall; with 1 rev. of the tire you will travel about 94 inches (circumference of the tire); if you put on 36 inch tall tires; 1 revolution of the tire moves you 122 inches.

Also as far as officers being required to calibrate radar guns; I think it only applies to city and county officers (and they actually have to ask if you want it to be calibrated during the trafic stop) but the law says it doesn't apply to georgia state troopers.