Calibrate Speedometer

[AZVIPERS]

I am changing the stock 17" rims on my 98 Gts to the Hre 18" rims. What do I need to do or install to calibrate the speedometer?

 

[ruckdr]

AZVIPERS,
Original Equipment Front 275/35-18
Original Equipment Rear 335/30-18
(Original Equipment Front 275/40-17)
(Original Equipment Rear 335/35-17)
If you use the Original Equipment tires for the 18 inch rims, listed above, the overall diameter difference between the 18" wheels/tires, and the 17" wheels/tires should be within 1/2" ; No calibration necessary.