My Sporty came with 205-70- 15's and I switched to a 235-75-15 A/T. To figure out my actual speed, I Compare my odometer to mile markers. I found it was 10% off. I found my odometer was reading 200-215 miles @ my usual fill up, but it used to read 240-250. That's about right if there is a 10% difference. The tire calculater says there is 9.8% difference in the 205-70-15 and the 235. If the kia speedo is slow from factory, than maybe the 205-70 instead of 205-75 is the tire that runs true with the speedo.

99 Sportage 2Dr, 1.5" body lift, 30x9.50 Cooper M/T's, high lift, CB, custom bumpers, Warn manual hubs, Tom Tom GPS, snorkel.
99 Jeep Cherokee 3" lift, 31" mud terrains