After putting the 235's on my sportage, I have dropped to about 20-21 mpg instead of the 24 I was getting before. At there is a tire calculater that says your speedo is now 6.5% too slow. When your speedo says 60mph, you are actually going 63.9mph. Also, check your tire pressure. It will make more difference on the bigger tires. The tire shop put my tires @32psi, but the max psi is 50. I run them at about 46-48 and I can feel the difference, besides at the pump. The ride is a little rougher, but I drive a 50 mile commute, so less rolling resistance, the better.

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