In my experiance, there are 2 things you can do.

1) Put on *removable* ground affects. - I actually tried this on my early bronco. Did it help? Yes, but not much. Was it worth the trouble? No, not really. It was a PITA. Not to mention that many people were doing a lot of pointing and snickering. Sure, I can take it, 'cause I'm certifiably insane, but many can't. <img src="/forums/images/graemlins/smile.gif" alt="" /> <img src="/forums/images/graemlins/lol.gif" alt="" />

2) Pizza cutter tires. - If you can believe it, the best mileage I ever got was from a set of 33x9.5 that I tried on for size. I burned a whole tank and actually gained a few MPG. This is due less friction and frontal area. Is my tall/skinny tire data empirical? It's darn close.

If I add my experiance to those that have noticed the same thing, it leads me to that the Rodeo will be something like a 235/85/16.

Tall/skinny tires may be a point worth pondering. Maybe it's not a resolution, but could be a clue to some help.