your mileage will be affected by the type of tire just as much as the size.
I have a 2005 reg cab 2.3 5sp manual Ranger, it has 11.25" front rotors and 3:73 rear gears. had it since new, currently at 315,000 miles. its seen a few sets of tires.
this was my work truck, 100% pavement, mix of suburban and country driving.
came with 225/70-15 on 6" wheels, which was OK. I ran the Conti's in the summer and Goodyear snow (not winterforce) in the winter. oddly, the Goodyear snows handled better than the Conti's.
235/75-15s produced a small difference in acceleration & braking, a little longer letting the clutch out but easy to get used to. mileage about the same. ran a set of Goodyear Wranglers and later General Grabber AT2s in that size. I like that size.
for a while I had a set of Goodyear Triple Treads in 245/70-16. big difference in clutch, acceleration, braking, hills etc. I did not like those. too heavy, they overwhelmed the Ranger and bounced too much. not good for a daily driver. dropped the mileage a bit.
currently running General KSI Slollom 225/70-16. being a dedicated winter tire they are squishy, and cost a mile or 2 per gallon.
before you screw with the speedometer check it with a GPS unit. according to GPS my larger tires are more accurate than the factory sizes were.
what size front rotors does a 97 have?
you'll need to consider your rear gear ratio, my guess is a 225/70-15 is a good choice for you.