it all depends, of course, on the size of the tires. This calculator will show the percentage you must add/subtract, depending on the size tires you choose.
Tire Size Calculator - tire & wheel plus sizing
'91 Tracker 8V, 1.6L, 5 sp, 4wd, 2dr, conv, CAMI, horribly rusty
'97 Suzuki Vitara 8v, 1.6L 5 sp, 4wd, 2dr, tintop, horribly purple
'61 NSU Quickly - 150mpg