Well the obvious answer is to see if there's a hump in the tire... Most tires have a thin molded rib/line just above the bead. When mounted on a rim this line should sit about 1-3mm's above the rim, BUT more important then the 1-3mm's is that this line should sit the same amount above the rim all the way around the wheel and on both sides. A close look at while slowly spinning the wheel is usually enough to follow this line and it's proximity to the rim. Andy.