Tire size question

[DebW]

I'd suggest finding the make and model of the rim and going to the manufacturer's web site. They should provide specs on the tire sizes that rim can accomodate. If that doesn't work, you could take off the tire and measure the rim inner width in mm. There is a chart here http://www.sheldonbrown.com/tire-sizing.html (near bottom of page) that gives recommended tire widths for a given rim width.