I have an older LeMond Zurich with Mavic Open 20 wheels. There is a sticker on them that says 622×13 – 6106. I found this chart that gives suggestions for tire sizing for various rim widths over at Sheldon Brown’s site.
I measured the inside of the rim and I think they are about 13mm wide (interior measurement). I would like to mount 28mm tires but according to that chart I can only use tires up to 25mm wide. Is that correct? I looked at the frame/fork/seat tube and it appears to me that the bike could handle 28mm tires. What do you think?