I put a 100/90 x 18 on the front of my R26 and it is just a tad bit too big and is rubbing very very slightly on one side of the fender. The fender does look to be centered and the wheel is straight enough, not perfect, but good enough for the small rides I take the bike on.
My local shop matched me up to the 100/90 saying it was only slightly wider than my 3.50 x 18. But that little bit is just too much. So I'm looking for a stock english size tire to try next. Brand isn't important to me since I don't ride this bike hard...Cheng Shin, King, whatever will hold air will be better than the dry rotted one I removed.
Anyone know where I can get one?