Originally Posted by due ruote

I forgot to mention:

There is some minor squish to the chainstays from a kickstand installation. See pic below.

Rear spacing is 126mm. This surprised me for a 1971 bike. Maybe someone cold set it. String test looks good.

I tried my 32mm Paselas. The rear fit fine - see pic. The front had even more room but the American Classic axle must be slightly oversized by '70's standards, as it wouldn't seat in the fork ends, so no pic of that one.

I would guess you could go to 35mm without much trouble, depending on the tires and rims of course. These frames are also reputed to be excellent for 650b conversions.