Originally Posted by
Mulberry20
There is no way in hell you can or should run 28 tires on wheels of that era and width.
Even the old ETRTO recommendations are only one size away from allowing it, and they're
extremely conservative.
They will not seat properly even if they can be mounted at all.
They should seat just fine, actually. The concern with running wide clinchers on narrow rims isn't that the bead won't seat, it's that the narrow "neck" of the tire as it leaves the rim doesn't provide stiff bracing against side shear forces from the contact patch. So the tire may feel squirmier, and it may take less side force in a corner (for a given bicycle load and inflation firmness) to cause the sidewalls to "buckle"/"collapse," which would cause a sudden change in handling.
But a 28mm on 13mm-internal really isn't getting all that deep into "crazy" territory. Tons of people have done it extensively without incident. I've ridden such a setup for a couple thousand miles so far, the beads seat evenly around the rim no problem and it mostly feels alright.
The fact it is a 3 mm difference is totally irrelevant. A 28 mm tire will likely size 29 or 30 nowadays.
28mm tires often size 29 or 30 nowadays because people are mounting them on super-wide rims. Many new tires that are listed as 28mm will size
less than 28mm if they're mounted on 90's-style 13mm-internal rims. For example, the 28-630 Paselas that I have mounted on the Sun M13II rims on my old Miyata inflate to just under 27mm according to my calipers.