I don't mean permanently, but just for fun? Like 27.5 or even 26, just to see how far you could take it? (Assuming a disc road bike for simplicity.)
I was thinking it won't. I have 40mm tires on there at the moment, with very little breathing room. (Those are 28mm in the photo.) I was thinking it widened linearly, and then I took a closer look at the seat stays -- they are almost parallel where the wheel on the smaller rim would land.Damn, that might work...