-
( @Danyutz )
Apols for the blurry first image.
23mm Conti GP4000SII on 23mm wide Kinlin Xc-279 rim.
Perspective of the second image throws the measurement a bit but when looking at it straight on, there's nearly 40mm between the legs at the point a tyre sidewall might rub.
Looks like height rather than width would be the limiting factor.
28s for sure, widthways should be able to fit 32s but could be very close to crown (which at that point is all alu by the way, so you could file the fork to fit the tyre).
Getting wheels at the end of the week, I'll tell you then.