Originally Posted by
big john
It's the rim that makes it difficult to mount the tire. Some tires are harder than others but rims that don't have a low "valley" in the center don't have a place for the tire to go to relieve the effective diameter. I don't see how having a tube in there could have an effect on it, the tube will get out of the way.
First part is true. The Mavic UST rims have a very shallow valley.
Second part is empirically true - the difference between fitting the Yksion tires on the UST rims, with and without a tube, is night and day. It seems that the tolerances are just so tight that the little bit of interference of the tube doesn't allow the tire bead enough space to lengthen that apparent radius.
If anybody out there using the UST rims and Yksion wheels has a different experience, I'd be interested to hear.