Tubs

I have the possibility to buy some Assos tubular rims and been doing some research but how true is what this person is saying -

"Leeh,

Your 20mm rim width is probably about right for a 22-23mm or larger tub. Remember that the rim doesn't go 180 degrees around the tyre. Because they don't have the hooked flanges of a tyre rim, the tub rim actually covers less of the tyre section than a conventional rim.

With tubs, the rim width has less effect than normal tyre/inners, where the rim width affects the shape and cross section that the tyre/tube forms. Even the 2.2"/56mm mountainbike tubs around now are fitted to only 25mm wide rims.

With tubs, the most important measurement is the diameter of curve of the tyre seat. You should find that a circle approximately the size of your tub cross section ie 22mm should sit nicely on the curve of the rim tyre seat without any gaps, allowing for the thickness of any adhesive. Try a mountainbike handlebar, 1" quill stem, wedding ring, or 7/8" 22.2mm copper pipe. Alternatively, pump up the tub a little and offer it up to the rim section to check. Don't worry about the pressure turning it inside out. It can take full pressure even off the rim.

If the tub is too small for the rim, there wil be gaps at the sides. This stops the glue/tape working at the sides, and the tub can roll. The tubs will also be far harder to get sat straight. Fit the tub on the rim without adhesive and see what it looks like, a sheet of paper should be a nice tight fit in the gaps around the sides.

Less serious is a big tub on a small rim, where the centreline of the tub isn't in contact with the rim, but there's still not really enough adhesive in contact to be safe.

This is why, even though those Assos rims were really narrow at 16mm wide, the curve of the tyre seat was still shaped to take up to a 22mm tub.

I hope that helps....All the best"