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Let's say I have presta valve, so the outer hole in the rim is 6 mm (the visible hole). However rim can have inner "wall" inside with inner hole in it -- to my surprise the hole has bigger diameter.

Is it sign of low quality or is it norm around rim manufacturers?

My first reaction is "low quality" because bigger hole allows the tube to be rotated slightly, while the tight hole forces tube to be seated correctly with valve perpendicular to the rim.

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That's usual. I've had many rims in many sizes, width, walls, etc; and most of them are like that. But I don't know about rims for tubeless.

I think that they are made like that for two main reasons. In first place, to allow for slack for the valve when you mount it, even thought they are standarized sometimes you can get a "fatty" valve depending on the tube brand. The second reason, if to compensate for deflexion of the tube material under pressure, so it won't get pinned and punctured when you inflate. Because sometimes the valve it's thicker at the base.

Bye

3

The area at the bottom of the valve stem where the stem joins the inner tube has a larger diameter than the stem itself, and hence requires a larger hole in the inner wall of the rim.

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