From that Sheldon site on tyre width
For example, a 700 x 20 C road tire would be a 20-622; a 700 x 38 hybrid tire would be a 38-622. The width difference between these sizes would make them less-than ideal replacements for one another, but any rim that could fit one of them would work after a fashion with the other.
This is what I have found on the set of wheels I have for the Offroad Tandem. 26" wheels and 29mm rims. They are wide and most T's use a 2.3 tyre for comfort. I use a 2.1 and if just a short event will use 1.8's. And then there are the slicks for road use and they are 1.3's.That is going narrower but the majority of MTB's have a 17mm rim and some of these are fitted with really wide 2.8 tyres.
And as I mentioned- some cyclocross bikes are fitted with Aksiums and use a 32 tyre. So unless you are going for a really wide tyre- some are listed in excess of 40- then a standard rim will fit your tyre
As you can see- most of the replies have been about handbuilt wheels and there could be a good reason for this but there are plenty of "Off the shelf" wheels made that are good. All grades and makes of wheels will serve a purpose but the quality does go up with price--------"""Allegedly""".
If you ask me to stick my neck out and name a wheel I would like to buy- It would be a Krysium to suit my pocket or Shimano Ultegras as I have been very pleased with my "Old" set. They would be the performance wheel that I could afford but I still would not dismiss the handbuilts.
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How long was I in the army? Five foot seven.
Spike Milligan