It's inner width is 21mm. Got some pictures.
http://smg.photobucket.com/albums/v8...ire%20Seating/ Seems like there's too much tube, as if it's bunching up or something. A little bit of rim tape is actually exposed in the left low spot in pic 2. The rest seems to be seated, even though it's weird. The low spots are staggered. The tube is meant for 700x28-32c. I read that others were having seating problems with this rim also. It's a WTB Laserdisc Trail 29er.