I've been using the Topeak beam rack for commuting for about a year. I've never had a problem with the rack twisting, as long as I tighten the clamp down. However, I'm considering going over to the Arkel beam rack and Tailrider trunk bag because the clamp on the Topeak has begun to bother the insides of my thighs when I ride. Not sure when it started (no, I haven't gained weight since I started using the Topeak), but it's started to annoy me.