Bicycle Racks

you could add a piece of cloth in between the frame and the rack clamp, and don't overtight the clamp,

I initially used a length of foam pipe insulation to slide over my top tube (and under brake cable) before setting into the hang bracket. Key is to not stress the top tube with too much compression, but also don't leave it loose to bounce up and down concentrating travel forces on a small area.

Many people use "hang and dangle" racks for carbon framed bikes without any long term problems - others cringe at even the thought. Kinda something that depends on your "comfort zone" and risk tolerance.

I was due for a new rack anyway, so I quickly switched to a "platform" hitch rack - Yakima HoldUp - that works by wheel grab with no frame contact. Thule, Saris, Kuat, 1UpUSA, and others have similar product offerings if you are interested. Has been a great rack and takes only seconds to load/unload.