Ages ago with my wife's bike at the time, she sat sideways on the rear rack and I rode, for only a few kilometres and I was super careful. I was skeptical but was surprised that all went well. Even the rear wheel spokes didn't complain, and that 32 spokes 700 bike is used by my daughter and still fine. I'm sure I've readjusted spoke tensions at some point, but other than a slightly depressed top of rack, everything survived.