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I don't quite understand the dynamics of the teeth during the pedal stroke, but on my XL Q rings the difference in height between top and bottom is massive, which means setting up the FD is a pain and the chance of the chain coming off if you shift whilst going over really rough tarmac is much higher.
In a word, faff. But if I was being supported by a team of world-class mechanics then I wouldn't expect to be having to pull over for a bike change caused solely by oval rings during the most important 3 weeks of my career. We'll never probably find out what the real problem was.
Aren't they meant to put slightly more chain tension on when they're at the 'high' point. I'd have thought it was negligable / manageable though.