I had the same problem on my new Orbea on one of my first rides and it was the brakes rubbing. Once I fixed that, I was flying! I'm so glad you guys are talking about this, because I had also been wondering if the flex could cause them to rub inadvertently while I'm riding, because off and on during rides sometimes it still seems like I'm pushing harder than I should, but when I stop to look at the brakes, they look fine! I think I'll adjust the cables and see if that helps overall.

-Jessica