My knees bother me for the first mile or two, every single ride. I do try to pedal a little slower at first to warm up. The other crazy time they bother me isn't when I exert them but rather if I shift to a higher gear that seems like 'I am floating', in other words with no pressure or work required. My knees ache at pedaling air. Can't explain it any better than that, but that has stayed with me all season long.