Under 90gi with no snow/slush, inbetween lights my legs are just flapping. This is not good for my knees to do for over ten minutes. Flapping with nearly no resistance at over 100 rpm on flat streets for an hour has me creaking and in pain for hours. Slow takeoffs do not hurt them one bit. Ten years of mostly 52-14 in the city, 52-16 in the country hills, the only time that my knees can tolerate a significantly lower gear is when there's enough snow and wind to provide ample resistance. I'm definitely too old to be part of the hipster horde.