Sorry, I didn't mention that I don't ride fixed gear, I just have a freewheel. I've also rode BMX bikes for 5 years and had fallen on my knees many times, so maybe my knees are just getting cashed out. Usually when I ride over 30 miles, I'll start to feel it. The most I felt it was when I did a 90 mile bike charity ride, but it might be possible that my seat isn't dialed in either. Thanks for all of your help.