I just finished building my first fixie, and I've been riding for 3 weeks so far, every day roughly 5-10 miles in Philadelphia (not that hilly). I feel like I can skid properly, by putting myself up on the handlebars nice and far and locking up comfortably. However, I feel sore fairly often now, but I'm hoping it's not from the fixie. I'm convinced that they would help you build up knee strength. I guess I was wondering if anyone had any routine stretches that really help them feel good before riding? I used to ride a 12 speed bike set in top gear all the time and I never shifted...that was for about 6 months. I think that is almost definitely the contributing factor to knee pain, although during that time period I felt fine and was hauling ass everywhere. Currently I ride 42:15. Should I give it time and see if my knees improve, or drop the ratio down immediately? I'm pretty worried, because fixed is the new love of my life and I don't want to ruin myself because of something simple I'm not noticing. Thanks for any input.