Why do my knees hurt when I ride my single speed?
Knee pain can be caused by several different issues, most of which are addressed in the "Knee problems" section of the Rec.Bicycles FAQ. Single speeders, in particular, often experience some knee pain from riding. In addition to the suggestions mentioned on Rec.Bicycles, you may want to consider a lower gearing (related to question/answer #3), and/or a high-float pedal design like the Speedplay Frog, Time Atac, or Crank Bros. Eggbeaters.
Q: I just recently got into single speed riding. While it is wicked fun, I'm concerned about effects on my ancient knees. Can you shed any light on whether pushing big gears will damage ones knees? Is this a good training tool as many seem to insist? - Rob
A: Ahh the beautiful simplicity of the single speed bike. You can’t beat it…unless you choose a more efficient gear ratio. And there in lies your battle, the most appropriate choice of gearing to allow for your most efficient cadence for your terrain; which is easier said then done.
During your outings I am sure you have realized that there are really 3 intensities of single speed riding. Too hard, low cadence that you can barely turn over; too easy, cadence so high it makes you want to curl up and take a nap; and the sweet spot which is just right. That sweet spot is the time when you are moving in harmony with your surroundings, your speed is high but your HR and power output are low making this your (you guessed it) most efficient cadence for that terrain. Since you are motoring along with such minimal effort you could continue indefinitely, while your time at the other 2 intensities is not only limited, but they could pose some problems. The too hard - low cadence intensity seems obvious, it is high tension requires lots of power output and will cause muscle fatigue sooner than you want to admit. But will it affect your knees? More likely your knees will affect your riding. If you are predisposed to knee problems, or experience pain during running or squats you could very well have pain with repeated bouts of low cadence, high tension riding. If you do, first check your seat position and make sure it isn’t too low. But generally the problem is caused by a weakened quadriceps muscle that isn’t pulling the patella across the joint in perfect alignment. If that is the case you can strengthen the muscle by doing a ¾ leg extension exercise in the weight room. If that isn’t the case or you are unsure, I recommend a visit to your physician. As for the too easy - high cadence intensity, while it will drive your HR up due to the rapid movement (which will eventually exhaust you) it is a low power effort and therefore you should last as long as you have the patience to persevere. So is single speed riding a good training tool? Heck yah! This is the best way to focus on the trail in front of you without nagging misfiring or chain-suck issues. So get out and ride, and if your knees start to hurt, go home.
You can't expect 1 gear to cover all bases. If you ride towns and fairly flat areas at average cadence, then you may be ok. But mountain bikes and single speeding, to me, is pointless. That's why we have a range of 24 or 27 gears, so that whatever terrain we ride on, we have a gear that suits. The only thing I can think of worse for your knees than singlespeeding.... Is single speeding with a Biopace chainset! eeek!