03-06-2017, 08:37 AM
For what it's worth, the knee pain is likely due to something other than the length of the ride. In most cases, it can be traced back to poor use of gears and/or poor fit and you are only noticing the affects the more time you spend on the bike.
You seem to be mechanically-minded, so you probably make ample use of your gears, but it is really common to see people mashing away at a very slow cadence in a hard gear. This is going to put more stress on your knees and tire you out more quickly. It is safer and more efficient to pedal at a higher cadence, I say at 80 rpm minimum, but most people seem to agree that 90 is ideal and it neatly meshes with the generally agreed-upon ideal cadence for running at 180 spm. For city riding, this can be especially problematic since you are stopping and starting more often, and therefore should be changing gears more often as well, and using the full selection available to you (the small chain-ring exists for a reason people!).
Fit can be a bit more tricky to dial down perfectly on your own, but is something that a lot of people also get wrong. The key dimension with regard to knee pain is the distance between the seat and the bottom-bracket. Increasing the distance will increase the knee angle through the entire pedal stroke. The lower the angle of the knee at the top of the stroke, the more likely you are to have problems with your knee. Too high and you will have problems with power through the bottom of the stroke and you will likely also rock your hips or point your toes which will cause you other issues. The simple rule of thumb is to raise your seat as high as you can while still being able to pedal without rocking your hips. Normally you will find that your leg is noticeably, but just slightly, bent at the bottom of the pedal stroke if set in this position. Note that if you raise the seat, the reach of the bike (distance from your seat to the handle bars) will also likely increase with normal bike geometry, so you'll probably want to adjust the height of the handle bars or the seat position to compensate.
You seem to be mechanically-minded, so you probably make ample use of your gears, but it is really common to see people mashing away at a very slow cadence in a hard gear. This is going to put more stress on your knees and tire you out more quickly. It is safer and more efficient to pedal at a higher cadence, I say at 80 rpm minimum, but most people seem to agree that 90 is ideal and it neatly meshes with the generally agreed-upon ideal cadence for running at 180 spm. For city riding, this can be especially problematic since you are stopping and starting more often, and therefore should be changing gears more often as well, and using the full selection available to you (the small chain-ring exists for a reason people!).
Fit can be a bit more tricky to dial down perfectly on your own, but is something that a lot of people also get wrong. The key dimension with regard to knee pain is the distance between the seat and the bottom-bracket. Increasing the distance will increase the knee angle through the entire pedal stroke. The lower the angle of the knee at the top of the stroke, the more likely you are to have problems with your knee. Too high and you will have problems with power through the bottom of the stroke and you will likely also rock your hips or point your toes which will cause you other issues. The simple rule of thumb is to raise your seat as high as you can while still being able to pedal without rocking your hips. Normally you will find that your leg is noticeably, but just slightly, bent at the bottom of the pedal stroke if set in this position. Note that if you raise the seat, the reach of the bike (distance from your seat to the handle bars) will also likely increase with normal bike geometry, so you'll probably want to adjust the height of the handle bars or the seat position to compensate.