Pain behind my knee
 

I've been on a new bike for about a month. Anytime I ride more than 10 miles I'm getting pain behind my left knee. Either muscle or ligament strain.

I tried lowering the saddle and then I got pain in the front of both knees. Back to what I feel like is a good fit and getting the strain pain behind the left knee. Any other fit things I should try? Since it's only happening on one side I'm not sure if it is even fit related

Legs same length? Don't laugh.

yeah, it's odd how that works... my legs aren't the same length. It only takes a millimeter of difference. Lower the saddle a bit. Keep in mind that different shoes or different shorts can change the distance to the pedal. Hang in there, I hurt my knee a few months ago because of this (and I've been riding for years); it took a couple of months before the pain was completely gone.

What kind of gearing are you using? Are you spinning enough? Pushing/mashing too hard in a higher gear?

Are you stretching adequately? The seat combined with tight hamstrings could be an issue.

Thanks guys. I didn't really consider legs being different lengths. I would guess most people's are slightly different lengths. I don't think mine are noticeably different.

I probably could also stretch more than I do

Seems like an endurance issue. But why is it localized to one side? Check with a rehab therapist.