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Discussion Starter · #1 ·
I have two bikes. One with 170s (which is my usual length I have always ridden) and one with 172.5s (cross bike and the added length was due to Burney's suggest that longer arms = more leverage to power through the rough stuff).

I've mostly been doing very short (30-40 minutes) evening rides on the 172.5 bike and have been suffering from pain in my left knee behind and to the inside of the knee cap (where lower inner thigh meets upper inner calf). Feels like I hyperextended it. I haven't checked lately, but both bikes are set up very closely, with saddle height adjustments made to accommodate the added arm length.

Am I missing something? Should I replace the 172s with a pair of 170s and re-set-up? What other suggestions do you have?

The bike with the 170 causes me no discomfort. Is this a KOPS issue?
 

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Could be lots of things.

1) From your gallery pics, you seem to be riding a pretty small frame (50cm?). Maybe 172.5 is simply too long for your leg length.

2) If your seat height is already maxed out completely, then yeah, going to a longer crank w/out lowering your seat slightly (2.5mm) could be a prob. I've heard of guys getting injured by having their seats just a few mm beyond their max, so caution is warranted.

3) Some people are sensitive to Q-factor, i.e. how far apart your pedals are. If your feet are spread too far apart, it can cause slightly awkward pedaling and/or knee pain. So, if your new crank has a significantly worse/wider Q-factor, could be an issue. Most high-quality double cranks are usually ok in this regard, however. Still, might be worth it to measure both cranks and compare, just to eliminate the possibility.

...
 

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Discussion Starter · #5 ·
Thanks for the input everyone. Definitely helpful.

1) Same shoes, same cleats. Although I do have two pairs of near identical shoes and need to make some slight cleat adjustments on my right leg. Not sure that would effect my left leg.

2) Yes, I ride a small frame (48-50) with a 52 top tube.

3) Saddle height was adjusted for the longer crank arm length. Perhaps not effectively enough.

4) Same exact cranks, pedals and pedal washers on both bikes. The only difference is the crank arm length. Cranks are SRAM Rival, pedals at CB Eggbeater SL, and I have two 1 mm washers stacked between each pedal and crank arm. These were recommended to me by my fitter and I've seen an improvement in my pedal stroke and comfort since installing them.

I'll re-evaluate my KOPS and other measurements this weekend and see what the deal is.

I've taken nearly two full weeks off the bike because of this "injury" to make sure I didn't re-aggravate it and because summer is busy for work and I am working crazy hours.
 
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