I hope someone can help me. I'm trying to find shorter crank arms for my comfort bike. I'm 5'3" and current cranks are 170mm. I've been having a lot of knee pain and it has been suggested that a shorter crank may help. My current setup is a Shimano FC-M191, 28/38/48 teeth crankset. Problem is that this right crank arm has 4 spindles (for lack of a better word) and all the after market arms I'm finding have 5. Does anyone know where I can get 155 or 160 mm crank arms that will work or will I need to replace the whole crankset?