My girl friend has shortish legs and uses a small frame with the stock 175mm cranks. We have both noticed that it looks like her saddle is too low as her knees come up a long way at the top of the pedal stroke. Upon checking the saddle is at the correct height and could not go up any further.

Would using 170mm cranks make much difference? Anyone have any experience of doing this?

Easy answer. Probably a tiny bit but just measure and work out how different the extra 5mm down is going to be and make that decision. If neccesary just ask her to take her foot off the pedal and lower it that amount.

Ah but the saddle can go up another 5mm as well with the shorter cranks so 10mm total difference.

Good idea though. I'll try tonight.