Just had to drop in. I`m not a `Fifty Plus` (I`m 38) but the title of this thread was too much to resist. I raced on 177.5`s as a Junior/Senior. Had no knee issues, problems with position, etc. Admittedly, I wasn`t often spinning along but that wasn`t ever my intention. I have a bit of a strange body. 6`2 with a 29 inch inseam...the lower leg (what`s that bone called???) being extremely short. Well suited to cycling, quite strange looking otherwise.

Starting off with that kind of leverage, I chose to maximize it. Seemed to work. A few medals from Nationals and a couple other results. I think the trick is to find what works for you. We all have our own riding styles. A fluid, super smooth rider is going to be lost on 177.5`s, while I would have been throwing away a bit of genetic luck with 170`s. I`m glad the OP found a crank to suit his riding style. No length is `best` for everyone. Your physiology, riding style, etc., have to be taken into account. Have fun, all.