I just bought a pair of 170mm QuAx cranks from Goudurix. I installed them on my 26" mUni and went on a couple rides, on trails and hills which I frequent. They were great! My hill climbing was as good or better than with 165s. The big difference, though, was the q-factor on the QuAx cranks. They stick out an extra inch on either side, compared to the Ventures which I typically ran.
After having the good experience with the 170s, I put on 150s for my next ride. This helped me identify some differences between the cranks. On the 150s, I felt that I had more strength throughout the 360 degrees of the pedal cycle, while I felt weaker at the 6:00 and 12:00 position with the 170s. On a steep downhill single track, I was able to make it down with the 150s, but I was in a kind of a panic, whereas I felt more confident going down the hill with the 170s. I used the brake with both sets of cranks. I noticed with the 170s that I was tending not to ride straight, but rather in a subtle slalom. I’m sure that’d diminish with practice.
Back to the q-factor. I did not notice that added Q was desirable or detrimental. Some previous posts on q-factor stated that added Q was good for duck-footed riders. I am pigeon toed, so maybe added q is not necessary in this regard. I never had a problem bashing my ankles on the cranks, even with the straight Ventures, though the sharp right-angles in the profile of the Ventures are doing a number on my shoes.
A wider stance is supposed to be desirable for mUni, which suggests that added Q is desirable for this type of riding. However, I am a mUni handle-bar freak, riding most of the time with both hands on the bar ends. My stability seems to come from the handle-bars, so I don’t know how important it is to have added width/stability at the feet.
So, I am still confused about whether or not added q-factor, which I got moving from Venture 165s to QuAx 170…is a good thing.
I have a possible answer to the question of why more people in the past ran 170mm cranks. Perhaps it is because more riders held their arms out in the air. Without the increased leverage of holding the seat or a handle, it seems that the leverage would need to be put in the cranks.