Interesting info here… I’ve been experimenting with crank length a lot in the last year or so, especially with shorter cranks for DH and XC. On the one hand I am really happy with the shorter cranks, and I think practicing has improved my overall riding (but you have to first improve your skill a lot and fitness before you can try shorter cranks!).
I have been riding 125s on my 36 for XC and now feel very comfortable (at first the lack of control was scary and it totally exhausted me physically). I have also successfully tried XC with 100s on the 36, and while possible, it’s just too short for most XC (#1 exhausting! but also climbing ability is reduced to momentum only).
However, recently I’ve been having a little pain/discomfort in my previoulsy injured right knee (ACL reconstruction and miniscus damage) and unfortunately I think the short cranks are part of the problem… About a month ago I did a big muni tour that I have in the past done with 150/127 cranks where I did >600m climbing on 137mm cranks on my 29+ and afterwards I really felt it in the joint Then last week I did a big muni tour with >1200m vertical (didn’t ride all the uphill) with 137mm cranks on my 29+ where I rode probably close to 700m vertical uphill and afterwards my previously injured knee again felt overworked and weak for 2-3 days (I did an XC ride 2 days later on the 36 with 125s and could still feel the weakness).
After riding primarily 125mm on the 36 and 127mm on the 29 for XC for most of the winter, the last 2 weeks I rode the 36 XC with 150s, the 29+ XC with 137s and enjoyed the longer cranks. This week I did 2 big muni tours with 137mm cranks on the 29+ and intentionally walked more uphil than I usually would: 3 days ago I did 1800m vertical with a lot of walking and around 400m uphill riding and today I did another big muni tour (1030m vertical) where I walked a lot and rode about 300m uphill. While my muscles seem able to push the 137mm cranks pretty well even on steep uphills, the 150mm I used the last years seem to be nicer to my knees. If I really push with the 137s I seem to overtax the knee.
To summarize (what’s used to mostly be in my signature but that seems to be gone in the new forum update):
freestyle 20" 89mm (although I would like to try 100s some time)
trials 19" 140mm
26" muni 117/137
29"+ muni 117/137 or 127/150 — ideally 120-130 for XC, 120-137 for DH only and 137-150 for muni tours with lots of climbing.
As for technical downhill (no major uphill): On my ride today I rode a DH trail with 350m vertical drop for the first time but rode it twice, back to back. The first time I rode with 137s and the second time with 127s. The trail was not extremely steep but very narrow and pretty rocky but without any big drops. The upper part of the trail was difficult while the lower part was less technical (so faster). On my first run with the 137s I had no major UPDs (although a number of controlled dismounts) while I had 2 major crashes with the 117s – bruised my knee a little – and successfully rode 3-4 key passages with 137s that I had to dismount on the 117s. However, some of the downhill sections felt easier and more flow with the 117s. I guess my feeling was this: as I was riding with the 117s, even in pretty technical rocky/rooty downhill sections, I felt better with the 117s up until I lost control and then it was much harder to gracefully recover on the 117s as compared to the 137s… of course, I’m not used to riding DH with 117s so that might improve with practice… I was wanting to compare my speed from analyzing and comparing the two tracks but haven’t done that yet.
So I may switch back to the 127/150mm cranks on the 29+, as I feel more comfortable with 127s on downhill and XC, and the 150mm seems to be better for long uphills, although I think I would ideally like 125/145 but the KH spirits don’t come in 125. (a triple crank 125/135/145 or 120/130/145 would be awesome but the spacing is too close).
Uh, sorry for the near stream-of-consciousness disorganized rambling… but kind of my thoughts and been riding alone all the time (I guess most others are too now, and I should be thankful I can even ride in these strange times).