I bought a 29 trainer from UDC a few months ago. It came with 150’s. I switched to Coker 127’s and was much better. Curiosity got me and went to 102’s. These were even better. (totally flat road riding) I figured it would be too much, but I ordered a set of Nimbus Ventures 75’s anyway. Put them on and after some trying was able to ride down the road. I was thinking I was getting it, when I came to a stop and shot the uni out in front and landed flat on my back. Lack of torque and no brake. Little road rash was all, no biggy.
So a couple questions come to mind. Does anyone ride 75’s on a 29 regularly, or is that just too short?
Is there a “Too short” for riding due to not enough movement, resulting in leg muscle issues.
I was surprised at the speed difference between 75’s and 102’s…thanks
I ride a 700c, and 75mm cranks are what I use. It works fine where I live, which is pretty hilly. I recall riding the Unicon 15 marathon course (which was very hilly- ask anyone who rode it), and climbed up faster than I ever thought possible, and much faster than I did on a 36"/145mm Schlumpf in 1:1. The slideshow of the terrain is at the bottom: http://www.uniconxv.co.nz/participants/competition/venues/
Partly that is from having a lightwheel, but once you get used to it, the 75mm cranks are great for climbing. The grades where I ride get to 10-15%.
Wow, 75mm… Now that really is “heroic.” 
How are they going downhill? That’s what I’m curious about.
The older pages of this exchange are mostly from before I joined the site, and there are some interesting and less obvious points going back there. What adelman has to say about a larger range of motion engaging more muscle fibers, making more stored energy available for long rides, is food for thought. But fighting the wobble from wonky pedaling on long cranks probably wastes energy too.
I find long cranks use more energy because of the greater range of motion and also because you tend to be using a bigger, heavier wheel.
At low resistance with short cranks, the movement is so small- it feels like you’re gliding with little effort/movement. I could ride all day with a 75mm/700c. On long cranks/big wheel (125mm/36"), I know my legs have had a good workout after a couple of hours.
I have a 32km training ride with a few climbs and I’m a few minutes faster on the 75mm/700c than my 110/36" record (which was set jsut before I won the Marathon at Unicon 13- I was quite fit then!).
Downhill- hard to answer- it depends on steepness, and the weight/momentum of the wheel/rider. The 75mm/700c feels similar to 110/36" in terms of controllability for me.
I have tested 75/700c compared to 125/36" on flat road. I was faster on the 36er. Going downhill with short cranks on a small wheel is harder than on a big wheel with long cranks. For me, a 700c uni cant beat a 36er.
Thanks for the comments. Mine is a 700x45c so a bit heavier than yours. I’m not looking for all out top end speed as in for racing, but more the fastest for cruising along for some distance. The rail-trail I’m riding is flat and smooth. I’m riding with my wife, her on a heavyweight cruiser and my 36 is pulling away from her. I prefer to spin than just dog along, so maybe 75’s are the answer in this case.
This thread reminded me of this thread:
giggle 
Crank Size for muni climbs - criteria to consider
For muni riding, people talk about hill climbing capability on various sizes of cranks a lot. In my opinion, it really depends on the slope and smoothness of terrain involved. And for slope, I think what is relevant is how close the slope is to the max slope you can climb with your skill and endurance.
On a paved (or smooth) climb with a grade shy of 20 percent, you can actually get a smooth climb on a 125mm crank on a 29 inch muni - which is a bit of a large wheel and somewhat of a small crank size.
But as the hill gets steeper than that - like say 24 percent or higher, the capabilities of wheel size and crank size really dramatically differ, and the climbing technique has to be spot-on.
The smoothness of the terrain is almost more of a determining factor for crank size as well - especially when the terrain forces you to slow down almost to a stop for moments - where you have to restart your momentum.
So the more you are pushing your climbing to your personal limits, I think you end up using 150mm cranks, and perhaps a muni wheel as small as 24inch. But for muni, it would seem that the Kris Holm recommended 150mm cranks on a 26" muni - can ride the largest variety of terrain with decent speed. And to ride with a smaller size crank, they can be fun but you have to make sure you are not riding close to the limit of your capabilities for climbs - as the limited motion of the leg with smaller crank size creates fatigue in that area of muscle quicker. 165mm can feel good and very controlled, but not at high speed for great durations, and I don’t think it has a lot of sustained top-speed potential.
I’ll go out and experiment with the 165s again. High cadence for 8-10miles and track my time vs the 150s, for a week and see how my legs adjusts to them;)
Upd
Curious, UPD. How did your legs adjust to them?
Oh, jeeze its been awhile since this last post…hmm let me try to remember what I was trying to accomplish…
Oh right, I was going between 165s and 150s, funny of all the people, you would ask me.
I determined, Im definitely a long cranker. Im no good on hills less than the terribly long 165s. 150s on the 36er on flat and slight incline is ok, but I like to climb steep for miles on the 26er and even contemplating on going longer like a 175 or 180.
Too some that might sound ridiculously long, but really, I dont mind it;)
Dang what’s wrong with me…while everybody’s going shorter, Im going longer…just bought a pair of 175s Truvative to try out, I ll let you if I like it:D
This I also found out. I have a KH26 and just this week put variable cranks on it for 127 and 110mm sizes. Though it was ok to ride on flat asphalt with the 110, when I tried 127mm in the forest, it burnt a lot of energy and going up really hurt my knees. I might change it back to 150mm. Then again now that I have an Oracle 29" with 150mm cranks, it is more comfy that the 26" also in the forest with climbs. As long as the wheel keeps rolling, climbs are very well doable.
Thank you for that, UPD.
I’m likely buying a Nimbus 29er strictly for road, brakeless (until I can afford the brake), handlebar-less, and live in relatively flat Illinois; that said, when there’s a hill there’s a HILL. This thread has helped me, yet every time I think to go short on cranks, an experience like today’s three posters on here gets me thinking twice.
I have 150mm on my KH24, and 150mm also on my Torker Street 26 (cheap, slow). I’m thinking, esp since brakeless, I should go with 125mm minimum on the 29er, but I’m open to suggestions. It’ll be all road, Schwalbe 2.0 slicks. Can I brake with legs on 125mm cranks? I’ll likely be riding 10 milers, tops, and usually less. I’m just not a distance nut (I usually ride MUni on my Brakeless KH24 at forest preserves, county parks, and in the woods).
I’m coming back to uni after riding as a kid, been at it for 2015 only, so fairly basic, but I can ride. Im 5 foot 8.5 inches tall, (gotta get that half-inch in there…lol),176 pounds.
I’m not really into 36ers, for some reason, as I just ride alone for cardio and enjoy my strength training, guitar-playing, and other sports (ultimate frisbee) enough that I really don’t want a face-plant from ten feet in the air to break an arm from a high-seated uni. Lol.
Thanks for any and all suggestions. Please don’t feel bashful to tell me what’s what. ��Steve
You can also get the Spirit cranks in 137/117 (or 137/110 if you can find some old stock). I find that 137mm is a really nice balance between power and spinability. I have them on both my 26er and 36er at the moment.