Hi everyone,
Just recently i have switched over to the 125mm hole on my 24x3 GMuni with125/150 moments and thought i would share some thoughts with you all.
When i put my muni together i got the dual hole cranks with the thought of changing to the 125mm crank position to make my Muni resemble the same specs as my 36"- and predominantly use it for longer distance road riding. My thinking changed though after the UNICON XV xc race where the first few riders- martin, tony, beau, scott were all on 24’ wheels with 125mm cranks- I came in 5th on my 24" with 150mm.
The 125mm cranks are a great length for quick consistently high cadences and are a good climbing length too- seem to be a bit smoother than the 150mm on moderate climbs and is only slightly harder on really technical climbs. On the DH sections control is a little lessened but if you are good at utilizing a brake it can be easily overcome for all but the steepest of the steep sections.
An added thing to note is how the crank length affects riding in high gear. For fire roads of easy to moderate undulation the 125mm position is smoother and quicker than the 150mm. It is true that i have to downshift to 1:1 on some climbs that i otherwise would have done in high gear- but the higher cadence that can be maintained on the shorter cranks could be as quick as grinding away in high gear. As for the Dh sections that i previously had been tackling in high gear (long cranks)- i can still do lots of them with the 125s and if i can’t i usually would not be able to contol them properly in the 150mm cranks anyway. So if i am downshifting in these situations anyway the shorter cranks are quicker anyhow.
One day on the way back from my regular ride i decided to set my GMuni back up with the 150mm setup and felt like an absolute goof. It just felt so ineficcient and long. I think i can push the high gear quite well because of all the bike riding i have been doing recently (40km commute to/from work daily). So if you have strong legs and good fitness it is a great way to make your rides so much more interesting.
I would like to experiment with 137s but don’t really want to fork out a lot of cash for something that i might not like. I am really looking forward to riding this set up a lot more in the next little while and even competing in some 12/24 hour endurance events to see how they go as leg strength deteriorates.
So for all you people still riding long cranks on your 24"- give some short ones a go- you will be supprised at the extra speed and similar control you can achieve with them.
I’ve been doing some experimenting with crank length for muni as well. In the past month I’ve ridden 100mm, 137mm (what I normally use), and 165mm lengths. My usual riding is gravel/shale + roots on rolling hills. I ride a brakeless KH24 and am somewhat tall (6’3"). My experiences are as follows:
100mm: Extremely fast on the flats with almost no ability to recover from an unanticipated root or rock at full speed. Flats and gradual climbs are good, steep climbs are impossible. Steep or rough downhill is terrifying. When I ride mostly flat, hard-packed singletrack these are great for the speed, but still require a lot of concentration to avoid UPDs.
137mm: The length I use most. A good amount of control while still enabling you to carry real speed. Moderate climbing and descending is great, as you can spin comfortably while still having enough leverage to be in control. Steep climbing is mostly a fitness test. These are very much a ‘middle ground’ for the terrain I ride: too short on some sections, too long on others.
165mm: No speed, lots of control. I’m able to consistently ride at much lower speeds than with 137mm. Tons of power and long, technical climbs/descents are much more relaxed (and enjoyable?) than with shorter lengths. Maintaining anything faster than jogging speed is tiring, and the experience is not ‘zooming through the trees’ but instead ‘crawling over rocks and roots’.
Summary: I somewhat support Napalm’s finding that shorter cranks give a surprising amount of control (minus stupidly short lengths like 100mm) while providing more speed. I think a big part of finding a good length is deciding on what experience you’re after. I mostly enjoy ‘zooming’, so I tend to like shorter cranks, but if you’re more into ‘crawling’, a longer length might work better.
Until now I have tried 137, 150 and 165s on my 24x3 MUni and 137 and 165 on my geared 26x2.5 (I use this one only for distance and not for downhill riding).
On the ungeared 24" downhill uni the 165mm cranks are way too long. The 137s where quite cool on the easier trails but as soon as there are drops and jumps to steep terrain this crank length is horrible because you often need all fingers on the handle which makes it impossible to use the brake and that means riding completely out of control after landing which I am not really comfortable with The fewer pedal hits are nice tough. Overall I prefer the 150s. They are not that slow and you have enough control for most hills. I use the break anyway whenever I can but… well… I just prefer being in control of my uni than the other way round
For the geared distance uni things are a bit different. Recently I experimented a bit with crank lenghts on that uni too and I mostly agree with napalm. On slight uphills I could either ride in high gear with 165 cranks or in low gear with 137. The shorter cranks are a bit slower but it’s not nearly as exhausting. That’s why I would prefer the short cranks over the long ones if there are no really long climbs. For riding up mountains the longer cranks are the first choice. I also thought it was easier to ride over bumpy terrain in high gear with the shorter cranks.
I used 127mm on my Nimbus 26x3 MUni for two years. I found that with 150mm my knees hurt too much after a long ride and it was easier (smoother) to climb inclines with the shorter cranks. 170mm is just way too long for my legs (I´m 170cm tall).
I recently switched to 140mm cranks for my MUni but haven´t really had the time to get a lot of riding experience with them. My hope is that my knees will still like me while improving control on the rougher downhill sections.
Hey Fromthewoods- when i used to use the KH front bumper with magura/spooner i found it was possible to grip the handle with all fingers except my middle finger and use it to modulate the braking for situations like this. It takes a little while to co-ordinate yourself so that you just don’t cram the brake on when you grip the handle for drops/jumps. With a good bit of practice it can act independently and give you control in really nasty situations while still allowing for you to keep yourself attached nicely to the uni. The whole ‘making your braking forces independent of your gripping the saddle forces’ idea is something that i think has improved my riding a lot- especailly in super steep and technical terrain.
Thanks for the advice. I have used the 137s before my broken shoulder about 8 monts ago. Since then my riding has improved really a lot (it feels like I am better about 100% now ) so I am now thinking about giving it a try again and learn that breaking skill. It could be of good use with 150s too so why not
EDIT:
I was wondering about whether shorter cranks make it easier to not slip off the pedals when riding fast over bumpy terrain. When I tried the 165s on my 26er for drops I had some nasty bails because it felt like the torque threw me off the pedals.
Actually I had 150mm cranks, but didn’t know that the others were using shorter cranks. 150mm is the shortest I’ve used on my 24" muni, though after reading your post I’m now considering switching to Onza Tensile 140mm.
It is amazing what can be achieved on short cranks off road.
The biggest loss is control on steep descents, and it can be frightening and even dangerous. However, you get a faster cruising speed, and more momentum, and it makes little difference going up hill. There is a slight reduction in pedal strikes.
However, if you can learn to spin on 150s, then the extra torque is always available on the descents. If you rely on shorter cranks to go fast, you will come up against the limits of the leverage sooner or later.
The more I ride, the less crank size is an issue. All my unis have 150s or 125s on at the moment.
Up till unicon, i was exclusively riding with 125s + guni. i dropped back to 150s since i felt so weak on the hills. I’ll probably switch back; the hills around where we ride aren’t that steep for a muni. I think 125s are nice for muni.
ive experimented a bit with the 137’s off my old trials uni for muni and i LOVED the size… although i got rid of my trials uni so the 137’s went with it.
but im building up a street 24 and im thinking about going the 137 route again. this helped.
I use 145 cranks on my Muni.
for sure I am not going quickly and everybody is waiting for me : I spin very slowly
(I had the same problem with road bikes I had to use tremendous gears to keep up)
but for steep descents 140/145 is the minimum I can afford (it’s even a bit short) but longer is just too long …
The fewer pedal hits are nice tough. Overall I prefer the 150s. They are not that slow and you have enough control for most hills. I use the break anyway whenever I can but… well… I just prefer being in control of my uni than the other way round 
) so I am now thinking about giving it a try again and learn that breaking skill. It could be of good use with 150s too so why not 
