125mm cranks on Nightfox

When I got my Nightfox a few months ago, I decided I’d just go with the 138mm Venture II cranks it came with. I think that was a prudent decision that allowed me to get comfortable freemounting and riding. The first 36er I test rode had 125mm cranks, and I wasn’t able to freemount it, but I was later able to freemount my Nightfox with 138 cranks on the second attempt. Once I got used to the 138s, I wanted to try out some 125s, but I wasn’t sure if I wanted to buy a new set and find out I didn’t like them.

As luck would have it, my wife just bought me a Nimbus Signature trials that came with 125mm Venture II cranks, and some of my trails buddies suggested that longer cranks would be better for jumping and trails stuff, something like 137/138mm. Well, that was a no brainer, and after borrowing a crank puller from one of our local unicycle club members, I swapped out the cranks between the Nightfox and the trials, and I think it was good choice for both.

I took the Nightfox for a spin today, and it was pretty cool. Even though it was a bit harder to freemount, I was able get it 50% of the time today, and I suspect that will get better as I get more familiar with it.

The ride was sooooo much better with the 125s! It felt more natural, and my cadence was noticeably better and more even. I also just naturally rode faster. I actually like the resistance the shorter cranks provided and reminded me more of what it’s like to ride a geared bicycle in a higher gear. Also, less leg movement caused less bouncing around, less crotch pain, and a smoother overall ride. I do feel a little less in control, but I felt even worse when I first got the Nightfox with the 138s, and I expect with repeated riding I’ll have more control. I didn’t have a single UPD today during my 8 mile ride, but there were a couple of times I felt close. I also haven’t ridden my Nightfox much lately, and I’m a little out of practice, so that probably played into it. I have, admittedly, been fairly distracted with the trials unicycle and learning tricks, hopping up stairs, etc. :slight_smile:

Uphills were not as hard as I though they would be, although coming back I ran into a nasty headwind, and half of the way back is uphill, so it was a bit tough getting home. I really didn’t enjoy fighting that wind, especially while trying to get used to the shorter cranks.

The other thing I should have spent more time considering was the saddle height. With shorter cranks, I probably should have raised the height with the shorter cranks. My knees were a bit sore, so I’ll play with that a little later on and try to find out what works best. I think subconsciously I sort of wanted to keep it a bit low for this first spin since I was intimidated by the shorter cranks and wanted to make it easier to control, but now that I’ve tried 'em out, I’m more comfortable.

As an aside, the longer cranks worked out well on the trials unicycle. I had to lower the seat, which required cutting an inch or so off the seat post, but I could still do all the tricks I just learned. It did feel a little odd, though. I’ve never used cranks that long on a 20" unicycle, but it does seem more stable.

I’m hoping to upgrade to an external d’brake on the Nightfox. I was already intimidated enough with going down steep (or even slightly steep) hills using 138 cranks, and it’s even worse on the 125s. I’d also like to be able to slow down a little faster. With the 125s, it takes me a long time to stop, and while I know that an instant stop would cause a UPD, I would still like to decrease that stopping distance. My best chance for riding the 36er on a regular bases is the multi-use trail that runs close to my house, and there’s just times when I’ll need to be able to decelerate faster, and it’s not just a safety issue for me. There’s small children and pets on those trails, and I don’t want anyone or any animals getting hurt. It would also just make me feel more comfortable. I know it’s hard to compare, but I love having the brake on my muni. It helps me to ride a lot more confidently knowing that I can slow down faster and with more control when I need to, especially on steep declines.

If I go that route, I’ll probably use the 127/150mm KH ISIS Spirit DH Cranks. I’ve also been curious about taking the 36er off road, and the option of extending the cranks to 150mm seems pretty cool.

As you know, I am a total beginner. I have a 24" Muni, not the best model available but decent. It has 152mm cranks. I have a 20" as well with 126mm cranks and I find them incredibly difficult to operate. I am talking about the shortness of them of course. I may well invest in another 24" but with a smoother tyre on for hard surface riding when able to do it, but I am sure I still need these 152mm cranks (as fitted as standard issue). What is so apparently great about shorter cranks one asks? I have bother with shorter ones, or is it a skill thing…?? More experience sort of thing… !!
I have to say none of my cranks are the tip top quality, but perfectly serviceable…

There’s a trade-off between shorter cranks and control, but as you get better at riding and better leg strength, within reason, you might be able to go faster with shorter cranks. With a “direct drive” system like most unicycles and penny farthings, your basic options for changing “gears” is the size of the wheel and the size of the cranks. Generally, the larger the wheel and the shorter the cranks, the faster you may be able to go. There’s also other benefits to shorter cranks. You don’t have to move your legs as much, and it may save saddle soreness on longer rides.

I really liked using the shorter cranks on my 36er today as it allowed me to have a faster, smoother ride with less saddle soreness. However, on my 24" muni, I’d prefer to keep my 150mm cranks. I’m probably the slowest muni on the trail, but I like the control and climbing leverage it gives me. I don’t really care how fast I go on the trails, and I dismount frequently, so saddle soreness isn’t a big issue. Others prefer shorter cranks and bigger wheels on their munis. That’s just how I personally like it. Depending on your height, style of riding, leg strength and experience, you may want shorter or longer cranks. The best I can offer is to read all you can and then experiment.

Saskatchewanian made an excellent chart that demonstrates the gain ratio for different combinations of crank lengths and wheel sizes here:

It shows that the gain ratio on your 20" with 126mm cranks is about 2, which is about the same ratio for your 24" with 152mm cranks. Different crank lengths with different wheels sizes will yield different gain ratios, and depending on what you’re doing, you might want a higher or lower gain ratio.

That said, I have a friend who uses 150mm cranks on his KH 36er, and he rides farther and faster than any of us. He’s also a spinning instructor, so he’s likely excellent at pedaling extremely fast on longer cranks, but it does show that you can still ride fast on longer cranks. It’s just easier for most of us to use shorter cranks to go faster.

125mm cranks are fairly standard for a 20" unicycle. All four 20" unicycles I’ve bought over the decades had approx. that same length crank. You may just need to give yourself more time to adjust to them, but there’s certainly nothing wrong with getting longer cranks if that is your preference. Also, if you’re very tall, the 20" may just be too small for you.

I say whatever makes your riding experience more enjoyable is the best option for you. Once you’ve gained more experience, leg strength and riding ability, you may want to reevaluate things and change it up a bit.

The 127/150mm KH ISIS Spirit DH Cranks are great for the 36, I have them on my Oracle 36.

Where I live is very hilly so I have to switch back and forth between both lengths depending on which route I take that particular day. Also: brakes on a 36 really help when going downhill (they save your knees!!) and, yes, it is even harder to go downhill with shorter cranks (even with a brake!).

When I first bought my 36 I used the 137/165 moment cranks combo for quite a while… They made the 36 much easier to control when living in a hilly place. Once I got really confortable with the 36 I moved on to the 127/150 combo which I find ideal for my surroundings…

Thanks Bradford, that was so well described, even I understood it. You may be right about the 20" possibly being too small for me. I did struggle quite hard with riding it now, although I used to be reasonable on a 20" years ago. I don’t care what anyone says, one can easily forget how to ride a unicycle after twenty years… I did…!!

You’re welcome. I thought my answer was a little wordy and convoluted, so I’m glad it gave you some insight.

And yes, a unicycle ain’t no bike, and you can forget how. I certainly did! A lot of people I’ve met and ride with forgot how to ride and have rediscovered it. I really love all the different types of unicycles that are available now as well as the larger unicycle community. Almost none of that was available when I learned. We picked a good time to get back into it! :slight_smile:

Cool! I really do like the idea of having the dual hole cranks for this. That also makes it easier for me to share my 36er with those new to that size wheel. I know from experience how difficult it is to ride a 36er for the 1st time with 125s.


I started out with the 165mm on the 36er 2 yrs ago, and that gave me alot of confidence on the trails, then slowly worked my way down on the smoother, more momentum shorter cranks. Triple hole cranks, I enjoy all 3 holes depending on the terrain, 127,110,88mm.
Its a blast to hit the trails on the 127, where I can crank up moderately steep hills, and fly down them. You just gotta have good faith in your abilities to not crash that hard:D

Triple hole cranks? That’s waaay cool, dude! :sunglasses: Plus, 165s? That’s almost a bicycle length crank. (I think 170s are common on mtbs.) You must have had incredible leverage. I can imagine that would have made you feel more confident. I like the way you worked up (or down) to the shorter cranks, and kudos to you for taking your 36er on trails! I still don’t even like to go fast on my 36er, and the idea of riding off road scares the bejesus outta me :astonished: , but I still want to do it!

Oh, and as far as the 20" possibly being too small, it may be, but you can probably work your way down to it. It thought it would be all but impossible to free mount and ride a 12", but I did it! The picture below was taken of me following a July 4th parade this summer we rode in. It’s totally silly, but I really want one of these (this one belonged to the three year old great-grandson of the guy in the background).