Hi All,
I think the topic on how different crank lengths effect Speed has been worked to death. However my question is very slightly different.
What I was hoping to find out how many more mph can get from switching from a 150mm to a 100 or 125 on my 24in muni.
The hope being is my current financially strapped time I can use my 24inch for 5-10miles rides and make this possible by swapping back and forth from the normal 150 to a smaller size depending on whether I’m riding for distance or my usual woodland/hill rides
Based on this video I’d say going from 150 to 127 would give about 7% increase in speed and from 150 to 102 about 22% increase.
On my 24" (actual wheel OD 25.5") with 125 cranks I get about 6mph at a very relaxed road speed.
Of course this handy chart gives a great comparison of crank lengths:
Just thought I’d throw in, riding will be a heap easier if you use a dedicated road tyre, and better with a bigger diameter. Muni wheels are very tiring for road if you compare it to a road specific tyre.
Thank you for the graph and your personal experience, found it hugely helpful
Speaking as a 65 year old pensioner, who regularly rides 10 miles on a 26" muni with 165 cranks and has recently managed 10 miles on a 20" giraffe, may I suggest that, as you are on a budget, rather than spend your money on different cranks, you use whatever equipment you have and work on improving your fitness, technique and stamina
Wouldn’t cost anything but your time:)
But I must thank you, as you have just given me an idea for my next ride - 10 miles on my 20" uni - just need storm Ciara to die down & it’ll be my next ride - can’t wait!
Very true, need to find a middle ground in regards of tyres as don’t really want to keep swapping tyres over every other day or so. At least cranks you can get with three different holes 100,125 and 150
WOW 10miles in a 20” that’s amazing!!
I should look into my fitness as you rightly stated the winter weather and the storm over the last few days hasn’t helped
This also assumes that he can spin his legs faster with the shorter cranks. If he cant increase his RPM on the 102, potentially due to fear of crashing through lack of control, then he wouldnt travel any faster with shorter cranks.
Numbers don’t tell the whole story
Extra leverage and speed is great, but only if you can “stay on”.
Have you actually swapped pedals on a unicycle, yet?
If you haven’t get ready for a big change. My experience:
1.) I went from a 125mm to 150mm on my 24" muni, and it felt like shit!!!
I couldn’t ride. Damn. Felt like a total beginner. Took me a long 3-4 weeks to finally get it. Why? The extra length affects leverage, response timing, and stability. Did I go faster or slower?(…I didn’t even think about that).
a.) Forces you to change seat height. The crank put’s the pedal lower to the ground, so your inseam length get’s longer. Riding lower is a minor thing to get used to, but it is a change.
b.) Forces you to raise your knees higher. The longer crank brings the pedal up higher at 12 o’clock. Strange feeling. More bent knee mass increases cause more unicycle wobbling. Must learn to engage your core and calibrate your left and right leg motion to be dead even for less wobbling.
c.) Extra force applied “faster”. Not what you want. Throw’s off your whole pedal force and timing. You actually need to “slow down” to catch up to the action. Hard to explain but anyone who has gone from short to long cranks knows this very very well. It sounds like an oxymoron but, basically you have to trust yourself and “slow down” your whole body action to ride.
d.) Benefits? Actually, in the case going from shorter to longer. Yes, I gained tremendous leverage to go up hills. The reduction in speed was slightly noticeable.
What about getting speed from short to longer cranks? You don’t automatically go faster. With the shorter cranks now it feels weird. a.) Instead, of the nice smooth round rotation you are used to doing…it feels like your are pumping your legs straight up/down!!! Yes, it feels easier but now your lateral balance is thrown off.
b.) Guess what, the longer cranks with more mass going up/down helps to stabilize you. With shorter cranks and lower knee raise you lose that stability. If you are a beginner and need to flail your arms a bit…well you will be flailing them a lot more.
c.) Also, you need to raise that seat up, again. However, only after you master the stability issue can you start to apply “more pedal cadence” for extra speed. If you are not rock solid stable, forget about speed.
Bottom line the crank length changes some major static and dynamic physics involved. If you are already experienced with different unicycle wheel sizes and cranks it’s no big deal, but the first time you do this it is a big deal. Like most of use we “forget” that learning experience. Good luck.
I learnt about 1 & 1/2yrs ago on a 20inch with 125s I then once learnt moved on to 24inch still with 125s but because I was doing a lot of muni riding I changed to 150s and found it a lot easier (but again I was new at the time) since then I haven’t changed from 150s although I have riden my sons 20inch uni with 100s on briefly, which like you said feels like a lot of up-down rather than circular movement.
Experience definitely makes a difference. The better you are at riding the more you adjust easily to the change.
I ride two different length cranks between left and right and the only thing I noticed when I made the change was that my seat height felt different. Apart from that didn’t feel any different to ride.
I’ve always been really bad at swapping between unicycle sizes and even cranks on the same uni. 29 to 36, 36 to 29, 36/150 to 36/127, 29 to 24…, 36 to 19 ahhhhh !! Couldn’t ride properly for the first 20 minutes, and then took a week to get accustomed again.
Mounting of course suffers, but so does turning, especially tight turns, rough ground and a combination of all. Steep hills require different techniques and feel for different wheels/cranks.
The only solution is practice and attention to your weak points.
So now I make an effort to swap unicycles and cranks often, try to remember the bits I have trouble with and concentrate on those. One day I’ll just jump from one to other without a care, but I suspect by that time I’ll be too old to ride.
I was a pity I got home after dark last night with the family and then we had to eat and all, but I seriously thought of riding around with the storm picking up. Thought it could be cool to see how much side-wind I could take before falling off.
With my 24” Muni with stock 145 mm cranks I made hilly road rides up to 13 miles at a speed around 6 mph with a a heavy Duro Wildlife Leopard 3.0 Muni tire.
This is without spinning “fast”.
Only on my first outing with a group of really experienced riders I have seen what fast spinning is.
I tried 125 mm two times and first couple of minutes it felt quite weird but quickly it became clear that I could ride at higher cadence.
Since both rides were part of group training with frequent stops I did not get a higher average speed.
I switched back to 145mm because I was preparing for a hill climbing event and wanted to train in the correct set up.
Since the event I’ve been riding the 27.5 Muni but I did replace the stock 145 mm cranks for 136 mm.
IMHO the distance you’re looking after is totally doable without changing to shorter cranks.
But shorter cranks will make you faster.
And eventually you’ll be able to climb at 24.125 mm as well
Contrary to what I often read on this forum I found the shorter cranks easier to mount.
Perhaps because I have a lousy free mounting technique with too much weight on the back pedal.
In my case that means that the lower leverage of the shorter crank is a plus.
My local climb that I started uphill practice on:
Distance: 0.9 km
Avg Grade: 5.6 %
Initially at 24-145 I could not make it to the top due to my legs burning up.
After some training I could make it several times in a row
And eventually I could easily ride it several times in a row at 27.5-136
Some math, from the crank ration tables (My own version of the table includes also 27.5” wheel size)
24-145 has a gain ratio of 2.10
24-125 has a gain ratio of 2.44
27.5-136 has a gain ration of 2.57
The table suggests you can go up to 3.6 for hilly road riding.
Awesome advice on high plus highly encouraging, not too fussed about getting high speed just quick enough to keep up with my 9yr old on a bike with minimum exhaustion
Summary is by the sound of things is, anything is possible with enough training
That’s an interesting point of view. With the legs doing a larger range of motion, it should be more of a destabilizing thing. But if your topic is Muni, there may be something to that, as having a “wider stance” on the pedals not only helps with leverage, but also gives you a larger “step”. Your feet can be farther apart, which can help with stability/control on the chunky stuff.
Yup, so true. My “size flexibility” is not what it once was, when I was always jumping from one uni to another. Currently 90+ percent of all my riding is done with 150 cranks, on 26" and 36" wheels. I jumped onto a 20" with 89mm cranks the other day, to be in a picture with the two girls that ride them in the Cirque du Soleil Amaluna show (the Sakaino sisters from Japan; excellent show!). I hadn’t thought about the cranks, just that the seat was going to be really low. The short cranks made me look/feel like a beginner rider for a moment, even with them holding me up (on their unis). One of these days I’ve got to try those out on my Freestyle uni – which I hardly ever ride…
Sounds like you want to try the “bitch-slap” test. It can be surprising with sudden gusts!
This is true. But riding a 24" with 150mm cranks on anything smooth is basically a waste of energy. That’s just too long, even for light Muni.
Nick, what I didn’t read in your posts was whether or not you have an ISIS crankset. If it’s a Nimbus, you probably do. That means the cranks are going to be more pricey than square taper, a factor to consider. If you do buy some cranks, I would recommend the KH 117/137s. You get a decently short size for the road, and a fast size for all but the most challenging of trails. I used to use 145s on my 24" Muni, which had a Profile hub (and no brakes). That size was a great compromise between speed and leverage, for me.
But those cranks are $120 US (and out of stock), so your other option is to buy a less-expensive 24" uni to ride with the wife & kids, and set it up for comfortable Road riding. Maybe start with a bigger wheel also, like 26 as a compromise. Then try 102mm cranks, unless your area is hilly. They’re not too short. I once raced a marathon (mostly flat) on a 36" with 102s.
Your cheapest solution is to buy another tire, but like you said, changing the tire is a pain if you want to do it frequently. So if you don’t have square taper cranks on your current uni, I’d just save up for a road machine, and be extra happy being able to ride them both without needing tools. 
Thanks John for your view.
In regards to your question, I have maybe the very original KH 24 frame that kris made, it has one of those KH fusion thick seats. It did have the original 8splined hubs/cranks but have replaced it with a nimbus isis hub. As of yesterday I decided to get nimbus vcx cranks 100-125-150, which since reading the recent posts sounds like they maybe the wrong size to what others recommend. Was originally going to put that money to a new 29er but savings were going forward 2 steps back 1 so decided to upgrade the current uni instead
Actually those 100-125-150 cranks should be pretty cool. Ride the 125s for a while, but then give the 100 holes a chance. With a smooth tire, at least, you will really enjoy them on the road, once you get used to them. 125 is the size used for Track racing, and good for a wide variety of riding. Also can be fun for fast Muni if the trail isn’t too technical. Enjoy!
100-125-150 sounds pretty good to me. I don’t expect you to use the 150 hole much, but 125mm and 100mm both sound about right for what you want, and gives you some choice.
If you do eventually upgrade to the 29" in the future, it’s also a good size for that, and you could potentially swap them over to that uni at that point.
I will also agree that 100/125/150 should be a very good choice for trying out different sizes and drastically change the nature of your unicycle between settings.
I highly suggest getting a good quality quick release seatpost clamp to go along with it as you will want to adjust your seat every time you change petal positions.
Don’t take that chart too seriously. The numbers are math based and show the effective gear ratio between the radius of the tire vs the radius of the cranks. The categories on the other hand are subjective based completely on my experience at the time that I made the chart.