Crank lengh advice needed please.

I’ve searched the forum and read a lot on crank length, but I’m still unsure what to do so would appreciate some suggestions.

I’ve been learning now for about 2 months and can pretty well ride as far as my legs will allow on flattish bike tracks and the road (no off roading yet) and can successfully freemount about 30% of the time - so overall I’m pretty happy but I feel that now I need to start getting some miles under the wheels to really build up my skill…however I’m finding that on the flat and smooth I’m just not going as fast as I’d like. Today over a 3 mile ride my max speed was 8.5 mph (legs flying!) but my general comfortable speed was only about 6 mph - which I think is too slow and makes my ride feel a bit unsteady and wobbly.

I would like to add at least 2 or 3 mph (or more?) to those speeds but can’t figure out what crank length’s to get, so all suggestions welcome.

The facts are:
24" Onza Muni
Hookworm tyre
165mm cranks
I’m 48 and not as fit as I should be - but getting fitter!

My options seem to be 150, 140 or 127

I have to say that 8.5 mph on a 24" MUni with 165’s is impressive. I was in a similar situation and the solution was a 29’er with 125’s. Shorter cranks will make spinning much easier, but you will lose a lot of leverage for mounting, braking and controlling speed. I am putting 150’s on my Onza MUni, and I suspect they will be a better fit for that kind of riding.

I am finding that 8.5-9 mph is a comfortable cruising speed on my 29’er, and that when I really get into the zone I can go good distances at 12mph. I commute to work 4 miles, and it takes 25 minutes, but much of the time loss is due to a 1 mile downhill section that I ride slower. My time is getting better in that section as I get more comfortable using the hand brake.

In the end crank length seems to be a fairly personal decision. There are folks on this forum that like long cranks, and some espouse the benefits of really short (89mm) cranks.

I hope this doesn’t just confuse the issue more.

I went from 165mm cranks to 150mm cranks, I definitely prefer the 150s. That said, I cannot make any comments about extra speed but I found the 150s did not hurt my knees and the spinning of the pedals seemed smoother (less peddling induced wobble).

I live in a hilly area so need long cranks but it could be an idea would be to get the KH Moment 125-150 cranks (if they fit on the Onza). That would give you more options.

I swapped from 165s to 150s on my 26" muni a few years ago and I’d never go back. On a 24 I’d say go for 140s, or even try 125s if you’re only riding easy flat stuff. (Or get a bigger wheel)


A few inches of wheel size will make a much bigger speed difference than a few centimeters of crank length.

An extra inch in wheel size adds an extra 3.14 inches to distance per revolution.

have to add to the genreal consensus, if you’re not riding heavily technical and want to go faster a 29er is your best bet, i went down the 140s on a 24" route and although it is noticebaly faster, a 29er is nicer.

I have 125 mm cranks on a Nimbus 24" with a hookworm tire, and find it comfortable to ride. I do not go very fast (and I generally have not been measuring my speed) but the leg motion is understated. I have been on a 26" with 165 mm cranks and it feels very strange. There was just so much pumping with my knees to get anywhere! For road riding I would definitely recommend shorter cranks. You will be more comfortable, even with some hills and may get more speed as a bonus.

If the arrow misses, look to the archer, not to the bow.

When I first got into riding seriously, I experimented extensively with crank lengths. On my 24 and 28, I went down to 80mm and tried all or most of the following:

80, 89, 110, 114, 125, 127, 150, 170mm

I did long rides, fast rides, and rough rides. I rode 20, 24, 26, 28 and Coker and sometimes rode 10 or 20 miles a night 3 or 4 nights a week.

And the conclusion I reached is that the choice of crank length is little more than “fine tuning”.

If your cranks are “too short”, there will be an “absolute limit” on how steep a hill you can ride up (or down under complete control). If your cranks are “too long” you can improve your spinning technique. So longer cranks are more versatile.

Slightly shorter cranks increase your cruising speed, but only when you are confident with that length. Before you are confident, you tend to compensate for the lack of control. A rule of thumb is if you cannot idle on this set up, then your cranks are too short for comfortable fast cruising.

The difference (proved by maths and by practical experiment) is that if your cranks are about 10% shorter, you will cruise about 10% faster. However, it soon breaks down: if you halve the length of your cranks, you do not go twice as fast - otherwise we’d all be racing about at 100mph on 1mm cranks.

165 mm cranks are pretty long (ideal for muni, unwieldy for fast riding) and if you drop to 150s, you will get an extra mph or so.

But there is no substitute for practising. There are people in this forum who can ride faster on a 24 with 125s than I can on a 28 with 114s. They are also younger, better looking and probably richer too.:o

The spin rate doesn’t change with shorter cranks, but it may feel smoother and easier to spin. That said, if you want speed then you’ll need a larger wheel. For muni, anything shorter than 150 at your skill level is going to make climbing vert diffucult. If you have yet to try muni, I’d stick with the 165’s until you learn how to climb on rough terrain, then drop to a 150 after you know what you’re doing. Speed is nothing, for that you can ride a bike, try managing that 8.5 mph speed on single track or downhill, that’ll work for sure :slight_smile:

The spin rate does increase with shorter cranks. That’s half the reason for going shorter!

And as for speed, if you want to go fast, you wouldn’t ride a bike either, you’d drive a car.

Good answers everybody - thanks, made me think through my original thoughts.
I’m only after more speed to make my ride smoother and feel more controlled, in actual fact the best way to do that is to learn to ride smoother and with more control!!
Therefore I figure that I should leave my crank length alone and just do more, and harder, riding on the stuff that gives me a problem.
Since starting to ride a Unicycle I’ve found I like it more than I thought I would - I can feel a collection starting!!

Never forget about the Constant Footspeed Hypothesis.

It’s a bit of fun from the earlier days of the forum.
When the humour was honest, usefull and didn’t have to be explained.

Read here and here for more info.

happy reading.

And welcome to the forum.

Isn’t that kind of like saying:

Off-road is nothing, for that you could take an ATV
Trials is nothing, for that you could use a latter.
Freestyle is nothing, for that you could just dance.

To quote a cheesy UDC poster “It’s the challenge” The challenge maybe Speed or Muni or Trials or Freestyle or whatever. It’s all good!:):wink:

Edit: My new 36er arrives Wednesday - “It’s the challenge!”

I think you got the answer to your question. And if you want to ride fast on flat and smooth as opposed to MUni… that’s where you add a unicycle to your collection - so you got that right too. A 24" MUni is hardly the best uni for fast on flat.

No, but it can be fun. :smiley: When I had my first Nimbus 1 24" with a 28mm tyre and 102s, I used to scoot about the local country park flat out against the stopwatch. I was young then.:o

I also did 24 miles on it once, and did quite a lot of road work on it.

But it isn’t the best option, I agree.