Speed versus wheel size?

are there any general guidelines over what wheel size determines its average speed? I am wondering this since I rode around my apartment complex today on my 20" and I figured that if I wanted to take this thing out somewhere like the store or a friends place less than 2 miles away that it would take alot out of me; unless I buy a coker of course then the sky is the limit.

Changing the wheel size changes your gear ratio, going with smaller cranks will also efectivily give you a larger gear/gain ratio.

Just like on a bike larger gear/gain ratios will allow you to go faster but are harder to controll at lower speeds.

(wheel size in inches X 3.14 X 60 X average pedaling RPM)
…divided by…
…(5280X 12)

= speed in mph.
Its easier to pedal a bigger wheel faster than a smaller one w/ the same size cranks, so your rpm will increase when going up in wheel size.

To get your max speed increase by reducing crank size, you could divide your old crank size by the new and multiply that by your old speed (you will theoretically be able to pedal that many times faster).

If it is just a ride for a couple of miles, then wheelsize is not a major limiting factor. The effort to ride a small wheel is very small compared to the amount of patience you need to go long distances on it. That is the reason most people will choose a car first or a bike rather than travelling by unicycle. You will find as your technique improves and you flail and fall less, it will take less out of you. And as you push the limit of distance, you will face new challenges like the pain of inner-thigh chafing, and things you don’t encounter with short rides. Sore lower back muscles is something I got when I started riding for miles on my 20", but it went away as my back got stronger I think.

I found that by increasing wheel size gradually- 20, 24, 28/29, 36, I never felt uncomfortable with my wheels. I don’t know many people who have jumped straight from a 20" to a coker but I’m sure the skills are still transferable, it might just take a little while to get the hang of freemounting. The bigger the wheel the harder the work is- so while a coker rides faster than a 20", it also takes more energy to get it up to speed and keep it there especially uphill, so the gradual increase in wheelsize probably helps build you up for that.

So that being said, I think the rider is an important factor in the equation of wheelsize and average speed. Someone not confident on a 36" might average faster on a 28", but with enough practise is likely to go faster on 36". Also terrain- I find myself faster downhill or flat on 36" but faster on steep uphills on 28".

I have ridden a 28" for 20km in an hour, but over a ten and a half hour period I only averaged 14.5km/h including rest breaks, riding 152km around Mt Taranaki in 2007. I haven’t measured myself on the 36" for an hour of riding, my max speed ever was 35.1km/h but usually it stays between 15-30km/h. My best time on a 36" around Mt Taranaki was 8 hours 26, which is an average of about 18km/h including rest breaks, mostly every 10km plus a few more.

So while getting you there faster, a bigger wheel will give you a more intense ride- the short cranks vs the big heavy wheel means you have to stomp down pretty hard to get it up to speed, due to lack of leverage. Definitely go to the store and your friends place before deciding to get a big wheel- the practise and the experience will be valuable. You will not regret it if you do get one- they are heaps of fun!

Good luck reaching the sky with your riding!

I’ve ridden 16, 20, 24, 26, 28 and 36 inch wheels, and various crank lengths from about 80mm to 170mm.

There is some truth in the idea short cranks will “speed up” a small wheel. The performance of a 20" uni with 5" cranks is similar to that of a 24" uni with 6" cranks. (I used inches to make the comparison more obvious: in each case, the wheel diameter is four times the crank length.)

However, over long distance, and uneven terrain, the bigger wheel will always be faster, at least up to the point where the rider lacks confidence and slows down to compensate.

So if you go straight from a 20" to a Coker, you won’t get the full speed benefit of the bigger wheel until you’ve done a few hours in the saddle.

As you become a better rider, the crank length becomes less crucial.

A factor that is often overlooked in these discussions is the tyre. My 28 has a skinny high pressure tyre, and on anything but the smoothest surface I have no doubt that this is slower than a softer, chunkier tyre. This is the opposite to what would happen on a bicycle, and is because of the need to adjust your front/back balance on a unicycle every time the surface under the tyre changes slightly. The fatter softer tyre smooths out the minor changes.

For speed:
Wheel diameter,

In more or less that order.


Coker=faster… Maybe its just that Ive spent enough time in the saddle of other unis, but Ive clocked maybe a total of 2 minutes(generous) on a 36er and learning curve aside coker will be much much much much much much much much much faster than a 20".

I could make 5 pedal rotations get off and get back on a coker and still be further than I would if I was ridding a 20 and not getting off.

I guess the key word in what you said is “full”. Of course the more time you put in the better you will get.

You answered your own question.

Of course the Coker is faster, but it takes practice and confidence to ride the Coker 36/20 as fast as a 20, ceteris paribus.

If only that were true! But I don’t agree to that. In my opinion and experience it is the opposite if anything. With the same crank length, I can spin somewhat faster on a smaller wheel. I think the reason is twofold, both have to do with the smaller wheel leading to less speed:

  1. There is less resistance on a small wheel.
  2. There is more confidence and control on a small wheel.

I would have to disagree on that one, at least in my case. I have way more confidence and control doing rolling hops and big drops on my 24" MUni, vs my KH trials. Could also be that I just haven’t logged enough time with the 19 as I have with my MUni. But when I try the same stuff on my trials, it just feels much too “squirrelly”, especially at higher speeds.

Terry, I think that part of the “squirrelliness” is due to the ratio of crank length to wheel size. I’m going to guess on your crank size but 26":6" is not the same as 21":5.5" which is part of it (I used the ODs of the tires for muni and trials, not their nominal sizes). Also the wheel is lighter on a trials, so the rotational momentum is less, which is why it doesn’t like to go as straight or curve as nicely as your muni.

Yeah I just feel much more secure on my MUni vs my trials; kinda like I’d rather be in a hummer than a yugo in a crash! Bigger, heavier, with more metal around ya! :stuck_out_tongue: The advantage with a trials is obviously the lighter weight and smaller wheel that is less in your way for doing unispins, and easier for crank flips and such as the rev is much faster, meaning you don’t have to jump as high and stay in the air as long as you would with a 24" wheel-unless you could just spin the bigger wheel a lot faster to make up for the slower 360+ rotation, compared to the 19.

I was practicing today on my 16". An older guy came up to me since he knows how to uni. It took him a few times to get it on my small wheel. Then he was cruisin. He told me a bigger wheel is easier. I hope hes right!