# How much is your average speed affected by different unicycle sizes?

Do others find that they average around the same speed on multiple different unicycles over a few kilometers? Having regularly timed my commute home (the distance varies depending on the route but it usually not more than 6km) and calculating average speed, I often come out around the 16km/h (10mph) mark or just below (some much slower times I often discount if I have had long delays with road crossings). And this does not seem to vary too much, with my 24", 26" or even 36".

Maybe the journey is simply too short to really compare? Also perhaps it is because the gearing on all of them is reasonably close. Also, don’t get me wrong I can obviously get higher top speeds on my 36", even with lower gearing than the other two, but if I just cycle and don’t really push too hard this is the kind of speed I seem to end up at. Do others experience the same thing? Do people have a natural tendency to a speed that feels right? I imagine this would vary much more for a different discipline, like muni, so I suppose I am really asking about road usage.

P.S. A little on the gearing. My 24x3" appears to have a diameter of ≈25½" and currently runs 89mm cranks when I commute on it. To get the diameter, I measured it directly first (albeit crudely with a tape measure), along with the distance of a single roll divided by π as a second check. Obviously this is not super accurate, since I was not sitting on the uni, which would cause compression and affect the result, plus multiple rolls and diving the distance by the roll number to get an average would also help for accuracy, but hey, I assume it is in the ballpark at least.

Anyway, taking this as the figure and calculating the gain ratio, I end up with ≈3.6 for the 24x3 w/89mm cranks. Repeating the same method with my 26x3" and 100mm cranks I get ≈3.5. And assuming my 36" really is 36" (I didn’t even bother measuring that), I get a gain ratio of ≈3 for 150mm cranks (which is what I currently have mounted, though I have used 140mm [3.3] and 125mm [3.7] in the past).

Within reasonable limits, if you choose the crank sizes to produce a similar “gain ratio” you will get broadly comparable speeds.

Of course this does not work if you push it to ridiculous extremes: 25mm cranks on a 4 inch wheel will not average the same speed as 125s on a 20 inch wheel, and nor will 228mm cranks on a 36!

(1) Cruising speed (on the straight and level), (2) maximum achievable speed, and (3) average speed over a journey with junctions, turns and hills, are very different things.

You may find you cruise faster on a 29 with shorter cranks, just because there is less to worry about. The 36 will probably have a higher maximum speed. For average journey speed, the less nimble 36 loses time at every obstacle that forces you to slow down and speed up again.

I went through a short period of commuting a few years ago and I tested my entire fleet: 20, 24, 28, 29 and 36. I found the 29 with 125s was the best all round size for me on my particular route. However, the 36 is the one I’d choose for a long road ride — even though my longest ever road ride was on the 28.

There’s no inherent logic to this, just things that work well for you and things that don’t.

That’s really interesting, and it makes sense, thanks for posting. Makes me think my 26" is going to be fine for most purposes, different cranks and different tires make a different beast. And there is a maximum speed that is reasonable for safety anyway, at least for the risk averse like myself.

I guess I don’t know how much my “average” speed is affected by different unicycle sizes. I ride the 36" when I want to get somewhere on pavement. When I’m on my 26" Muni I’m on dirt (sometimes I’m also on dirt on the 36" but usually easier trails). When I ride my 24", it usually means I’m just going up and down the street, or I’m at a unicycle convention, hoping to go really fast in spite of a too-small wheel. When I ride my 20", sadly, it usually means I’m getting around the office faster. Occasionally I will practice some tricks to make sure I’m still able to do them.

When I’m riding my Giraffe I’m showing off; speed is not in the equation. When I ride my 45" Big Wheel, it’s probably a parade, or before or after a parade. You get the idea. I can see a 29" with appropriately short cranks being pretty good for the commute, as Mikefule described. The 36 is more of a beast, and more work if you have to deal with pedestrians, intersections, etc.

Let’s see. I used to commute on my 24" sometimes, 3 miles each way with some mild hills. But the purpose of that was to train for Track racing, so I was always trying to go fast and not trying to be comfortable. It occurs to me that at that time, my next biggest wheel was my original Muni (26" wheel crammed in Schwinn frame) which didn’t really work. The 24" was still also my Muni at that time!

I only ride with stock size cranks, so 150mm for the 26", 29", 32" and 36". Not sure what the stock length is for the 24" and 19" trial. There I certainly see difference in speed, though I don’t have an average speed of 16kph. On the 29" I have between 14 and 15 kph and on the 36" when leisurely riding I get 17". Last time when riding 15.5km with my 24" it took about 1 hour and 20 minutes (roughly 11km per hour, but I didn’t have to stop here and there for traffic lights). For me the different wheel sizes do make a difference for speed.

Looking at a few models of 19" trials I see that 127mm/130m or 138mm/140mm are the most common. For 24" unicycles, they tend to have 125/127mm, 140mm or 150/152mm depending on their primary use case. For example, a machine intended for a new user or a muni, where in (both cases) control is more important than speed, you will see 140mm or 150mm, while most other styles will typically come with 125mm as stock cranks.

Calculating gain ratio is relatively simple by the way, you just divide the wheel radius by the crank length. The result gives you how much distance you would travel forward relative to the distance travelled by your feet in any unit of your choice.

There are a couple of complications to keep in mind however before you do this easy calculation. While the final value is independent of units, you do need to first convert either the wheel radius and or the crank length so that you are only working with one unit type. On unicycles and bikes we use a mix, with wheel sizes typically expressed in inches and crank lengths in millimetres. It doesn’t matter which you favour, as long as you use the same type in your equation. The other thing you have to keep in mind is that the reported wheel sizes like, 24", 26", 29", etc. are all approximations based on a “typical” tyre for that type of rim (with typical often being when this wheel size was first introduced/marketed). In reality, we know that tyre width can vary dramatically, particularly on a unicycle used for muni, and this in turn can make a big change to the diameter.

In any case, I’ll give some examples below with the wheel sizes you mention and common, stock crank sizes. I’ll make the assumption that the wheel diameter is real/correct, except for in the case of 19" trials, given these are pretty much universally wide and hence the outer diameter is closer to 20" in almost all cases.

So first let’s convert those wheel diameters from inches to mm (rounding to the nearest mm)

20" = 508mm
24" = 610mm
26" = 660mm
29" = 737mm
32" = 813mm
36" = 914mm

Now to calculate the gain ratios (to two decimal places), you can just do the following

19"-138mm: (508 / 2) / 138 = 1.84
19"-127mm: (508 / 2) / 127 = 2.00
24"-150mm: (610 / 2) / 150 = 2.03
24"-140mm: (610 / 2) / 140 = 2.18
26"-150mm: (660 / 2) / 150 = 2.20
24"-125mm: (610 / 2) / 125 = 2.44
29"-150mm: (737 / 2) / 150 = 2.46
32"-150mm: (813 / 2) / 150 = 2.71
36"-150mm: (914 / 2) / 150 = 3.05

At this point you will realise that my 24"x3"-89mm is actually very highly geared compared with typical stock unicycle setups (easily exceeding everything listed above), given I calculated its gain ratio to 3.64!

Finally, a couple of interesting side points from the above:

• The 'Standard 24" unicycle' (i.e. 125mm cranks) has a slightly higher gain ratio (2.44) than a typical 26", since these normally have 150mm cranks (2.20). So the 24"-125mm will likely to be marginally faster out of the box, despite the slightly smaller wheel size, even for those that have not honed their racing skills. In fact, a 24"-125mm is surprisingly close to a typical 29"-150mm (2.46). Plus there is a nice weight saving in addition. In summary, you should expect the 24"-125mm combo to be quick in relative terms to everything listed above (bar the 32"-150mm and 36"-150mm), which actually makes perfect sense given some of the records recorded.
• A fairly common question I have seen here in the past is 'How can I cycle at 36" speeds on my 29"?'. Now there are several ways to answer this (plus it actually leads to more questions to be honest) but if we were to naively answer it using crank length gearing, as a way to approximate a stock 36"-150mm combo, then the above calculation suggests that 121mm cranks on a (true) 29" gets you to the same gain ratio (3.05). Of course I have never seen cranks of that exact length but you do find Kris Holm Spirit multi-holed cranks with 117mm positioned holes, same for Mad4One (Agile and Techno) cranks, and there are Impact Eiffel Tower cranks with 118mm, all of which work out at a gain ratio of ≈3.1. Plus there are a ton of 125mm cranks which would give you a gain ratio of 2.95 on a 29". So any of those is likely close enough.

When I look at this again with more data from calculating a bunch of gain ratios, my new take from all of this is that I am gearing up all my unicycles sufficiently to be able to go that around 16km/h (10mph). The 36" is currently a little lowly geared compared to the others but it is easier to average these kinds of speeds on a 36" because of its other characteristics. In addition, I had planned on dropping the crank size down again to either 140 or 125, which would bring it more in line with the two other unis.

Actually these are even closing in terms of gearing than I thought. They are almost identical. It was just rounding that made them seem further part. With no rounding you see this:

24"-125mm: (609.6 / 2) / 125 = 2.4384
29"-150mm: (736.6 / 2) / 150 = 2.45533333333

Yesterday I went for an almost 30km round trip on my 24"x3"-89mm. Thinking of this thread and as an extra check on my speed, it occured to me to time myself on the way home. I tried my not push myself but just go at a normal/comfortable pace. On my return home I noted it took 56 mins. I then roughly mapped out the route I went via Google maps to check the length.

https://goo.gl/maps/MoE6iurET8spz2NE8

For this return journey Google says I cycled 14km (8.6 miles). This means I averaged around the 15km/h (9.3mph) mark. The home route starts faily flat and then goes uphill, with 133m (436ft) of ascent over the course of it. Since this is only slightly slower than 16km/h speed I feel that I tend to hover around, along with the hills, and considering how long I had already cycled, that seems about what I would expect. Maybe I should re-do it one evening on the 36" as a further comparison.

Just a thought. An easy way to calculate gain ratio is this equation, where X is your wheel diameter in inches and Y your crank length in millimetres.

( X * 12.7 ) / Y

Once you changed X and Y, paste it into a search engine like google.com, duckduckgo.com or wolframalpha.com.

How is the traffic when you ride through Oslo like that. Is the path with the yellow lines in the middle only for cyclists? I once went to the Viking museum around where your turnaround point was. Remember my ex was in a very bad mood that day. I didn’t ride unicycle back then.

Traffic wasn’t so bad. Almost the entire route can be cycled with cycle paths or it is possible (and permitted) to cycle on what Brits call the pavement (and Americans call sidewalk). So I didn’t cycle much in the main road. The only bit that would be a little uncomfortable cycling along would be along Bygdøyveien (near the Viking ship museum), where there is no cycle path or pavement and cars go fairly quick, but as you can see from the mapped route, I don’t go that way but rather along Wedels vei, and the cycle/walking path that leads from it, and this section is just hard packed dirt.

On the way down my route was a little different from the link above, for example and I cycled through (rather than past) Arker Brygge. This is pedestrian and with the lock down very much eased here in Norway, completely packed with people. Here I really appreciated having the 24" because I would not have attempted to cycle among them with a 36".

I’ve already seen and used similar calculations for road riding, I think it’s too simplistic. In term of speed, at equal ratios a bigger wheel will always be more efficient. A larger wheel has more inertia and is less sensitive to road defects. On a bigger wheel (and/or with a schlumpf hub), with the same ratio, you can use longer cranks, which is a biomechanical advantage to recruit more muscle fibers.

I suggest : (wheel size - constant penalty) / crank size.

But I agree with you that on some routes I didn’t notice big differences in speed between several of my unicycles. In town, with the frequent stops, for years I had noticed average speeds between 20 and 21km/h (on a G36, G29, light36 or on a bike…). Which is totally different as soon as I use them for a specific use/training.

Yeah I am not trying to say it is exactly the same. Gearing wise it is but yes it feels different and probably, “more relaxed” on a bigger wheel. I recall someone in an older thread mentioning that they could get good speed with short cranks on a small uni but after a few kilometres you can start to feel like a hamster in a wheel, and I understand that way of thinking. So, I’m not planning on selling my 36" just yet!

I also realise that my regular commute is perhaps a little short to really compare average speeds, not least because there are lots of crossing points where I can be slowed down. For example 6km in 23½ mins is 16km/h but 1½ slower and you are 15km/h avg. I can easily get slowed by this much and more at crossing points. I have not been religious about checking my speed for every commute, so for the small sample size perhaps my average speed on the 36" is often higher but I have been more unlucky with lights, the times I have measured. There is also a chance I am getting competitive with myself and subconsciously trying harder on the little wheel, to get those 36er speeds.

Anyway, I suppose what I can take away from this is that its another reminder that crank length can make a big difference and if you want a speed boost for a short commute (i.e. 10km or less) a bigger uni or geared hub is not the only way. A satisfying speed can be obtained on a pretty small uni with short cranks.

P.S. I also still suspect, that with sufficiently high gearing, I tend to hover close to the same kinds of speed (for these kinds of distances). I doubt I am ever going to be one of those people averaging over 20km/h, even I I put very short cranks on a 36er.

We agree, putting shorter cranks allows you to go faster (or at least less tired for the same speed), but in my opinion there should be no reason to hesitate between a 24" / 89mm and a 29" /110mm. There is too many advantages to go big (few drawbacks: it costs money and takes more space to buy a unicycle than a pair of cranks). Bigger is always better!

You are right, crossing points ruin the comparison. I like to challenge myself on my different unicycles, and I was surprised to see that my times were often close on my commutes, when I know that there are big differences in ideal conditions.

Yeah, again that was the primary start and thought process of this thread. The observation of how close my times are with different unicycles sizes … but I not trying to push any agenda that bigger unicycles are unneeded. They are great. On the flip side for anyone already running a smaller uni who is planning on getting a bigger one, they should not be surprised/disappointed if they do not see a big improvement (especially if they already ran cranks on the short side).

Also worth keeping in mind the advantages of small, highly geared unis for certain types of commutes, e.g. mixed modal, where you use the uni for parts, and public transport for other bits. A 24" takes up a lot less space than a 36" on a bus or train. Another being where your commute mixes you with pedestrians. Even with short cranks I feel more controlled in a crowed place than on a 36" and I am probably less intimidating to those around me. Of course, a 29" is perhaps a better compromise in these scenarios being both small enough and fast enough.

To resurrect this thread now that I have a 36", I’ve found it somewhat interesting to compare times. I’m not checking my average speed, but going generally uphill to a destination just under 10km away, my 26 with 150mm cranks is roughly the same speed as my 36 with 127mm, mainly because I went way slower on a pretty steep uphill, and being on the sidewalk with driveway depressions did not help my momentum at all. By the time I reached my destination, I was only two minutes faster than I had been on my 26" (though neither are entirely accurate as both trips included quick conversations with random people), and considerably more tired. Of course, on the way home I cut my time in half and I wasn’t even trying to go fast… but that’s what hills do. Anyways, for trips with few hills the 36er will easily go faster, but if there’s a whole bunch of hills I’m unsure which would be a better choice. I also wonder if overall the same trip would be faster on the 36 if I moved the cranks around so it had 150mm, because that might give that little edge on the hills and probably wouldn’t affect the other parts much.

I ride faster on my 36er with 150mm cranks than on my 27.5 with 145mm cranks. Part of that is the difference between a street tire at 60 psi as opposed to a knobby tire at 30 psi however. I wouldn’t want to go shorter than 150mm on the cranks though. I can still climb fairly well with them and I’m able to go as fast as I want to go.