My son has a Koxx-One Uni… stock tire says “20 x 2.5” On unicycle.com the Trials tires which are labeled 19" says the tires size is 20x2.5
But they also have a section for 20/24 inch tires… a bit confusing.
So, my question is will the Creepy Crawler fit his rim?
The short answer is yes. 
The long answer: Trials rims are slightly smaller to accommodate larger tire volumes while still having the same outer diameter. On trials bicycles they put a larger volume tire on the back but a smaller volume tire on the front. What this means is that there are two different sizes of trials tires, usually labeled as front or back. Unicycles use the back size as it has more volume which gives more bounce. The ones that unicycle.com sell are the back size which is actually for a 19" rim even though the outside diameter matches a 20" tire. The easiest way to tell them apart is by the width, at least in the case of the creepy crawler the rear one is 20x2.5 while the front one is only 20x2.0. UDC puts trials tires in a category all their own because they are actually 19" rim and will not fit a standard 20" even though they are labeled as 20". It’s confusing when you don’t know what’s going on but once you understand it’s pretty simple.
Another way to make a clear difference of the two sizes is to use the ETRTO markings (european standard measurements).
On the sidewall (or manufacturer website) you will find values line (XX-YYY) where XX is the width and YYY is the diameter.
In short:
19" (also labelled “Trial / 20”) are 387mm in diameter
20" (also labelled “Freestyle”) are 406mm in diameter
In case of doubt, you can have a look at the Tires section of the German site where all the tires are sorted by ETRTO diameter.
Virtually EVERY model tire has a slightly different diameter, this can even vary a bit between two tires of the same brand and model.
Yes it’s confusing. Many trials tires are labeled 20"x 2.5"
All (effective 19") trials tires are 2.5", 2.6", or 2.7" wide (most are 2.5"). I don’t think I’ve ever seen a true 20" that had those widths. Look for something like ‘Won’t fit on regular 20" rims’.
Dear forum! Not sure where to post this question.
I have been a happy owner of an Equinox trials unicycle for the last 5 years. During that time, my technique and riding preferences have solidified. I am now questioning the need for a 19" tire and am contemplating installing a 20" wheel and tire in the Equinox frame.
I am not a big jumper. I am good with going up and down things less than about 1 foot, and I assume this wouldn’t damage a 20" rim with a tire under reasonable pressure.
I currently run 35 PSI on my 19" tire. I am wondering if the response and turning would be significantly different with a 20" setup. In particular, I wonder if, during sudden changes of direction or during tight turns, there would be improvement in response on the 20" setup.
I don’t have a 20" setup to compare. My only comparison is with my 24". It has a lighter, more rounded tire with a lower profile. The 24" tire is 2’1", not significantly wider than the rim. Comparing my 24" setup to my 19" may be comparing apples and oranges, but the 24" feels more responsive. My theory is that a 20" rim/tire setup on my Equinox would improve the responsiveness.
So, to anyone who’s ridden a variety of conditions on both 20" and 19" setups, could you please comment on the differences, if they exist? And if you think the differences are negligible when the 19" trials tire is under higher pressure, I’d like to know that, too.
Thanks for your input!
I’m not sure your question makes sense.
Maybe try a tyre like this.
https://www.municycle.com.au/catalogue/UP-TYR-19-OBR-GK_item.html?ref_cat_id=Tyres
It’s significantly lighter and possibly a touch bigger than a creepy crawly, still fits the 19” rim.
If you wanted to go with a 20” rim and tyre, you could, but you probably wouldn’t be running a 2.5” wide tyre, because of frame clearance.
This kind of question is a variant of the «I want a tire more versatile than the Duro» but trial wheels (19") being a one trick pony with only trial style tires, it means comparing with the almost-identical 20".
If your behavior struggle is caused by the square profile or its knobs, you can try to shave the outter knobs to make it closer to round and smooth (there are discussions about that on this forum). The lazy way (always my favorite) is to replace with something already smooth (in this case a 20" freestyle wheelset).
As long as you do not go overboard with the 20" tire size (staying in the 2.1"/2.2" area), you should have no clearance problem.
The only other catch to beware if you buy the wheelset as a whole: some freestyle unicycle like the Equinox are using a narrower hub (90mm bearing-to-bearing). So as long as the new hub is still 100mm you are good 
I am pretty sure the Equinox spacing is 100mm. The current tire I’m using is the Cyko Lite, and it’s completely worn in the center and significantly worn on the sides. There is no need for me to shave it down at this point. Next time I ride, I’ll pump the tire up to 45 psi, rather than my normal 35 psi. This should shrink the contact patch and perhaps tighten up the response. Thanks for the replies.
You are right, I had a brain fart. It is the Nimbus Eclipse that has a narrow 92mm hub:
I remembered the gold hub that was light but not compatible with most frames and my brain did the mix-up 
I took my trials out today, pumped the tire up to 50 psi. Definite improvement in responsiveness, but difficult on uneven surfaces. While riding over a small root, I momentarily launched the uni into the air. 50 psi is not optimum for the mixed riding conditions / techniques of my typical workout. I am wondering if a 20" with a less voluminous tire could improve the responsiveness without my having to pump the tire to such high pressure.
It’s hard to completely isolate the individual parts of a setup, but since I have and ride both a 20" freestyle and a 19" flatland uni, here are my 2 cents:
Short answer: yes. I’ll have to admit that my freestyle uni pretty much get’s zero maintenance from me, to the point that I only pump up the tire when it’s REALLY necessary. So I can tell you with confidence that a typical (1.95" wide I think) freestyle tire will be a lot more responsive then a 19" slick, even if the 20" is at lower pressures. (And even more so when comparing to a normal square profiled 19" trials tire)
For hops less than 1ft, a 20" is fine to hop on at “normal” tire pressures. Obviously less easy to get height vs. a 19", but I think that is fairly obvious.
The thing is: when it comes to dealing with imperfections, I think a freestyle tire is a bit worse. Not necessarily when it comes to head on riding over a root, but more with cracks in the pavement or similar that may come in at any weird angle.
(I’ve tried to factor out the fact that I tend to have different seat heights, crank lengths and goals on my 19" vs the 20")
finnspin, thanks for your comments. I remember reading something else by you, on another thread, where you mentioned some 19" / 20" differences, but I couldn’t find the thread. So, needless to say, I’m super happy you commented, here.