Hi All,
I have a oldish nimbus 26inch nimbus unicycle (red with Migira brakes added) and I currently have a 3inch tyre on it which rides great. However I was wondering what it would be like to stick a Kendra 4 inch tyre on it. So I have a few questions:
The reason I was considering it was that I was thinking that he may increase my average mph since it would add some size to the wheel.
Let’s start with the first one. It will not fit
Hi Nick,
The short answer in order:
If your goal is to go faster, going for a slick or lightly-treaded tire and shorter cranks will accomplish your goal better. Or you can also go for a larger wheel (but that is cheating as your initial goal it to improve your existing ride).
As for 4" and more, they require a dedicated frame for clearance and they are fun and designed for some off-road situation not speeding on the road. You can find a thread of fat uni pics that will illustrate the shape of fat frames. There is also discussion about selfsteering and other fat-related discussions spread over the forum.
If you can post a pic or just the info of tire/rim/cranks, you can even get some more specific recommendations on how to make it more a cruiser 
That will be slower. The relatively small increase in wheel size comes with more weight and likely much higher rolling resistance (you will be running lower pressure). If you want a quick hack to go faster with the same wheel, drop a size or two in cranks. That will have a far better chance of speeding you up.
Thank you! Shame it wouldn’t fit but glad to hear that it wouldn’t help in speed so not missing out. I do mostly muni but it would of been nice to get closer to matching a 29inch unicycles speed so slick tyre wouldn’t be suitable. Will look into cranks, normally use 125s on the road and 150s for muni, might need to learn to use 100s
To expand a bit, the actual outer diameter of your wheel will depend on a bunch of factors like your rim width, your exact model of tyre and to some extend the pressure. We do not know these but nonetheless let’s wildly guess 
Let’s say the 26x3 is around 700mm in diameter and the 26x4 got you all the way to 800mm (I doubt that to be honest but we will roll with it for now). So what is the gain ratio of these (a measurement of gearing)? Assuming 150mm cranks that the 26" likely came with:
(700/2)/150 = 2.33
(700/2)/150 = 2.67
Now instead, let’s stick with the original tyre and drop the crank size down to 125
(700/2)/125 = 2.80
In fact even if you went down to a smaller tyre, (e.g. something that dropped the wheel down to exactly 26 inches 660.4mm) but used the smaller cranks
(660.4/2)/125 = 2.64
Your gain ratio is still roughly as good as your theoretical 800mm diameter but now you have a much, much lighter wheel.
And this is of course another factor. What you use the tyre for. The increased rollover of bigger tyres can makes it easier to attack roots and other imperfections at speed compared with narrower ones. They inspire confidence since they absorb a lot of the impact caused by imperfections in the ground. So yeah, for that gain ratio is a little simplistic. Nonetheless for road usage and I pretty confident that a 4 inch thick tyre will only slow you down.
You can get reasonable speeds with 100mm cranks on a 26, cycling on paved surfaces. Looking at my most recent ride on Strava (from last night). I cycled 10.22km (6.35 miles) on a 26 with 100mm cranks (and 2.35"wide tyre), through town, with traffic lights and other obstacles and averaged 16.8 km/h (10.4mph), without the need to really nail it. I was just commuting home.
Could I go faster, yes but I think it is a reasonable example of my cruising speed through Oslo on a unicycle of that setup.
P.S. If you want to switch between 100, 125 and 150 buy the VCX+ triple holed cranks and make it really easy to switch sizes. I have them myself on my 26 and love them.
Thanks! I actually have those cranks and find them very useful but never got used to 100mm. I’m also on strava and my average on 125mm is 8.5-9mph but that is really trying to get a PB. So impressed with 10.5, if I could do that I would be happy
I just found you.
My 26" was basically the same model originally. I have since switched the frame a URC frame, which would actually accept 4", though I have yet to try that (though I do sometimes run a 4" on my 24", when there is a lot of snow).
