Need help finding out if a tire will fit on a Nimbus II 20"

Hey guys and gals,
I just bought a used Nimbus 20" with a KH rim and I was trying to figure out if the Maxxis Creepy Crawler 20" x 2.5" Trials Tire would fit/if there would be enough clearance between the rim and the frame. I already purchased the tire so I may have to return it if it doesn’t fit.

Here’s some pics of what I bought at the trading post:

I believe the rim that is coming with the nimbus is actually a 19" like on this

I’m also confused because the listing for the tire I ordered is labeled 20" but it looks exactly like the one on the KH linked above

Anyways let me know if anybody has any advice or experience with these products.


Bike tire sizing is silly, the 19" tire size is the silliest of them all as the outer diameter is the same (20") but the inner is smaller (~15").

THe best way to tell is to look at the ISO # on your existing tire. If you find a label with XX-387* then it is a trials 19" wheel, if there is XX-406 then it’s a BMX 20" wheel.

  • replace XX with tire width in mm

I believe you have a relativity rare KH 20 flatland rim that fits the 20" tires rather than the 19", but check the ISO # to be sure.

You have a 20", not 19". The Nimbus II only came as a 20". Kris made a 20" rim as well as a 19", that is what is fitted. Quite rare now… but very nice rim.

I can see that it is a Wall tyre in the picture… the Wall is only made as 20". You will also find the ISO figure on it of 406.

A little history behind 20" and 19" tyres… When trials biking was first starting they stipulated that the rear tyre must be 20” in diameter. The bike riders wanted tyres with more cushioning for their rear wheel so Monty took a 1” smaller old scooter rim and tyre (which is nominally 20" in diameter) and used that instead of the standard 20" tyre. To go further to conform with the regulations, Monty got the tyre printed with 20x2.5". This of course just add to our confusion! Always trust ISO dimensions.

Oops! Roger pretty much said it all. Your new 20 x 2.5 tire won’t fit.

The KH20 flatland is indeed a good rim. It is rare only because it is no longer sold. I bought one of the last ones at the end of 2013, as part of what was essentially a trials unicycle. A real trials rim with a real trials tire is a bit stronger than the KH20FL, but if you get the fattest tire you can find (assuming it fits your Nimbus II frame), you will still have a very strong wheel, plus you will have a much bigger variety of tires to choose from, including ones with little or no tread. Trials tires are always incredibly knobby and will get full of dogshit if you ride in urban or suburban areas. I use a 20 x 2.4 slick tire. A lot of people say that it’s a trials tire because it’s so fat, but technically it is not. I weigh 200 pounds and ride down the stairs a lot, but months go by without my wheel needing to be trued.

There was a problem with KH hubs from about 20009 to 2015 or so. They creaked a lot, and I guess would eventually fail, but that is a different issue, and there are plenty of threads about it.

That looks a lot like the unicycle that I disassembled last night and put in a box this morning and dropped off to be shipped.

All the correct information is in this thread. That is the 20" flat rim and was purchased new 5ish years ago. It’s laced to a Nimbus hub and that is a Nimbus II 20" frame.

Yeah, I replaced my KH hub with a Nimbus hub too. It didn’t go so well because I didn’t know what I was doing, but then I did it again a lot more carefully, and have had an awesome wheel ever since.

it is a pity that we can not get the KH rim any more. I think that Kris was in front of the curve with this one. Impact now do a similar rim to the KH flatland 20" rim. Although it is in my opinion is using a better profile and hence should be stronger.

Yes, it is odd that KH discontinued the flatland rim. The Impact rim you linked to, as it has no drill-outs, would probably be my preference if I were looking for a new 20" rim, but right now I am not. The 20" Nimbus Dominator2, though 42mm wide instead 47mm, is also fairly similar. Some say that the slightly narrower rim, making the tire thicker, is better, but I haven’t tried it.

The Dominator 2 rim is the stronger rim of the two. I have tried both the combinations and of the 2, I prefer the wider. Although these things are very subjective.

I did mine twice to get it to my satisfaction. The life of a perfectionist is not an easy one.

For my first rebuild, I tried to reuse the same spokes, which apparently is feasible if you label them and put them back in their previous roles as leading, trailing and inside and outside spokes, but I didn’t know about that, so I just threw them on randomly. Every few weeks, I would be riding along and hear a “ping!” and another spoke had snapped. Wanting to fix something so messed up doesn’t really qualify me as a perfectionist. I think it would annoy just about anyone who rides.

So I bought 40 new spokes (182mm) on Ebay and re-did the whole thing according to this tutorial. Since then, I have only once or twice had to do some very minor truing. No snapped spokes, no funny noises, no wobble.