40mm bearings for a KH Moment

While I wait for my Hunter to be built with 42mm holders I would like to use my newly built wheel, but my current frame has 40mm holders. UDC says there are no 40mm bearings that fit a KH ISIS axel. Are they correct or can someone lead me to a supplier?

How about some of these;
I don’t know if UDC US stock them, but I doubt the shipping from the UK would be a lot.


An old innertube cuttout works great for me. It even stretches to fit the bearing, and squishes to the exact shape required. I used my profile hub and KH frame for a long time without problems doing just that.

I was thinking about that exact idea just the other day actually, but had never seen anyone suggest it. Therefore I guessed it wasn’t a good idea otherwise more people would have posted about it. I’m glad to hear that someone has tried it and it works though.


I have seen the spacer that allows you to use a 40mm in a 42mm holder but I have the opposite problem and need 40mm bearings for a KH moment hub.

Ah, my bad. Sorry. I should have read it properly.

I think UDC are right though. I’ve seen a few bearing debates on here in the past, and don’t think that anyone managed to get the size they actually need.


What frame is it? alot of the old main cap bearing caps that were made for 40mm bearings would actualy fit 42mm ones no problem.

It is a Torker aluminum 29’r, but I don’t want to damage it just because I am impatiant waiting for my new frame.

I’m pretty sure the new AX frames have machined holders which will unfortunatly prevent you from using 42mm bearings.

I too would like some of these bearings. I think the concensus is that they are not made.

It is one issue if the bearing caps “just fit”. This issue determines if one can assemble their unicycle at all.

It is an entirely different issue if the caps fit well enough that they don’t put uneven pressure on the bearing’s outer races. This issue determines the useful lifespan of the bearing.

Unless the cap is designed to fit the bearing (not “just fit”) it is likely the bearing’s life will be shortened. The question is, how severe is the effect…

I used 42 mm bearings in a 40 mm frame for a long time with no problems, not they are in a 42mm frame and are still going strong.

Why don’t they just make all frames with 42mm holders as a standard, and have them come with the 1mm thick circular shims for those hubs that use 40s.

Because that makes sense.


and wouldn’t cost any more to make, either.

Actually, the standard bearing size is 22x44x12

I think a special size was made up for the 22x42 ISIS uni size, unavailable at bearing houses, etc. They would have used 22x44 for the uni ISIS standard, I guess, except the manufactures didn’t want to redo all their frames.

17x40, and 20x42 are standard sizes. I think only the Torker DX series, and the ISIS use a custom run of a unique size.

The market is likely just not there to justify the cost of making 1000 22x40 bearings. I haven’t researched this though. I am just guessing that you might have to sell hundreds for 10 $ each just to recoup the tooling costs of the first batch.

This question has been raised in several threads. Currently it cannot be done.

The general explaination is that 42x22 bearings are common, and 40x22 bearings are not. I guess the fact the a new thread is started about this once every couple of weeks is not proof enough that there would be a market for the bearings if KH were to do a limited run of them. Maybe Nimbus will answer the call?

I would have bought Moments if they’d done the limited run. Instead they lost my business. I’ll still consider it for my spare muni if they were to make 'em, though. I could always use to beef that wheel up. Otherwise I have to go with the twice as expensive profiles.

It is I think because the 22x40 bearings would be too thin and not last long enough. ISIS on bikes had big problems initially with teeny weeny skinny bearings that lasted about a week, and the unicycle people wanted to avoid that.

People with machined 40mm bearing holders, possibly the best solution is to get them machined out to 42mm, I know people have done this with some frames, surely no frame is built to such tight tolerances that there’s not enough material between the bearing and the bolts at the side to fit in a 2mm extra diameter? I reckon it’d be easy enough on the 40mm machined bearing frame I’ve got (DM).


I’d argue that if 2mm makes such a big difference that 22x40 bearings are too thin vs 22x42 than that same 2mm difference will toast a frame orginally made to 40mm specs. Either 2mm matters or it doesn’t, I’d think.