Product improvement suggestion for KH/Schlumpf hub

I tried to PM Kris Holm with the text below but after doing all the typing, the forum software told me that Kris has chosen not to receive PMs. Therefore, this now is a “public letter” to Kris, with the added advantage that anyone can respond.


Thanks for the suggestion. We did think about this and it’s a good idea. However, on the other hand it would be non-standard for 42 mm bearing housings. The idea was to make the hub so that, as much as possible, it could fit any frame with 42 mm bearings and standard bearing spacing. So in the end we went with knurling for that reason.


That was a fast response :slight_smile:

But, well, for one thing, the KH frame has a knurled bearing holder (also the top half, on one side) for a reason, hasn’t it? So the KH frame is better suited to this hub than just any frame.

Besides, if you make the adaptation only to the c-clamps, you won’t lose compatibility with any frame. The hub would then come with dedicated bearing clamps (or even just one special clamp) which is a negligible cost compared to the hub itself.

Because only the inside dimension of the bearing housing is standard (42 x 12 mm), but not the outside shape or bolt location, we can’t make a clamp that would be sure to fit the top half of every housing, unfortunately. Thanks for the feedback though; if you have other ideas let me know! If you want to do them off the newsgroup you can also email info (at) or use the form at



I think in practice the bearings have wound up finicky enough that they’re not plausibly usable in frames other than the KH. I certainly wouldn’t use a KH/Schlumpf hub in a uni without machined bearing holders, for example. One of Corbin’s hub failures was supposedly because he’d Dremelled his bearing holders to 42mm, but the tolerances weren’t good enough. Other failures have supposedly been because people over-tightened the bearing holders–but if you under-tighten them, you get the failure mode Klaus mentions, which can easily cause a crash.

The hubs would probably be more reliable with some sort of real lever arm.

To be fair, Corbin doesn’t have any tool with which to measure roundness. He could’ve Dremelled out an octagon for all we know. :slight_smile:

Edit: Also, we don’t know if he centered his “Dremel job”… he’s got several degrees of freedom with which to drift off center.

Sure, it may have been a hacky job, but I wouldn’t expect a Nimbus frame to do any better. Another way to think about it is, what frames other than the KH could you safely run a KH/Schlumpf hub in right now? Personally, I wouldn’t try it in anything else.

Seriously. Would you spend $1300 on a hub and risk destroying it in a “modified” frame or would rather play it safe and spend another $200-$300 on a compatiable (i.e. KH) frame? I think the answer (for me at least) would be pretty obvious? :slight_smile:

There are a couple of Triton frames running KH guni hubs. Mine is running swell. Actually, the only reason I didn’t buy the KH is because it wasn’t out yet, but I like my unicycle very much.

Osmundo, what cranks are those? They look like the nimbus cranks I tried out on my KH/Schlumpf hub, but they didn’t fit bc they tightened against the frame quite easily.

This pic is from my first week of ownership. I had the same prob with the cranks and now I run the heavier moments. Come to think of it…I think I went with the nimbus’ because you recommended them! If I weren’t so lazy I’d look back and see.

Yeah, I remember talking about the weight differences between the KH Moments and the Qu-Ax Lightweight ISIS cranks with you when you were gathering parts for your geared 36, but not about the Nimbus ISIS cranks that have q-factor.

Months after you had your geared 36 set up, I had made a thread about the Nimbus ISIS cranks w/ Qfactor and that I was going to try them out since they were half the weight of the Moments, but they definitely did not fit well.

That pic looks like you have the Nimbus ISIS (with Q) cranks not the lightweight no-q Qu-Ax ones. They are shaped much differently. I still have not tried the lightweight qu-ax no q cranks out yet, but Ken and Tom seemed to have success with them, others have not.

EDIT: I dug up my old thread dealing with the issue of lack of a good lightweight ISIS crank with Q factor that is compatible with the KH/Schlumpf hub:
Lightweight ISIS cranks with some Q factor?

Why would the factory-machined Nimbus bearing holders (probably made in the same factory, with the same machinery as the KHU holders) be the same quality as a man holding a Dremel, and not the KHU?

I had those Nimbus cranks with my original KH/Schlumpf and one just touched the KH frame. In the newer model, along with the larger internal bearing, Florian has increased the axle length by 4mm so that this kind of thing doesn’t happen.

I’m now using the same light Nimbus 150mm cranks with the new longer axle KH/Schlumpf and it fits fine - a comfy millimeter or two to spare between crank and frame.

Moments are too heavy for road riding! :slight_smile:


My suggestion for improving the KH-Schlumpf hub is that the crank bolts should be made to fit an 8mm allen key, rather than the current 6mm. Its tricky to tighten the crank bolts to the recommended torque of 50-55Nm without rounding the bolts. My guess is that there may not be enough material in the bolt itself to accomodate an 8mm allen key hole, but if they could be changed it would be great.

I came across this problem of cranks rubbing on the frame for the first time recently with KH Moment cranks on a KH29 frame. I fixed it by placing a spacer between the bearing and crank. I’d imagine the same fix would work with the Nimbus cranks on the KH-Schlumpf hub.

I read that the recommended torque has been toned down, I think munirocks wrote that in the thread about broken Schlumpfs but I’m too lazy to check, let alone provide a link.

The recommended torque for the bearings has been reduced to <5Nm for the smooth side, 5-6Nm for the knurled site, but the recommended torque for the cranks has remained the same, 50-55Nm.

I like the idea of something greater than 6mm, but yeah I would bet there’s not enough material there e.g. the revised hub includes changes to the shifter shaft to allow for more material in the button.

Re stopping the cranks hitting the frame I don’t think a spacer is a good solution with the geared hub. I had this issue and Florian suggested milling the cranks as the way to go.

I would have thought that a more secure way of holding the the knurled bearing would be to manufacture it with 2 tabs that are clamped between the lower bearing holder and the frame. Something like this; -O- That would then be compatible with any frame, and very very secure.

Oh, and Osmondo, as far as I know, there are only 2 of us with geared hubs in our Triton frame, but my one is the original road hub with the torque arm. Therefore yours would be the only KH-Schlumpf Triton-Sponge unicycle so far.


I completely agree that Moments are too heavy for road riding. I am glad that the 4mm has made it so that the Nimbus cranks fit without touching the frame now on your uni…but I am still skeptical about them. A 4mm increase means that it is only an extra 2mm on both sides, and based on my experience with the Nimbus cranks, that hardly seems like enough to prevent them from hitting the frame.

I am curious of others’ experience with the new hub w/ longer axle and if they are still running into crank problems.

I still have the older version of the hub (without the even larger bearings and without the 4mm increase), so I am basically stuck using Moments.