Gear-slip in Schlumpf Gen-2 hub

Has anyone else had one so far? It happened to me last week.

I was riding on a paved street in high gear and tried to downshift. The uni had been working beautifully since I’d gotten the new hub many months ago, and I’ve downshifted with no difficulty or problem thousands of times. But on this occasion, the unicycle went into coast mode, causing me to fall flat on my back. Luckily I was wearing a back pack (and the helmet and wrist guards didn’t hurt, tho they didn’t help either), so I wasn’t badly hurt.

I had a few gear-slips on my Generation-1 hub, but I hadn’t even heard of anyone having it happen with the newer hub.

I checked my guni by pushing the gear buttons back and forth as I moved the cranks in a complete circle, but it appears that the gears are fine. I can’t figure out what happened, and I’ve shifted a few times since then without difficulty (when I wasn’t too scared).

My guess is that I clicked the button in JUST ENOUGH to make this happen (too strongly for nothing to happen but too weakly for it to shift properly).

Has this happened to ANYONE else?

Yes, the “sweet spot” of the shift button is an issue, just like with Florian’s bicycle bottom brackets. It is possible to do a sorta-shift with the button. If the button it is not fully engaged, free play can result. And regardless of how many shift pins are in your hub. (Gen 2 have more than Gen. 1)

Did it coast for a little bit or for more than a fraction of a rotation?

Sounds more like a missed shift or a failure to engage than a gear slip. Not the same thing as what happened to me with the Gen-1 hub, which was a gear slip.

The Gen-2 hub was designed to keep the gears meshing together tightly once engaged.

You could learn how to engage the sweet spot at will and be able to coast down hills?

Can I please see a photo of a geared uni?

I think this happened to me a couple of times when I first got my Schlumpf. Engaging the button was a bit hit and miss, and I’m sure that a couple of my UPDs weren’t completely my fault. However, if you’re turning the cranks at just the right speed, then the moment of freewheeling can last for half a revolution or so.

But there certainly is a ‘sweet spot’ though where the cranks totally disengage from the hub. I’ve only found this for sure when pushing the button with my fingers and moving the cranks by hand when the uni is stationary though. I would expect that the additional forces involved when it is travelling would cause it to bounce in to one gear or the other though.


Ken, I really can’t say whether it was a gear-slip or a missed shift. What is the difference?

On my first-generation hub, I had a very nasty splat at the top of a hill when I tried to up-shift. The gears temporarily didn’t catch, and I fell back like a stick; the only time I’ve ever needed my helmet (tho only a bit, since I bent my head upwards as I fell). That’s basically what happened this time.

So I’d guess that you’d call it a missed shift?

Semach, I don’t think it’s possible for the cranks to freely coast for a half-rev. Basically the most they’ll do is go thru 30 degrees (there are 12 pins), which is a LOT less than 180 degrees of a half revolution, tho occasionally those 30 degrees feel like a lot. A twelfth of a rotation on a geared-up 29" uni is good for about a foot of coasting – but that’s it. On the old hub, it didn’t always engage until the end of a sixth of a rev, which could be two feet. That was disconcerting and caused some UPDs. But this recent slip of mine was worse – it didn’t engage at all.

But when I picked myself and the uni up, I checked it out, and it seemed ok; it wasn’t still in slip mode.

How does that have gears?
How does it work?
How fast can you go?
How much do they cost?

What I meant was that if the cranks are turning slightly slower than the wheel, then that 30’ arc of non-engagement will move around with the wheel enough for it to effectively be larger than 30’. I guess that in theory, shifting at exactly the right moment, and keeping the cranks in the middle of the 30’ then you could keep them disengaged for ever - but the skill/luck involved there would be incredible!




Thanks I didn’t think of that.

They’re in the hub - which is why it’s chunky. They use a planetary gearing system; bicycle geared hubs work the same way. You need a frame which can accommodate the gearing mechanism by providing a torque arm attachment.

The shifter mechanism works by you kicking the button that sticks out where the crank bolt usually is. Kick one side for high gear, the other side for low gear.

The gear ratio is something like 1:1.4 (?) on the standard Schlumpf hubs. On the KH/Schlumpf splined hubs it’s going to be 1:1.5.

If you put a 1:1.5 hub on a 20" wheel it gears it up so that you get a “virtual” wheel of 30". For a 24", you get a virtual 36" - coker size. On a 29er (or 36er!) this would translate to something huge :wink:

Schlumpf 29ers are currently reckoned to be faster than a coker on the straight flat ground, though this varies depending on the rider.

nb: although the virtual wheel size is very big, it’s still not the same as having a real wheel that big. A 24" with 1:1.5 gearing will behave a bit like a coker, in terms of cadence vs ground speed. However, you don’t have the large diameter and mass of the Coker wheel there so it’s still not going to be as smooth. I’ve not ridden a geared uni yet but personally, I’d be very very surprised if you could get a geared 24" to come close to a coker in terms of speedy cruising.

The cool thing would be that if one were to buy a 24" KH/Schlumpf, it’d go quite fast (e.g. for less technical riding, and for getting to muni trails), but could shift down for technical sections, natural trials etc. Also you could probably just about manage urban trials and street on it too: an all rounder with a particular aptitude for muni.

Lots and lots :frowning: And the KH Schlumpfs will probably cost even more. Best to look on your local UDC to find out what they’re quoting for Schlumpfs in your local currency, but it’s fairly steep at the moment.

FWIW here, the term “sweet spot” usually refers to something nirvanic. Like a fully engaged shift. Missing the shift means to me that the “sweet spot” in the shift button actuation was not achieved.

In other words, what happened to Dave (and Semach and Ken and …) was not sweet!

Another possible issue, this from Florian’s site:

“Indeed, each SCHLUMPF gearing system (like the ones for bicycles) has a slot screw, where you can add some drops of bicycle oil or some special SCHLUMPF grease once or twice a year, if you want to keep highest efficiency for many ten thousand miles.”

Those of you who have had a Schlumpf for more than a year, have you ever added any grease?

It should be called the poop spot.

A unique case of pedals out of position.

The hub has epicyclic gearing (a.k.a. planetary gearing). There is an animation of epicyclic gearing here that should give you an idea how it works.

Greg Harper made an epicyclic geared hub. You can see the project and an inside view of the gears at the Greg Harper Fletcher Memorial Home.

The ratios are the same for the original and the KH version; both 1:1.5 (and 1:1 too :slight_smile: )