yes it happens, at least it did for me, not just once, several times… that’s why on don’t ride a schlumpf at the moment on my 26" (for a time i took the caps out and shifted gear bay hand…) an other reason was the weight, because i do alot of hiking in my muniing… …but it looks like i’m going back to a schlumpf on the 26er…
Am I right if I assume that UPDs because of shifting by accident can be quite nasty? Another reason for wearing my protection gear 
i’m not sure, but mostly when i shifted by accident it was from low to high gear, when it was really technical, with hopping, so it wasn’t that nasty (means not in highspeed, but maybe nasty because of the unfriedly upd-terrain… if you know what i mean 
), and it kinda shocked me everytime, because i wasn’t ready for that…
Yes, I know what you mean 
What I was thinking about was the half rev (or how long does the shifting process last?) you are coasting after shifting. Isn’t that an issue when you have a lot of pressure on the pedals?
I’ve had two unintended shiftings in the two years I’ve had my Schlumpf. Both from low gear to high, and both with 165mm cranks. On the first one I was just riding down the street at a very modest speed and my heel hit the button just right. There was a fair amount of slop in the gears on that shift so I landed flat on my butt. Fortunately, I had my backpack on with my laptop in it. So my computer protected my valuable equipment (my butt) from serious damage.
On the second event I was riding pretty fast through town when I accidentally shifted into high gear. There was virtually no slop in that shift and I seemlessly shifted into high gear and kept riding. Woo Hoo! What a feeling!
Geoff
A couple of things I have come across with my Schlumpfs:
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Serious mud can be problematic because it fills up the little screw in the shifter buttons. The dirt has to be taken out of there before any adjustments are tried on the screws.
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Accidental shifts haven’t happened often but I think they are more likely to occur in technical terrain, which is where they are the most unpleasant…
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Sometimes the shifting happens at an unexpected time, quite a bit later than initiated, which can lead to UPDs. This is usually when shifting up.
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On my now retired 26er hub (waiting forever for the replacement) I noticed that sometimes when I did small drops (in low gear) the cranks would slip one slot further or something like that. I haven’t ever heard of anyone else who experienced that, though.
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The 150mm cranks are fine for most of my rides but I am thinking about getting some 165s for steeper climbs. Accidental shifts would be pretty much impossible on those too, I guess, especially with not so large feet.
The shifting process (generally) takes 1/16th of a revolution. There is a thread called “Schlumpf shifting techniques” that describes some of the common things that happen when shifting. Sometimes when there is a lot of pressure and you shift, it will not engage right away until you change the pressure, it is hard to explain. There is a lot of input in that thread of the best ways to shift and ways to make shifting extremely predictable.
Shifting is very easy for me now. Your pedal choice and your shoe choice will also affect how easy/hard shifting is.
As long as you have pressure on the pedals, the hub won’t shift. The button basically initiates the shifting, but only when you release the pressure from the pedals, it will execute. That is one reason why there can be an unpredicable delay between hitting the button and changing the gear - possibly resulting in a UPD. The coasting can be up to 1/2 rev (at least it feels like that) or none at all. In most cases, when you reduce the pressure from the pedals before hitting the button, it shifts very smoothly without any delay (as said: in most cases, but not always).
I guess that you don’t want to shift in rough terrain, usually you will stay in low gear and use the high gear only on nice surfaces where you can go fast.
I suggest you simply try it. You will need to make your own experience and simply get used to the way how it works.
Sure I will, but my new Schlumpf Uni is shipped today so I have a few days to wait left. And it really helps to talk about riding a GUni while waiting for it 
That’s VERY good because the UPDs I was thinking about where with lots of pressure on the front pedal. When there would be a slop of about half a rev there would be nothing left than a faceplant :o
But there’s no guarantee for that. If you just release the pressure for a moment, to balance or whatever, it will shift.
If it gets a bit more technical or for riding single trails I will wear my fullface helmet. I will have to deal with that if it happens
As best I can recall I’ve only had a few accidental shifts. Like everybody else it was from low to high gear. Most often its because I’m concentrating while I’m riding rough terrain and my feet and ankle tend to “cheat” closure towards the cranks as I ride. I guess they move in enough that the side of my shoe begins to rub against the shift button and “pop” gear change! Typically no problem, it’s just another UPD. And as its’ from low-to-high I’m not going very fast anyhow…
I’ve had the opposite problem as well; not being able to shift into high gear. It is important to check your equipment periodically (if don’t already). I was trying to shift up on the fly and I could tell the shift rod was moving but the high gear refused to engage! Turns out the frame bearing clamps on the knurled side of the hub were a tad loose so the high gear couldn’t engage! It was a subtle thing as the wheel didn’t feel loose in the frame.
Riding in high-gear I’ve never had a accidental down shift (now that could be dangerous).
As best I can recall I’ve only had a few accidental shifts. Like everybody else it was from low to high gear. Most often its because I’m concentrating while I’m riding rough terrain and my feet and ankle tend to “cheat” closure towards the cranks as I ride. I guess they move in enough that the side of my shoe begins to rub against the shift button and “pop” gear change! Typically no problem, it’s just another UPD. And as its’ from low-to-high I’m not going very fast anyhow…
I’ve had the opposite problem as well; not being able to shift into high gear. It is important to check your equipment periodically (if don’t already). I was trying to shift up on the fly and I could tell the shift rod was moving but the high gear refused to engage! Turns out the frame bearing clamps on the knurled side of the hub were a tad loose so the high gear couldn’t engage! It was a subtle thing as the wheel didn’t feel loose in the frame.
Riding in high-gear I’ve never had a accidental down shift (now that could be dangerous).
There is a thread where the torque of the clamp screws was discussed. I think it is recommended to use 5 Nm, but on my KH29 it works very well with 4 Nm. There is also a warning that the bearings may get damaged when the torque is too high.
Unfortunately a torque wrench that starts at 2 or 3 Nm is quite expensive 
Shifting Latency vs Slop
In the interests of making sure we’re talking about the same thing, there are two factors at play in the unpredictability of shifting. Maybe we can agree on terminology.
There is the difference in time or revolutions between successfully hitting the shifter button and the gears actually shifting. If there is a lot of pressure on the pedals this can take some time. For example: When you are approaching a hill and you attempt to shift from high gear to low gear, if you keep a hard and consistent pressure on the pedals then the gears might take a while before they shift. This shifting will occur during that split second when the pressure is decreased, then “click” you’re in low gear. I don’t have a good term for this delay. “Shifting Latency” doesn’t exactly have much of a ring to it, maybe it’ll work.
The second factor in unpredictability (and for me much more of a problem) is the “slop”. This happens after you hit the button and when the gears are in the act of shifting. There is an unpredictable degree of arc during which your cranks will be free-wheeling. My understanding of this is that the slop will be no greater that 1/12 of a complete revolution (30 degrees max) but yeah it sure FEELS like 1/2 of a revolution. It might only be 1 degree of free wheeling which is really nice and very smooth. But if it is 30 degrees of slop that can get quite scary, especially if you are up shifting while riding down hill and your guni starts to race down hill and out from under you. If the guni picks up that much momentum and the hill is steep then it can require a fair amount of force to stop the wheel and get it back underneath you. Add to that the factor that in high gear the wheel has a bigger advantage of leverage against your legs. Then there’s the bit that you weren’t really expecting this to happen anyway. 30 degrees of slop up shifting while riding downhill is a great recipe for a UPD. In that situation I usually apply the break a little during the whole shifting process. This limits the speed of the free wheeling (slop) phase and also lightens the pressure on the pedals which limits the “shifting latency”.
Does this sound about right? Anybody have a better term than “Shifting Latency”? (Please say “Yes”)
Geoff
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Geoff, that sounds perfect!
I like Shifting Latency. My best example of it is when trying to shift down when on a downhill. That is when I have most consistent back-pressure on the pedals and it can be many revolutions of trying to hold back the gathering speed of high gear before the down-shift happens (and needs a ‘flick’ or pelvic-thrust to release pressure momentarily, which is hard to control). So I usually try to shift before the downhill starts if I’m not going ride it out in high gear.
I wonder if the feeling of a half-revolution of freewheeling is due to the whole system rotating? So the cranks could really be disengaged for half a revolution of the wheel in motion, but the they only move 30 degrees relative to the hub - they just slide as the whole thing turns. It can be a bit off-putting, but very rarely does it seem to upset my pedalling rhythm. I guess there is a lot of ‘momentum’ in the circular motion of your feet so they will keep going around even if the pressure changes for a split second.
Still, there’s nothing as satisfying as a smooth shift with no detectable slop. It happens maybe 5-10% of the time. Like butter sliding over Teflon. Mmmhmm.
Sam
“The second factor in unpredictability (and for me much more of a problem) is the “slop”. This happens after you hit the button and when the gears are in the act of shifting. There is an unpredictable degree of arc during which your cranks will be free-wheeling. My understanding of this is that the slop will be no greater that 1/12 of a complete revolution (30 degrees max) but yeah it sure FEELS like 1/2 of a revolution.”
my experiance:
using schlumpf grease at temperatures below 0° (my record is -16° ) its up to 2 revolutions.
using sewing machine oil at same temperatures its max 1/4 revolution.
so do the same as in your car - change oil before season changes
but beware, sewing machin oil rinse out, if you bring the hub in warm places as your favourite carpet…
That’s funny because when I sent an email to Florian, moaning about the leaking oil, he replied that they were doing their best to make it suitable for carpet floors, but yet haven’t been successful. As we all know by now, all hubs are leaking when oil is used, but I stay with it. Instead of adding 5 ml per year, I add 1 ml every 2nd month. Furthermore, I asked Florian if I can use different oils, like transmission oil (I still had some left from my motorcycle). He replied that almost every oil would be ok.