Is there a "Safe Mode" on a Schlumpf?

I’m doing an occasional commute home from work and I plan to continue doing it when I get my 36" Schlumpf.

The risky thing is that 5 miles of this commute is on highway 101. There’s a bike lane, but it’s still a busy highway.

Don’t misunderstand, I feel confident about the KH Schlumpf setup. But I’m reading a bunch of old threads that suggest that slippage of the knurled bearing is possible. Or that an unexpected freewheel event is possible.

What I’d love to hear is that there is something I can do to make sure that if any of these gremlins ever pop up, that it NEVER happens when I’m on the highway, a few short feet from 60+mph traffic.

Would I be correct that staying in first gear decreases the chance of these problems popping up? Is there anything I can do to create a “safe mode” when I’m on the highway?

Is there something I can look for in a visual inspection before and after each big ride to make sure things are in shape?

Schlumpf bearing “slippage”, if it happens, can be scary and catch the rider off guard. It usually only happens either during abrupt and heavy back pressuring, or when climbing a steep incline while exerting significant down force. This can occur even if the bearing cap is properly torqued, because of heat build up, and also because the inside of the caps are smooth, without corresponding grooves to lock the bearing in place.

I have found great success with aluminum tape inserted into both the top frame cap and the knurled bearing cap.
Once the bearing cap is secured at the recommended torque, the ridges in the bearing will firmly ‘"seat’" into the aluminum tape, creating a very solid and secure, interlocking non-slip grip. It has worked perfectly for me after many tests that recreated what caused my rather long slide/slip a couple months ago.

I saw your thread. You can imagine that I want to make sure that never happens to me on the highway. It’s one of the things that got me thinking about this. The more details, the better - thanks!

Didn’t KH leak out plans of a future change that will eliminate the bearing slippage… but also said not to wait for it… could be a while… sounds like you’ll want to wait for this.

No, not yet available, but it won’t be something you can retro fit, and necessitates buying a brand new Schlumpf hub. Until then, my fix is immediate, and costs about 10 cents! Best of all, it works!

The slip happens when the knurled bearing can spin inside the bearing housing
It’s most likely to occur if the bearing caps are not adequatly tightened

But could happen if enough force is applied with adequately tight caps

There is only twist force being transferred I’m
High gear

The future fix is the frame has a lip on the inside edge
Of the bearing housing. Whilst the cap does not. There will be a corresponding
Recess in the hub to fit the lip and prevent the knurled side bearing from spinning
This next generation of hub will be around when current hubs are sold. Think significantly later

The solution of adding a strip of tape , I feel, is not a good one. I’m this set up there are 2 planes on which a slip could occur. Knurled bearing to tape AND tape to frame

One idea I’ve read was to bond the bearing cap to the knurled bearing. I’m guessing with epoxy. The cap then stays attached even when
Wheel removed from the frame

The simple answer to original question. As far as I understand. Bearing slip cannot cause a freewheel in LOW GEAR
So stay in 1st for that section of route

I think there might be other ways a free wheel might occur however


Again, the aluminum tape fix is working perfectly for me, hasn’t budged or shown any signs of the adhesive weakening, and I ride several days a week in extreme conditions. I have purposely tried to get it to slip using massive back pressure and the like, and it has held solid as can be.

All I’m saying is you shouldn’t discount it until you try it. And I had mentioned this fix to Kris a while back, after many successful test rides, and he likes the idea. At least until the new hubs are available.

Just keep your bearings properly tightened, with blue LocTite, and you’ll be fine in that context. I almost never have this issue anymore, and when I do it’s because I had to remove the bearing covers and didn’t get them back to the proper tension.

When it does fail, it’s almost always when you first shift into high gear, or when you have to put emergency back pressure on the cranks. It won’t happen when you’re just riding along.

Im no extreme muni rider. Im not putting my schlumpf through the rigors that other forum members do
It may be for this and only this reason that I’ve never had the bearing slip problem

I am however meticulous about keeping the bearing housing surfaces clean and debris free whenever opened. And tightening the bolts to 5 Nm

The knurled surface has made marks in the aluminum and the ’ teeth’ sit nicely in these marks

I think as long as the OP is careful about maintenance, riding a geared hub along a highway, bearing slip is not a big concern

Am I right in thinking you have only had the bearing slip regularly (and fixing this with Al tape) after having the frame media blasted to strip the paint?
If this is the case the simple answer might be just don’t have the frame blasted

I ride hard and fast on my Schlumpf. I also have the KH disc cranks with a 180mm rotor. I have done some massively quick stops using the brake in high gear, which puts tons of torque on the hub. I have never had a bearing slip problem. Just make sure your bearing caps are tight enough.

This is something I don’t know about. Is this a measurement of the torque on the bolt? How do you measure this?

Sounds like having that bearing housing tightened just right is a key factor.

You can measure it by tightening it with a torque wrench. A torque wrench is a good investment for a Schlumpf owner.

torque wrenches

I agree, you can , and some people do manage their schlumpf hubs without torque wrenches.

But I feel much more confident with them

I have 2

one in the 10-80 Nm range for the crank bolt.
(the manual specifies 50Nm for this, but I feel this a bit too tight and set mine at 40)

and a second low torque in the 1-5Nm range for the bearing caps and the set screw inside the buttons (5 and 2 Nm respectively)

The problem with slippage is worsened because folks are fearful of overtightening the bearing side, so perhaps the slippage has become more common. I had one slip during my brief guni use, it was as Tholub said “right after I had removed the wheel”. I retorqued the bearing cap on the trail and it was fine.

Eric’s idea about using epoxy on the drive side bearing cap is a good idea, red loctitite would also work and be a little less messy and more easilly cleaned up.

Be sure and clean the paint from your bearing cap and bearing holder before the first install so you have metal to metal.

One thing to consider is that you have a knurled steel bearing frictioning against smooth aluminum, the aluminum can match the knurl, but it will only be a perfct match the first time the cap is torqued, thereafter you risk breaking down the bearing holder/cap surface. Also keep in mind that aluminum will oxidize over time with exposure to water and air, whiich could increase future slippage.

From an engineering standpoint, adding a shim, be it aluminized tape or a thin piece of metal is akin to adding a second sheer surface, so it could make the problem worse in time. The torque bar that was previously used on the Schlumpf, as is used on geared bike hub and bike hubs that have a foot brake, would be the best choice.

It’s hard to know if something will work unless you test it. Otherwise you’re just speculating.

“It works for me” doesn’t constitute testing.

And saying something else is a better idea, having not tested it at all doesn’t constitute a logical conclusion.

Well I’ve “tested” not having aluminum tape, and it’s working fine for me, therefore I’ve “proven” that aluminum tape is unnecessary.

This is my poor man’s torque wrench, which works perfectly fine and is very accurate:


Yes. In first gear, the cranks are 1:1 connected to the wheel. There is no reaction torque to go anywhere. I made use of this once on a ride when the bearing started slipping and I had no tools. In low gear, I could safely ride home.

Yes it’s always at a ‘peak’ in torque. I’ve had it once when cranking up a bridge, and recently when I accelerated after a corner. In both cases I was in high gear for quite some time already. Oh and in both cases I could gracefully and safely dismount - but then again I wasn’t going fast.

Super! I’ve had a similar idea but with a spring instead of a weight. I hadn’t gotten around to making it yet. Your idea is even simpler, cheaper and more flexible. While torque wrenches are the opposite: expensive and having a small range.