Seeking advice on a G29 build (titanium frame?)

(edit: TL;DR: Is there a good reason not to get a titanium frame for a G29 build, aside of the price?)

I have a KH26 frame and two wheels, one with a Schlumpf hub and 2.3" road tire; the other with a 3.0" Duro tire. I use the road wheel to commute every day and the latter for muni. As I’m more and more obsessed with muni-ing, I’m tired of switching wheels (and tuning the brake every time which is a real PITA). I started to think to make (or, restore) this KH26 a dedicated muni, and build a new commuter. Ideally it would be a G29.

The hub is a 4th gen (M0800+) to be migrated, worked great, not too much to worry. For the rim I’m thinking to get a carbon one, as 29" carbon rims are inexpensive and there are plenty of choices; I can also get 36 holes customly drilled. For cranks, saddle and seatpost, I already have spare parts for them, so really not much to think about.

Now the problem is down to the frame. I can always grab a KH29 frame, but I also have the chance to get a custom made titanium frame. So my main question is, is there a good reason not to get a titanium frame, if price isn’t an issue?

Edit: the build is done! See P46 for pics and P50 for its full specs.

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I remember having seen issues with the Schlumpf’s bearings slipping in the bearings holders. From Florian’s website for the new generation:

  • New technique of twisting protection (eliminates the risk of slipping with titanium frames or insufficient tightening torque, as well as the risk of damaging the outer ball bearings if the tightening torque is too high).

That could be an instant dealbreaker… is the new technique which requires to drill a hole on the bearing cap, as I’ve read in another post?

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I found the post mentioning the slipping issue:

And Kris’ reply:


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I thought about it a little bit deeper:

Why would a Schlumpf slip in a titanium frame, but other (simple) hubs don't?

The answer might be that the Schlumpf carries more torque than non-geared hubs.

Now, what if I cut a piece from a soda can, and put it between the knurled bearing and the bearing cap? The bearing slips because it can’t “bite” into the titanium surface, but it can bite into the aluminum piece right?

When a Schlumpf hub bearings are not hold in high gear, then the hub becomes a freewheel - in both directions. That’s what happens when the bearings slip…
I guess the soda can won’t help there, as the shim may be able to slip in the bearings holders.

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I’m a bit confused, the hub becomes a freewheel, as in the disconnected state between the high and low gear? Why would the bearing slip in this state, does it actually shrink a bit at this point?

It’s more what the rider experiences I expect - when I didn’t tighten the bearing cap enough on the knurled side once it was fine until I tried to engage high, then the bearing just span in the holder, effectively freewheeling, and it was an instant upd


I’m not 100% sure, but I guess the explication lies in how the internal mechanism works. I won’t add more details as I’m completely unsure about the exact mechanical issue.

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Oh I think I misunderstood Maxence’s comment, he was describing what happens when the bearing slips.

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How long will your commute be? Also have you considered going for a brakeless 29"? It would let you swap the wheel a bit easier and with long enough cranks on a Schlumpf you can control your speed. I find with my commuting I learn the riskier spots and don’t go full speed in case I need to slow down or stop quicker and it reduces a lot of accident risk. I run a dual wheel 29" build depending on weather for a 13km commute.

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The commute is short, but I do prefer riding it wherever I go in the downtown.

I don’t use the brake much so I don’t see a problem going brakeless, although I’m not planning to switch wheels on the new 29er (the 26er will be a dedicated muni so no need to switch wheels anymore).

The way the Schlumpfs work (or any planetary system) is essentialy down to 3 main parts. The input force (cranks), the output (the tire/rim) and a fixed part (the knurled bearing). When we talk about ‘‘slipping’’, it’s the knurled bearing that is turning, making the input and output parts free in any direction. That only happens when there’s enough force difference between the input and output to make the fixed part compensate for that. And it goes on until the force that makes it slip goes away, then you’re probably down on your feet (or butt).

Frames made of harder material have a tendency to slip, see Titanium and Steel frames. The last and the new generation of Schlumpfs have this issue fixed with an actual stopper versus something based on friction.

Ti frames are sexy, they need to be well built to be worth it though. My old Triton Sponge weights the same as a KH of the same size, and is very stiff and strong (I bought it used in 2010!). A Ti frame that is lighter than an aluminium frame will most likely be more flexy and might not be as good to ride.

It’s only hard to find a builder to make a Ti frame right now (I know I know, I’ll get to it). Other than that, they are beautiful and solid machined when well built :slight_smile:


Thank you very much Jacob, that’s a great ELI5-level explanation!

So it’s all down to increasing the friction between the knurled bearing and the bearing housing. Some potential options:

  • Use an aluminum bearing cap instead, which apparently worked for saskatchewanian;
  • Make the inside of the bearing housing knurled too, is that possible?
  • Weld a small bit on the bottom of the bearing, drill a hole correspondingly on the bearing cap to lock that bit, so to implement a mechanical stopper like the latest generation. Is this possible?
  • Overtighten the bearing cap, to more than the suggested 5-6 Nm. I know this is possibly the worst idea, as the user manual explicitly stated that it will damage the bearing and ruin the warranty - but, just asking scaredly in a whisper, what makes the Schlumpf’s bearing special that it get damaged in such a case? Because I have bearings on normal hubs overtightened to, like 10Nm or so (not actually measured), it only makes the wheel less smooth.

BTW the kind guy who makes the titanium frame offered to lend his own frame to me to have a test before I decide whether or not to order one. What would be the best practise to try to reproduce this issue? Like doing abrupt start and stops on high gear?

The main issue is that you are not potentially damaging an easily replaceable bearing as on a standard hub, you are potentially damaging the torque brace part of the hub (the part with the knurled surface). Even if that part is fine, the bearing inside it is a lot harder to replace than the normal unicycle bearings (or even the bearing on the other side of the Schlumpf hub.)
I’m not sure if it is actually more fragile than a regular hubs bearing, but while on a normal hub it’s not a big deal if it wears out prematurely if you overtighten it, on this it is.

I wouldn’t weld on it, but I know @jaco_flans has retrofitted the previous generations “mechanical locking system”, by milling slots into the torque brace. It seems possible to do this with this new system too, drilling (and probably reaming) a hole into it and fitting a dowel with a nice press fit.


I may be wrong but I thought this version actually had an improvement on the knurling system.

It was this little block or tab that slotted in the bearing cap edge of KH frames (and perhaps others)

My comments here carry my own personal bias. But I’d steer clear of using Ti for the frame and go with either a KH frame that has the double brake tabs - not sure they’re yet available in 29er though, or get one from Flansberrium.

Why? These are going to be in my view the best fit for the special system pictured above so the slipping issue is resolved.

Next - even though I’ve not yet personally tired it, if I was rebuilding my older hub into a new 29” wheel with carbon rim I’d get hold of the BrakeFast adapter in 36h and build the disc system on the inboard.

Yes there will be some issues to resolve getting this to fit and work, so it does require some DIY skills. But it is a massive upgrade and the disc being put on the hub also takes away much of the risks of slipping knurling anyway.

Roger’s video is super clear on how to set this system up and would just require care and attention and some patience.

The cost of this part and the time invested in my view massively outweighs a Ti frame.

I would probably enjoy a Ti 36er frame for a fixed geared carbon ride, but for Schlumpfs I really like the KH frames for the best bearing fit. Others surely work but I just like the KH (or Flansberrium) route.

Again it’s all coming from my bias towards these components but when you’re planning to build a new carbon wheel up, using the BrakeFast system just feels like a best route - as it kind of also adds some protection to your hubs flanges… and you get a neat disc brake system akin to the new hubs :star_struck::gear:


Indeed! I never noticed the little block before but it is there. This makes things much easier, so as long as I have those slots on the bearing housing I’m all good right?

And we can see the knurled part has already slipped, maybe it’s because I didn’t align the nubs with the slots while installing.

Edit: the more I stare at those three slots the more suspicious they become. The images @mindbalance linked shows the nubs are stopped at the edge of the bearing housing, not in any of these slots - did I just accidentally pressed them out with the nubs misaligned? But they seem so evenly spaced and symmetrical…

They look like squished frame to me - and if so the knurled bearing won’t have been held so well when positioned like that, and may have been prone to slipping. My hub is the generation before yours and doesn’t have that catch on it

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I think you may have done so. I’ve never physically handled this kind of hub so I can’t say I know how it feels to align that nub.

The good news is. If you were to move this to a new frame for 29” wheel, then it would be possible to align it correctly with the nub positioned as per the photos above. My only thought is again this would need to be using bearing mounts / caps as per the KH design as I feel they have the tolerances that grab the corner of that nub and help lock the bearing in place.

I’d also pay close attention to the text on the bearing that should say: UP. And ensure that is facing up, into the fork / frame leg.

As for how you can fix this now with this frame. If you can get the nub closing positioned to where it looks (as best it can) in that photo and then swap your bearing caps around - they could be interchangeable - there’s a chance that the other cap has a firmer edge / corner to catch it.

This is the puzzling point. I could perhaps just be chance or maybe the former owner tried different locations.

Regrettably I suspect to use this with 100% original grip if not moving to a new wheel build, it would be a case of getting a new frame.

Edit: looking and thinking again -

These edge indents might in fact be how it is designed to push into the frame. The photos I shared before don’t show how it looks with the caps installed, but the nub looks pretty chunky so my guess is they are squashed into the frame / cap when first mounted as KH caps are pretty snug when tightened down as they should. So… it may just be a case of putting that nub in the correct edge space and ensuring your cap aligns or is able to squash afresh into it and… GRIP!

Looking forward to seeing what you build up :smiley:

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