Internally routing or Hiding Di2

What kind of loads are on the piece of steerer between the two headset bearings anyway?

Significant. If you hit a bump, or brake, and the front wheel tries to go forwards then the fork legs will try to bend backwards. The steerer is constrained by the upper and lower headset bearings, but there will be quite a lot of load on the bit in the middle, which is essentially what's stopping the fork legs from disappearing under your bottom bracket. Headset bearings are only skinny wee things and won't resolve those sorts of forces.

It's your teeth but I'd drill it. Never seen a steerer snap, carbon is strong and steerers have the chunkiest walls on a bike.

But then I won't need the fancy BMC stem that arrived today and if I go down the special headset route, I may be able to internalise the rear brake hose too. Depends whether the gap is large enough for a hose I guess

So, anyone know of any non-tapered 56mm OD, 54mm ID head tubes? I could always machine one from thick wall 2.25“ OD 4130 tubing, but it seems like hard work.

Ah of course, makes sense. The question was only half tongue in cheek, couldn’t figure out where the loads were coming from but knew there had to be something.

i don't think the above description is true at all. the headset works under permanent compression, preload if you like, and its job is to transfer loads and efforts to the actual headtube, the fork blades, etc. in fact the steerer itself is/should only be subject to the steering rotationnal efforts - if headset properly installed.

Does anyone have the software and know how to model it and test? :)

The headset preload is merely to ensure the headset bearings don't become loose. If it was enough to deal with the fore and aft stresses on the fork, the headset would be locked rigid. There's a reason headsets have two bearings, not one. And that relies on the fork steerer being strong enough and stiff enough to keep the fork legs in roughly the right place. If you don't believe it's true, try riding your bike without the top bearing in the headset, and just preloading the bottom bearing. Or don't, if you value your teeth/face.

Yep, I've got PTC Creo CAD software with the FEA plug-in. Don't need that to work out that a 7mm deep bearing isn't going to be enough to keep your forks pointing in the right direction under heavy breaking though.

@motoko Yes, drilled behind the stem.

@PhilDAS I used a hylix fork on my last build, there is no room in the fork crown for routing the front brake line through the fork. I used an endoscope to check.

Yeah I’d accepted the fact I’d always have the front brake running externally

Nice writeup. Carbon or alloy bars?

Zipp Service Course SL70 Ergo Aluminium bars.

@PhilDAS Shame!

Even if you could get a cable or hose into the steerer and through the crown, how would you retrieve it near the brake given the forks usually have internal routing going up to the outside of the crown?

I drilled the internal routing to use it as an exit (which never happened). The internal routing always makes a bend at the end of the fork leg to go out, perfect for drilling into it.

You'll have to start at the bottom when you're running your hose since you'll never find that hole when you start from the steerer.

Something to consider when I have the fork in my hand.

I wonder how much having relatively stiff hoses running into the fork steerer would effect the steering

I've been looking in to perfecting all of this for my next build. And since the space inside a steerer is so limited, I've been thinking about losing the sleeve or any other form of star nut/expander plug.

And I'm currently looking into 2 options, go for a One Up EDC lockring for my pre-load. This means I don't need a top cap, thus not needing a star nut of expander plug. https://www.oneupcomponents.com/collections/edc

The second option would be a problem solver adjustable headset spacer between the stem and headset. Not sure about the looks though.

I used Shimano SM-BH59 which you don't feel at all.

The EDC looks like a nice system, even without running cables down the steerer, I'd like on other bikes to have tools in there.
Maybe no good on a carbon steerer though? I wouldn't want to tap a thread into one anyway.

The previously mentioned Pro Tharsis stem has a built in pre load thread since it's designed for having the di2 battery in the steerer rather than an expanding wedge

@Jaap

https://bikerumor.com/2012/02/21/found-acros-the-clamp-adjustable-headset/

Options for fat headtubes

https://acros-components.com/en/products/core/headsets/10076/is52/is52-bearing-kit-integrated-cable-routing

https://acros-components.com/en/products/core/headsets/10074/zs56-upper-part-for-integrated-cable-routing-icr

Acros headsets are shit on various canyons.

Very fat headtubes are what we're doing, had to measure up the internal bike for Di2 bits earlier. Wireless jobby is going to live in the stem so can be disconnected easily if needed.

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Front brake goes into the steerer, then out the leg, dunno if that's the kind of thing people were looking for?

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Looks ideal yeah