Monster, Monsteur, Monstour , 26/29+ and Expedition and Adventure bikes

some odd cleaning/sexual ritual...

It takes all sorts...

Yes, I realise it's for digging the hole beforehand, but it still strikes me as a process that should be quarantined as much as possible.
I also rather like the idea of it doubling up as a mudguard.

unless you have terrible aim

You called?

I imagine one of these would make a pretty good shovel.

https://www.tritoncycles.co.uk/accessories-c11/mudguards-c146/pdw-origami-front-downtube-mudguard-p408

Neat idea, but treating and sealing the frame must be a right ballache. Also getting enough pressure in there to be worth it.

Now that I think about it I wonder how safe it is riding around on a frame pressurised to 150 bar/2000 psi. If a big rock dings it it mjght blow up. That's a lot of pressure.

Edit: maybe you could fill it with helium for the climbs

Someone in the comments on the Pinkbike article reckoned you'd need crazy heavy tubing to reach the claimed 150 bar.
That said, that will be 150 bar with an acceptable margin for error. I suspect that the frame probably isn't really safety rated for 150 bar, but could hold that much. At the recommended 20 bar, the tubing weight is almost certainly not super heavy, and if the frame were to suddenly depressurise, it would be a lot less catastrophic.

(Probably. IANAE)

You’d take a bike that’s relying on pressurized air in it’s tubes on expedition in remote locations? I doubt it’s aimed at people who actually do expeditions/long tours.

If you’re concerned about weight fill it with pressurized helium. Probably won’t stay in for too long though.

Reminds me of this

https://www.youtube.com/watch?v=O4RLOo6bchU

The best.

Anyway. The issues I see are volume related. I'm no engineer, but forks can do 200psi, but in tiny tiny volume and they still blow quite dramatically.
2000psi in a downtube seems like it'll be 1. causing extra stress 2. needlessly risky.
Don't hydraulic presses crush shit at those pressues? and how the hell do you control it's output?

I can see how a downtube could take 20bar (see below), but can't see how it's connected to the toptube reservoir? If it goes via the headtube, then there must be a clever junction to stop the air blowing through the headset bearings.

Force exerted on a inner surface of steel tube, 40mm diameter @ 20Bar = 20*10^6 * 0.04 * pi = 25kN. Tensile strength of Reynolds 853 is 1400MPa, so in theory, a wall thickness of t = 25kN / (1400MPa * tube length 1m) = 0.2mm should be able to contain 20bar. Please correct me if I'm wrong.

The point isn't the 20bar. It's the alleged 150bar (where the fuck are you even going to do that?), which means it's been tested up to that amount and deemed the maximum safe net give or take.
The difference between 20bar and 150 is quite significant. Any way of calculating that exponentially? (mathematics makes my brain BSOD)

Pretty sure there's encyclopedic amounts of paper to fill out for that amount of contained pressure and use.

Sorry, I was out by a factor of 10 in my calculation, so wall thickness of 2mm would suffice for 20bar.

Yeah, 150Bar would need around a 1.4cm wall thickness. Not sure how that is possible. Paging @mdcc_tester to enlighten us all.

Just built a lavender drop bar mtb tandem with 1x9 and meaty 2.3 nokian freeride tyres. Just waiting for chainring to arrive and to tape bars.
Cool that it is happy with 700c and phat 26” tyres. Has mounts for everything but only two bottle cages. When I can afford it it’ll get some new wheels-

You need to calculate the hoop stress for the given pressure. This is the force balance between the walls (F=stress*t*L*2) and the projected area the pressure acts on, not the curved area (F=P*L*2*r).

I think you've quoted the ultimate tensile strength there (1.4 GPa) which would lead to true explosion-style failure. The yield stress would be a better target, you'd be able to ride the frame after that loading. For typical 4130 (Cro-moly) steel that's ~460MPa (ref) and gives a radius-thickness ratio of 15/460, or a wall thickness of ~0.46 mm for a 28.6 mm tube. Not dainty, but not a gas pipe by any stretch.

a wall thickness of ~0.46 mm for a 28.6 mm tube. Not dainty, but not a gas pipe

Thinner than an actual frame tube, in fact. Generally you need something better than 4130 to get away with <0.6mm walls in the main tubes of a frame. You also need to account for the tensile load from the two ends being forced apart by the contained pressure, and of course all the usual frame loads which don't disappear just because your pipes are full of gas. In practice, that probably means that using the frame tube as the pressure vessel is probably no better than using the frame tube as a frame tube and adding a completely separate pressure vessel alongside it, should you be minded to use your bike to transport pressurised gas. If the issue is getting tubeless tyres to seat, you'd probably be better off carrying a gas which is liquid at a relatively low pressure at ambient temperature, as that makes your pressure vessel much lighter. People who run very low pressures on off road 4×4s and knock their tyres off the bead seat as an occupational hazard have been doing it for decades
https://www.youtube.com/watch?v=1QDLx6HSOAw

Lavender!

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Hot damn, that's brutally good!

Just wanted to show (with some back-of-the-envelope-typed-during-a-coffee-break sums) that you didn't need anything too crazy to sustain that kinda load.
Also worth noting that this is a classic plane-stress situation (ie very thin walls) so you only really have the axial load to consider. Would be interesting to see how much the load of the rider etc cancels with that of the internal pressure...

Just wanted to show (with some back-of-the-envelope-typed-during-a-coff­ee-break sums) that you didn't need anything too crazy to sustain that kinda load

Fair point. I was just pointing out that the problem is really at the ends, mostly in how you cap your pressure tube in a way which is practical when the tube has to extend past the caps to the frame joints. A 60mm diameter × 300mm long pressure vessel inserted into the downtube gives twice the volume of just the top and down tubes, allowing for lower pressure and simplifying fabrication :)

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@mdcc_tester So for idiots like me, and aside from an independently made, purpose specific vessel that goes in the middle. Is it a good idea or just a vanity piece?

It's not just a vanity piece.
Oh no.
This is so much more than just a vanity piece.

It's a beautiful vanity piece handcrafted by an artisan. Can you not see the mug dangling in potentia? The instagram likes just waiting to be clicked?

Jokes aside, it's a nice exercise in engineering but there are probably better ways to get the same result.

So it's about time we called amey then.

That's what I was interested in. The viability of it as it is, as opposed to NAHBS wankery of answering questions no one asked.

He has tubeless as well

@amey would you buy?

I like the paint job.