on the back of my ‘why do I go through hope freehubs every 200km’ thread, I had a brainfart.

XACD built me ‘Nanny’, my chi ti frame. Everything about it is fantastic, apart from the fact it flexes too much around the drivetrain, causing axle flex and buggeration to components.

So we have the blueprint already for a great bike that fits me perfectly, I do want to keep full fat/29+ compatability, what should I change on the design spec to lessen rear end flex around the axle?

(note, doprouts recently checked, they are aligned. Also, when I had this built we did talk about me being big so some tube thicknesses were increased already from standard)

Thoughts appreciated!

Maybe don’t use titanium and use 4130 butted tubing? Something like a Marino (yes I’ve bought one in the last 12 months) – he will make pretty much anything you want.

My frame for all round use has come in at 3.1kgs with rear axle and seat clamp fitted. I’d say that’s reassuringly strong! It seems comfortable (could be the 650b 2.6” tyres below g that) but I don’t feel any flex.

If you’re running such big plus tyres then any minor benefit from frame material flex is probably redundant and actually the last thing you want.

thanks Joe.

Interesting idea with Marino, had not thought about that. The only reason I went Chi Ti before was not the Ti, but purely as it was the cheapest way to try out geometry that I wanted.

Agree that frame ‘give’ for comfort is not needed given the bike only runs with big tires.

I guess the question is – what is it that will reduce flex? larger diameter chain stays + seat stays?

I have asked he famous Porter, will investigate with marino as well.

My mate got a custom frame built a few years back, called it Terrex as it’s a bloody bulldozer of a thing, super slack and bombproof, he loves it. This guy did it for him –

https://stb-cycling.co.uk/custom-steel-hardtail/

either larger diameter tubes or thicker walled tubing or a different material

Nicolai do custom frames. I guy I used to ride with was 7ft, 20st and VERY fast downhill. To my knowledge it never broke and looked like it would survive a bomb blast.

Hi,

My Ti is flexing around BB area and I’m probably 1/3 of your size/weight xD

I also suggest steel. Also try sandwiched/composite BB/stays yoke. Much stiffer than simple plate.

Cheers!
I.

This shouldn’t be flexy…. https://en.nicolai-bicycles.com/frames/argon-fat/

Why dont you try bracing the seat and chain stays?

You’d probably only need to do the drive side but both sides would make it even stiffer.

I would agree with using steel but the wait list on Marino is huuuuuge, I waited 14 months for mine.

Also if you’re used to a nice build quality you won’t get it at marino.

BTR or Curtis do nice stuff frames. Pricey though.

I would agree with using steel but the wait list on Marino is huuuuuge, I waited 14 months for mine.

Also if you’re used to a nice build quality you won’t get it at marino.

In defence of Marino my hardtail frame was 8 months to arrive. I think the full suss bikes seem to take a lot longer and alignment on those can be a bit hit and miss.

The welding on my marino frame looks pretty good to me – perhaps the internal routing is a little less refined than more premium brands. This is reflected in the price though – I paid £399 delivered (no paint at my request) for a Reynolds 725 tubing frame with complete custom geometry / choice of gussets / choice of bb / choice of head tube / choice of cable routing etc.

Yes the braizing on a Curtis is quite a lot nicer – but you pay your money and take your choice. I did consider a Curtis but decided I’d rather buy the Marino and get a Pike Ultimate and fancier wheels with the money saved. I think the Curtis frame (no paint) would have been £1175 for reference.

One thing about Marino that is a bit annoying is the lack of communication. I get the feeling there’s just the one guy managing the operation and fielding loads of emails. Everyone has been sat at home ordering custom frames and I think he’s been a bit overwhelmed. He does seem to comment from time to time on the Facebook Marino owners page though.

mate, just buy a Ti Fargo. i am heavier than you, and mine dont flex.
and with a rohloff hub it is pretty bombproof.

@ton he wants fat and 29er plus. I think he had an surly ice cream? Before that?

I agree with @boxwithawindow. You love the frame, it is made of ti. Just get it strengthened.

Even with some plate added it will be cheaper, lighter and quicker than a new frame.

You might even be able to get a new rear triangle put on with thicker tubing.

ti fargo takes 3” tyres.

Who would change his ti-frame though – isn’t it hard to cut / weld ti? I don’t think Enigma do amendments anymore do they – as they’re busy making their own frames…..

If you can find someone to weld it, perhaps some rear triangle bracing may solve the issue though 🤷‍♂️

As above ti is the wrong material.

In fact ti isn’t a very good material for bikes full stop.

Get a steel or aluminium bike.

Try bike mielec in poland for a custom alloy frame. The website is ancient but they are good.

In fact ti isn’t a very good material for bikes full stop

and obviously you have documented proof of this fact ?

I’d still try getting a solid steel bolted axle made first for the current bike.

I’ve done trussed stays in steel (12.7mm dia in my case). It gives you plenty of tube in lateral bending but the width of a single tube for tyre / chainring clearance without crimping or flexy plates.

For you it could work with 17mm twin trussed chainstay tubes and maybe 22mm seatstays. Unfortunately quite labour intensive and I doubt anyone commercial would be interested in making one.

Or maybe an additional pair of stays between chainstays and seatstays? Would need careful design to avoid heel clipping and hitting the chain.

That Nicolai looks a good option – it is rated for Gates so will have passed the stiffness tests. But I still think you’d have issues with the current hub as only addressing half the problem.

ti fargo takes 3” tyres.

@ton didn’t know they had increased it. I’m going to regret this but I’m off now to Google the fargo and it’s all your fault!

The frame spec you have doesn’t look to be particularly built for stiffness, just some thicker-walled tubes for toughness.

what is it that will reduce flex? larger diameter chain stays + seat stays?

A stiffer rear end may highlight front end flex and I’d expect a big or strong rider to be twisting that front triangle relatively easily. But yes larger OD stays would keep the rear triangle stiff if that’s all you wanted. Go for diameter for stiffness and back it up with wall thickness at the ends for durability or in the centres to avoid denting too easily, or crumpling if extreme ODs and very thin-wall.

The Nicolai is a good shout. They look ‘accurate’.. and like they’d need big tyres. You could also get a steel frame with a (maybe) a 38mm DT and 34.9mm TT, >19mm non-taper seat stays and tandem chainstays. It’d not be that light but no reason for it to feel dead or tank-like. Reynolds have some good butting profiles that would keep the weight down.

and obviously you have documented proof of this fact ?

@ton

Well 1) Raw material is expensive 2) its difficult so expensive to work 3) it has no advantage to justify this expense.

The best metal bikes use very carefully designed tube profiles – usually butted for steel and hydroformed and butted for aluminium. It’s very easy to design in stiffness or flex and implement those characteristics in the material. Its very easy and cheap to machine a bit away here and there.

Most low cost titanium bikes will use straight gauge tubes and will not be designed for the bike it’s used for. If you want fancy titanium tube profiles, you are going to pay for it.

Then we come to the matter of density and young’s modulus. This article does a reasonable effort of explaining why titanium is rubbish where chainstays meet the BB. A critical area for bike frame stiffness: https://www.renehersecycles.com/myth-2-titanium-is-lighter-than-steel/

So…. when you can get the same or better result in terms of weight and stiffness from a steel frame, which has much cheaper raw materials, and much cheaper to work then why choose titanium?

Because it looks pretty and doesn’t rust? The only valid justification.

Carbon fibre really is the ultimate bike frame material. It’s so easy to design in stiffness and flex where you want them, and the result is always lighter than an equivalent metal bike.

If you just want a stiff and light bike then aluminium is the choice as it will be cheaper than a carbon frame.

I do believe carbon frames should be cheaper than metal bikes, the labour cost is lower and less skilled for production line manufacture. The next decade will probably see them drop in price in the main stream – you already get chinese carbon frames at very low cost.

This article does a reasonable effort of explaining why titanium is rubbish where chainstays meet the BB. A critical area for bike frame stiffness: https://www.renehersecycles.com/myth-2-titanium-is-lighter-than-steel/

The point about OD and space is fair but not an issue on the OP’s bike and I’d argue that the frame stiffness either side of the BB is what’s important in any bike. The CS to BB join is important for durability but CS size is just a part overall frame pedalling stiffness.

So…. when you can get the same or better result in terms of weight and stiffness from a steel frame, which has much cheaper raw materials, and much cheaper to work then why choose titanium?

I’m with you that steel is a great material overall. But you can’t get the same or better result in weight and stiffness in steel. You can get close enough in weight at the same stiffness but you’re either at 953 costs (about same as ti) or you’ve got very thin walls and a much less dent resistant frame, something that isn’t a real concern with Ti. Personally I’d take the right stiffness and ride feel in steel and the weight will be what it is – not enough over Ti for me to care.

I do believe carbon frames should be cheaper than metal bikes, the labour cost is lower and less skilled for production line manufacture. The next decade will probably see them drop in price in the main stream – you already get chinese carbon frames at very low cost.

And the number of fork recalls in the bike industry? The cheaper + faster you make it the more QC is going to cost you and the more it slows your lead times. Cheap mass produced carbon stands for all the reasons I’m happy to pay £500-1000 for a good quality steel frameset.
You’re right that carbon fibre is the ultimate frame material though, if a brand is capable of designing + producing it well and you’re prepared to pay for it.

Trot along to Bespoked 2021

https://www.bespoked.cc/

Hi Folks,

really interesting thoughts all, thank you. I think, in this scenario, you can really start to see the issues between a bike that I ‘designed’ with the angles and size I wanted, but with no real clue as to tube thicknesses and diameters other than that very generically offered by the builders (esp the Chi-Ti route which is very much ‘we build what you tell us’ with only marginal guidance offered, as well as help from other folks who have gone down this path)

It was a great & cheap way to find out what sizing/geo worked for me, but the constraints start to become apparent in lack of real design/engineering when it comes to materials. To choose butting, profiles etc increases costs of chi-ti rapidly, to the point where it does make more sense to just use a proper UK builder (really want to use Ben @ Kinetics) who really know what they are doing, and use steel.

Nikolai does look lovely, but only 177 rear end and would require custom geo that becomes eye waveringly expensive. So thats a no.

Salsa also lovely, but again, was looking for a 197mm rear axle.

Re. the solid thru-axle, I think, in my other thread, this was ‘confirmed’ as adding nothing to the stiffness of the actual hub-axle or hub – it only adds the benefit of clamping force and thus rigidity (which I have already tried with a bolt through axle at good Nm).

However, over and above all of this, my real realisation is whether I should continue to pursue the 29+/full fat angle. I never ride full fat anymore (well, very rarely on beaches and when there is tons of snow), and 29+ still has a lot of caveats of use by a big bloke. The rate of failures of components (mostly wheel related) on the 29+ set up is compounded by the scarcity and cost of replacements of fat/chubby components.

In doing a wee inventory, the list of issues over the last 2.5yrs is:
The axle bolt rounding on the mastodon (required new lowers, warrantied, but took ages)
3x stans hugo rims (now on LB 50mm carbon – much better)
Lots of spokes at really inopportune moments…BANG!
2x hope fatsno rear hubs, 5x hope freehubs, 6000 pawls, about 5 full bearing sets and at least 20 inner free hub bearings (they only last a few rides then start to get notch, which is when problems begin)
1x Cinch Fat crankset (never again)
2x DHF3″ and 2x DHR3″ tires, at 80 bloody quid each, (mostly tearing holes in them on rocky terrain)

The other jarring thing is that on my current normal bike (29 full sus), and indeed on previous normal bike (another 29 full sus), the rate of failures was low/non-existent.

I just don’t think it’s worth chucking money at +/fat anymore, I’m going for a boring 29er hardtail.

Thank you all for all the input again. Anyone wanna buy some 29+ wheels?

and apologies for the long post, that is pure train of thought in written form

outside of a new frame, could you add reasonable stiffness by putting a (bigger) though axel in the dropouts? 12mm has some benefits over a qr

I’m going for a boring 29er hardtail.

Then take @tons advice. He’s bought that many bikes if he says buy a fargo then it’s going to be good advice!

Then take @tons advice. He’s bought that many bikes if he says buy a fargo then it’s going to be good advice!

I’m assuming he will make buy it for me for Christmas 🙂

That is not a boring hardtail, but I’ll put it on my wish list

i said a fargo ti because i saw you post mentioned ti.

but if i was gonna buy a boring hardtail for proper offroadingm (which i dont do much of now ) i would be building a Surly krampus with a air fork, pike ?.
and some surly sunrise bars, magura 4 pots, shimano 2×11 with a dt e bike specific wheelset.

robust boring hardtail.

I’m not convinced about the axle theory (apart from the bit about an M12 through axle isn’t tightened to anywhere near the correct torque to achieve maximum clamp load).

Your problem appears to be centred around deflection approx 1/3 down the axle in the poorly supported freehub and pawl area. A solid steel axle will be massively stiffer than your current hollow aluminium one. M10 end bolts screwing into each end of the new steel axle can also be tightened to somewhere near the correct torque. So you get a much stiffer axle and decent clamping load. This seems a very easy and relatively cheap option compared to a brand new custom frame. This advice may be wrong, but it is based on making a number of steel frames in the shed – many with “unique” chainstay arrangements 🙂 and 27 years in an automotive structural fatigue and durability lab (i.e. testing / breaking / improving stuff).

But I’d still 100% advocate a steel frame made by Ben at Kinetics – he does great stuff 🙂

I agree on the fix but is going to make one for him?

A solid steel axle will be massively stiffer than your current hollow aluminium one. M10 end bolts screwing into each end of the new steel axle can also be tightened to somewhere near the correct torque.

I agree on the fix but is going to make one for him?

That is a great question. @mick_r – you don’t happen to have the capability (or know someone who might?)

I could probably make a gash one using the shank of a big cap head bolt or some EN16 as raw material. Would prove a theory but pretty pointless as it will quickly go nasty and rusty.

A friend on our industrial estate has a machine shop (that specialises in shafts so might have some decent stainless). I’ll pedal past after work tomorrow – I’ve stuck a regular Hope QR axle in my bag as an example (I run the aluminium M10 bolted 135mm axles on that orange frame ^up there because of the horizontal dropouts). If he is interested, do you have a spare fat axle in your scrap pile to copy from? Otherwise is it not the kind of thing Kinetics Ben thrives on?

If you’re not convinced about full fat/29+ anymore could you not get a bike that runs 29 x 2.6 instead? They’re still pretty big tyres snd you wouldn’t need special hubs/BB widths like on a fat bike.

Don’t have. scrap pile axle, Hope kept the last one.

However, I can easily bang an axle out of either of the rear hubs no problem, that would be amazing @mick_r , just let me know if he is interested. Amazing.

I had not thought of asking Ben, that would be option 2 I guess 🙂

He would be OK to do it – 304 stainless which isn’t the toughest or most corrosion resistant but probably more than OK. £50 which covers him and the machine for an hour including material. They’d just finished a 3.5m shaft so this is pretty easy in comparison….

I’d knock you up a couple of aluminium top-hat inserts for the M10 bolts but would want to see some photos and dimensions of your dropouts just to make sure it would work. I don’t mind knocking up a trial steel axle from an M20 bolt just to check it doesn’t go crunch when you thrutch up a hill (it is basically a shaft with 17mm ends and 2 x M10 holes). PM me if you want to have a play. No problem if you don’t.

Wow, superb.

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