[Closed] Potential bike bodge of the decade

Ambitious 😀 ! I guess if you hacked out the old bb from a frame with a wide enough downtube, you could possibly fashion that into a brace that would fit round the seattube....?

Instant death

Whatever I do will be overbuilt, so it won't snap and kill me. Most likely scenario is it'll work loose.

I guess if you hacked out the old bb from a frame with a wide enough downtube, you could possibly fashion that into a brace that would fit round the seattube….?

Hmm not a bad idea. My thought was to use thick sheet 6061 or 7075 and drill two BB shell sized holes in it, then fold the front of it to brace against the downtube. Then pack the void with a hard resin and drill and bolt through the gap between the downtube and seat tube. There are two challenges with this: drilling an accurate hole of the right size in the sheet; and finding the right alloy that can be bent in this way without losing strength or requiring complex annealing. I guess I could drill and bolt the whole thing maybe instead, and possibly bond it all in place too.

Sounds like a great idea.

Is there any way you could knock something up that screws into the existing BB shell with arms either side that would hold the new BB shell. then have a brace bracketed to the seat tube to stop it slipping downwards??

Probably wouldn't be strong enough, but I can see it in my head....

Do it for science

Needs more cutlery.

I can't think of a single reason not to do this. Definitely do it.

Can I have your Audi if you die? (the one with the gearbox bodge)

Alignment is definitely an issue, not insurmountable, but not easy.

Just do it all in carbon fibre. Use a tube with an ID of 46mm and a press fit bottom bracket.

Or just switch to a longer, say 140mm+ stem. 😉

To prevent any drilling to your frame could you attache a new BB shell using BB chain tensioners from the existing BB and some kind of clamp round the seat tube?

It would have to be braced against the downtube and seat tube to counter rotational forces.

With spoons, I hope.

Can I have your Audi if you die? (the one with the gearbox bodge)

It's a Passat and the gearbox was repaired and works fine I'll have you know!

Is there any way you could knock something up that screws into the existing BB shell with arms either side that would hold the new BB shell. then have a brace bracketed to the seat tube to stop it slipping downwards??

Thought about it but bonding to the outside of the existing BB tube would give a bit of extra strength

Just do it all in carbon fibre.

Considered it, but I have no experience with CF. I could take a cast of the existing BB cluster and make a form out of resin over which to lay the CF, This is actually not a bad idea and might be better than my original plan.

To prevent any drilling to your frame

I wouldn't drill the frame - just drill the brackets and bolt them to each other to hold it in place. The load would have to be spread across the existing tubes by packing the resin inside the voids.

Madness...
Live with it or sell it and buy a longer one.

How about two metal dogbones either side of each BB, that you screw in with BB cups (replacing the HT2 spacers)?

Bin Dun, in steel mind, and for diferent reasons.

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buy a longer one

You really think if I had the money for a new bike just sitting around doing nothing I'd be considering this? You do realise that some people cannot just buy whatever they want, right? That money is a finite thing?

Bin dun. In steel mind,

Would be much easier in steel.

Moar reach.... could you not fashion some rearward pedal extensions to achieve the same thing 🤔

Layback seat post?

This is by far your stupidest idea...You have to do it. I've nothing more constructive to add...

Layback seat post?

The cockpit is fine, even with a 35mm stem. The problem is the pedals are too far foward. So when standing, I am too close to the bars. I run a 50mm stem to help counter that but any longer and the steering gets a nasty flop.

Moar reach…. could you not fashion some rearward pedal extensions to achieve the same thing

Thought about it but you'd need a parallelogram arrangement with linkages and bearings. Possible if you had a CNC shop but not for me to do.

Could also fashion a new headtube that sticks out of the front of the bike but that'd be way more dangerous!

Clown shoes with SPDs at the toe end?

Bin Dun, in steel mind, and for diferent reasons

i met the original owner of that frame.. he was a sick bikes rider (chuckle) - -was built like that as apparently the tubing wasn't made long enough...

DrP

Now I'm thinking cut the BB off an old frame (possibly even steel) keeping part of the downtube which could be cut at an angle to fashion a gusset. Bolt and glue that around the existing downtube, then wrap the whole lot in carbon fibre. The angle of the gusset would allow the carbon wrap to be in tension which is what it'd need.

Clown shoes with SPDs at the toe end?

That requires riding with SPDs which this kind of bike does not suit. you're not wrong though - I had been riding more with my instep for control but I realised that pedalling more with my toes could add a good couple of cm to the effective reach, and it did too - I ride it up hills like that now.

Where's @bencooper when you need him.

He'd tell you it was a stupid idea and then he'd do it anyway.

There's most of a really good idea in there, geometry wise it all seems to make sense - lower, longer, etc. You'd end up with shorter chainstays, but you might like that.

I think what you might struggle with (if you did get it welded up) is the effect it could have on things like anti-squat - where the chainring ends up relative to the pivot might have the bike pedalling like a pig. I guess if the new shell is directly behind the old one, then it's in line with the pivot as per the original, but will still have an effect.

You mention the jig holding the frame by the BB - wondering if the ISCG tabs might help - if you cut out a BB shell plus tabs from an old/broken frame, you might be able to bolt it all together using the tabs and weld from there.

Admittedly I know nothing about nothing. But I'm wondering how the lowering and rearward shifting of the BB shell might affect Anti-Squat and the pedalling characteristics of the bike.

I haven't had a single pivot bike since my 2004 Marin Attack Trail. So I'm pretty certain things have progressed a LOT since then. But aren't they carefully designed to give the required characteristics?

True, if BB shell lowered then also your centre of gravity will be equally lowered so your 100% Anti-Squat intersection point (centre of gravity intersecting with front contact patch) moves proportionally down but I don't have a clue what that means in respect of the new chain lines in each individual gear.

Also the new pivot position would have an affect on the leverage rates on the shock?

My non-hambini brain is 'guessing' that as the BB is now further away from the pivot your weight on the cranks is inducing greater torque around the pivot which when the rear wheel tries to move up away from the ground over bumps, added to your extra torque means a higher leverage to the shock? Possibly needing you to jiggery pokery with your damping?

But awesome idea dude, love it! and especially the fact that you have the know-how to even conceive of the idea, make sure to wrap yourself up nice and safe when you test it and when you have it figured out come back and pleas help me figure out a way to hack-bodge my 2016 medium spectral to have more reach too, haha

EDIT: TLDR: what honorouablegeorge said, their post wasn't there when i started typing haha

If it doesn't involve table cutlery you won't even get past registration.

I hadn't considered anti-squat. The pivot is already pretty high, so perhaps it would be better to keep it the same height rather than lowering it. But then again, it was designed around a triple chainset where you were meant to climb in the little ring, and it would be going to 1x where it'd be doing its climbing effectively in the middle ring, which would also be larger than the current middle ring.

Also the new pivot position would have an affect on the leverage rates on the shock?

Hmm well when pedalling, maybe, but the shock can have plenty of compression damping dialled in, it's a Manitou SPV job. But not when descending really as everything else remains the same, the swingarm is in the same place as is the pivot.

If @bencooper had the facilities to weld alu I'd be on the blower...

There's also the option of welding a second headtube onto the existing one. Pedlaling unaffected, longer reach, slacker HA, tapered - you get it all.

True, and perhaps the frame mod people would do that. But isn't it a greater risk? Then again, it's an Orange so the whole thing is welded bits of alu.

That said - I'd have to slam the saddle forward to get a decent pedalling position if the BB stays where it is and it only just makes it ok, so I'd have no room for adjustment.

I'd imagine a new headtube could be made strong enough with gussets and the like, heat treatment permitting, and it might be an easier area to work in than around the chainset/BB

A slacker/longer bike is going to rotate the seat tube forward a little too, so it'll help seat angle.

(I'm really hoping you'll try this, I'm fascinated)

Just do it all in carbon fibre. Use a tube with an ID of 46mm and a press fit bottom bracket.

Or you could use something like this: BB30 to BSA Adapter

Fibreglass wrap all the (aluminium) surfaces you plan to bond to avoid galvanic corrosion, and then go nuts with teh Carbonz....

Or a reversible mod would be to fashion a pair of connecting plates, use some old BB cups to anchor the new shell to the existing shell...

I kind of see how extending the BB or headtube could work, in both cases can be a tube with flat plates welded on both sides. Rather than welding the frame and needing to dismantle/re-heat treat it you could put notches the BB/head tube have a tab on the bracket that fits in that so it doesn't rotate when mechanically fixed with a piece of threaded bar.

These are very highly stressed areas to be meddling with though, surely it'd be safer and easier to sell the existing bike/frame and a 2nd hand replacement that is correctly sized.

Headtube would definitely have to be welded though, which means going back to those fabricators I spoke to. They didn't seem to want the job though so I am a bit reluctant.

Moving the BB would result in an interesting bike I think. The thing is already very manoevrable because the wheels are small and hence chainstays are shorter than they would be on a 29er (I think) and my CoG is quite close to the rear wheel. Moving the BB could allow me to put my CoG even further back. So it will remain manoevrable but have a moderate reach (still won't really be long) and have masses of travel still.

Of course 40mm extra is about the minimum. I could move it more than that...!

surely it’d be safer and easier to sell the existing bike/frame and a 2nd hand replacement that is correctly sized.

Sure, if you can find me a frame that's 150mm+ travel, suits a 170mm fork, is non boost, 26" and has a reach of 460mm+ for £50 let me know 🙂

twisty

it’d be safer and easier to sell the existing bike/frame and a 2nd hand replacement that is correctly sized.

It would have been safer and easier if Hilary hadn't climbed Everest

It would have been safer and easier if Hilary hadn’t climbed Everest

Not for Tenzing

Does anyone have a broken alu frame you want to donate to the project? Will pay postage.

Back to the subject, how about using something like Scotch Weld 420?