LittlePixel

There's a possibility I'd be moving out of London in the next year and if my design freelancing starts to take off a proper day-to-day folder (Sorry Twenty!) would be a neccessity for jobs back in the city after a train trip. I rode an old L3 a few years ago on loan from a friend - the bike that got me back into cycling and away from a few pounds of tummy actually - and though it was pretty good it really did weigh more than I'd like to carry on a train regularly.

With this in mind and inspired by Steve Parry's amazing lightweights I'm considering the idea of taking the plunge with a similar deal to build over time as a project - i.e. To get the best bits from the two bikes and making a nice light hybrid from the shuffle. Lose all the stuff I don't need - rack, mudguards, gears, horrid bars and go all out weight-weenie with carbon and Ti to make it real easy to lump about on the train.

Naively perhaps - but I presume it's a fairly simple job combining the parts of the two frames (unless someone here knows different) but for the problem of getting parts without having to buy the all bits I don't want - ie the Merc rear/forks and the Brompton steel frame. Anyone have any experience of getting these parts? Buying two whole bikes would probably be a bit much eh?

In theory I should be able to go to a Brompton dealer and say "my Brompy had a crash and I need some new un-bent forks and since my insurer paid out I'd like to go for some Titanium ones' so why couldn't they supply these without me regaling them with a silly white lie?

The other thing is the fold and issues with single speed. I would love to think I could make a Brompy Fixie - no need for those loping cables or rear brakes, with yet less weight but it's plain to with the rear triangle folding where it does I'd lose the chain tension without the sprung tensioner.

But could it work with it? A derailleur tugs in one direction but a Brompton tensioner looks like it might be able to work at keeping the chain together even if it's running fixed... Anyone have any ideas on this notion? Running it single-speed with a freewheel would be my silver compromise but I just wondered what people thought. I long for a folder like the Swift or Brompton where the rear triangle pivots on bearings surrounding the bb shell so when it hinges round the chain length remains exactly the same. If I was designing my perfect folder that'd be it's USP...

Thoughts/opinions/appreciated. I want the lightest folder in christendom (probably)

spambait11

About the fixie:
Even if it did work, you'd have to do something to the hub (get a new one perhaps?) AND make sure that the cog would not loosen on you when you stop, since you said you'd get rid of the the brakes. I've read that James Haury has done a suicide hub, but he's probably not using a tensioner. My opinion is that your chainline won't be straight, you'll have too much chain slack too be efficient, and you'll need that chain slack otherwise the rear part of your Brommie hybrid won't fold.

About the single speed:
I've done this to my L6, and had a ss rear wheel built (110mm) because I kept breaking spokes on my SRAM rear wheel. Anyway, from experience, the biggest chainring you can put on is 60T: anything bigger and your front wheel will not be able to hook onto the chainstay because it will bash against the chainring. I'm thinking of swapping mine out for a 58T in the future, but we'll see. This also means I've changed to 165mm cranks since B.'s biggest chainring is 50T, I believe. (According to Sheldon Brown's gear inch calculator, 60x15 with ETRTO 349s and 165mm cranks = 64.3 gear inches)

I've tried to eliminate as much chain as possible, and found a couple things: you can only remove so many links (and probably not as many as you would like) because you need the extra chain in order for the rear triangle to fold (same problem with a Bike Friday); and you want to leave at least 1 or 2 extra links anyway so that you can remove your rear wheel in case of a flat - if you can't take the chain off the tensioner because the chain is wrapped around it so tight, you can't remove the rear wheel since the tensior must come off FIRST before you can remove the rear wheel...yadda...yadda...yadda...

In short, this is just the long about way of saying stick to the single-speed idea.

Oh another thing: I think Wav was able to obtain a Ti rear triangle and fork. You might want to ask him directly about it.

LittlePixel

Thanks for the input!
I kinda invisaged it being a new hub. Track hubs are 120 though eh so it would be ok to spread the triangle 10mm I guess...?


Gosh - I've been there done that with my Twenty and am glad to report I now have a proper track hub built into a nice wheel rather than the constant nagging feeling 'will the glue fail?'

Really? even with the chainring on the inside of the crank?

Ahh... I kinda remembered it the other way - ie the chain slackens as you fold. It's a funny thing tensioning. I've never really worked out why a Rohloff has to have a tensioner - on a 'hardtail' bike...

...And what hub are you using? I haven't researched 110mm rear hubs. Are they hard to find?

I'm toying with the idea of the Schlumf speed-drive up front so there's a sensible-sized chainring and a lower-gear-but-not-at-the-rear as a way of doing this.

I'm kinda getting that...

I've written to a couple of UK dealers; I'll ask him though.
Many thanks...

easy racer

Hi Littlepixel,
Your best bet for a shop to get just the brompton parts you need is Kinetics.
They let me just buy a frame, and rear triangle from them, with no hassle whatsoever.

Though, thinking it, if you want to make an offer for my brompton project it could be yours.
I haven't ridden this bike since I bought the bits, and it still needs a few bits to get it totally finished, but it's close to rideable.

My Brompton

There are a few changes since that photo, namely the kogswell rear hub, and a singlespeed sprocket. The only problem is the tensioner needs me to re-align the rear axle to give it enough axle to hang on, which I just can't be bothered to do.

Sorry for the blatant sales pitch, but I wouldn't mind the money to go towards a recumbent I've found on eBay.

Fear&Trembling

You can buy the Ti rear triangle, forks and Ti post directly from a Brompton dealer. However, it will end up costing a fair amount...

I do not believe a fixie Brompton is possible (even with a RD as tensioner). However, Ben at Kinetics would probably be able to build a pimped ss ride. A few months ago he made a sub-9Kg SS Brompton in Orange that was very impressive.

Steve P may also be able to help...

Samb76

Hi,

Maybe another solution is to buy both the titanium brommie and merc, swap the bits you want to and ebay the bike you don't want. Even though you might not get the greatest price for it, it might be cheaper than buying bits individually.

I'm not sure the fixed idea would work in the long term - brompton transmissions have a hard life as it is - I used to get through a couple of chains and sprockets every six months.
I read in a few brompton gear-upgrade projects that the rear fork can be spead a few mm, you'll probably get away with it.

spambait11

Hm. The cromo rear triangle could handle it, but I won't speculate about the titanium one. However, I remember when CRM was modifying his Dahon Boardwalk, he said the his wheelbuilder re-spaced a track hub to fit 110mm, so it might just be a matter of removing spacers. I'll also agree with someone who posted above that getting as long an axle as you can is helpful.

Oh - one other thing about that axle: Brompton's are machined flat on both sides and are 9.5mm if I recall, but I'd double check the size. At the time, I couldn't find an axle in that size which was manchined flat, so my axle is 10mm and my dropouts are slightly "widened" to fit.

Lastly, a note about widening the chainstays. There's a certain point which can be widened, but remember to doublecheck whether the front tire's hook is able to latch itself onto the chainstay. If the chainstay's angle is too different, the front tire hook may not be able to attach properly, and you'll probably end up customizing a new front hook as well.


That's how I did mine, but I know it's slightly off as I can hear the tensioner work when I pedal. However, this probably depends on what kind of single speed cog you have back there, and whether you can space it at all, length of the bottom bracket, etc. Having the tensioner means you don't have to make it super critically straight.


Hm. I think I am going to doublecheck this. I remember trying this out (i.e. removing links) and something not happening quite rightly.


BMX hubs are usually 110mm. But make sure the track hubs can be spaced to 110mm. If I knew that from the beginning...


Why would you do this? That's the easy way out.

invisiblehand

You can get the titanium bits from a local Brompton dealer. Here in DC, the local dealer is at College Park/Mt. Airy Bicycles. A few months ago I asked Larry Black--owner of the shop--how much the titanium fork and rear triangle would be with shipping (UK to his shop) and he quoted something like $685.

Erika and I were thinking of getting a pair of Merc/Bromptons and upgrading them. We picked up a Merc for a long-run test. After a month, I decided that the ergonomics are poor for me; but they work fine for her. However, we like to travel together (imagine that!) so we are thinking of selling the bike for something better for longer distances with a less compact fold.

LittlePixel

Sweet - I'll maybe get onto Ben when I get to starting it...

That's a kind offer sir; Think I'll pass for now though as I don't exactly have the readies now to get started. Was worth a punt though How's 'Goldie The Intrepid Twenty' coming along by the way?

In the long game of a project I think I could deal with that cost. There's always ebay for a full donor bike at a bit less than brand new... I dunno. Maybe this is just a blue sky idea....!?!?!

Tis a shame that. I concur - was just seeing if anyone had somehow broken the laws of physics some way...

That Brompton Orange is a sweet colour. Shame the Merc colours are less inspiring. Maybe I could get the Merc anodised? (the costs keep rising haha)

A good solid idea there. I get the wheat bike and someone gets the chaff. How to word that listing!

Opinion differs then. I guess a BMX or respaced track hub would be better to be sure; wouldn't want cracks in that nice new triangle!

Thanks for the info about flattened axles and the tire hook too Spambait. There's more to this meets a first glance then eh?

Because any chainring over about 48t starts to look a bit unwieldy on such a cute lil bike

easy racer

Hi Littlepixel,
It now sports a new set of wheels, with Sturmey Archer hub brakes, a seven-speed cassette (of which I can only use six), a rapidfire shifter, a rear rack, and most unusually an XT rear mech!

The only things left to get (probably?), are a nice set of mudguards.
I'm thinking of getting a set of black ones, like the ones they put on ICE recumbent trikes.

I'll try and get some new pictures, if your interested?

LWaB

I haven't come across a fixed Brompton but have seen one with a coaster brake. He'd fitted a stop to the chainstay that prevented the slightly strengthened tensioner from actually hitting the chainstay. Personally, I'd be worried about breaking the plastic tensioner when backpedalling anyway.

LittlePixel

I got a quote from SJS cycles stating thus:
Which is pretty useful to know for me or anyone else. Not quite as expensive as I feared either...

Fear&Trembling

That's not too bad, but you will have to factor in labour costs. Not tempted by the Ti seatpost? I think they are about £80 a pop. Mercs are still going for £330 on ebay, so you should be able to do it for under a grand after a few weight weenie-esque mods.

I would double-check that the Merc and Brompton forks and rear triangle are interchangeable. I assume they are, but you should email SP in case they need a bit of machining/bodging..

LittlePixel

Yes also tempted by titanium or carbon post. Tis a shame they don't do a ti stem as well. That would own!
I was doing some idle Brompton surfing and found this page which is a cornucopia of Brompton tips, info and discussion:
https://users.belgacom.net/bn886679/b...ns/Tricks.html

LittlePixel

Okay so the plot thickens. Doing an Image search for Brompton I found this on a Japanese site...



Sweet huh?
But look: It's got no tensioner. My Kanji is non-existant so I can't be sure—but it looks for all the world like a fixie to me. So I have an idea. When 'riding' the chain tension is not really going to be an issue - the flex in the suspension rubber bush is only tiny so theoretically it should be fine. So then the problem is folding.

I have in mind now an idea (if the chain gets slacker when you fold) that you could use some sort of tensioner to keep the chain on when folded only and then disengage it when in use. If that were possible (seems likely to me) then apart from a bit more faffing when folding it could be the solution.

Can anyone confirm once and for all about whether the chain gets slacker or tighter when you fold the wheel under???

Full page of this bike (and other nice Brommies)

Fear&Trembling

I admire your perseverance.

I have seen this hybrid before. If it is fixed (I note a single front brake, more likely ss) - the chain looks rather slack (presumably to accommodate rear suspension movement, but he may have a harder elastomer that reduces movement) and there is also a rear QR skewer – neither are ideal for riding a fixed wheel IMO. If he does fold the bike (a guy with a fixed Birdy never bothers!), the chain will unship, or at least I think it will – but it would not be difficult to stick it back on with a slack chain and QR.

14R 

It looks like the fork is Merc(ish) with the brakes behind the fork, not in front.

spambait11

The QR shouldn't matter because of the vertical dropouts. Chain slack, though, is an issue.

I'll also agree that that B. above never gets folded. It also looks like s/he has a maunakea-like stem.

14R 

Now, on a very serious subject, where can I find a 16" suspension fork like those in the mentioned site?

14R 

It looks like google is the intelligence gathering tool for the 21st century: I found a 16" suspension fork used by a tri designed for children with disabilities (perfect for me I guess). Here is the link

maunakea

https://www.ikd21.co.jp/bro/1speed/index.html

The Japanese reads:
"Sngle-speed conversion model.
In keeping with the single speed concept, everything unnecessary for operating the bike has been totally eliminated."

Nothing about foldability. The phrase "soukou ni" could be word play that I don't understand.

14R 

I was about to say that. Maybe that bike doesn't even fold (the stem seems unfoldable).

Fear&Trembling

So the search for a bona fide fixed Brommie continues...

LittlePixel

To me the way to fix the chain tension would be an eccentric bottom bracket. Are they available in normal bb shell sizes does anyone know? I've found lots for tandems but the shell is bigger than standard. Either that or a White industries ENO eccentric hub. The problem then being it's 135 OLN width. Doesn't look like an easily respaced item.

A half-link chain might be a poor second but even then it might not be tight enough.
Or I could just use a magic gear calculator... Or be incredibly lucky.

I did some jiggery-pokery in Illustrator over a big Brompy picture and have determined that the chain definitely slackens upon folding. Which makes this all kinda doable. I want to have the first (maybe second) fixie Brompton!

LWaB

Not available or possible.