135mm Titanium Rear Triangle for Brompton
 

A 3rd party startup is offering a 135mm Brompton titanium rear triangle for those who may be interested in mounting a Rohloff or Alfine hub.

They are also offering chain tensioner with adjustable chain line.

https://vostok.bike/

Thanks for posting this. It looks very tempting.

nice. before this was available i had to perform this slightly nervous procedure..

all went well, the 2x10 is a fast joy to use, and has tight gearing with the range of an ordinary peleton racer. it weighs 11.1 kg complete with schlumpf, rack and pedals

Can't understand how a cassette would work on a Brompton.Fine until you fold it...I had a 5 speed freewheel on a Brompton and the chain was forever falling off when it folded..I had to keep the chain on in the folded position by using clothes pegs (pins in USA speak)

if you use a long-cage derailer it will take up most of the slack. was planning to add an extra tensioner on the lower jockey wheel a la steve parry. however havent got around to that as it has worked well without it, this because it turns out the chain rests itself in a predictable way on the derailer.

if you lay the bike on the side the chain might work itself off. but i hardly ever do that, so the parry solution has been put on hold. in my case it would suffice with a shorter tensioner than pictured. an alternative solution is using a bigger jockey wheel, but the chain is close to the ground as it is.

Anyone find out how much the vostok ti rear triangles cost?

re- chain slack: will one of the new sram or shimano clutch mtb rear derailleurs do a better job tensioning the chain?

Is this the same Russian company that has been making these parts as OEM for Brompton for several years now?

i dont know if they are vostok, but there are third party titanium forks and triangles sold on british ebay. they are expensive enough so that buying a second-hand ti brommie seems a better idea, especially if you need a spare bike, and who doesnt:)? you then get the pedal bolt, chainstays and sometimes seat post titanium as well. and lighter headset, lighter wheels with a different front hub and reduced spokes.

the derailer i use is a long-cage road dura-ace. it doesnt quite tension the chain, so a steve-parry tensioner could be handy. birdy uses one quite similar. longer cage mtb derailers might be better, but you have to see to that the chain does not get too close to the ground. with an mtb-derailer a gear changer made for straight handlebars is easier to find.

How did you attach the rear derailleur to the dropouts?

Great DIY! You're a man (woman?) after my own heart.

They sold it via indigogo for a while - this may give you an idea of the price: https://www.indiegogo.com/projects/v...ories-bicycle/

jur: thanks!

leoho5; i used a standard merida derailleur holder that sits directly on the axle, chose to have it on the inside, and thus had to widen the triangle a little extra; this way the chain is better cleared from the tubing when on the smallest cog.

when having the hub and derailleur setup ready and mounted it was easy to therafter center the rim with the help of tensioning the spokes. used the double-butted spokes from brompton, dont remember their length, but they come in two lengths with 2 mm difference for their front and rear wheels, the shorter model i used on the cassette side.

actually i took half of the spokes from a front wheel, then transplanted half of the spokes from a rear wheel onto it. so the front wheel is also assymetrical, but lengthwise and not sidewise. the shorter spokes there on the inside of the flanges and all going in the same lengtwise direction.

Thanks for the info on the derailleur hanger. May I ask how you kept the derailleur hanger from rotating around the axle?

Looks like a great product but at usd 568 plus shipping- is it hand made by Swedish wirgins and coated in organic panda milk?

(Sorry, just joking- I am 1/4 Swedish myself.)

I guess for a serious commuter or tourer it could be worth the money. Still much cheaper than a car... I always liked the IGH`s with no parts like pull chains and clickboxes sticking out on the side of the bike. You still need the chain tensioner on a B.

When are we getting a strong elastic "belt" that can be used without a chain tensioner on folders? That would be nice.

leoho5; here is a photo of the derailleur hanger. it stabilizes itself against the dropout with its rounded edge

Hi Kais01-

How much did you spread the rear triangle - from 126 to 130 or 135mm? I've spread a few 700c frames from 126-130 with a nice hozan frame spreader - have to spread it to about 140 and let it sit to account for frame springing back; I can only imagine that spreading the little short chainstays of a brompton must be quite difficult.

I can't see the picture in your post #3 very well; is that a picture of you spreading the frame?

I do not own a brompton yet, looking for a used one, and I want to convert it to cassette and rear derailleur. I like the kinetics rear triangle with 135 and disk mount but that's quite pricey and I would prefer to at least try this before investing in a whole new triangle.

hi rec,
before i did the operation i was in contact with a fellow in england that made 130 and 135 mm conversions professionally. he had widened a number of brompton steel rear triangles without problems, had made a jig for it. when he tried it on a titanium version it unfortunately cracked, in its welding.

so i would cation against a frame spreader. maybe if you have two extra of them and mount the two extra to protect the forward part of the tubing while the third makes the spreading. be careful.

so i instead bought a set of pipe benders, they were also slightly expensive:) the tactic was to make the bend along the pipes, not their roots. worked beatifully, the tubing was softer than expected, and there was no problem to bend the dropouts back.

made like 5 small bends right next to each other, just so that the metal would give, alternating between seatstays and chainstays. afterwards it looks like just one bend.

when doing this you have to bear in mind that the lower part of the triangle is asymmetric. the right chainstay is more medial than the one on the left, and there is a slight indent on the right stay to make room for the tyre. if i remember correctly i had to increase this indent 1-2 cm forward, because the wheel will sit a little more forward after the operation. this also means there might not be enough room for schwalbe marathons; standard bromptons work fine, but there is a slight squeeze against the bb tube when folded.

kais1, thanks so much for all this info. what an incredible success story spreading a titanium rear triangle and then successfully mounting a traditional derailleur. ben cooper @ kinetics is the only person i know of who is willing to spread a ti rear triangle. even juliane neuss won't do it. he does not offer a guarantee though since it is not known how the modified ti triangle will hold up.

There could be a small market for affordable 135 OLD rear triangles in steel, but it's still a pricey change if you include the IGH and the time spent by the LBS to put things together.

At this point, for those not owning a Brompton already, the more affordable solution seems to be just ordering a new Brompton from Kinetics.

It's a shame Brompton doesn't offer this as an option when building bikes at the factory :-/

You can order a 135mm rear triangle from kinetics w/o a Brompton hanging to it:

Brompton Forks & Rear Frames ? Kinetics

Depending on your abilities, your existing lot of parts in a shed and the love to your existing Brompton it may be a better deal or not, compared to ordering a complete bike. ;)

When adding the cost of the Kinetics rear triangle (£400), the Alfine hub (£250), and LBS cost of labor (3 hours @ £40 = £120)… I'll wait until I get a brand new Brompton.

Kais01- Had no idea that your conversion is on a titanium rear triangle, very impressive and brave. Sounds like a very involved and fun project; have never heard of pipe benders but fortunately I have a friend who has a custom muffler shop and has also done some frame building so I would get his help.

Windfried - Some may consider the labor a hassle, others would consider doing the conversion fun and rewarding with any potential cost savings a bonus. I have lots of tools, parts and experience and would put myself in the latter group. It's fantastic that kinetics and vostok are around to help both diy-ers and those needing more gear range than Brompton currently offers. I do agree that it really is a shame that Brompton doesn't offer something like this out of the factory though.

leoho5 and rec; thank you for very kind words. the project was indeed successful, but maybe not for everyone. i felt lucky when i discovered the pliability of the titanium tubing, but as the ti brompton parts historically seem to have been made in batches, not all of them are necessarily as easy to form.

multihub gears have been mentioned, but personally i dont fancy them too much because of their weight and drag, the latter likely increased even more on a small wheeled bike. also getting repairs and parts for exotic hubs can be troublesome, especially when on a more remote trip. or anywhere just a few years into the future.

but there are alternative and cheaper ways to get tighter and faster gearing on a brompton. one of the easiest is to combine the ordinary 3sp hub with the high/low brompton derailer, and 13/15 cogs. that way the difference between gears is down to 15 to 18 percent, better than the bwr 6sp. chainwheel according to taste, i would choose around 60t.

or if you stay with the bwr, buy a 3sp kit for the brompton stock derailer and go for 13-15-17

on my 90s brommie i combined 13 and 14t cogs with the stock 5sp sturmey archer hub. 10 tight gears. takes some metallurgy, there is without tweaking not room for the 14t cog on the inner position, the 14 also needs an offset in medial direction, this has to be arranged for. easy enough with an angle grinder. the rear triangle of the 90s bike does not take the derailer mechanism, a one-off mount has to be made. mine has worked nicely, but when time came for a renewal i was tempted to fit a 10sp derailer and schlumpf.

have been thinking about bypassing the schlumpf with a big chainwheel, but would need a bit over 80t to get to where i am today, problem is the brompton will not take more than about 72 and fold. en excentric mechanism to loosen the chainwheel a bit when folding might be an alternative. we'll see. for now the yellow 2x10 works just fine.

here is a photo of my 2sp sub 10kg commuter with a 69t chainwheel, so you can see how that looks. not ideal for hilly areas, but with fresh knees and spd pedals it gets you there. loads of joy underways. sometimes 2 speeds are all you need. one for start and hills, one for underways. once went 45km averaging 34,5 kmh on that bike having fun in a club ride peleton.

Interesting. Very.

I am surprised you can fold with a 72T... I have found a 58T to be the maximum on mine from 2015. The front wheel's hook interferes. I haven't looked to see if I can change that but I am happy with the current 2sp gearing and 58T.