Brompton rear triangle widening , custom gearing thread
 

Hi I want to start a thread around this subject to get a central thread and conclusion on fitting wider hubs to a brompton. Ie to use afline /nexus hubs or rear drailers.

I am going to outline my situation, but any information would be welcome to provide a comprehensive database of the possibilities. I want a thread to be informative and not just offer me solutions, but cover all aspects. Ie fitting 8 speed SA without widening triangle, rolhoff etc.


I am aware there is information elsewhere on the Web, but I have found it difficult to summarise the different approaches that people have taken. Ie cold setting, welding,cutting down hubs, altering chainline.

I am considering using a spare shimano Cespro rear hub on my sporty brommie (5 speed). I have a friend who is offering to remove the brake arm fron the rear triangle and replace with a slightly larger version using a mig welder. The frame would be widened to 135mm OLD to take a standard hub, he has also offered to put a drailer hanger on. 9 speed would go with road race STI levers my preferred option and be lighter than an IHG. I then may go for a Steven perry ish front mech option. I have a 56tooth front. I have not found much information about rear mechs and interference with folding.

Data base begin. No opinions, just facts LOL

Post your wisdom /links, ....etc here.....

Hi what a great idea for a thread!!
Here are some links thanks CPQ.

http://audiblesight.com/?page_id=1679

http://mistymornings.net/blogs/mm/?p=45

I will be interested to see what is possible. I think the ability to run any hub and derailier gearing would be a real plus on a Brompton.

Here is another link, the bike has been modified to take a Rohloff hub and V brakes. Unfortunately there is no real detail on how the dropout spacing was increased.
http://www.magbaztravels.com/content/view/104/29

Like cpg, I am curious to see what is possible. It is always interesting to me to see what people do to mod their bikes.

99%+ of Brompton owners will find what they want with the standard 13 different gearing configurations and I note that the 6-speed has a wider range of gears than any single chainring bike, but for others, modding and tweaking is where the fun is. Looking forward to seeing what you two come up with!

Opening out the Brompton rear forks to accomodate an OLD of 135mm will probably cause clearance problems between the tyre tread and the cross piece near to the rear fork hinge. http://mistymornings.net/blogs/mm/?p=174

Be careful with MIG welding bike frames. Too much heat can create a large heat affected zone which is a point of weakness. The Brompton frame components are brazed so I would be inclined to braze on the things you need. If you weld near a brazed joint, the braze can contaminate the weld which, besides causing spattering, will also weaken the weld.

My partner and I are very happy with the Nexus 8/double chainring (with front changer) setup on our bikes. A vast improvement on the Brompton six speed in terms of both range and ease of use.

Perhaps I should toddle off and get my flame proof suit on ;)

Very interesting, good information there, thanks Syklist. Are you the author of those articles?
Would you still get tyre clearance problems with a narrow tyre such as a Kojak?

Please tell us about your nexus mod. There are a few ways of doing it.

Nexus and afline hubs can be used with a "versa" 11 or 8 speed road race sti levers.

I started with a 2-speed, later added a Schlumpf Speed Drive giving 4 gears, then swapped the back wheel for a SA 5-speed hub while removing the Schlumpf, giving 10 speeds. Commuted like that for a while, now back at 2 speeds.

That seems fairly straightforward and dispels some concers. Altough the article is written based on normal sized bikes with their larger rear triages than those on a Brompton meaning the normal size bike will bend easier.

See if these fellas can shed some light they know what there doing! - http://fudgescyclestore.com/index.php?c=5618&brand

rear width was spread to 135 here. : http://www.kinetics-online.co.uk/fol...n-rohloff-kit/

which actually uses a custom replacement rear portion , apparently..
he also sells a custom replacement fork to disc brake both wheels
http://www.kinetics-online.co.uk/fol...rear-triangle/

they also sell a SA 8 speed modified Brommy.. removing axle nut width off the left side , can work.
Rohloff cannot be narrowed, so fork assembly in the rear has to be modified.


S-RF5(N) seems to have the driver like the BWR, so a 10 speed hub
using your 2 speed cog set off the 6 speed bike may work .

Gears in hub , .63/.75/1/1.33/1.6, NB overlocknut width as narrow as 111mm or 119..

my own Brommy M3L, 15t cog Schlumpf MD [54/'21.6t'] (50/20 comes out an even number)

Yes I am the author of those articles. As regards clearance with Kojak tyres: I have no idea, I need Schwalbe Marathons on my Brompton :)

However, I have added a post about the clearance between wheel/hub and rear forks. http://mistymornings.net/blogs/mm/?p=191 As you can see, it is all a bit of a tight fit.

Seriously? ;) BWR gear range 302%, Nexus 8 gear range 307%, Alfine 11 gear range 409%, Rohloff gear range 526%. Pinion 18 gear range 600%.

Thanks that usefull information. I dont mind running a jokack tyre on the rear to get clearance, but it would be goodto retain ability to run standard tyre. Would it make sence to use micro adjusters on the rear drop outs????

Spoke clearence looks dodgy to go to 135mm.

Also dual drive could be about 350 per cent with a 38 11 cassete.

bang a dent in the cross brace to get more clearance.

Mk4 rear section added a dent to inside of the left chainstay ..




I noted the touring bag add ons in Syklist's pictures .. of 2 Front panniers

To the back of the Brompton Baq support frame ..

that done just shifting where the Ortlieb pannier hooks are in the top rail slots?
and presumably just leaving the rear touring bag's pockets flat, and empty?

I also see a telescoping steering riser and using figure 8 bend trekking bars..

I tend to use a block of wood and a welding clamp to 'dent' the forks. You have a bit more control over the size of the dent. A picture of the Mk4 dent would be nice :)

Piggy back frame, yes the rear touring bag pockets are flat. I never found them to be particularly useful at the best of times :)

went to the archive page and the pictures were not loading so at least this way I could see it .

Just finished a modification to an older steel bag frame added 3 struts to the base sticking out 9"

and a flat piece across the front can load packages and a milk crate on top of it

My Xmas self Prezzie was the O bag and then got the Large add on pockets ..

so I saw your piggy back frame and pocket envy kicked in ...





Non UK english readers .. 'Jubilee clips' is Hose Clamps..

I have used 2 hammers to make some dents , like to get chainring clearance on the outside of chainstays.

Its like having a ball peen punch with a wooden handle.

but yea you can carve the shapr you want to press in outof hardwood or aluminum
then squeeze it in to the tube with a C clamp , but may want a half round cup shape
to support the other side so you only scrunch 1 side.

Oh, very good - thanks for the correction. I doubt very much that I'll ever see a folder with a pinion, slightly less unlikely a folder with a rohloff, but they do exist. The alfine 11 and nexus 8 are nice possibilities though.

stick on one of Schlumpf's 2 speed cranks and the overdrive 2nd gear is 160% or 250%

mountain drive has as if a 20t and a 50t chainring.. BSR 3 speed is non overlapping ..
so all 6 ratios are different.

right, Pinion mid drive gearbox is such that the frame is custom built around it.

You're welcome. I think you will find that the Alfine 11 is a bit lacking in the reliability department, it seemed to be the last time I checked. IIRC it is sensitive to cable stretch which is a bigger problem with folding bikes as the cables get stretched when you fold the bike. The Alfine 11 is also significantly more expensive than the Shimano 8 speed hubs.

I thought about using the Alfine 11 hubs but on balance I am glad that I stuck with the Nexus 8 hubs combined with double chainrings. The range is simiilar to an Alfine 11 but the cost of the conversion (and hence replacement parts) was significantly less. The only drawback is that the Brompton chain tensioner does not cope well with big differences in chainring size (50/34 t for example).

By the way the Brompt-o-lieb , the question arises about whether the newer bag frames are like that ,
that Is the New nylon/aluminum tube Bag frame, the older ones were steel .

Many people think the that three to six speeds is all that is necessary on a folding bike, but I beg to differ. I installed a Shimano XT/XTR 10-speed drive line on my old Birdy, and found it to be a revelation. I could climb the steepest hills without getting out of of the seat, and steep descents were no problem either. The only issue with my kit was that the end of the medium-cage derailleur came a little close to the ground. This would be a bigger issue with a Brompton, but would probably be okay with a shorter cage.

I have not tried to modify my Brompton yet. I have widened the triangle on fullsize steel road bikes without any issues, steel is not so difficult to bend. A fair amount of cold forming is done to align the various components before a bike is assembled, so it shouldn't be a big issue. I used a threaded shaft with nuts and washers to spread the triangle, and a Park tool to measure the distance from the axle flange to the wheel at all points to make sure the bend was flat. On a shorter triangle (like on a Brompton) the dropouts will bend outward as the triangle is opened, this will have to be corrected.

I would consider using a Nexxus internal hub, but I find they don't shift as smoothly as the Sturmey Archer units. If I were to convert, I would probably add a derailleur hanger and a 9-11 speed driveline, with rapidfire shifters.

That's what intrigues me. I have a triple with 10 cog cassette on one bike but have never felt the need for more than 6 gears on my folder. The idea of having the room, the tools, the time and the inclination to modify the frame of a folder to fit a different hub seems foreign to me but obviously there are those who find it worthwhile. To each his own and I am eager to see what you all come up with.

Re 6 speeds. I feel as many folders are not good out of the saddle you actually need more speeds. On slow cheap folders less speeds may be ok, because one is not going to get speed up in an upright position.
I want two things.
Modern road race shifter compatability.
A range of gears with small steps between.

may just need the right gear Ratios , for your terrain not a bunch of speeds which really is a parts count.

or how bout a NuVinci CVR hub ? just turn the gripshifter till the effort feels right.