Cycling UK Forum

I have a moden 2018 6 speed Brompton.


What choice are there for the 3 speed gear cable given the Brompton one is 10 pounds?

I replaced mine recently, required by swapping my S bars for something a little higher. I felt the same way, then I looked around at what I could obtain, online on the day, in the way of inners and outers. It looked as though I wouldn't be saving very much so I just bit the bullet - especially as I wasnt completely certain what nipples and ferrules were needed. Given that the 3sp and rear brake cables point upwards at the end I wouldn't recommend compromising on rust or water ingress resistance.
I'm sure I used to be able to get cheaper options from my lbs - but he isn't there anymore...

I put segmented housing on my Brompton and it became now my choice anywhere else, both for shift and brake cables. On the single Brompton rear shift cable, you save about 40g.

IME a common fate for cables in a well-used Brompton is for the housing to fail by fatigue near the swingarm pivot, due to the stress arising from repeated folding. In a 6s model there are three cables and if one has started to fail this way the others won't be far behind.

Presumably segmented housing may help the housing last better at the fold? I wonder if the inner cable might then eventually fatigue instead? Also does the segmented housing scuff the frame paint worse than standard stuff?

IIRC Brompton currently use Jagwire housing and inner cables which have a black low friction/self lubricating coating. IME you can substitute these for conventional cables/housing/lube in most cases and that (plus reusing any special fitting there might be, and perhaps resizing the nipple in some cases) is what most independent bike shops do (in good part because of Brompton's policy on supplying spare parts to independents being so arcane). However what I don't know is if the housing Brompton uses might be designed to flex better than standard housings or not.

cheers

The set of genuine Brompton cables I bought a couple of months ago did indeed use Jagwire housings. The shifter cables used LEX which is their entry level range and the brake cables used CGX - SL which is the next tier up. They both look pretty conventional really, apart perhaps from the SL bit which refers to the Slick Lube liner. See it all here: https://jagwire.com/guides/housing
Nothing too special about the housings then. The ferrules I'm not so sure about - I had some spares floating around in my toolbox and most of my brake ferrules, for example, were too thick to seat in the brake callipers. Then there are the seals on the "business" ends... add all this to some big gaps in the stock list the day I looked and thats the reason I bought OEM. Sometime over the next year I'll be shopping for the components for next time.
I wondered about segmented housings too - Jagwires top range is segmented but I was remembering seeing segments sold loose a little while back. A good way to negotiate a tight bend perhaps, but I could see any liner suffering from being repeatedly bent backwards and forwards between segments during the fold and I felt that excluding muck and water was the important factor. Never mind the paintwork issue...

the claimed differences between the CEX (basic coil reinforced brake housing) and CGX-SL are

a) the 'slick lube' - which just means there is lubricant inside the housing already and
b) they claim 'steel' for CEX and 'high carbon steel' for CGX

I wonder if there is any real difference in the steel coil reinforcements?

IME when the housings fail at the fold, the outer coating (which is PVC I think) cracks up (or wears though) and the shift cable housing (LEX with linear reinforcement) 'bursts' with wires poking out. However I'm not 100% sure which happens first; if it is flexed enough, the reinforcement wires might start breaking first and this may precipitate the rest of the failure.

What I can report is that I have seen (many times) on bikes of all kinds

1) the outer coating 'shrinking back' on cable housings of all kinds; most commonly you see this if you pull a ferrule off an old cable housing; typically the last 3mm or so of the steel reinforcement will be bare, because the coating has shrunk. Also

2) wherever gear housing flexes (eg near the head tube as the steering moves in a conventional bike with bar-mounted shifters), the outer coating first cracks (or simply wears through), then the reinforcement rusts, and then the reinforcement bursts out of the outer coating. So this is arguably a mixture of corrosion and fatigue.

However the fold in a Brompton is a far more aggressive than the typical flexing seen in cable housing in other bikes, so maybe something different happens.

One mad idea is to try an additional coating over the cable housing near the fold, such that if the PVC coating cracks, it doesn't immediately cause corrosion. The additional coating could be heat shrink insulation or simply a wind of insulation tape perhaps.

cheers

I have the segmented housing on Brompton for a year+ now with about 3 foldings/unfoldings per week. I have a triple front mech there and the segmented housing is particularly helpful with the sharp turn of the cable up the seat tube. I bring the latter fact up, because it might give insights into the likely long term durability of the housing in folding.

That turn up the seat tube is worse than any cable bending in the folding. The tension in the cable is abnormally high in the top front gear, due to the general difficulties of fitting a front mech onto Brompton and making it work. I presumably ride most often in that top gear as with 50T there it yields the standard 6sp Brompton gearing - the lower gears are for dealing with hills and we have some in my area making me shift lower.

Given that there had been no problems with the front shifting I presumable that the cables with the segmented housing should be quite resilient as far as the folding is concerned. Even though there is no folding involved in the front mech operation, the folding touches the liner just in terms of a cable under possible tension shifting inside the liner. The housing is segmented and, however you cut it, it does not care about the folding.

I lower the costs of the segmented housing by buying the relatively cheap TRLEQ and using its housing beads only and combining them with Jagwire liner, again relatively inexpensive. I do not use any ferrules. I finish the housing ends by spreading liner ends with a heat gun. A heat gun can be also used to repair the Jagwire liner if you inadvertently produce any kinks in it.

I cannot tell about any frame scuffing - just low on my radar.

If the 3sp shift cable is just the standard Sturmey Archer one, then the Oxford Products compatible cable+outer retails for £5 here, according to the packet of the spare in my shed.

Well according to a handy table wot I found on t'web the length should be one of:
Right 3spd Hub Gear:
S - 1220mm outer, 1379mm inner
H - 1320mm outer, 1479mm inner
M - 1265mm outer, 1424mm inner
P - 1291mm outer, 1450mm inner
I don't know how reliable the list is, I'd put 'em side by side to cut, but if you regard those as the minima required - I'd take a chance on buying anything longer.

I think the lengths are accurate for 2017-on shifters. Slightly longer cables are required for pre 2017 shifters. A full listing of cable lengths (for right front brake lever configuration, unverified accuracy) here

https://thebromptonman.blogspot.com/2018/01/cable-lengths.html

which (at this time) reads;

Full set lengths of cables for long wheel base bicycles.

Pre 2017 Shifters
Left 2spd DR:
S - 1145mm outer, 1269mm inner
H - 1283mm outer, 1362mm inner
M - 1187 outer, 1309mm inner
P - 1283mm outer, 1362mm inner

Right 3spd Hub Gear:
S - 1250 outer, 1411mm inner
H - 1360mm outer, 1521mm inner
M - 1302mm outer, 1463mm inner
P - 1344mm outer, 1505mm inner

2017+ Integrated Shifters
Left 2spd DR:
S - 1015mm outer, 1379mm inner
H - 1120mm outer, 1206mm inner
M - 1072mm outer, 1155mm inner
P - 1110mm outer, 1196mm inner

Right 3spd Hub Gear:
S - 1220mm outer, 1379mm inner
H - 1320mm outer, 1479mm inner
M - 1265mm outer, 1424mm inner
P - 1291mm outer, 1450mm inner

Brake: - 30deg/alu levers
Front:
S - 332mm / 485mm outer, 1050mm inner
H - 440mm / 485mm outer, 1050mm inner
M - 366mm / 485mm outer, 1050mm inner
P - 389mm / 485mm outer, 1050mm inner

Rear:
S - 1230mm outer, 1493mm inner
H - 1355mm outer, 1493mm inner
M - 1290mm outer, 1493mm inner
P - 1319mm outer, 1493mm inner

However there are some cable lengths (including some left front setup ones) mentioned here

https://yacf.co.uk/forum/index.php?topic=23131.25

and they suggest that the length of cable below the cable gatherer on the front brake (listed as 485mm in the previous list) isn't always identical.

IME even quite small differences in levers, handlebar etc can make appreciable differences in the required cable lengths. e.g. If non-standard (for Brompton) brake levers are used (eg with a 90-degree exit) then I have found that tying the (slightly longer than normal) brake cables together as a pair using a zip tie helps them not to be strained at the barrel adjusters.

cheers

If you're slightly inaccurate with cable length, erring on the long side, it still works, but looks bad when unfolded as the cables don't stay together under the main tube. I don't know how short they'd have to be to actually prevent folding.

I should have explane my request better. The latest Brompton 3 speed gear lever will not take a standard cabel as used by other gear shifters the nipple is to large. The is no such issual for the 2 speed shifter on the left particularly if you drill enty hole to 5 mm

Will a campag cable fit?

campag cable won't fit. As mentioned above you may need to trim the size of a standard nipple. This can be done by filing or grinding.

cheers

rogerzilla wrote:If you're slightly inaccurate with cable length, erring on the long side, it still works, but looks bad when unfolded as the cables don't stay together under the main tube. I don't know how short they'd have to be to actually prevent folding.

IIRC when the cables are a little bit too short, the first thing that happens is that you can't fold the bike unless you do the stem hinge and the frame hinge in a specific order, not without straining the cables anyway.

cheers

This may of interest in terms of how to service the gear levers on newer Bromptons. I reckon you can use a Shimano cable on both levers if you drill a 5mm hole for the cable insertion point.

https://www.youtube.com/watch?v=EwYEYO3h2Po