Brompton - Why Only 3 Speed Hub?

[simonhill]

Why do Brompton only use a 3 speed hub?

They do make a 6 speed version, but that uses a derailleur system on a 3 speed hub. I would have thought that a multi (8?) speed hub would be a better option. Am I missing something or is there a technical reason?

[Brucey]

Brompton have always used SA hubs, except when they could not do so, because the production facilities were being relocated, when they used SRAM instead. For many years they offered a 5s hub option, using twin toggle 5s hubs in the 1980s (you can spot the special frames with a cable pulley on the LHS too) and then the dog locking and ball locking single toggle 5s 'sprinter' internals in the 1990s. These hubs offered both a wider gear range and slightly more closely spaced ratios than the standard 3s offerings.

However even in the low torque world of small wheels the 5s hubs were not always reliable; in part this was because of failures to keep the things adjusted correctly, and the Brompton cable routing didn't help either. When a 3s hub is badly adjusted, it usually doesn't break immediately, but this is more likely to happen with the 5s models.

Because of folding and lifting requirements, any hub gear has ideally to be both narrow (~116mm OLN I think) and not too heavy. This rules out most other current IGHs if the virtues of the machines as they stand are to be preserved. Some folk do convert the machines to other IGHs but this needs different swingarms in many cases, and makes the machines relatively heavy to lift.

For the past few years the only 5s hub that SA have offered that might be suitable has been the X-RF5(W) model. But this is a little heavier than a 3s hub (the Brompton 3s has an aluminium planet cage for light weight) and has widely spaced gear ratios, so offers no advantage over 3s models in this respect. It also isn't reliable with the thumbshifter that SA has offered, unless said shifter is modified.

FWIW it is possible to combine the X-RF5(W) hub with the Brompton x2 drive parts and (with different sprockets fitted to give a half-step in the middle gears) this makes for a nifty 10s Brompton with closely spaced ratios that also cover a wide range. I have used this conversion on a few machines and it works well.

BTW the marginal weight increase of adding a Brompton x2 conversion to a machine with an IGH is relatively small; if it comes to more than ~250g I would be surprised; 'good value' for twice as many gears, I would have said.

cheers

[rfryer]

In addition to Brucey's points, it's worth remembering that all Bromptons need a chain tensioner in order to fold correctly; making this into a two speed derailleur is a cheap and effective enhancement.

The 6-speed system is actually very usable. I personally prefer the shift pattern to that on a typical road bike.

[John1054]

I've been very pleased with my Kinetics (Ben Cooper) Rohlof Brompton. The extra weight is more than balanced by the spread of gears. It depends on your usage as to what suits.

[simonhill]

Thanks for the replies, particularly Brucey's tech stuff.

I take the point about the need for a chain tensioner, so the derailleur sixer gives the extra gears and range without much (any?) extra hassle.

[Brucey]

I take the point about the need for a chain tensioner, so the derailleur sixer gives the extra gears and range without much (any?) extra hassle.

pretty much. The tensioner is about the same weight and complexity whether it is for a x2 setup or not, and the pusher mech is pretty simple too (being a two-position device with just one pivot); it usually carries on working OK even when it is blathered in crud.

cheers

[mercalia]

what about the Kinetics conversion to 8 speed SA then?

http://www.kinetics-online.co.uk/folding-bikes/brompton/brompton-8-speed-kit/

which looks very intersting and not too much compared to their Rohloff conversion?

[Brucey]

it is OK but sadly the hub itself is not very reliable, not very long lived and not very efficient (except in bottom gear).

Having said that, if you are going to have this hub, it might be the best place for it.

cheers

[mercalia]

it is OK but sadly the hub itself is not very reliable, not very long lived and not very efficient (except in bottom gear).

Having said that, if you are going to have this hub, it might be the best place for it.

cheers

well that probably explains why they dont sell Bromptons with the hub, only a kit. so thats one I will pass on, shame as the price would have been right.

[mercalia]

what about the NuVinci CVT hub?

"The NuVinci has a range of 380%, that’s between the 8-speed and 11-speed Alfine hubs, but it also had a stepless gear change – there’s no clicks, just a smooth transition from the bottom of the range to the top, using a twist shifter."

maintenance
"You need to change the fluid every 35,000km or so but other than that there's no maintenance, and because there are no gears, there's no indexing worries either."

seems too good to be true? why isnt every one using one?

http://www.kinetics-online.co.uk/folding-bikes/brompton/brompton-nuvinci-kit/

SJS has the hubs at £200 135 oln

https://www.sjscycles.co.uk/hubs-internal-hub-gear-brake/32-nuvinci-n360-hub-with-disc-brake-fitting-silver/?geoc=US

[Brucey]

what about the NuVinci CVT hub?....

....seems too good to be true? why isnt every one using one?...

quite heavy, and probably the least efficient bicycle transmission you can buy.



BTW the NV 360 transmission is cheap at the moment I think because there is an improved (wider range, otherwise similar) NV 380 model available now, which is the one that Kinetics offer.

cheers

[mercalia]

has anyone here ridden a bike with one? would be interested in comments

[Brucey]

different thread

https://forum.cyclinguk.org/viewtopic.php?f=5&t=116792

cheers

[mjr]

quite heavy, and probably the least efficient bicycle transmission you can buy.

A graph that raises more questions than it answers: Are there two curves for the NV there or have I misread it? If so, what do they mean? And why include SS but not any SA? Is it a Rohloff advert?

[Brucey]

quite heavy, and probably the least efficient bicycle transmission you can buy....

A graph that raises more questions than it answers: Are there two curves for the NV there or have I misread it? If so, what do they mean? And why include SS but not any SA? Is it a Rohloff advert?

There are two curves for every hub, as (cryptically) indicated in the key. One is for a load of 50W and the other at 200W. These tests are carried out at constant torque BTW, which may flatter transmissions that feel 'spongy' when you are actually pedalling on them. To allow for such effects in tests is difficult though, so I can see why they didn't bother.

Is it a Rohloff advertisement? Well, they may be playing 'home field advantage' as it were. Others have failed to get the same efficiency from (new?) Rohloff hubs on test, which raises the vexed questions of new vs used hubs, seal drag etc. Used hubs almost invariably are less draggy than brand new ones, because the hubs 'run in', i.e. the gear teeth lap themselves and the seals settle in etc. [Since that test was done, I think Rohloff have changed their seals, and the seal drag is almost certainly going to be different now.] Call me cynical but I expect (for cost reasons if nothing else) they did not buy and test a brand new rohloff hub, but probably had a (used, specially fettled...?) hub supplied by the manufacturer.

It is also possible that some of the hubs (with adjustable bearings) were saddled with factory settings when tested, which could have made them draggier than they should be.

No idea why they have omitted to test SA hubs, or the Premium N8, or the Alfine 8 hubs. BTW I expect the latter to be a little draggy in the seals (and because it is grease lubricated) when new but otherwise to perform slightly better under load than the A11 does in its 'good gears'. If the A8 is lubed with oil or SFG rather than the claggy stuff it comes with, I expect drag could be much improved.

cheers