More Gears For 3 Spd Brompton - What Are The Best Options?

[townbikemark]

I know they do a 6 spd derailleur, but as I have an aversion to derailleurs, opinions are sought on other options WRT hubgears; at least one company does Rohloff conversions, but that's overkill. I've noticed the 5 speed Sturmey Archer is roughly the same size as the 3 speed and then you have everything in between...

[UpWrong]

I bought the 8 speed conversion kit from Kinetics which uses the Sturmey Archer 8 speed wide ratio hub. It works well enough but 4th gear is really noisy and lossy. Also it has added considerable weight to the bike. If buying again I would definitely look at the 5 speed hubs, but historically the gear change adjustment has been finicky apparently. Not sure if there are now newer hubs available in the narrow widths with better gear change.

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

[UpWrong]

Just been looking at the Sturmey Archer site. I have the X-RF8(W) 120mm OLN, which weighs 1770g. The X-RF5(W) 119 OLN weighs 1220g.

I've been considering converting to the 2 speed derailleur for least weight, and have been thinking of selling the 8 speed upgrade kit. It's very low mileage and I'd be looking for around half of what Kinetics charge. PM me if interested.

[MLJ]

The 2-speed derailleur on the Brompton is really just a slider to move the chain between two sprockets on the hub gear. It is fairly reliable. I have had mine clog occasionally from gritting roads, but it is easily cleared with a stick or wire prod. The alternative might be to acquire the Schlumpf 2-speed BB gear but this adds weight. http://www.schlumpf.ch/

[UpWrong]

The reason I went for the IGH 8 spd solution was that I thought the double changes needed for the OEM 6 speed would annoy me. Changing to the next ratio incrementally presumably requires a change on the 3 spd hub and a change on the 2 spd derailleur. The 8 spd IGH gives you a wide range from a single shifter.

[mjr]

Wait a moment: what problem are you trying to solve?

[SA_SA_SA]

The 5 speed is really sensitive to adjustment and not even much wider in range, unless the new 256% wide version:

I still would not want an SA 5 speed on my folder instead of the 3 speed (that replaced it) due to the adjustment issue.

Brompton were meant to be developing a combo lever for their six speed but none yet......

[Brucey]

broad brush statements about SA 5s hubs don't really hold water because there are many different versions and shifters; they are all different from one another.

Some versions will fit inside some 3s hubshells, so this is a route that is worth pursuing because it will avoid you having to build another wheel. (The critical feature is where the LH ratchet is set inside the hub). It will also allow you to set the machine back to stock if/when you come to sell it. Having said this if you buy another wheel it is an easier swap.

Note that

a) Bromptons normally use a chain tensioner that uses a lot of space on the RH end of the axle. I think that some (if not all) SA hub centres meant for Bromptons use an axle that is longer on the RH side vs the total length. If you use a standard centre, you may have to switch to a different tensioner.

b) Because Bromptons fold, the cabling takes a real beating when the bike is folded; whilst the torque on the hub is lower than in a large wheel application (which gives the hub an easier life) the shifters can more easily go out of adjustment.

cheers

[pete75]

Note that

a) Bromptons normally use a chain tensioner that uses a lot of space on the RH end of the axle.


cheers

For that reason I don't understand why anyone should object to the Brompton 2 speed dérailleur - something similar is already hanging from the rear drop out anyway.

A very neat way to give yourself more gears would be the Schlumpf mountain drive - not cheap though.

[SA_SA_SA]

broad brush statements about SA 5s hubs don't really hold water because there are many different versions and shifters; they are all different from one another...

Sorry, I was referring to the modern single toggle chain/ cable versions (ie sprinter onwards, as used on Bromptons since 1994 till the end of UK SA stock.
If the modern sunrace hubs still have the closer spaced indexing (cf 3 speeds) then I would suspect they will still be sensitive. Also, the Guide roller (GRA in Brompton-speak) is a pain on the Brompton, and needs to be aligned correctly in line with the cable pulley whereas the simple flanged nut is self-aligning , removing a 3 speed Brompton wheel with simple (but custom) flanged nut is much easier.

I have had a UK and early Sunrace Sprinter internals modified as below
(should have got a 3 speed but I had thought 33% steps a step too far: but with toe clips they are OK).

The 1st taiwan Sunrace SA Sprinter internals could be fitted to a Brompton UK 5 speed shell by shifting the axle over to the non--chainside:
http://www.atob.org.uk/technical/brompton-5-speed-upgrade/
I don't know if this would work for any of the newer ones.

[Brucey]

The 1st taiwan Sunrace SA Sprinter internals could be fitted to a Brompton UK 5 speed shell by shifting the axle over to the non--chainside:
http://www.atob.org.uk/technical/brompton-5-speed-upgrade/
I don't know if this would work for any of the newer ones.

I don't think it says that you can 'move the axle to one side'; if it did then it would be a good way of knackering the hub if you move the axle laterally within it.

I guess it is a question of perspective but Brompton axles can either be viewed as 'long ones with a shorter left side' or 'short ones with a longer right side'; six of one....

Re the gear types; roughly from 1994 (ignoring different brake variants etc) there have been the following single-toggle 5s hubs;

a) the dog locking sprinter (UK)
b) the ball locking sprinter (UK)
c) the Taiwan-made ball locking 5s
d) the Taiwan made dog-locking (W) 5s.

None of these hubs have been issued with instructions that guarantee that the user will make clean shifts especially on the 1-2 shifts. In fact if you follow their recommendations you are almost certain to damage the hub.

You can interchange the centres from a) b) c), but they won't fit into the vast majority of shells used for 3s gears (although you can fit several different 3s centres into some 5s shells, and older twin toggle 5s internals do fit into older 3s shells).

b) and c) are meant to be the same hub but in practice are often not. I've dismantled several failed units and the Taiwan made ones appear to be of poorer quality internally, with burrs on the stepped gears and obviously defective material (that shows cracks perhaps even from new) in the irreplaceable centre control rod and its associated springs. I've also seen a few really badly worn cones etc in early Taiwan-built hubs, and heard of whole batches of early Taiwan-made hubs (both 3s and 5s hubs) that suffered premature and catastrophic wear internally; I think they got off to a pretty shaky start in fact. A further issue is that these parts are not always well lubricated.

A complication is that the (W) hub (as well as having different ratios) uses a different shifter with a shorter cable pull. This appears to work with the other hubs and may even work fairly well with a), even, but will basically destroy hubs b) and c) because of the shorter cable pull. The SL-S50 shifter for the (W) hub is additionally defective in that it has too much friction and doesn't give the same cable pulls or detents on upshifts and downshifts (amongst other things this means that gear #4 slipping is not improved despite a deeper engagement on the main clutch in gear #4 in the (W) hub design). On Bromptons the cable problems are exacerbated by the cable flexing and the relatively poor cable routing.

In a wider sense the SA gears are no more sensitive to correct cable adjustment than (say) a shimano nexus (7 or is, even if consequent slippage might sometimes more quickly damage the hub internals.

Most of the a) b) c) hub failures I have seen have been caused by shifts 1-2-1 not working correctly which then starts an evil chain of events. Further failures are caused by any kind of cable or adjustment problem that leaves the gear #4 setting even slightly wrong; this causes slipping in gear 4 and this can fairly quickly kill the hub. Of course the same problems with the actuator plate that blight the NIG 3s hubs also afflict the 5s hubs too; another good reason for not back-pedalling during gearshifts.... Also note that most of these hubs work better if the RH cone is shortened by about 1mm on its left side; there is a tolerancing issue with many of the sets of parts that I have seen.

Ironically an oft-cited reason for criticising the older twin toggle 5s hubs was that the shifting 1-2 and 4-5 is a bit quirky. The exact same issues exist in every single-toggle 5s hub too, it is just that SA has basically chosen to ignore them when writing their user manuals!

Once they are set up and lubricated correctly and if the correct shifting technique is used the ball-locking sprinter hub is a really nice hub (pretty much just as slick 2-3-4 as a 3s is 1-2-3) that seems perfectly reliable in a town bike. I think it is a considerably better design than either dog-locking version. However, between the build issues and the poor adjustment/shifting technique that is commonly inflicted upon them, most of them (all types) don't seem to last anywhere near as long as they should do or could do.

cheers

[SA_SA_SA]

The 1st taiwan Sunrace SA Sprinter internals could be fitted to a Brompton UK 5 speed shell by shifting the axle over to the non--chainside:
http://www.atob.org.uk/technical/brompton-5-speed-upgrade/
I don't know if this would work for any of the newer ones.

I don't think it says that you can 'move the axle to one side'; if it did then it would be a good way of knackering the hub if you move the axle laterally within it.
I guess it is a question of perspective but Brompton axles can either be viewed as 'long ones with a shorter left side' or 'short ones with a longer right side'; six of one....
....

The short axle was a custom for Brompton (by UK SA), Sunrace didn't make it at the time of the article, so the Sunrace axle in that article is just a standard 5 speed axle:-----
I think the Brompton rear frame dropouts are assymetric, so perhaps that is what mislead me, but with the axle sticking out so far leftwards, it really looks like its been shifted left .

My other criticisms mainly apply to such single toggle cable SA 5-speeds on Bromptons/folders, but even on a standard bike I don't think the 2 extra gears, and slightly narrower steps are a big enough advantage to trade against the simplicity of a non-NIG oil-based 3 speed: I suppose YMMV applies here
Hypothetically, I suppose the wider ratio 5 speed might be worth thinking of on a normal bike...but you didn't sound impressed, so perhaps the C50.

Also, I still think anything above a 3 speed should have the indexing in the hub, so that cable misalignment cannot damage the hub, just like a Rohloff, perhaps someone will think of such an affordable/acceptable mechanism someday....

NB my 2nd hub lost low gear: I can't remember how I changed gear, does giving the wrong instructions in the manual sound like the triumph of marketing over engineering :to you (

[Lotus-e-Clan]

Hello - newbie on here.

I have the dreaded 7 speed Sprinter (with brake) hub on my winter bike which has done just 100 hilly miles from new (I'm local to Yorkshire Dales) and the dreadful plastic thumb shifter has failed already - so I'm looking for alternatives.

I wonder if the Sturmey 8 speed shifter would work the old 7 ?

I found out on another forum that the cable pull ratio for the 8 is as follows:

"Sturmey-Archer 8 spd: 34.5mm total cable pull in seven even steps"

Does anyone know what the 7 speed sprinter pull ratio is?

Or suggest an alternative shifter for the 7 speed?

EDIT:
Just worked out that I can measure my SA 7 speed gear cable total pull (mm) to see if it would work with an 8 speed shifter. As shown in chart below, my SA 7 needs to have 29.5 mm total pull to work with the SA 8 shifter ...

GearPullChart.jpg (66.26 KiB) Viewed 4197 times

Thanks for help

[Brucey]

IIRC the SA 7s shifter is an oddball one; it pulls something mad like 12mm per click, and the shift pulley on the hub moves 45 degrees per shift.

I think that there are (were) two shifters for 7s; one a gripshift type and the other a thumbshifter. [Neither seemed that good to me but they often outlast the hubs, ahem.] Until relatively recently SJS had some spares etc for this hub but I don't think they have much left now. They are worth a try as is 'oldbiketrader' for this kind of thing.

There are a few shifters that pull more than 5mm/click (eg SRAM 7s) but IIRC the clicks are not uniformly spaced as is required for the SA hub. I don't think there is a good alternative shifter for the SA hub (even in terms of the shift ratio being vaguely similar)

BTW in the absence of the correct shifter my best idea for this problem was either to;

a) make a new (smaller) shift pulley for the hub or
b) buy (or more probably make) a 2.4:1 shiftmate type device, and use a 5mm/click shifter with it.

For b) the output pulley would have to be at least 30mm in diameter or larger, (else it would do more than 3/4 turn through the full shift sequence which would cause problems). If the input pulley is made too small, (a 30mm output pulley would need a 12.5mm input one) then the cable will fatigue too quickly. I think (from a cable fatigue perspective) the minimum input diameter ought to be around 20mm, which means an output pulley of 48mm; not an off-the shelf part, that.

A new hub pulley (option a)) would also be around 12.5-13mm dia to give 45 degrees/shift from a 5mm/click shifter, again too small I reckon.

A further option is to perhaps make a small 2.4:1 gearbox (which could be mounted on the chainstays behind the BB for example). This could have a 30mm input pulley and a 30mm output pulley. It would be a lot of faffing about though.

BTW there are lots of equal spaced ~5mm/click shifters; 7/8s SRAM X-series derailleur shifters are like this.

cheers

[RickH]

My, very much tongue in cheek, suggestion is 2 3 speed Bromptons with non-overlapping gear ratios. You carry one folded on the rack of the other & swap over whenever necessary!

Rick.