Brompton changing from 3 to 8 speed

[Philip Benstead]

On my Brompton I have a

AW 3 Wide 133.3 100 75 steel shell

I was thinking of changing to

X-RF8 http://www.sturmey-archer.com/en/products/detail/x-rf8

I note that SA only supply the following changers


SLS80 http://www.sturmey-archer.com/en/products/detail/sls80
Or
TSS86 http://www.sturmey-archer.com/en/products/detail/tss86

I prefer the quick-fire system of gear change so

Questions


1. Is there a quick-fire type gear changer that would work on this hub gear?

2. How does the SA compare with nextus hub gear?

X-RF8 http://www.sturmey-archer.com/en/products/detail/x-rf8

8 Speed Rear Hub
FEATURES
• 8-Speed internal gear hub with wide gear ratio of 325%
• Gear steps of 30%, 14%, 14%,14%, 14%, 14% and 30%
• Rotary gear selector without protrusions outside the frame
• 6061 Aluminium hub shell
• Available with 28, 32 or 36 spoke holes
• Compatible with 20 to 23 or 25 teeth sprocket
• High-polish alloy finish
• Weight - 1770g to 1790g
Gear Ratio
• Overall Range - 325%
• Gear 1 - 100% (Direct Drive)
• Gear 2 - 130% (Gear 1 + 30%)
• Gear 3 - 148% (Gear 2 + 14%)
• Gear 4 - 169% (Gear 3 + 14%)
• Gear 5 - 192% (Gear 4 + 14%)
• Gear 6 - 220% (Gear 5 + 14%)
• Gear 7 - 250% (Gear 6 + 14%)
• Gear 8 - 325% (Gear 7 + 30%)


SLS80 http://www.sturmey-archer.com/en/products/detail/sls80

8 Speed Thumb Shifter
FEATURES
• Available in HSJ204 with 22.2mm clamp or HSJ205 with 31.8mm clamp
• 1900mm Slick-Stainless cable
• Including cable adjuster
• Weight of HSJ204 - 97g
• Weight of HSJ205 - 103g

________________________________________
SPECIFICATION


TSS86 http://www.sturmey-archer.com/en/products/detail/tss86

8 Speed Twist Shifter
FEATURES
• 1900mm Slick-Stainless cable
• including cable adjuster
• Weight - 89g
________________________________________

[TonyR]

Have you checked the OLN dimension. The smallest for the 8 speed in 120mm and the Brompton IIRC is 115mm. If its a steel rear triangle you can reset it but the titanium one may be a different story. BICBW

[Brucey]

The SA 8s design is well suited to small wheelers (if it fits into the frame) in that it only gears up. However there is limited sprocket choice, so be sure that you can get a sensible range of gears.

BTW if you mount a thumbshifter upside down on the other handlebar, you can often work it with thumb and forefinger, much as you would a rapidfire shifter. There is no rapidfire shifter available for this hub; the cable pulls are detailed here;

http://www.sheldonbrown.com/cribsheet-IG-cable-pull.html

but they don't match other shifters quite perfectly (and these measurements contradict others I have seen for some shifters too BTW). I think the Alfine 8 trigger shifter might be closest but it isn't a perfect match.

cheers

[ljamesbee]

Do it!!

I may not be much help with technical aspects because I did the conversion a while ago, but let me know if you have any questions about mine. It's a 16 speed and it has worked amazingly well for 2-3 years. Modified for touring by adding an 8 speed sturmey archer hub gear and double chainrings at the front. If I remember correctly the gear range is something like 20-100" or 500%. Not as good as a rohloff at 526%, but pretty close. About the same weight though, and 1/5th the price.



Closeup of the gear arrangement. Note the chain guide cog on the rear triangle. When you need the mountain gears (the small front chainring), you just manually pull the chain up onto the guide cog and carry on cycling. The chain will then switch over to the 30t front chainring. Doesn't affect the folding.



I use the TSS86 shifter, but unlike most people, I quite like grip shifters. If the cable pull is correct, the thumb shifter will probably be great to use. Remember to stop pedalling when changing gears - I think shifting while still pedalling can screw things up. You can shift while stopped though which is good.

I think the nexus is much wider than the SA8 and therefore more difficult to fit. May be wrong about this though.

[Philip Benstead]

I have yet to measure my Brompton OLN but it been suggest that the 8 speed is 120 but Brompton is 115 how did you overcome this issue
Also what size cogs are available, I have only seen down to 19 but on Brompton you need I think 12 or 13?

[TonyR]

I have yet to measure my Brompton OLN but it been suggest that the 8 speed is 120 but Brompton is 115 how did you overcome this issue
Also what size cogs are available, I have only seen down to 19 but on Brompton you need I think 12 or 13?

You overcome it by cold setting the rear triangle i.e. spreading it apart to the correct width but check both measurements first to see if its necessary. With steel it is relatively straight forward apart from resetting the dropouts to be parallel. On titamium it is much harder. The Kinetics kit suggests that it may not need resetting but that may be because Ben has made some adjustments to the hub. http://www.kinetics-online.co.uk/foldin ... speed-kit/ It also needs a new crank and chain ring - you need a 33-ish tooth chain ring to match the hub gearing and a 20T rear. Be prepared for quite a bit of faffing and fixing. Kinetics for example use a modified chain tensioner to take up the increased slack, get the chain-line right and not hit the spokes. Kinetics do all sorts of other conversion kits as do Tiller Cycles - http://www.tillercycles.co.uk/page3.html. Be aware though that Ben at Kinetics has a reputation of doing things when he gets round to it so don't expect the instant gratification experience when you order. You may need to wait some time before he makes the bits up and ships them if you go down that route. Its more expensive than buying just the hub but it may save you a lot of grief and head scratching.

Also if you buy direct, make sure you get the right version - its the right hand most one in the SA spec sheet - http://www.sturmey-archer.com/files/cat ... 20HUBS.pdf

[simonineaston]

I use an SA 8 speed and a Brompton, although not together! The SA sprockets available for the 8 speed are : EDIT: 20, (not 19 ), 23 and 25.
http://www.sturmey-archer.com/files/cat ... 0X-RF8.pdf
I have this hub fitted on another of my 16" wheel bikes and use 25 / 40 teeth which gives a range of 26" to 83", which might be tad low for some firm-thighed individuals but is perfect for me, touring. I used an inexpensive 40 tooth crankset also from SA and popped it straight on the bottom bracket spindle on the Moulton and I don't see why you shouldn't do exactly that on a Brompton...

[Philip Benstead]

My Brompton OLN is 113mm I have 13 tooth cog which I was told the largest you can use on a Brompton without altering the frame.

I understand from other forum that one way to get over OLN issue is to replace the 2 lock nuts with thinner versions.

Question

Is it possible to fit a cog larger than 13 on Brompton without alteration of the frame?

Is it possible to fit a cog as small as 13 on an 8 speed SA?

[TonyR]

Question

Is it possible to fit a cog larger than 13 on Brompton without alteration of the frame?

It clearly is because the Kinetics kit uses a 20T without altering/changing the rear triangle although I suspect that they have modified the hub to do it. I seem to recall there are some changes you can make to do that. Normally the largest you can fit is around 15T although you can go up to 18T by crimping the stays out of the way or careful use of an angle grinder to remove the offending material . Try the Yahoo Brompton Talk group for specialist advice as its some time ago for me and I'm misty as to what needed to be done for what hubs.

Is it possible to fit a cog as small as 13 on an 8 speed SA?

No AFAIK. The mount for the cog is too large to do that. If you check the data sheet 20 is the nominal minimum for the SA 8 speed hub.

[steelframe]

I too have an S/A xrf-8w in my Brompton. Bought it as a kit from tillercycles and fittet it myself. Tiller do not offer the kit any more on their website, but asking them if they a willing to provide you with a kit is for free.

Regarding your questions, in short:
- You cannot use a 13 teeth sprocket with the xrf8
- you do not need to widen the Brommi's steel triangle (which would be necessary for the nexus or the alfine)
- you do have to lengthen the arms of the chain tensioner. There are various ways to do this yourself.
- using a smaller chain ring may be useful, but not totally necessary, depending on your needs an pedaling style. I run mine with the standard 50 teeth ring and a 25 teeth sprocket atm. Works generally well, but is a bit long in 8th for some. With a smaller sprocket than 25 you will need a smaller chain wheel
- you can use the rapid-fire of the shimano alfine. It works well, only the numbering of gears printed on the shifter is in reverse to the actual shifting with the xrf. Alternatively, there's a thumb-shifter from S/A. Or you use the standard Grip-shift-style one.

Biggest downsides: The xrf8 adds quite some weight and it tends to need fine adjusting of the cable length constantly. I have two of them, one in a Brompton, one in a Moulton and it's the same with both of them. Really often the xrf will not hit a gear perfectly when on the road, independently from how well you adjusted it before, from how well it finds the other gear and from how well it did hit the gear in question just two minutes before. You get used to this behaviour quickly, but it is not what I'd expect from a gearbox in 2015...
So today I'd probably go the easy way and upgrade to the six-speed BWR (if your Brompton was built after 2001). A lot lighter, with 302% roughly the same range and about in the pricerange as a xrf8 kit from tiller used to be (kinetics is more expensive).

Regarding the sprocket on your stock bike: The two and six-speed can take sprockets up to 16 an 12. Smaller than 12 is not possible, regarding bigger sizes I've occasionally read about 17 and 18, but never seen one of those. Other People say this would not be possible - not sure what's right. Regarding the 3-Speed AFAIK the biggest sprocket possible is 15. It may depend a bit if your backwheel has the old 3AW, the srf-3, the Sachs/Sram Torpedo, the SWR or the BWR built in.

[hercule]

I've not done a lot of miles on my Sturmey gear (16" Moulton) but also have another bike (big wheels) with the Nexus 8 hub. Direct comparisons are tricky, I bought the Nexus hub second hand and the wheel it came from was very "well used" so I suspect the hub has been well worn in. I also use the Jtek bar end shifters on both bikes so can't comment on the stock shifters.

The Nexus seems a much smoother and more efficient hub. Mine is nearly silent in all gears. It will shift in recent load or not. After nearly 5 years riding all I have done is adjust the cable tension slightly.

The Sturmey doesn't feel as smooth, I didn't realise at first that best practice is to stop pedalling when shifting, shift quality is much better if you do. It is really noisy particularly in 4th (I think) which some have described as being like a swarm of bees, to me it sounds like a bandsaw being started up! This may all be in the ears of the rider, I've never seen any pedestrians looking to see where the noise was coming from. I do have steel mudguards on this bike which of course could amplify the noise. First gear performance is much better than the Nexus (it's direct drive) and I think overall the spacing is much better than the Nexus which for me has an annoying gap between 5th and 6th. The Sturmey's range is also usefully wider than that of the Nexus.

If you don't want to cold set your Brompton's rear triangle then you are pretty much going to have to use the Sturmey. I managed to reduce the width of my 120mm OLN one by removing one of the left hand locknuts (I was assured by the dealer, a Sturmey specialist, that that would be OK) and grinding down the other one a few more mm. It still works!

As an alternative, I have a Brompton S6L which uses the BWR hub plus a 2-speed dérailleur - this gives pretty much the same gearing as the middle six gears of the Sturmey hub, with the same spacing. The combination is a lot lighter, the only complication is double shifting to get the gears in sequence. But I grew up with half step gearing so that's second nature for me! Overall it feels a lot more efficient too, and you get two direct drive gears instead of just the one.