Roegmann

I got a chance to get an 2012 3-spd Brommie for $600 or a 2015 6-spd with the -12% gearing for $1000.

I was thinking of getting the 3-spd and converting it to a Shimano 8-spd IGH. My efforts to find a Southern California mechanic who will do this have not been successful. Anyone “know a guy”, or am I being silly and stick with the 6-spd? I’ve read many a thread that loved their mod.

I do a lot of commuting with luggage (no so much touring; I plan to get a BF Llama for that).

bargainguy

Are you talking about an 8-speed Alfine hub? That one has a OLD of 135mm, whereas your nominal Brompton OLD is 112mm. So custom spreading of rear triangle, or buy a kit that already has a new rear triangle like the Kinetics below, tho won't be cheap.

Brompton Alfine Kits ? Kinetics

Probably the most cost effective way is to get a multispeed hub that nearly matches your Brommie OLD (no rear triangle spreading required), like a five-speed S/A S-RF5 with 111mm OLD, hub only at $125:

Sturmey Archer S-RF5|-Brommieplus-Products

...and have a wheel built around it and then installed (or buy one from brommieplus already built up but more $).

Yes, I agree you've got to find someone who knows what they're doing, as there might need to be modification to the cable routing to accommodate the Brommie fold. It wouldn't necessarily have to be a folding bike mechanic, just a mechanic who knows enough to allow for routing the cables to accommodate the fold.

1nterceptor

Test ride the 6 speed; see if it has enough range. If it does; the $400 difference will be worth it. How much does the 8 speed conversion cost?
After 2013; Brompton went from 1 piece crank arm/chainring to spider crank - standard 130 BCD ring. Makes it easier to change gearing; just
swap rings. If you don't mind losing the guard/protector; can buy aftermarket ring at any shop.

Brompton's luggage system(also the fenders); make them excellent commuters. Plenty of front bag options; colors, designs, materials, etc.
I'm using a Demano messenger bag that's waterproof by itself. Can fit a 17inch laptop. Has side pockets on both sides; can hold waterbottles:
Large pizza; tiny bike - challenge accepted by 1nterceptor, on Flickr

Roegmann

From what I’ve gleaned it is an improvement over the older ones. I’ve accepted that the mod will not be cheap. I was using the “cheaper” 3-spd to off set some of the cost. I have a Downtube Mini and like the IGH flexibility.

If I got the 6-spd, I’d probably use the Kinetics kit to upgrade it to s 9spd, albeit without the IGH flexibility.

berlinonaut

I'd personally avoid the 3-speed as it has the weight of the 6-speed in combination with a gear-range not much more than the two-speed: the worst of both worlds. Also 2013 brought changes that were useful: better rims, JIS bottom bracket with interchangable chainwheel, better brake-levers. So the more expensive one would be clearly worth a higher price for me. 1000$ for a 2015 6-speed seems to be a fair price but I do not know the US-market and it depends on if it has a light or rack and if the bars are the version of your choice.

If you want to convert the bike to 8-speed you have the choice between the S/A XRF8w, the Shimano Nexus, the Nexus premium and the Alfine-8. Any of these conversions adds about 1kg on top of the weight of a 6-speed and offer about the same gear-range as the 6-speed (the S/A slightly more) but with finer steps (as they have two more gears within the same range). The main advantage is a more comfortable way of shifting. If you have to carry your bike a lot it is worth thinking about if this is worth a kilogram of weight.

The XRF8w can be brought down to about 112mm OLD, thus no need to modify the rear frame. You have to modify the chain-tensioner a bit but this is not really difficult. The Alfine-8 needs 135mm and can AFAIK not be brought to a lower old. Therefor I'd avoid it - it does not offer an advantage over the Nexus Premium but you'd either have to spread the rear-frame massively or to exchange the rear frame and in this case you can go for the rohloff or an alfine-11.

The two Nexus-models can be brought down to about 123mm OLD, spreading of the rear frame is necessary but within reasonable limits. Still a non reversible modification. The Nexus premium is of higher quality than the Nexus, so the choice between the two is a no brainer. The hub has to be modified including the cog has to be made a bit slimmer. The modification can be done at home but you'll need skills and a bit of trial and error.

So from the "do it yourself"-perspective the Xrf-8 seems the most attractive option, the more as you simply can buy a kit a kinetics/Ben Cooper. However: I own two XRF8w and would not recommend it in comparison to the Nexus 8 premium for a number of reasons - I have outlined them recently in another thread here in the forum.
The five-gear SRF5w seems attractive, too and I know someone who is really happy with it. Weightwise in the same ballpark as the 6-speed but with a single shifter. Too bad it has huge gear steps and a smaller range - basically it is a 3-speed with 2 more gears.

rangewise:

133% 2-speed
176% 3-speed
256% 5-speed S/A SRF5w
302% 6-speed BWR
306% 8-speed Shimano
325% 8-speed S/A XRF8w

I did not like the XRF8w for various reasons and did not like the 8-speed shimano for weight, price and modification of the rear-frame. The 6-speed has huge gear steps. Too bad. My solution was to modify the BWR to 9-speed. 44-chainwheel and cogs of 12-14-16 offer a range of 327% in steps of 14-18% while weightwise still being in the ballpark of the 6-speed. For me the best compromise and I can recommend it. Cost of the modification was about 70 Euros. The 6-speed with the lower -12%-gearing would be the perfect starting point for this mod. Here is a playground to compare gear-variants: Bicycle Gear Calculator

2_i 

Could you provide any more details? I have no idea what is the needed standard for the cogs - have not looked there ever yet. What spacers are you using? What shifter? A thinner chain? Thanks.

fietsbob

Newer SA 4 speed has more potential, as I read the specs 28 hole hub shell takes the classic AW cog 13t , and is 120 OLD..

I have a BSR 3 speed 54: 15, added a 2 speed geared crankset 3 low range gears run though a reduction gear
between the pedals and the chainring

so pedals turn 2.5x faster.. my 54t acts like a 21.6t [50, 20 is even numbers, if you prefer]

berlinonaut

It is not much rocket science involved. I used cogs from a shimano cassette (in my case a Shimano CS-HG500-10/11-32) and the stock spacer from the 6-speed. The small 12-teeth cog has a built in spacer. You have to dremel on the 12-teeth a bit to make the ring that keeps the cogs in place fit. I'd recommend to use a donor-cassette with the smallest cog being smaller than 12 as the smallest cog will look a bit different and will probably not survive for long when being dremeled to the necessary amount. Any shimano-derailleur cog will physicaly fit the BWR-freewheel so you have quite a bit of choice. The setup with 12-14-16 on the BWR in combination with the 44 chainwheel offered the best shifting steps for my taste but your mileage may vary.

The derailleur has to go a tiny bit further outside so i cut an old credit-card to form (2 layers are perfect) to fit into the derailleur on top of the first axle nut and act as a spacer - my very own form of credit-card-supported touring. Shifterwise I am using an S/A SL-S30 3-speed thumbshifter on the right and a optically identical Sunrace M90 friction thumb-shifter on the left. I like these better than the stock shifters - but you can use those too: 3-speed hub shifter obviously does not need to be touched, 2-speed needs a 3rd position in the middle to be cut at the inside part of the shifter - you have to figure out the correct postition for this.
To make the shifting work you have to adjust the little screws on the derailleur that limit it's end position as you would with any derailleur.

And I am running a 10-speed chain as the cogs came from a 10-speed casette. Possibly a 9-speed cassette and/or chain will work as well and safe on cost. So in the end for me cost was ~25 € for the cassette, ~20€ for the chain and ~25€ for the shifters, the latter are not even necessary. The whole mod took about 1,5 hours.

Before and after:



Shifter







inside the original 2-speed shifter, not yet cut a 3rd position



cassette





cogs mounted



You can see the spacer between frame and derailleur in this picture - at this point in time it was not made from a credit card but a perfectly made aluminium spacer that came with the Xrf8w kit i bought from tillercycles in the uk. I had to replace it as I refitted the 8-speed to another Brompton and needed it for that purpose. Also the 12-teeth has been dremeled a bit more intensively in the meantime to make the ring fit more solidly - no trouble at all with the shifting.

2_i 

Wow, thanks for all the details. In the meantime I also found a pdf on the conversion here. At first, though, I thought that the conversion increased the gear range, but now I see that this is to reduce gear spacing. Right?

I sort of can live with the gear spacing on a 6-speed but my concern is in the low gears. Some places I might take the Brompton to have tough long ascents. At the same time I don't want to lose the pleasure of overtaking racers on road bikes while riding a loaded Brompton. Yes, after they wake up the Nature usually goes back to normal but then I already saw the look on their face .

I have tons of cogs and spacers so am half way there, but with the gear range, I should presumably start with a second chainring. Even for this, I must first cope with at least some of the backlog in the projects...

P.S. There some Ti Parts Workshop conversion kit floating around for some incredible amount of $$$

Roegmann

Thank you berlinonaut. The 6speed comes with the dynamo light and Brompton front bag also, so it really is a deal. As for the hub, I'm leaning towards your BWR fix or the Nexus Premium.

12boy

Interesting question. If you have a 110 or 130 bcd crank set it is fairly easy to add a second chainring , say 38 teeth, that you can. manually shift if needed. Chain rings at vuelta are not expensive. If I were deciding between the 3 and 6 speeds I would check the overall condition closely, particularly slop in the rea,r triangle hinge and smoothness in the headset. The Brompton 3 speeds both get above 80 gear inches which is more the issue with small wheels than getting low gears, at least for me.

reppans

Great mod belinonaut! Never read about 3 cog mod for the Brompton before. Like 2_i, I too can live with the 6 speed spacing (although that 9 spacing looks awesome) but find I need lower gearing if caught in the mountains, esp with touring gear weight. My 44T 88" top gear is fine for me on this bike, don't mind coasting faster downhills and >30mph gets scary on the small wheels anyways.

I'd be happy with a plug-n-play/bolt-on smaller chainring w/manual finger derailleur, but there's not enough clearance when folded.... looks like you have to widen the bottom bracket some.

Anyone do this with a late model B.... and with the new bottom bracket (post recall)?

1nterceptor

Big thanks to @berlinonaut for the comprehensive explanation/comparison of possible gearing. I'm aware of the 3 cog mod for a while. Been contemplating this to my 6 speed titanium; less range but also less weight(getting rid of BWR hub).

Did a simple ring swap many years ago 44T to 39T:
Catching a few roadies by surprise on the flats & hills.

reppans

Thanks, yes I know that's an option but one that forfeits the higher ratios. The -12% 6spd ratios work quite well for the vast majority of my riding - think I really only need one additional lower gear.

1nterceptor

Then you should consider the 3rd cog modification. Say you get 12, 14, then 17/18. I think the max is 19.
Going bigger than 16 will require some shaving of the rear triangle. Won't affect it's integrity/safety. You'll
still have your hi; 12T. But increase your low range 17, 18, 19.

reppans

Yes, that's what I was originally think too.... however, once you get off that nice even 16/14/12 ratio, going over 16T on one cog will then shift 4th and 7th gear too close to, if not overlapping, 3rd and 6th gears, and then similarly leave large gaps to 5th and 8th.

Just guessing, but 18/15/12 sounds like it will similarly run foul of the IGH ratios too.

Askar

Berlinonaut
I understand you've modified the old 2 speed shifter. Please advice. How to install cable to new Sunrace 3 speed shifter?

fietsbob

tricky thing is the head of the gear cable is at the back where the shifter is,
and so you need to create another head at the end that is cut off ...

Perhaps seek one fixed with a set screw?

berlinonaut

For the derailleur shifter on the left side: I did not modify it. Just use any ordinary gear cable for the Sunrade Version. The trick ist to use the dogleg of the Bromptons made from 2017 on as on those the shifter cable is mounted the "right way round" and clamped on the dogleg (in opposite to the version used until 2016). The dogleg part of the shifting is cheap - less then 6 € if I remember correctly. Before the 2017 dogleg existed I used a screwable fitting intended for motorbikes on the front of the derailleur cable - worked as well, was dead cheap but a bit ugly to look at.

For the 3-speed shifter (on the right side): Just any ordinary shifter cable will fit. No issues at all. Do not get the question regarding the 3-speed shifter.

berlinonaut

It is no issue at all. Why do you claim to be able to give advice on something that you have never done and obviously do not have a clue about as well?

fietsbob

how do you make a double ended cable? smart arse..

show your work.






...

berlinonaut

Well - look at post 8 in this very thread. Possibly that's why Askar asked me by my name to answer his question. But as you obviously again did not bother to read the threads that you are posting to you could obviously not recognize that. Maybe you are just too dumb, too. Otherwise you would know that their is no need for a "double-ended" cable and I explained why in this very thread. As you do not know that I am wondering even more what gives you the feeling to be competent to give any advice in this thread....

Schwinnsta

Is the Sunrace M90 a 3-speed friction shifter?

Thanks

berlinonaut

It is a friction shifter. That means by definition you can shift as many gears as you like or are able to with the given amount of cable pull.

Schwinnsta

Understood, but they sell the two shifters that look like yours but one is multi speed rear cassette, 9 speed friction in this case but they also sell a 3-speed friction shifter here. So I think they pull different amounts and I was not sure if the 3-speed would work.
thanks