Making a fairly old (c15 years) 6-speed Brompton easier on hills

[Tenkaykev]

Btw: The sprocket-set for the SRAM is no longer avail. from Brompton for some time already. No issues to get a single 13t as this is used on the 3-speed as well. Getting a 15t can become a bit of a task and you won't get it from Brompton apart from maybe a longterm Brompton shop that has old stock. As it is an ordinary 3-spline sprocket there are other sources, namely Sturmey Archer but you should check thickness and form of the sprocket if it fits what is needed. If you lack an oldschool Brompton dealership SJS can be a source as can - as others mentioned - SPA be for chainrings and chainsets. Tillercycles has been out of business already for a while but Graham handed over at least the chainring side of his business to another small shop and I remember the webpage used to be forwarded to this shop. This is no longer the case but this is the shop in question: https://www.brommiemods.co.uk/

Brommiemods we’re outstandingly good when I modded Mrs Tenkaykev’s and my own Brommies. Highly recommended 👍

 

[Mr_T_Wales]

Btw: The sprocket-set for the SRAM is no longer avail. from Brompton for some time already. No issues to get a single 13t as this is used on the 3-speed as well. Getting a 15t can become a bit of a task and you won't get it from Brompton apart from maybe a longterm Brompton shop that has old stock. As it is an ordinary 3-spline sprocket there are other sources, namely Sturmey Archer but you should check thickness and form of the sprocket if it fits what is needed. If you lack an oldschool Brompton dealership SJS can be a source as can - as others mentioned - SPA be for chainrings and chainsets. Tillercycles has been out of business already for a while but Graham handed over at least the chainring side of his business to another small shop and I remember the webpage used to be forwarded to this shop. This is no longer the case but this is the shop in question: https://www.brommiemods.co.uk/

Thanks, I did notice than when I searched for the sprocket set I had on the Brilliant Bikes site it didn't come up with anything. Honestly, I didn't expect it to be simple (or cheap) but it's more complicated than I thought!

Ebay does seem to have 3-spline options - eg

https://www.ebay.co.uk/itm/261101251168?hash=item3ccad8ea60:g:qoIAAMXQn11RbN1o

but some of them seem to have a ridge and I think the Brompton ones are flat.

If I'm not sure that 44T is enough of a change (from 50T) then I'm starting to think that this is the best option as I could leave the sprocket alone, as I think they are in good shape. I guess I'd need to change at some point if things start slipping and at that point I could consider slightly bigger ones perhaps.

https://www.bike-discount.de/en/buy/shimano-alfine-fc-s501-crank-with-single-chainguard-1080150

 

[T4tomo]

If I'm not sure that 44T is enough of a change (from 50T) then I'm starting to think that this is the best option as I could leave the sprocket alone, as I think they are in good shape. I guess I'd need to change at some point if things start slipping and at that point I could consider slightly bigger ones perhaps.

that's step1 anyway, and then see how you get on. if its still a tad high, then you are only really looking for either say a 16T to replace the 15T, running 13/16 or maybe a 17T and run with 15/17 at the back, utilising your existing 15 in the outward position.
the SRAM compatible sprockets are 3mm 3 spline I think (but check your existing ones)

I also don't think that little ridge on the ebay ones bothers you in the slightest, its just decorative.

 

[Mr_T_Wales]

Thanks, the ridge thing just made me think that it's not flat so it may impact how it sits. I've have to get the bike out and snoop around.

The main thing for me is whether the set below should work (possible with some grinding if I want a 100% folding pedal). There is a 39T option and then I can go lower eventually potentially next time I need to replace the back sprockets.

https://www.bike-discount.de/en/buy/shimano-alfine-fc-s501-crank-with-single-chainguard-1080150

 

[TheDoctor]

Surely the easiest option is just to get a Stronglight ST55 chainset? Fit the crank with chain wheel, leave the existing left hand crank alone, and all is good.

 

[Kendide]

Btw: The sprocket-set for the SRAM is no longer avail. from Brompton for some time already. No issues to get a single 13t as this is used on the 3-speed as well. Getting a 15t can become a bit of a task and you won't get it from Brompton apart from maybe a longterm Brompton shop that has old stock. As it is an ordinary 3-spline sprocket there are other sources, namely Sturmey Archer but you should check thickness and form of the sprocket if it fits what is needed. If you lack an oldschool Brompton dealership SJS can be a source as can - as others mentioned - SPA be for chainrings and chainsets. Tillercycles has been out of business already for a while but Graham handed over at least the chainring side of his business to another small shop and I remember the webpage used to be forwarded to this shop. This is no longer the case but this is the shop in question: https://www.brommiemods.co.uk/

Would it be possible to grind off 6 of the splines on the current 6 gear SA sprockets to fit the SRAM hub?
I recall doing something similar to sprockets from Shimano freewheels to fit SA 3 speeds on vintage Moultons with success. I used the spacers off the freewheel as well. I think they had to be reduced in thickness by rubbing on sandpaper.

 

[Mr_T_Wales]

Surely the easiest option is just to get a Stronglight ST55 chainset? Fit the crank with chain wheel, leave the existing left hand crank alone, and all is good.

I did see that but I think I'd need to change the bottom bracket thing, and if so then could I keep the left crank? I could be way off there though.

Another thing is that there is no chainguard and I'd like a fixed strong one. The plastic one I have now is always a bit flakey.

 

[T4tomo]

Thanks, the ridge thing just made me think that it's not flat so it may impact how it sits. I've have to get the bike out and snoop around.

The main thing for me is whether the set below should work (possible with some grinding if I want a 100% folding pedal). There is a 39T option and then I can go lower eventually potentially next time I need to replace the back sprockets.

https://www.bike-discount.de/en/buy/shimano-alfine-fc-s501-crank-with-single-chainguard-1080150

someone which more knowledge that me i.e one of the brompton modders, needs to answer this:

will a hollowtech II BB with external cups work fine on a brommie?​

​

It may throw the chainline out of wonk or interfere with the fold​

​

 

[berlinonaut]

will a hollowtech II BB with external cups work fine on a brommie?

Yes it will. Obviously you'll need the right kind - it must be BSA threaded 68mm. And depending from the chainset you may need to fiddle with spacers or not. Just converted a Brommi to Hollowtech recently and much to my surprise everything worked flawlessy out of the box w/o need for spacers or anything - but your mileage may vary massively and in many cases it will.

 

[berlinonaut]

Would it be possible to grind off 6 of the splines on the current 6 gear SA sprockets to fit the SRAM hub?
I recall doing something similar to sprockets from Shimano freewheels to fit SA 3 speeds on vintage Moultons with success. I used the spacers off the freewheel as well. I think they had to be reduced in thickness by rubbing on sandpaper.

I've heard of things like that have been done but don't have any own experience. As far as I know the drivers of S/A 3, S/A Sprinter and SRAM 3 are identical in terms of what sprocket fits the driver, so if it worked there it will probably work anywhere, to quote Frank Sinatra (which I never expected to do in a folding bike forum ).

 

[Mr_T_Wales]

Right, I've ordered a 39T crankarm/chainring set that comes with a JIS bottom bracket. I need to get a tool or two I think, and reduce the chain size (by 4 links I think as I'm going from 50T to 39T).

I'll report back with how it goes. I'm guessing not too well but I'm crossing everything!

 

[u_i]

Right, I've ordered a 39T crankarm/chainring set that comes with a JIS bottom bracket. I need to get a tool or two I think, and reduce the chain size (by 4 links I think as I'm going from 50T to 39T).

I'll report back with how it goes. I'm guessing not too well but I'm crossing everything!

I do not think that you actually need to shorten the chain. The Brompton tensioner has an astounding capacity. Obviously, you may want to shorten just because you can.

 

[Mr_T_Wales]

I do not think that you actually need to shorten the chain. The Brompton tensioner has an astounding capacity. Obviously, you may want to shorten just because you can.

It seems like going from 50T to 39T is a lot though? I did Google this and people have gone from 44T to 39T, or something like this, and left the chain alone and it seemed OK. One guy did this but when the bike was serviced they recommended shortening the chain.

I did order a very cheap chain tool for this and if it seems like it will work I will shorten, but maybe in stages just to be sure.

I'll just be happy if I can get the damn thing to work so I don't need to take a bike in pieces to a bike shop.

I'll add that I've had issues with the tensioner before. I can't recall what as it was a while ago but I think it was getting the right tightening or something so anything that helps me not having to worry about that is a good thing for me

 

[u_i]

I have a front derailleur on Brompton and go from 50 to 20T and the Brompton's tensioner swallows it. Is it ideal? No, actually the chain is a bit loose when I fold with the chain on 20T. However, you do not even want to go half of this way. I normally try to make minimal changes and see where things are going and leave myself as much retreat route as possible. After I settle in a new place and feel that it is good, I progress with the further refurnishing.

 

[Mr_T_Wales]

I have a front derailleur on Brompton and go from 50 to 20T and the Brompton's tensioner swallows it. Is it ideal? No, actually the chain is a bit loose when I fold with the chain on 20T. However, you do not even want to go half of this way. I normally try to make minimal changes and see where things are going and leave myself as much retreat route as possible. After I settle in a new place and feel that it is good, I progress with the further refurnishing.

You have a 20T cog on the front? That must be amazing for going up hills. I've not heard of anything as small as that before.