Talk to me about Brompton gear upgrades ...

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CopperBrompton

CopperBrompton

Bicycle: a means of transport between cake-stops
Location
London
Ok, tried with the 60 and that looks like a good range, but I think I'm missing something about how this works ...

I start in MD and go through gears 1, 2, 3. To get gear 4, I surely have to press for DD *and* go back to gear 1 on the lever to get gear 4? It's that double-shifting that's my objection to the standard Brompton 6-speed.
 

Rohloff_Brompton_Rider

Formerly just_fixed
Ah ok fair enough, I've come from a Brompton M6L with speed drive so it's lot lot easier for me.

I see what you want now....the 8 speed sturmey is the cheapest modern kit but the old 5 speed might do you?
 
OP
OP
CopperBrompton

CopperBrompton

Bicycle: a means of transport between cake-stops
Location
London
Yeah, I have actually owned the 5-speed in the past (not a deliberate selection, just a very good secondhand price) and that was a decent range, so that would be another option if it's easily available as a conversion?
 

T4tomo

Guru
Ok, tried with the 60 and that looks like a good range, but I think I'm missing something about how this works ...

I start in MD and go through gears 1, 2, 3. To get gear 4, I surely have to press for DD *and* go back to gear 1 on the lever to get gear 4? It's that double-shifting that's my objection to the standard Brompton 6-speed.

It's one double shift in the range as opposed to standard 6 speed where every shift is a double shift - odd gears on one cog and even on another. It basically fills in the jumps in the 3 speed range and adds one gear higher or lower depending on what sprocket you were running on your 3 speed.

I briefly looked at the SA 8 speed hubs - if you go that route make sure you get a kit with a smaller chainring, otherwise you end up with a crazily high geared range.
 
OP
OP
CopperBrompton

CopperBrompton

Bicycle: a means of transport between cake-stops
Location
London
Thanks. Comparing what I have to what I want:

- Want one gear lower than 1st
1st
- Want a gear between 1st and 2nd
2nd
3rd
- Want at least one higher gear
- Ideally two

Based on that, what chainring would you recommend with the 8-speed SA?
 

T4tomo

Guru
No idea as you haven't said what size chain ring and sprocket you currently run. :smile:

The hub gear calculator linked to half way up page 1 of this thread will tell you, just pump thenumbers in there. Kinetics in Glasgow seemed to do a sensible sized sprocket, although anecdotally his service can be haphazard timewise when he is busy.

Also double check the 5 speed hub, that might give you what you want for cheaper with or without a change of sprocket.
 
OP
OP
CopperBrompton

CopperBrompton

Bicycle: a means of transport between cake-stops
Location
London
Ah, didn't realise there was more than one standard setup with the M3L. I am not mechanical. :-)

I shall investigate when I'm next home.
 
OP
OP
CopperBrompton

CopperBrompton

Bicycle: a means of transport between cake-stops
Location
London
Ok, so I have the 50-tooth chainring. Can't see an easy way to count the rear sprocket teeth but as the bike is standard, I assume it's 13-inch. That means I currently have:
47.7​
63.7​
84.7​

I now see what you mean about the SA-8, as with the same chainring that would give me
63.9​
83.0​
94.5​
107.9​
122.6​
140.5​
159.7​
207.6​
which would be just a little silly. :-) Even with a 44-inch chainring, it would start at 56", and only gets sensible with a 44-inch chainring and 20-inch cog - is that even possible?

The 5-speed actually looks the most sensible way to do it:
42.4​
50.3​
63.7​
80.8​
95.5​

I assume any Brompton dealer could quote me a price for an upgrade from SA 3-speed to 5-speed?
 

rualexander

Legendary Member
No, sorry I don't know which if any of the current models were used by Brompton.
Best bet for an upgrade would be the x-rf5(w) which according to Sheldon Brown's gear calculator gives a range of 25 to 64 gear inches, using a 50 tooth chainring and a 20 tooth sprocket.
The 119mm over locknut version would probably be the one to fit a Brompton.
 
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