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Old 09-05-07, 10:02 AM   #1
colonelclink4
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Brompton Gearing Upgrade

I know this has been discussed once in the past. But I feel a need to bring it up again. Yes, I'm new. Hi.
I'm planning to buy a Brompton in the near future but I really want the versatility of having a greater selection of gears.
Here's what I'm proposing.

Can I replace the 3 speed hub with an 8 speed hub? I'm looking at buying a used L3 and it's got a 3 speed SRAM hub.

I guess the big question is about spacing. Can it be done? If not, what alternatives are there?

Schlumf looks like a last resort.
Rohloff is stupid expensive.

I read somewhere that Merc has an 8 speed version. I may be interested in that, but I can't find one anywhere online.

I want a folder with the compactness of a Brompton and the versatility of an 8 speed hub.

Help!
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Old 09-05-07, 02:30 PM   #2
LittlePixel
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Hi - welcome to the forums!

One thing you could do is retrofit a Brompton 2-speed rear derailleur to double up the hub's gears.

I think most 'off the shelf hubs' like the SRAM s7, nexus, SA 8 et al have a wider OLN spacing [ie need wider dropouts] making fitting them to a Brompton rear triangle nye-on prohibitive unless you know someone with a blowtorch that can make the necessary mods to the rear to accept the wider axle.

A lot of Brompton users double up their gears with a Steve Parry front derailleur install, which is probably a cheaper option than the Schlumpf Mountain or Speed drive, One can also consider the 'quick-and-dirty-ghetto option' of fitting a double chainring up front but no shifter, and then just getting oily fingers switching cogs manually when a different combo is needed for a big hill or whatever.

I do believe there are people who will do a Rohloff conversion though like you say - prohibitively costly to mere mortals.

EvilV on this forum has an SP derailleur - hopefully he'll chime in on this thread but you might want to search his posts to find out more about the mod.

Hope that's some help. Probably throws up more questions than answers, but 'them's the breaks'
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Old 09-05-07, 02:53 PM   #3
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I'm sure the 5 speed Sturmey Archer hub below will fit, as it was previously used on the T series of Bromptons. There seems to be a new one going cheaply below if you act quickly. A 5 speed would give you ample range. Could be a real bargain modification:

http://cgi.ebay.co.uk/ws/eBayISAPI.d...tchlink:top:uk
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Old 09-05-07, 05:26 PM   #4
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Hi

This link shows the work required to fit a Nexus 8 speed.
http://www.atob.org.uk/44/epage2.htm

The Schlumf drive seems to be very good but is expensive and may be difficult to repair.
The Roloff is even more expensive and difficult to install.
There is plenty of information on the Yahoo - Bromptontalk group.

The five speed mentioned would be worth investigating.

Edd
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Old 09-07-07, 03:02 PM   #5
EvilV
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Quote:
Originally Posted by colonelclink4 View Post
I know this has been discussed once in the past. But I feel a need to bring it up again. Yes, I'm new. Hi.
I'm planning to buy a Brompton in the near future but I really want the versatility of having a greater selection of gears.
Here's what I'm proposing.

Can I replace the 3 speed hub with an 8 speed hub? I'm looking at buying a used L3 and it's got a 3 speed SRAM hub.

I guess the big question is about spacing. Can it be done? If not, what alternatives are there?

Schlumf looks like a last resort.
Rohloff is stupid expensive.

I read somewhere that Merc has an 8 speed version. I may be interested in that, but I can't find one anywhere online.

I want a folder with the compactness of a Brompton and the versatility of an 8 speed hub.

Help!
Hi.

Sorry I've been away for a few days.

The 7 speed Merc is not in the UK yet. Sorry Colonelclink - I don't know where you are. Merc are imported and rebadged bikes made in Taiwan by a company called Grace Gallant - http://www.flamingobike.com/products...p?pid=56&cid=3

The UK importer will not be getting a new container until the original stock is sold I suppose. The currently available bikes are all 3 speed SRF-3 equipped. As Little_Pixel said, I have fitted a front mech and twin chainwheels. This works pretty well. I bought a front deraillier mounting clamp from a guy on the Brompton Talk Yahoo email list for 40 with a cheap front mech and lever thrown in. It went straight on and works great. I have a 52 / 39 front sprocket arrangement, which basically gives me 6 gears, only four of which are unique. It works like this:

53 tooth chainwheel gives 81, 61, 45 gear inches.

39 tooth chainwheel gives around a 25% reduction allowing the following ranges:

60, 45, 35 gear inches.

Clearly the top two gears of the second range are almost exactly the same as the bottom two of the top range. In effect, I get to drop down on steep hills to a useable climbing gear. The range works well for me in practice, and this solution is quite cheap.

I'm not sure about what implications there would be in retro fitting the 7 speed nexus. All kinds of issues might crop up like the spread of the rear triangle and the fact that the changing mechanism is I think on different sides.

See here for a photo of the conversion:

front shifter idea

Last edited by EvilV; 09-08-07 at 01:53 AM.
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Old 09-07-07, 04:11 PM   #6
invisiblehand
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Quote:
Originally Posted by Edd View Post
Hi

This link shows the work required to fit a Nexus 8 speed.
http://www.atob.org.uk/44/epage2.htm

The Schlumf drive seems to be very good but is expensive and may be difficult to repair.
The Roloff is even more expensive and difficult to install.
There is plenty of information on the Yahoo - Bromptontalk group.

The five speed mentioned would be worth investigating.

Edd
Hmmmm, too much work for me.

-G
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Old 09-07-07, 04:12 PM   #7
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Quote:
Originally Posted by Edd View Post
Hi

This link shows the work required to fit a Nexus 8 speed.
http://www.atob.org.uk/44/epage2.htm

The Schlumf drive seems to be very good but is expensive and may be difficult to repair.
The Roloff is even more expensive and difficult to install.
There is plenty of information on the Yahoo - Bromptontalk group.

The five speed mentioned would be worth investigating.

Edd
How hard is it to spread a Brompton's rear drop outs?
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Old 09-07-07, 07:47 PM   #8
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Invisiblehand I don't know.
The frame spreader described looks like a good way of doing it.
When I spread my Moulton for a Sram Dual Drive hub I used a vice and manual force and 'eyeballed' it!
Turned out perfectly. I sure the method described would be much more accurate.

Edd
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Old 09-12-07, 09:01 AM   #9
colonelclink4
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I recently called Sturmey Archer. I found out the spacing differences for their 8 speed XRF8.
The hub's spacing is 115mm. The brompton frame ranges between 109mm and 112mm depending on the year and model.
However, I just thought of a SNAFU. The hub requires either a 25 or a 23 tooth cog. That would probably interfere with the chain tensioner. There are other chain tensioners on the market though right? Anyone ever tried this before?
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Old 09-12-07, 10:37 AM   #10
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Quote:
Originally Posted by colonelclink4 View Post
I recently called Sturmey Archer. I found out the spacing differences for their 8 speed XRF8.
The hub's spacing is 115mm. The brompton frame ranges between 109mm and 112mm depending on the year and model.
However, I just thought of a SNAFU. The hub requires either a 25 or a 23 tooth cog. That would probably interfere with the chain tensioner. There are other chain tensioners on the market though right? Anyone ever tried this before?
My recollection is that the chain tensioner is not the issue with the XRF8; although I believe you are on the right track. The problem is that the smallest cog that can fit on the hub has 19 teeth. The largest cog that can fit in the present configuration of the rear triangle is 17 teeth.

Now that I think about it, my memory is bad enough such that it might be the tensioner; but I recall that the chain would have to go through one of the stays if the cog were bigger than 17 teeth. The guys and gals at BromptonTalk discussed this issue at length some time back.

-G

EDIT: You can get the 19 tooth cogs at the Harris Cyclery among other online shops. You can also get the cogs for 1/8" and 3/32" chains as well in all three sizes ... 19, 23, and 25.
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