Modding a Brompton B75

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Tenkaykev

Guru
Location
Poole
As you can see from the pictures of the B75 it is the old M-stem in conjunction with the old M bars.

Just to clarify my earlier post, I have the old style (2015) M stem with old style M bars.

JK does the old style M bars, but wider. I swapped the original bars for the JK ones, and with a bit of trimming, a little at a time, was able to fit 130mm Ergon grips.

If you don't mind a bit of assymetry you can leave the right hand side of the bar longer for extra hardware space.
 
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DBrown67

Well-Known Member
Well so far so good... now for the gearing. I've decided I want a 6 speed. Obviously the B75 only comes with 3 speed (-12%).

I rang a Brompton Junction shop (thought they'd be best placed) to ask if they could sell a B75 with 6 speed conversion as an "official" dealer done mod. They said yes and confirmed it would be around £100 to do it. They keep the original parts removed of course. But I'd get the 6 speed upgrade (-12%) with the colour I want for around £845. Sounds very reasonable to me. Saves all the messing of trying to fit a kit myself.

But would you trust a local Halfords to do this job? (for -10% British Cycling discount) I'm in Leeds and Brompton Junction in London is too far to go in person. I'd assume their deal to modify the bike would be somewhat similar.

If that deal is right I'm definitely not messing with double chain rings etc.etc.
 
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Pale Rider

Legendary Member
But would you trust a local Halfords to do this job?

No.

Putting a second sprocket on the back and routing the cable is a job for someone with experience of working on a Brompton.

Halford's mechanics are generally poor, and even if the ones in your local branch are not, they will have little knowledge of Brompton having only recently taken on the brand.

Is there not an independent dealer in Leeds?
 
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DBrown67

Well-Known Member
No.

Putting a second sprocket on the back and routing the cable is a job for someone with experience of working on a Brompton.

Halford's mechanics are generally poor, and even if the ones in your local branch are not, they will have little knowledge of Brompton having only recently taken on the brand.

Is there not an independent dealer in Leeds?

Well I was kinda thinking like you to be fair. It might be worth foregoing the discount and just getting it from Brompton Junction and having it couriered to me. They work on them day in day out.

"Dealers" in Leeds are going to be the likes of Halfords, Evans and Cycle Republic.
 

Pale Rider

Legendary Member
Well I was kinda thinking like you to be fair. It might be worth foregoing the discount and just getting it from Brompton Junction and having it couriered to me. They work on them day in day out.

"Dealers" in Leeds are going to be the likes of Halfords, Evans and Cycle Republic.

Will the London dealer courier the bike?

Brompton are a bit funny about protecting dealer's patches.

That's why on the Evans site it says 'in store collection only' for Bromptons.

If it has to be one of the chain (ho-ho) dealers, Evans has been selling Bromptons for years so there's a chance the Leeds branch has someone who knows what they are doing with them.
 

Kell

Veteran
Simply putting a second sprocket on a 3-spd doesn't give you the same range as a 6-speed though.

£100 doesn't sound too bad to have it done at the outset TBH.

I know they get to keep your parts, but a BWR hub on its own is £150. Plus the sprockets, and your time.
 

Nibor

Bewildered
Location
Accrington
You could seee if Blazing saddles at Hebden Bridge could do it they are only an hour away and a great Brompton dealer.
 
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DBrown67

Well-Known Member
I noticed two of you mentioned putting a second sprocket on the back. This conversion would need the entire hub/wheel replacing for the BWR so the sprockets should be fine? That's why I thought the conversion price was so reasonable. Maybe I'm confusing what you guys meant.

EDIT: Confirmed. I'd have to collect the bike from Brompton Junction in person. For a folding bike in 2019 I find this policy pretty ridiculous. So I'd need somewhere local. I think Cycle Republic might be best or try that shop in Hebden Bridge.
 
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berlinonaut

Veteran
Location
Berlin Germany
I noticed two of you mentioned putting a second sprocket on the back. This conversion would need the entire hub/wheel replacing for the BWR so the sprockets should be fine?
And you were right about the need to replace the whole hub/wheel. 100£ for the upgrade aftermarket sound absolutely fair, given the cost of the parts let alone the labor time and the price difference on a new bike would already be 85£ according to Bromton's bike builder.
 

Pale Rider

Legendary Member
Is the three speed hub different to the three speed hub - used with two sprockets - on the six speed?

I appreciate the shop is getting the 'old' bits, but I'm surprised they would replace the hub, sprockets, and add the extra gear changer for £100.
 

rualexander

Legendary Member
Is the three speed hub different to the three speed hub - used with two sprockets - on the six speed?

Yes, the 3 speed Brompton uses the Sturmey Archer BSR (Brompton standard ratio) hub and the 6 speed uses the Sturmey Archer BWR (Bromton wide ratio) hub.
The hub driver is different on the two hubs too, with the 6 speed having the splined driver to take two sprockets.
 

Kell

Veteran
I must admit, I didn't realise the hub driver was different, but as mentioned above, the 3-spd hub has a much narrower spread of gears.

Compared to the standard 3-spd, the standard 6-spd has two gears below and one gear higher. I've had the chain pusher fail on mine before and only had 1st, 3rd and 5th gears and they were comically far apart.
 
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