Modding a Brompton B75

[DBrown67]

To be honest it's lower gearing I really want. There's a hill near me and on the lowest gear of middle ring of my MTB I still can't get up it with electric assistance turned off. That's why 6 speed -12% really appeals to me. I believe the rear sprockets can be changed to lower it a bit further still. I definitely want a <30 gear inches for first.

For me the ideal gear set up would be setting off in 3rd or even 4th and using the 4th/5th for cruising. That way the first two at least are hill climbers. I nearly always free wheel down hills, hardly ever pedal going down. The standard 3 speed I test rode was awful for me (gear wise). 1st too high and had to get off and push up nearby hills. And I never got it in 3rd.

 

[Kell]

There are definitely lots of ways to tinker with the gearing - even within the OEM options from Brompton.

I did run the 44T chainring for about 6 months as there's a hill of a hill on my commute. I've now gone back to the standard 50T chainring upfront as the 44T might have made the hill climbing easier, but it compromised the ride everywhere else.

I've also tried the 12T/16T 2-speed sprockets to see if they would work, but it made the spacing between the gears very uneven.

Very close between 4 and 5, and then a huge gap to 6th.

For me, that is. YMMV.

 

[berlinonaut]

To be honest it's lower gearing I really want. (...) I definitely want a <30 gear inches for first.

You can go for a conversion of the BWR to nine speed like I did it to add a little bit of spread to the BWR - cheap, good and reliable:https://www.bikeforums.net/20170010-post8.html and https://www.cyclechat.net/threads/anybody-installed-a-modified-3rd-gear-to-a-bwr-hub.243473/
If you want to go really short you can fit a Schlumpf Mountain Drive.
From a short gear perspective the S/A XRF-8w would also be an option - the first is very short. However - personally I never made big friends with the hub. Now it lives in my Brecki and there it does a really good job. However, everyone's mileage and taste vary.
You can add another, smaller chainring to the front.
There are a lot of ways to Rome, cheap ones and expensive ones, each with their specific upsides and their specific downsides.

 

[chriscross1966]

100 quid for a dealer upgrade to a six-speed is an absolute steal.... if you can put up with Brompton's 6-speed system, just the derailleur system (chain pusher and tensioner, I know) is 60 quid for the parts, so charging you 40 quid for a six-speed wheel swap-out and their time, minus I guess the use to them that the old tensioner and wheel have as service parts seems OK... but.... once you've added mudguards you're up to the price of a regular M6L... which has the modern bars, shifters and more importantly, brake levers...

 

[DBrown67]

An M6L on the Brompton site in a standard colour (no extra charge) is £1170. A modded B75 with 6 speed and mudguards is £905. That's still a big saving to get the colour I actually want. That is, of course, provided the estimate given by Brompton Junction is accurate.

 

[Pale Rider]

100 quid for a dealer upgrade to a six-speed is an absolute steal.... if you can put up with Brompton's 6-speed system, just the derailleur system (chain pusher and tensioner, I know) is 60 quid for the parts, so charging you 40 quid for a six-speed wheel swap-out and their time, minus I guess the use to them that the old tensioner and wheel have as service parts seems OK... but.... once you've added mudguards you're up to the price of a regular M6L... which has the modern bars, shifters and more importantly, brake levers...

And the folding pedal, don't forget the folding pedal.

I wonder if Brompton Junction have quoted just to add an extra sprocket on the back, rather than for a new BWR hub as well.

 

[chriscross1966]

And the folding pedal, don't forget the folding pedal.

I wonder if Brompton Junction have quoted just to add an extra sprocket on the back, rather than for a new BWR hub as well.

List prices on a BWR wheel vs a BSR wheel is only 20 quid, so not exactly a huge price difference, given that a big Brompton dealer will likely replace several 3-speed rear wheels every month, so it will get used and not sit on the shelf.... that massive service tail is where the money is for the shop anyway, and a new rim and a wheel rebuild will cost you pretty much what a new wheel will, I personally would pay for the wheel rebuild but with a better rim, a lot of folks won't cos lets face it, a lot of Brompton commuters aren't "keen" owners, it's just a tool to get them to work, and to them a new part for the same price as a refurbished part is "better".....

 

[DBrown67]

Well I contacted Evans in Leeds today and they basically quoted very similar to Brompton Junction in London, at just under £900 all in for a B75 converted to 6 speed. Even better, they gave two prices because they couldn't be sure if they could retro fit the older style gear selectors as they need to fit the +/- on the left handle bar... so they quoted to fit the newer style integrated selectors/levers and that was around £950. They offered to put this is in writing if I decide to go ahead.

I also took a colour swab in with me of the two pack paint I used on my car restoration in the summer. I knew the B75 would be close, but it's difficult to judge in a shop how close. I couldn't believe it was an exact match. Not just close, but practically exact. What a coincidence! I didn't even know the B75 had been made till after I'd finished the car, yet I'd been thinking of a used Brompton, stripping it down and having it painted. Saves me a big job!

 

[ukoldschool]

It would be cheaper and better in the long run to just buy a 6 month old 6 speed and have it painted... will end up less than the £950 quoted and be a much better bike. The components on the old bromptons are really not very good

 

[ukoldschool]

https://www.ebay.co.uk/itm/Brompton-M6L-Folding-Bike/274139575893?hash=item3fd3fdf655:g:tYAAAOSwXSZd8kAm&LH_BIN=1&autorefresh=true

https://www.ebay.co.uk/itm/Brompton...sh=item2f3ac80da7:g:VN8AAOSwRiJd7LVo&LH_BIN=1

 

[DBrown67]

Not very good components? So everyone put up with poor components yet Brompton still sold loads of bikes? I don't buy that. They are incremental improvements. Doesn't mean the older parts are "poor". And this conversion is fitting the newer shifters and brake levers anyway.

And how much do you think a professional painter is going to charge to spray the 2 pack paint? (which I cannot do). Gotta be looking at around £100-£150 minimum. Plus the time to dismantle and reassemble to do the job properly... and collecting a 2nd hand bike to boot. I think I'll stick with the B75 conversion.

I don't want to sound disparaging. I value your input. It is an option I agree. But I cannot agree on the "poor parts" and the end cost.

 

[DBrown67]

To add to this I was about to place an order when I learned the shop was relocating. So I will have to look elsewhere now. But they were very helpful and gave me this list of parts for the conversion:

B75 - EV363746 - £745
6 spd wheel - QRW3SS-BWR (9025053) - £160
Chain pusher - EV211447 - £10.25
Derailleur assembly - 102995 - £25 (??? see query below)
Shifter (L/R) - QGSHIFTL2A / QGSHIFTR3A (9002832 / 9002849) - £25 / £30
Cables - QGSCAB2DR-M / QGSCAB3HUB-M (9002764 / 9002726) - £10 each
Sprockets - QRSPR13DR-SHMNO / QRSPR16DR-SHMNO (9024056 / 9024070) - £5 each
Chain - QCHAIN102DR (9022076) - £12
Labour cost - £60

Deduction - 3 speed wheel - £160 back (something I'd have to sell if I did the conversion myself)

Total with updated levers/shifters: £937.25 (pretty reasonable imo)

I don't know how familiar people on here are with part numbers etc. I just wondered if anything obvious was amiss with this list. My only query is with the "Derailleur assembly". Is this the chain tensioner? Because I know the 6 speed uses a different tensioner (QCTADR) so the one on the B75 will need swapping out, but I could not find any record of the number in the list anywhere (102995).

 

[u_i]

My only query is with the "Derailleur assembly". Is this the chain tensioner? Because I know the 6 speed uses a different tensioner (QCTADR) so the one on the B75 will need swapping out, but I could not find any record of the number in the list anywhere (102995).

This is likely the collection of pieces that connect the pusher to the shift cable. 'Assembly' is used there and the price is about right.

 

[12boy]

I think the derailleur is the chain tensioner...1 and 3 speeds jockey wheels do not move from side to side, but those with a chain pusher ( 2 and 6 speeds) have jockey wheels that move from side to side to help keep the chain inline with either the 2 sprockets. Actual derailleur have no movement in the jockey wheels as the whole thing moves. You could get credit for the old tensioner and the original chain should be fine. Seems pretty fair price wise. Anyway, the heart wants what the heart wants in terms of new vs used and paint colors.

 

[ukoldschool]

Not very good components? So everyone put up with poor components yet Brompton still sold loads of bikes? I don't buy that. They are incremental improvements. Doesn't mean the older parts are "poor".

The new components are much better than the old ones, that's why they introduced.....
The analogy of all the people that bought bromptons with the old components is moot as they didn't have the option of newer ones....

Look its entirely up to you. You seem to have made your mind up.
I think its bonkers, but then I also think invalid car blue is a hideous colour