Brompton as ridden including toolkit (8.88 kg / 19.58 lbs)

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OtterSpace
Posts: 217
Joined: Sun Mar 08, 2020 6:28 am
Location: California Silicon Valley

by OtterSpace

Hello everyone,

As I wait for parts to arrive and bad weather to pass I decided to finally capture my Brompton build to go along with my other threads here:
Focus Izalco Max Rim (4.47 kg / 9.85 lbs)
45kph Ebike Rocketship - Scott Solace eRIDE 2023
Specialized Tarmac SL6 S-Works Ultralight Rim 49cm

Latest pics on this bike:
1.jpg
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I was always curious about Bromptons but never seriously considered buying one. However, on 2nd April 2022 I purchased a used Brompton when I saw one come up at a price I couldn't resist. Weight as purchased was 12.48 kg / 27.51 lbs.
Brompton.png
I spent the next few months parting it out and rebuilding it to be a better bike.

Researching Bromptons was quite an experience as most owners fall into one of two camps either:
  • Bromptons are the best bike ever and cannot be improved except by adding a Brooks saddle or Ergon grips. Think of a late 2000's hipster here.
  • Rich East Asians who don't have room or desire for a conventional bike. Think of a Singapore uncle here. Thankfully they are open to changing the bike but there is often little cohesion behind their build choices.
A big shout out to Twisted Wheels for his video on a Brompton build that came out around the same time I purchased my bike. His video was the greatest single source of info I could find on Brompton rebuilds.

This Brompton build was by far the hardest build I've done as the ingenious but archaic design, small size, implications of the fold, lack of documention on aftermarket parts, and cascading implications of single part changes make for a challenging build.

Although the Brompton isn't everyone's cup of tea hopefully everyone can learn something interesting from this build as I slowly detail the component choices.

I'll have to tread carefully when explaining some parts as almost everything comes from China given the lack of enough interest in modifying Bromptons to generate much of a dedicated market in the "West"
Attachments
Brompton updates 2022.jpg
Last edited by OtterSpace on Sun Mar 10, 2024 9:28 pm, edited 5 times in total.

OtterSpace
Posts: 217
Joined: Sun Mar 08, 2020 6:28 am
Location: California Silicon Valley

by OtterSpace

I finished a spreadsheet covering this build that I'll continue to update through the life of the build.

Unfortunately I did most of the work on this build around two years ago so documenting it now is a bit more challenging as some of the parts have been sold. Because of this the claimed pre part weights are a bit off (62.35g) the measured pre weight as I add up to the known post weight.

Curent measured weight is 8.88 kg with a total bike cost of $2,467

:beerchug:
Last edited by OtterSpace on Wed Feb 07, 2024 2:42 am, edited 2 times in total.

by Weenie


Visit starbike.com Online Retailer for HighEnd cycling components
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OtterSpace
Posts: 217
Joined: Sun Mar 08, 2020 6:28 am
Location: California Silicon Valley

by OtterSpace

I'll start the story with something that I think fits the tone of this build well of matching Brompton's design energy of just make it work no matter how ridiculous with my desire for modern parts that work well but don't weigh a ton.

The stock Brompton came with a pump that they mount on the rear triangle where it can get dirty as shown below.
brompton pump.jpg
My solution after upgrading all the parts was to find a good Lezyne pump with a simliar OD to the new seatpost's ID to minimize rattling, tie it to a plug, and make sure the plug isn't wider than the seattube ID so the post can still slide normally. Proper British Engineering
pump.PNG
Is there a better way to do this? Yes. Does it work? Yes. Do I care enough to find a better solution? Probably not. BROMPTON

They also have a toolkit that you store in the frame and costs $100 and weighs a reported 0.49 lbs (0.22 kg)
Brompton toolkit.jpg
brompton toolkit2.png
After upgrading all the components to modern designs I was able to reduce the toolkit down to a slimmed down Wera 004182 wrapped in a tpu tube to prevent rattling and keep it all in place.
toolkit.PNG
Everything fits in the bike so I never forget it, the toolkit and spares stay clean, the look of the bike is not impacted, and can just grab the bike and go.

Because of this I consider all of this weight to be part of the bike unlike how I would capture other builds.

Feb 12th 2024 edit: I made a carbon 15mm wrench for the rear wheel to add to the toolkit. It fits with the other tools folded up in the innertube and stashed in the frame.
wrench.jpg
Last edited by OtterSpace on Tue Feb 13, 2024 3:02 am, edited 1 time in total.

OtterSpace
Posts: 217
Joined: Sun Mar 08, 2020 6:28 am
Location: California Silicon Valley

by OtterSpace

Brompton gearing is quite unusal for a conventional cyclist due to the small (16 inch / ETRTO 349) wheels and internal hub. To understand how this gearing translates to a conventional 700c bike the best way is to leverage online gearing calculators. Importantly tire width has a comparatively large impact on total wheel diameter vs changing out a 700c tire.

Thankfully there are tons of gearing options to tailor the bike to your needs but the small rear dropout in the rear triangle and rear wheel width are highly limiting.

Lets look at how a 50/34 11-34 700c bike compares to the stock gearing of a 6 speed Brompton and the eventual gearing I deployed.

Conventional goes from 27.1 gear inches in 34f 34r to 123 gear inches in 50f 11r.
Conventional.png
Stock 6 speed Brompton gearing using the 3 speed sturmey archer hub and two external cogs (13T & 16T) goes from 33.1 to 100 gear inches which is not that different from a conventional bike. The biggest adjustment are from the sturmey archer, its heavy as a brick, loud, and not very efficient. Many Brompton owners opt for a smaller front chainring for an easier gear which effectively moves the chart left.
Brompton 6s.png
After riding the bike stock for awhile, even on some bay area road ride climbs, I opted for a rear derailleur system and a single front chainring. It drops a lot of weight, is more efficient, quieter, but does not have as good range and has negative implications on the fold which I'll post about later. The front chain ring decides if you want to prioritize top speed or climbing. Unlike many I opted to not loose as much high speed gearing for riding on the flat. However, from personal experience when desending past 40km/hr the Brompton platform is not exactly confidence inspiring and the same goes for heavy sprints.

With the 60T and a 11-28 cassette the bike goes from 35.6 gear inches in 60f 28r to 90.6 gear inches in 60f 11r.
Brompton Update.png
There are tons of other cool options depending on what the user is prioritizing. However most (4/5) are expensive, most (4/5) require an aftermarket rear triangle, and some (2/5) are fiddly. I'll capture some for reference below including a not recommended 6th option.

To edit in more details and pics:
Shimano internally geared hub
Other internally geared hub
Custom FD
In crank ratio changer
Conventional RD mount
2x with no FD

poulhansen
Posts: 297
Joined: Wed Nov 25, 2020 12:49 pm
Location: Danmark

by poulhansen

Is 8.8 kg your goal or your result?
Cannondale Super Six HiMod 2017 6.7 kg
Cannondale six13, 2004, 5.50kg
Focus Izalco Max, 2023 4.418 kg

OtterSpace
Posts: 217
Joined: Sun Mar 08, 2020 6:28 am
Location: California Silicon Valley

by OtterSpace

poulhansen wrote:
Tue Feb 06, 2024 12:28 am
Is 8.8 kg your goal or your result?
8.88 kg is the current result including tools and spares and a not yet pictured front fender.

It is still slightly WIP but I don't expect any huge changes in weight. My main goal was to have a bike I could bring with me in normal checked airline luggage so I could bike around when I travel for work.

Aftermarket titanium frames and or carbon rear triangle and fork could get this down to sub 6.8kg but I don't use this bike enough to justify that expense.

This build took tons of research so basically I'm info dumping for others if anyone else chooses to build up a Brompton in the future.

mike
Resident Pro
Posts: 2983
Joined: Tue Mar 18, 2003 9:42 pm

by mike

love it! considered getting a brompton for travel or a bike friday.

3phase
Posts: 124
Joined: Tue Oct 30, 2018 4:26 am

by 3phase

I bought a Brompton while on quarantine in Japan during Covid. It's such a useful bike specially when I cycle with my son at the park, I don't have to bring my road bike with me. And yes, I live here in Singapore and you can all see the highly-modded Bromptons here and I now one guy selling some sort of rare Nickel special edition for almost 10KUSD, it's bonkers here. Mine is 2 speed which is all you really need here, weighs around 8.3kg, replaced some of the plastic parts with reputable ones, removed the fenders, rack, replaced to tan wall tyres. Might replace the wheels with something from SMC to make it lighter when I bring it to work. I really don't understand some of them modding it to 7 speed, and they don't even do bike touring with it. It's a fun bike

OtterSpace
Posts: 217
Joined: Sun Mar 08, 2020 6:28 am
Location: California Silicon Valley

by OtterSpace

3phase wrote:
Fri Mar 08, 2024 5:57 am
I bought a Brompton while on quarantine in Japan during Covid. It's such a useful bike specially when I cycle with my son at the park, I don't have to bring my road bike with me. And yes, I live here in Singapore and you can all see the highly-modded Bromptons here and I now one guy selling some sort of rare Nickel special edition for almost 10KUSD, it's bonkers here. Mine is 2 speed which is all you really need here, weighs around 8.3kg, replaced some of the plastic parts with reputable ones, removed the fenders, rack, replaced to tan wall tyres. Might replace the wheels with something from SMC to make it lighter when I bring it to work. I really don't understand some of them modding it to 7 speed, and they don't even do bike touring with it. It's a fun bike
Thanks for the personal story. The Brompton platform is truely special and offers some unexpected challenges from being so small. The bike world would be a better place if other bikes got as much love and modification as Singapore Uncles place on Bromptons. The sky really is the limit in terms of pricing as a modified T line can get up to 15k USD if you go all out.

My opinion is that unless you need the fold or small size almost any bike is better but there are places where only Bromptons can be easily deployed and that is where they are amazing.

I loved the process of modifiying it to be a better bike for traveling but for anything lighter I would have to compromise the gearing range, compromise quality, or biggest of all spend a ton more money in this platform that is only a supplement for my other bikes.

Attached are a huge dump of pictures now that shifting is complete and only minor items need addressing like adding a garmin mount and finding a way to tension the chain while folded. Thankfully the chain is waxed so tensioning the chain while folded isn't a requirement more a nice to have.

If anyone has any questions about any particular part of the build I'll address that first and I plan to continue slowly info dumping as time allows as this bike is actually much more complex than first meets the eye.
1.jpg
3.jpg
5.jpg
6.jpg
7.jpg
8.jpg
10.jpg
11.jpg

mike
Resident Pro
Posts: 2983
Joined: Tue Mar 18, 2003 9:42 pm

by mike

love the carbon fenders! well done

OtterSpace
Posts: 217
Joined: Sun Mar 08, 2020 6:28 am
Location: California Silicon Valley

by OtterSpace

mike wrote:
Mon Mar 11, 2024 2:40 pm
love the carbon fenders! well done
Thanks. Like most things on the bike they took a bit of work and are not as simple as they seem.

Brompton calipers are wide and have long arms which complicate replacing them and as such they are typically the last item people update if they are sticking with rim.

Because of the caliper update I had to drill out slots for the calipers to sit and then covered the holes with vinyl wrap on both sides to cover my hand dremeling and prevent water from splashing through the holes. The main reason I added the front fender is to prevent the front brake cable from touching the wheel when steering.
fender.png
Additionally the front carbon fender came a little bit warped so I had to bend the mounting wires to tension out the warping which is hard to show.

The rear isnt on the bike and I received it without all the mounting drilling. I could similarly modify it but dont plan on riding in the rain often.

Stuff like this is normal for aliexpress items.

by Weenie


Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓    Broad Selection ✓    Worldwide Delivery ✓

www.starbike.com



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