Building up an ultralight Brompton?

[JeffOYB]

Anyone know how light someone has gotten their Brompton?

I see that they offer a ti rear triangle for like $400 and a ti fork for like $200.

I recall an ultralight seatpost option---is it carbon?

What about an ultralight handlebar?

Etc., etc.---what can you quickly get one down to using the fewest fairly standard parts? And working on the major items. And maybe also opting for a singlespeed with one brake, say.

I'm wondering if you can fairly reasonably get down to, say, 15 lbs.

OK, why limit it to Brompton...any other lightweight folders or conversions out there?

--Jeff Potter, http://AllBikeMag.com

[spambait11]

Kinetics (http://www.kinetics.org.uk/html/brompton.shtml) has made custom lightweight B.'s and so has Steve Parry (http://www.foldsoc.co.uk/spbromp.html), both in the UK.

15lbs? I'd go the modified Bike Friday route; in general, there are very few enthusiasts in this subforum who are weight weenies.

[juan162]

The only off the shelf folder close to that weight would be the now discontinued ultralight version of the Dahon Helios. I think the advertized weight was around 18lbs.

Juan

[tkatzir]

Anyone know how light someone has gotten their Brompton?

Leonard Rubin has the Ultimate Folding Bike (UFB) project.

The latest version is a Brompton with a Rohloff at 20 lb., or with derailleur gears at 17 lb.

Tal.

[easy racer]

Here is another thread that shows a more modern SP brompton:

http://www.bikeforums.net/showthread.php?t=181741

It also has my attempt at trying to make a brompton lighter, including a carbon seatpost from Avon Valley Cyclery in the UK.

andy

[14R]

Another option is using Merc parts. There is a thread about it (how to combine compatible parts of these two bikes into a super light Brompton-like beast)

[Baoping]

The only off the shelf folder close to that weight would be the now discontinued ultralight version of the Dahon Helios. I think the advertized weight was around 18lbs.

Juan

I was at a bike store recently and asked them to weigh the Helios and it weighed in at almost 24 pounds. The weights listed on the Dahon website are inaccurate. I think they weigh them without the pedals and rack, altho the Helios model doesn't have a rack or fenders, so I'm not sure why the difference.

I was also at a different store that sold Bromptons. They only had one demo, and it was an ultralight model, 3 speed. I had them weigh it and it was also 24 pounds.

[folder fanatic]

One of the reasons why I chose the C type or Companion model with no frills or accessories added like a frame pump or even fenders is to own a bike that hovers around 25 pounds-which was a big improvent over my 30 pound Dahon Boardwalk which came fully accessorized with fenders, rear rack, and other heavier components. When my Companion is folded up and carried onto commuter trains, private smaller cars, and other places where I cannot wheel it aboard, I find I can carry it with relative ease. And to add another point across I am not male, born with very much upper arm strength. And I only add components/accessories when absolutely needed. I don't like alot of clutter on any of my bikes unless absolutely neccessary.

[LittlePixel]

Anyone know how light someone has gotten their Brompton?
I don't know the *exact* weight but Steve Parry's Bromerc / Mercton hybrid is probably a contender with it's self styled 'lightest Brompton' tagline. It's a seductive idea - one I'm thinking about myself. Hefting an off-the-shelf Brompton around is a bit of a pain in my experience. I mailed Steve a while back and he reckoned on a replica of the one pictured below costing around £1,600 GBP

http://www.littlepixel.info/twenty/parry.jpg

It's true to say there aren't many 'weight-weenies' (who thought of that terrible name!?!?!) on this sub-forum which is healthy enough, but not a little odd considering folders are the only bikes that get regularly carried about - a good reason for shedding the odd pound here and there if you ask me.

To make a Brompy the mostest lightest foldy bikeh *evah*, one should fit:
1) Brompton 'Ultralight' Ti forks and rear triangle.
2) or build your own front carbon forks
3) Ti Seatpost (or the carbon one Easy_Racer mentions)
4) Ti axle (or a new carbon bottom-bracket)
5) Carbon Saddle (Fizik Arione Wing flex)
6) Carbon Cranks - shorter the better
7) Single Speed; better as a respaced flip-flop track hub with bmx freewheel rather than Brompton hub
8) Carbon flat bars. Cut off an inch or two from either end. No grips - wear gloves; carbon brake lever.
9) Merc (alu) frame swap. Remove powder coat and polish for minimal weight savings.
10) Ti eggbeater SPD pedals
11) Carbon chainring; ti bolts
12) No rear brake
13) Lightweight roller wheels; No Rack, No guards, No front carrier boss. (Maybe carry a clip-on-to-the-seatpost rear guard for downpours)
14) Stelvio tyres; reduce front spokes from 32 to 16
15) Thin 9 speed chain should save a few grams
16) Swap out steel bolts/washers (not the hinge!) with alu or Ti equivalents
16) Wash it *often* to get that pesky weight-adding heavy dirt off

Cost: about £2,000,000 of your earth pounds sterling.
But you can take it about with you with no effort at all by attaching it to a small helium balloon :)

That's my summer project... (well maybe not ALL the mods)

[spambait11]

13) Lightweight roller wheels...
Why the added weight, esp. if you're using the helium balloon?

(You might also want to look into lighter weight balloons, and drill extra holes into your heavy rims, handle post, and main frame.)

[LittlePixel]

haha - Well spotted.

In the bath earlier I lamented not adding a bit about filling the tyres with Helium - 120psi of helium's just gotta be lighter! ;)

I'll be drilling holes in the tyre and tubes too, using dental-floss for cabling, as well as running both rims on just 3 spokes a piece, like a SAAB...

[mingonn]

Stelvios are a must then the seat if you don't mind a harsher ride. From then on it $$ per gram goes up, and up and up.

What amazes me is how much lighter comparable priced road bikes to folders. Bigger frame, longer spokes, bigger wheels, front deraileur, etc and they often weigh the same or less. Those hinges must be heavy.

[juan162]

I was at a bike store recently and asked them to weigh the Helios and it weighed in at almost 24 pounds. The weights listed on the Dahon website are inaccurate. I think they weigh them without the pedals and rack, altho the Helios model doesn't have a rack or fenders, so I'm not sure why the difference.

I was also at a different store that sold Bromptons. They only had one demo, and it was an ultralight model, 3 speed. I had them weigh it and it was also 24 pounds.

That is the regular Helios. It's weight is supposed to be 23-24lbs. Dahon produced a very light weight one a couple years ago. That one is an 18 pounder. I doubt your LBS would have one in stock. You are also correct about the listed weight being without the pedals, but that is standard procedure for almost every company, including full size bike companies.

Juan

[Wavshrdr]

If anyone considers adding the Ti parts from a Brompton, I have a brand new Ti fork and rear triangle.

[James H Haury]

Why not just buy bromptons lightweight version of it's bike?The 2 speed is supposed to be about 21 lbs.

[pm124]

Some folks in the Birdy forum have managed to get their circa 1996 Birdies down to 8Kg using XTR and Dura Ace components. But asking why folders weigh so much makes a lot more sense than trying to get road bikes under 14 pounds/6Kg. After all, you have to carry folding bikes. Sometimes you have to carry them up 5 flights of stairs ;-)

[jur]

Why do folders weigh so much?

Very easy short answer: Frame.

Long answer: If you compare components on light roadies vs folders, the the differences boil down to very few parts, assuming others are similar or the same: Frame and wheels. It is not so easy obtaining the same lightweight wheels in 20" as in 700c, they are generally not available. However, the difference there can be quite small if you use say an American Classic Micro 58 hub, 16 spokes and a velocity Aerohead rim, plus Stelvios or GP tyres, the whole wheel package can be "very light", due to being smaller. That leaves only the frame.

The frame can be quite misleading on bikes; while the biggest part of a bike, it is very light, Litespeed Ghisallo frames are less than 800g, AFAIK? That's lighter than most back wheels. You can forget about getting a folding bike frame that light. The aluminium Swift frame is about 4lbs, plus just under 2lbs for the fork. Using a carbon or alloy fork may drop a pound or more, but then you're stuck. 6lbs or even 5lbs for a folder frame is a helluva lot more than 800g. The fact that folders can be lightish is due to the small wheel size.

So the difference is mainly in the frame.

[mingonn]

Thanks for the break down Jur. Not having light weight frames on folders seems strange since lifting and carrying is all in a days work. Always did think the rear triangle on my Dahons were a bit over done.

[spambait11]

And according to your comparison above (Ti vs. alu vs. what? cromoly and hi ten? :rolleyes: ), frame material is a factor.

[jur]

On one of those threads that was lost due to server issues, someone once asked about the frame weight of a Raleigh 20. As I had mine stripped down for painting, I weighed all the bits and came up with a shockingly high number, I think it was around 5kg for the lot. That makes it impossible to make a R20 into a weight weenie's dream.

On the Swift which has gained some reputation as being one of the lighter folders, the seatpost is quite a hefty beast. I am looking for alternatives already.

[LittlePixel]

jur - love your commute photo page. I must do the same some time now I'm doing a 12 miler (though wussing a bit on the rainy days) Maybe put a vid camera on the bars and get grabs later.

[Fear&Trembling]

On the Brompton forum a week or so ago, it was claimed that the Merc main frame was 1.5lbs lighter than the brommie frame.

[jur]

jur - love your commute photo page. I must do the same some time now I'm doing a 12 miler (though wussing a bit on the rainy days) Maybe put a vid camera on the bars and get grabs later.Thanks. Check out my (first) touring holiday in the new, improved signature.

[norfolk bolt]

i've just done a R20 folder with a nexus 7 bspeed. Came in at 11.4kg. Whats that in pounds?

[jur]

11.4*2.2=25lb

[caotropheus]

On one of those threads that was lost due to server issues, someone once asked about the frame weight of a Raleigh 20.

I was:)

[James H Haury]

I think it is about 25 lbs.

[adr5]

Stelvios are a must then the seat if you don't mind a harsher ride. From then on it $$ per gram goes up, and up and up.

What amazes me is how much lighter comparable priced road bikes to folders. Bigger frame, longer spokes, bigger wheels, front deraileur, etc and they often weigh the same or less. Those hinges must be heavy.

It's all about stiffness. To get a decent ride a bike must not flex too much. A triangulated frame, like a standard bike, is very stiff. So you can use lighter weight materials and still get good stiffness. Most folding bikes use a single tube connecting the front end to the rear of the bike. To get good stiffness you need to make the tube pretty thick. That adds weight to the frame. The hinges will also add extra weight.