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  1. #1
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    20"-wheeled Brompton

    After having owned multiple (10-20) full-size bikes, a Brompton, Tikit and NWT, I've come to the conclusion that 20" wheels are better in terms of performance and parts availability and the Brompton folding mechanism is the best. Has anyone tried to make a 20" Brompton-type setup? Methinks if would be the best of both worlds with only moderate increases in size.

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    coprolite fietsbob's Avatar
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    What if .. go for it if you think the demand is there..



    The Titanium UFB, project has a Kickstarter fund desire,
    perhaps rather than a 16" wheel there is more customers
    for a 451 go fast folder in the 17 pound category that has the M-soft
    shareholders And the like, with the needed disposable income,
    willing to break out the 10K a pop for that kit.


    Tell us about the Machine shop, and forge and or foundry,
    you have to make the hinges and the alignment jigs
    that you need to also make first, in order to manufacture these component parts..

    Perhaps a trip to the next Taipei Trade show.. the investment went there,
    so the manufacturing tooling can be created.

    At least you need to re manufacture the 2 extremities, rear and fork.
    Last edited by fietsbob; 04-17-12 at 12:03 PM.

  3. #3
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    I don't think it makes sense in terms of the way the rear triangle tucks under the frame, the wheel has to extend past the bottom bracket. So with 20" wheels the wheelbase would be too long.
    It might work with a Mezzo as it does with a Birdy as the rear wheel folds to the side of the frame.

  4. #4
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    Don't think it'll work because what chagzuki said the wheel folds right under. But if you wanted a bigger wheel the dahon curl is 18" and the wheel folds to the side also. But that's as close as you can get because of wheelsize limitation. Dahon's done it already but just a tad bigger and not really available to the north american market. Thors page for the curl goes into a black hole.

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    Thanks for the replies. I hadn't really thought about the wheelbase length issue, but just assumed that by changing the pivot point it would be possible to squeeze in a bigger wheel.

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    I always assumed that Brampton hinge is protected by patent. However, after little of googling, it appears that it was first filed in 1979 so perhaps it's expired?

    As far as using titanium for frame - it's hard to machine and 20x more expensive than aluminum so it's probably not the way to go. Also considering how different it is from steel or aluminum current frame designs most likely would not make the best use of it's properties.
    Last edited by bbmike; 04-17-12 at 03:11 PM.

  7. #7
    coprolite fietsbob's Avatar
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    well the Brompton company has also changed their hinge..
    they gained a production efficiency,in the process.

    older Mk2 bikes were brazed together by hand,
    and that included fitting the hinges on the ends of the tubes.

    now they are a casting, and the brazing is done in a torch array fixture .

    Batch produced Pro level steel Race bikes with lugged frames
    can be made that way also.
    Jigs and tooling speeds the per unit production.
    whether the savings goes into lowering cost, or raising profits, and who benefits,
    is a separate issue..
    Last edited by fietsbob; 04-17-12 at 03:28 PM.

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    Here's a bike with 20" wheel and using "brompton" hinge:

    http://www.oribikes.com/products/det...=0&cID=1&Key=1

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    Quote Originally Posted by wandt View Post
    Thanks for the replies. I hadn't really thought about the wheelbase length issue, but just assumed that by changing the pivot point it would be possible to squeeze in a bigger wheel.
    Having written that I considered it again and of course there's plenty of room to move the pivot/hinge towards the bottom bracket; you're right. So the fold would be longer and higher by the difference in wheel size, i.e. 56mm. Actually not so much higher, the frame tube would be higher but the seat post/saddle could protrude a little less.

  10. #10
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    And then considering it again actually there isn't plenty of room, perhaps just enough room to move the rear pivot forward an inch. Just about enough.

  11. #11
    coprolite fietsbob's Avatar
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    New rear triangle putting the axle further back, but essentially leaving
    the chainstay bridge where it is, so the tire, folded under, just clears the front of the BB..
    but then the wheel being bigger diameter, Wont fit under the top tube,
    maybe raising the head tube will by having the fork longer, not hit ,
    but that throws off the trail.

    so this will likely remain theoretical , just a bunch of hot air.

    there will be promotion if the funding is raised for this project
    to go back to the drawing-board. er CAD screen ..
    and all this sorted out by real engineers.
    Last edited by fietsbob; 04-17-12 at 05:31 PM.

  12. #12
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    Quote Originally Posted by bbmike View Post
    Here's a bike with 20" wheel and using "brompton" hinge:

    http://www.oribikes.com/products/det...=0&cID=1&Key=1
    These are mezzo variants and HOLY crap they look awesome! I have never seen these for sale in north america at all!

  13. #13
    Raleigh20 PugFixie, Merc LittlePixel's Avatar
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    You can fit moulton 17" (iso 369) or Birdy 18" (iso 355) wheels in there with skinny tyres - though the skinnyness leads to an overall circumference that's about the same as a normal iso349 with bigger typres so you don't really gain anything in terms of longer gearing.

  14. #14
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    Surely a 355 rim would fit with 1 3/8" tyres or do the numbers not reflect the real difference in rim diameter? I guess the effective shortening of the caliper brake reach would improve braking marginally.

  15. #15
    coprolite fietsbob's Avatar
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    folded , theOri has to get the wheel removed, as it shows in other models.
    so is not in the same fold and board the train league..
    more like a 20" wheel Bike friday, then with Hydroformed swoops like Tern.

    a CF bike that gets handled roughly often folding , seems a mis application.

  16. #16
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    Quote Originally Posted by fietsbob View Post
    folded , theOri has to get the wheel removed, as it shows in other models.
    so is not in the same fold and board the train league..
    more like a 20" wheel Bike friday, then with Hydroformed swoops like Tern.

    a CF bike that gets handled roughly often folding , seems a mis application.
    Ori is just an example that you can have 20" wheel on a frame that is hinged like Brompton. Rear wheel does not need to be removed.

  17. #17
    coprolite fietsbob's Avatar
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    Do, let us know when the Finance Economics and engineering of producing it
    is sorted out , and all can ride around on it.

  18. #18
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    Quote Originally Posted by fietsbob View Post
    Do, let us know when the Finance Economics and engineering of producing it
    is sorted out , and all can ride around on it.
    You forgot the patents

    I suspect that patents and trademarks (look and feel) influence folding designs more than economics and engineering.

  19. #19
    coprolite fietsbob's Avatar
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    well patents have expiration dates: for example Roger Durham had a patent
    on tubular BB spindles to be part of the right crank arm.
    it expired , and Shimano jumped on the Idea,

    though big publishers have a copyright renewal habit,
    Disney Corp and Acuff-Rose are good at that..

    you can still run afoul of copyright singing "happy birthday" for money.

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