Heavy duty Brompton rear mudguard bracket

Discussion in 'Folding Bikes' started by doginabag, 28 Apr 2018.

  1. doginabag

    doginabag Senior Member

    I have done a bit of work on my Brompton which I need to finish off this weekend.

    I find the bracketry that holds the rear mudguard is not really up to the job when the bike is folded as the weight of the bike is transfered through the fragile plastic mudguard. My original mudguard disintegrated after a while, I think it is particularly proneto damage when slinging it into storage spaces on the train.

    I have made a heavier duty bracket which supports the weight of the bike when folded without it being transfered through the mudguard itself so it should be much more resilient

    A pair of luggage wheels replace the silly little jockey wheel making it much more and you can actually roll it as intended and with much more ground clearance, which you normally need the full luggage rack for.

    It's a bit agricultural, if you are into weight saving you might want to look away.
    But, it's proof of concept and if after a bit of testing I am still happy with it, I might design something a bit more refined and get a local fabrication company to make a neater job of it.

    20180427_091703-1862x1397.jpg 20180427_095711-1397x1862.jpg 20180427_120111-1862x1397.jpg 20180427_120957-1862x1397.jpg 20180427_134322-1862x1397.jpg 20180427_134319-1862x1397.jpg 20180427_134532-1862x1397.jpg
    robrinay and scotjimland like this.
  2. scotjimland

    scotjimland Active Member

    Isambard Kingdom Brunel couldn't have made a better job .. and it's a lot stronger than the Brompton bracket, but as you said, could do with a bit of refining..

    I would use anodised aluminium flat bar to save weight and make a more elegant bracket .. easier to work with and doesn't require painting

    such as this from Homebase https://www.homebase.co.uk/anodised-aluminium-flat-bar-profile-2m-x-25mm_p414821
  3. Ianboydsnr

    Ianboydsnr Guest

    Looks like a well executed mod, very strong, how much heavier does it make it?

    Mine has the rack fitted, so doesn’t have that issue, though the mudguards do look cheap and not upto holding any weight, I assume the mudguard flexes enough to transfer the weight to the tyre,

    It looks like it’s still using the mudguard as a brace, which will put some more strain on the guard,

    Me personally I would have used 10mm stainless tube, flattened where it’s bolted, and braced to form a lightweight rack,

    But as long as it does the job, you could make it lighter by drilling lots of holes in it, you may not think it to heavy as is though,

    Your brake block looks very near the tyre on the close up picture of the back frame.
  4. OP

    doginabag Senior Member

    Well it's not quite the Clifton Suspension Bridge, but thanks for the sentiment all the same. :laugh:
    I could remake it out of ally but is would probably have to remain the same size to be strong enough. Or keep it in steel and use a smaller section.

    I will weigh it when I take it off for painting, but I would estimate around 350g.

    With the original wire supports they would eventually bend untill the mudguard was pushed against the tyre and would need bending periodically to push the guard back up.

    Yes it is still connected to the guard which stops the bracket rotating. I could look at tying it to the existing rollers if needed, but then it would be getting very close to being a rack.

    Brakes are just thrown back on to hold the mudguard in place, it's all coming back off for painting and full service.
  5. chriscross1966

    chriscross1966 Senior Member

    It looks like it would hold up to pretty much anything, but it isn't the most aesthetically pleasing thing I've ever seen...
  6. OP

    doginabag Senior Member

    Yep, it's not exactly pretty. It was a bit rushed as I needed the bike back to working for my commute and steel sizes were limited to what was in stock at my nearest store so it's chunkier than first intended anyway. But, it works and all the critical parts (wheels and fixing points) are in the right place so with it on the bike I may now start thinking about a more refined v2.0.

    But for now, it's painted up so looking slightly better, and looks aside I am already enjoying being able to roll it around with ease, and also simply having my rear mudguard back as it was teaming it down this morning!

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    Dogtrousers likes this.
  7. CopperBrompton

    CopperBrompton Bicycle: a means of transport between cake-stops

    A pretty version of that would be very welcome. The rack is also very agricultural (as well as heavy).
  8. chriscross1966

    chriscross1966 Senior Member

    The painted version looks a lot better.
  9. Kell

    Kell Über Member

    I thought I'd responded to this, but clearly didn't. (Maybe there's a thread somewhere else with a random post about mudguards on it.)

    What I thought I'd said was: Does it not need a cross-brace from the old support to the new one to stop it trying to rotate all the time?
  10. OP

    doginabag Senior Member

    Thank you both. It has brought a few puzzled looks from fellow bromptonites already.

    Excuse the somewhat unprofessional mark up, but do you mean like this?

  11. Kell

    Kell Über Member

    No quite - I meant creating a triangle with the existing support. A bit like this:


    It feels to me (non-qualified in any way in terms of engineering) that when the bike's in park mode, the weight will be trying to rotate the support and trying and stretch the mudguard.
  12. OP

    doginabag Senior Member

    Ok I see what you mean.
    Putting a tie there would not be ideal as it would likely bend the central support.
    If it was needed, then where I showed it wold be better, but it starts looking strangely similar to the rack.

    However, as it stands the fixing arrangement is no different to the standard brackets and small jockey wheel.
    The improvement (other than the improved stability from having two wheels) is that the bracket fixes to the outside of the mudguard rather than the inside. This removes the mudguard from the load path when folded which should be sufficient to stop it from breaking or being pushed hard against the tyre.

    I can see why you might want to put a tie in, but it may not actually be necessary. The original bracket doesn't need it, I suspect any rotation of the bracket is restrain by the mudguard going into tension, which it can seemingly take without issue. Or, it may be that the fixings to the frame are tight enough to apply sufficient friction to stop any rotation. I might slacken these fixings off for a while to allow free rotation of the bracket and see if that does cause any damage to the mudguard.
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