I have a Brompton customised by Kinetics and notice that when placed on its side the upper parts seems to be supported by:

  • at one end, by the frame hinge, and
  • in the middle (near the fork catch) by the front hydraulic disc brake caliper body pressing against the chainring guard.

There appears to be no other support, so if something is subsequently stacked on top of the bike, I'd guess it would stress the caliper and crank/chainring. Shopping-trolley mode with a loaded bag may also cause pressure between these parts.

  1. How does a normal Brompton, lain on its side, support itself in the middle?
  2. How much weight can sensibly be put on top?

The reason I ask is that I bought a chubby trailer which can hold the brompton but it provides no protection against something heavy being placed on top of the bag in transit. Given this problem with the custom Brompton I am curious as to how a normal Brompton behaves.

In case it make things clearer, I'm thinking of the brompton on its side being like a <, where the point is the frame hinge, the top is the handlebar side and the bottom is the rear triangle side. I'm trying to find out what contact point (or points) along the inside prevent a normal brompton flattening into -.

I don't have access to a normal brompton and have been unable to find detailed images of the inside of the fold. I'm fairly certain the middle isn't supported by the fork hook (that stops the fork moving outward, not inward). I'd guess the left fork blade eventually comes into contact with the right chainstay and that contact point provides the support but it would be nice to know for sure.

Here are a couple of pictures of my (not-very-clean) bike.

Despite appearances, the only places that the left side (front-of-hinge: fork,handlebars,etc) and right side (back-of-hinge: frame, rear triangle, etc) will be in contact when the bike is laid on its side are at frame-hinge and brake/crank (circled in red):

top down view

Close-up of the brake/crank contact point:

closeup of brake/crank

  • 1
    When we bought a Brompton for the wife, the dealer recommended to place it wheels down and put nothing on top.
    – Carel
    Feb 5, 2021 at 9:16
  • 1
    Can you add any info on the Kinetics modification? Does this impact the folding process? I'm not familiar with Bromptons other than knowing their fold process is unique already.
    – Criggie
    Feb 5, 2021 at 21:24
  • 1
    @Criggie kinetics-online.co.uk : Basically, rohloff hub, hope hydraulic disc brakes, son dynamo hub, custom fork/triangle with integrated rack. No impact on folding except you must position the left crank arm so it doesn't hit the rohloff shiftbox (see first image) or chainstay (if rotating the other way). Ends up wider due to the wider hubs. Ben claims +15mm but I think mine is more like +40mm (12" vs 10.6" standard, ignoring protruding trailer hitch (+2"))
    – jhnc
    Feb 6, 2021 at 1:08
  • Things I would try: remove the brake caliper and try to imagine what goes where if the folding movement was to continue (unless very fiddly to put back on); ask on another forum; ask both Brompton and Kinetics customer service (in my experience, people can be very reluctant to ring customer service/technical support; and when they do, they often get a great answer).
    – pateksan
    Feb 6, 2021 at 9:28

3 Answers 3


From a phyics or engineering point of view, I don't know, something on the order of 20/30 kgs, maybe?

From the warranty and manufacturer recommendation, the answer is 0. A folded Brompton (and other foldable bicycles) are not supposed nor meant to carry any weight.

You can still revert the order on your trailer, put the heavy stuff on the bottom (which is in any case a meaningful thing to do) and then the Brompton on top, fixed with some bungee rope or with some other kind of band/belt.

  • The problem is that the Brompton may be the heavy stuff - you wouldn't want it on top of your shopping, for example
    – Chris H
    Feb 5, 2021 at 10:06
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    @jhnc you may be luckier by searching for videos of people folding their Brompton, to understand how it works/looks like ... however, since your edit, I am now a bit puzzled by the folding of your Brompton. Would you mind sharing a short video, or a photo sequence, of you folding your Brompton?
    – EarlGrey
    Feb 5, 2021 at 15:31
  • 1
    @EarlGrey it folds exactly the same as a normal brompton, just wider due to the wider hubs. I'll try to upload some images.
    – jhnc
    Feb 5, 2021 at 16:59
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    did you get the fat-tire Brompton :D ?
    – EarlGrey
    Feb 5, 2021 at 17:08
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    @EarlGrey No, standard 35-349, marathon plus. Feel about as good as the 700x37c on my touring bike, except over large pot-holes.
    – jhnc
    Feb 5, 2021 at 17:44

I see two possible answers to help.

From https://www.radicaldesign.com/assets/uploads/products/20044-cyclone4-chubby-bicycletrailer-filled.jpg
Manufacturer's photo of a chubby trailer, loaded with bike.

  1. Label the outside of your case clearly with "TOP STOW ONLY" or "TOP LOAD ONLY in permanent high-contrast colour. This shows to anyone loading the case that it can't take being stacked underneath anything.

enter image description here Something like this, perhaps with fabric paint or sew on a fabric patch saying the same.

  1. Add a support mechanism inside the trailer. This might take the form of a "roll bar" framework of tubes, or it could be a 2x2" stick of wood that you position through the folded bike once it is packed in the case.

Either way the point is to prevent weight added on top of the folded bike.

  • 1
    Thanks for taking the time to answer. Useful notice. I'm not too worried about the issue: I can always engineer a workaround if needed (eg. rigid inserts for base and lid plus the equivalent of pizza savers through the spokes, for example). A few foam inserts would likely be enough when sticking in a car boot,etc. I'm just curious how a normal Brompton supports its middle.
    – jhnc
    Feb 5, 2021 at 22:25
  • @jhnc yeah that's why this isn't really an answer to the question... Bromptons are rare here because they're so expensive; the cheapest S series is $3145 NZ Even the authorised distributor doesn't list prices on their website !
    – Criggie
    Feb 5, 2021 at 22:38

The front axle hook goes around the chain stay (rear triangle). Depending on the position and type of the hook the fork end will lay on the chain stay.

enter image description here

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