The Downtown: a Better Brompton Bag from Ortlieb

Brompton sells a bag made by Ortleib.  The good folks at Bicycle Habitat have one in stock and it’s beautiful.  But they’re asking $350 for it!  That’s too much money.  Eric, at Bicycle Habitat, showed me the Ortlieb “Downtown” and we both agreed that with some tweaks (he reckoned one Sam-Adams’-worth, I figured closer to two) the bag would fit easily on my existing S-frame.  The Downtown retails for a still-steep, but slightly more reasonable, $150 (ouch! REI is selling it for $104).

I don’t normally drink Sam Adams, but in honor of Eric I got two from the corner bodega and broke out the tools.  Happily, the inner lining of the bag zips open to reveal the padding and guts within.  With a phillips screwdriver and torx wrench I removed some grommets, nuts, and bolts and the quick-release mount came off easily.  Then I measured and drilled new holes for the straightened bracket.

The finished product. Quick release with s-frame mounted.

Measuring for the S-frame, the bracket landed between the two existing mount points, about a half inch (at center) above its factory location.  I had to relocate the stabilizing cleat to the upper radius to clear the Brompton S-frame’s hardware.

The Downtown bag is slightly larger than the Brompton O bag (30 liters vs 22 liters, based on my own measurements) and is, in my opinion, better looking.  The mount certainly isn’t as elegant as the built-in Ortlieb/Brompton O bag mount (which is really nicely done).  But come on… the modified Downtown costs half (or 1/3) as much and is twice as flexible!  I can now use this bag on any of my other bikes with a rear rack (I’ll simply remove the bag from the S-frame and click it onto my other bikes’ rear pannier rack).

Also, I have the satisfaction of having built it myself.  Degree of difficulty: 1/2 Sam Adams.

3 thoughts on “The Downtown: a Better Brompton Bag from Ortlieb”

  1. hello dan,

    greetings my name is akbar from jakarta, indonesia.could you help me step by step DIY with picture.many thanks.

    warm regads,


  2. Hi, great idea. Just wondering if it lasted since i see you did this a couple of years ago. Also did you need to buy the brompton luggage frame separately?
    thanks in advance

  3. Hello Cameron. Yes, I bought the S-Frame separately. But that wasn’t easy in and of itself. Here’s an excerpt from an email that I got from my local Brompton shop after I tried to order the S-Frame from their site:

    “…we are not allowed to sell them (as per Brompton’s rules) because they do not want their customers to use the frame with after market bags.”

    I asked Brompton for confirmation about this, but got no response. Eventually I had to go to another vendor who either hadn’t heard of the prohibition or didn’t care. He sold me a frame for $33.

    The whole system has held up remarkably well. As I mentioned above, it’s super flexible too. I can remove the frame from the bag and use the frame with a wire basket that I modified (with an mounting bracket, which I got from Ortlieb for a few bucks) or use the bag on the racks of my other bikes.

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