Gear Luggage

Modified S Frame and New Bag

I made this bag before Basil’s under-seat bag, but hadn’t posted about it, so here’s the (belated) description of how that project went.

My extensive Brompton luggage collection lacks one thing — a bag significantly smaller than the T bag, or the Brompton basket, but large enough to carry gear for a longish ride.  Encouraged by discussion on the Brompton forum, I got a Brompton S frame from NYCeWheels, and dismantled it.  Then I sewed a bag to fit.  The result was a bag as tall as the S bag, but quite a bit narrower.

The S frame, dismembered:

If you are going to do this, by the way, spend a (very) few bucks, and get a pipe cutter, which will ensure perfect results.  Oh, and measure, over and over, before applying it to your frame.  Also, pay attention:  I marked the cut points with painter’s tape, and nearly ruined the whole project by considering cutting at the wrong side of the tape.    Measure, label, cut . . . by far the best approach.

The cuts I made reduced the width of the S frame by 4.5 inches.  That’s not a lot, but it is enough to make things  more manageable when I don’t need a full messenger bag.

Unfortunately, I was winging this whole process, and failed to take pictures of the construction. Below is how I reinforced the interior, though, so that the bag wouldn’t collapse.  I used plastic mesh, widely available wherever bad yarns are sold.  It’s sturdy, flexible, and easy to attach to seam allowances, thanks to all those little pre-existing holes.

Once I knew what the frame size was, I drafted the bag pattern and assembled it.  I designed the bottom with a curve.  That way, the mesh could be inserted without cutting it at squared-off seams.  The sides of the bag are just the cordura, with heavy-duty plastic sheeting cut to fit as support.  One side has a mesh pocket:

There’s a simple pocket on the other side.  I’ve been riding in the country, in this photo, so it’s got a bottle of Halt! at hand.

Hidden underneath the over-sized top flap are clips for the optional shoulder strap.  (No, I do not which to discuss the phenomenal quantity of cat hair that has accumulated on this bag even though it is kept out of the way of the herd of felines who share my abode.)

There’s a mesh pocket along the front, too.  I used laundry bags for the mesh, and ran elastic along the top edges of the pockets, to keep them snug against the bag.  That’s worked out quite well.

Here’s the back of the bag.  This is the crucial part of a Brompton bag, as it must accommodate the luggage block on the front of the Brommie.  The top opens towards the front — opposite to how typical luggage is made.  That’s so it can be flipped open from the seat of the bicycle, and items retrieved easily by the rider.  There’s a gap for the frame handle, and a  magnet under each of the tabs to the right and left of the handle.  They allow the top to self-close when flipped back over the bag.  The webbing loops make it easy to flip the top open.

The top is attached in front with two hidden webbing straps, which mean that it will be easy to remove when I re-make the top.  Is it glaringly obvious that the top is too big?  It works, but could be half as deep, and work just as well.  I didn’t really notice that as I was maniacally assembling it.  It’s slated for replacement.

The bag is lined with ripstop nylon, with pockets customized to my use, including open pockets along the back, a mesh sleeve to the left, a zipper pocket in front, and a key clip.   That’s worked out well, and there’s plenty of room for my  jacket or anything other smallish thing I might acquire or want to bring along . . . like lunch.  The side tops aren’t as supported as they probably should be, but, oddly, the bag works just fine.  (I can probably thank the S frame for that.)   I may do a modification there, though.

The whole bag is bigger than I intended, though, as I wished, it’s much less of a sail than the S bag.  (This one will hold my largest helmet, though, which is sometimes quite helpful.)  I do want a yet smaller bag; that’s next up on the agenda:  I want to coffeeneur with wi-fi, and (otherwise) the least amount of other gear possible. (Update: As noted above, that bag is also made, and the subject of this post.)

I have a hand rivet tool, but still haven’t riveted the resized frame together.  The bag’s sleeve (and the tight fit of the frame itself) holds the frame together well, and I’m considering getting some copper tubing to make a narrower bag.  Both bags will carry very light loads, so I’m tempted to skip the riveting all together, so that I can swap the tubing out for the different bag sizes.

14 replies on “Modified S Frame and New Bag”

I love your bags! In January I join the ranks of Brompton owners; meanwhile I’m keeping myself busy eyeing and dreaming of accessories. I can sew somewhat (once made a tent that actually worked), so now I’m encouraged to try some experimenting. Thanks for the ideas and for sharing your experience; you’ve given me food for thought about many of my considerations (bag that can hold my helmet? Oh, yes!). Also I want to thank you in general for the great blog; I appreciate the tips for newbies and more (sorry for your pedal scratches; thanks for the advice). One question: How far down does your fabric go on the inside frame side of the back? I can’t tell from the picture and I’ve never examined any B bags to see how they’re constructed. Thanks!

Seattle Rider, take a look at Jane’s pattern, and excellent tutorial, to see how the back of the bag is made. The bags themselves are made in the usual way (front, back, sides), with the sleeve for the Brompton frame sewn into/onto the back of the bag. If you’ve made a tent, you should find bag-making small potatoes! Thanks for your kind words about the blog; they’re much appreciated.

Now that is really neat! well thought out.

I did two of little custom bag for my best mate and i did Lejog on the Bromptons in 2011. simple roll top design on a cut down frame. Mainly to carry less and cut wind drag!

On bike

Paper mock up

Wow, Si, beautiful bag and amazing paper mock-up — very, very impressive! And doing Lejog (that’s Land’s End to John O’Groats — for US readers it’s cycling Great Britain more or less top to bottom) with custom bags is just fantastic — a great achievement all around!

Ta! Yer paper was easier to work with and experiement with – must admit the real bags were stitched up by my stepdad as he is a trimmer/upholster.

my mate and i used one of the custom bags each(10-12litres + a 3litre ortlieb saddle pack. that was enough space as we bought supplies on route and stayed in B&B. Took 7.5 days.

Small bags must be the fashion as even Brompton sell one now made for them by Ortlieb… v expensive though..

Your mock-up looks grand! I always do that, too, but never to the full finished point that you did; my results might be better if I did this so throughly. May need to follow your better example next time . . .

7.5 days? You and your mate did well!

Ortlieb’s good stuff, but the price really hurts . . . can’t quite get my head around it.

If you look at the paper mock up probably see all the little notes for my Stepdad plus samples of the fabric, edging etc..

still think your looks neater and better thought out!

Not dumb at all, Jim — in fact, quite the opposite, since the last thing you’d want is to damage the frame. I drilled the rivets out, starting with the skinniest bit I could find, and then working up until I was using one the size of the rivet head.

It sounds laborious, but I probably only used three bits — it didn’t take much. I’d just advise proceeding slowly and cautiously. You’ll feel the rivets responding, and it’s actually pretty easy to do.

Hi… finally got around to modifiying my s frame. Was really easy, in large part because of your helpful instructions. Didn’t do anything creative – just took off one side so that it matches up better with my gym bag, which I strap on with a bungee. This is a much better configuration for me because I have to do lots of folding/unfolding on my commute and with new configuration that’s easy to do without removing my bag. (Thought about buying one of the Brompton bags but none are really the right size and all are pretty expensive.)
Thanks for the help!

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