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.