Design a Bikepacking Frame Bag That Fits Your Bike

Start with the triangle you actually have

A frame bag is one of the friendliest projects in bikepacking: no complex closures, no waterproof zips to get perfect, and most of the work happens flat on a table. It's also the one piece of luggage that touches your bike in several places at once, so a bag that's 10mm too wide or has a strap in the wrong spot will rub paint and annoy your knees for an entire trip. Solve that at the design stage, not at the sewing machine.

Every frame is different, and the space inside is never the neat triangle the geometry charts suggest. Cables run through it, bottle bosses stick out and seat tubes curve.

Measure the space, not the geometry chart

Put the bike upright on level ground or in a work stand with the frame level. The most reliable method isn't a tape measure at all — it's a sheet of thin card.

• Hold the card flat against the non-drive side of the frame and trace the inside edges of the top tube, down tube and seat tube. You end up with the true shape of the opening, curves and all.
• Cut it out and offer it up to the frame, then check it with a tape: the length along the top tube, along the down tube and up the seat tube. Note those three numbers on the card.
• Mark every obstruction: gear cables and brake hoses, bottle cage bosses, a front derailleur clamp, external bearing cups and any mounting points you plan to use.
• Shave 8–10mm off every edge. That gap is for fabric, straps and paint protection. A bag that touches the tubes is the one that rubs.
• Work out your knee clearance. Sit on the bike, clip in and look down — your inner thigh usually passes 60–80mm out from the centre line in the rear half of the triangle. That sets your maximum bag width.

Decide what the bag has to carry

Volume comes from what you'll actually carry. A typical day-ride frame bag holds a multi-tool, tyre levers, a plug kit, a spare inner tube, a quick link, some food and a lightweight windproof.

Lay those items on the card cut-out to see the space they need. If it looks tight, keep the seat tube area free for a bottle cage — a half-frame bag at the front of the triangle is often more useful than a full triangle you can't drink around.

Place weight thoughtfully: heaviest items low and forward, near the bottom bracket. Tools stuffed into the top corner make the bike feel top-heavy when you're out of the saddle.

Turn the shape into a pattern

Transfer the trimmed card shape to pattern paper — baking paper or lightweight lining works well. Add 10mm seam allowance all round; drop to 8mm on tight curves so the fabric doesn't pucker.

Now decide the zip layout. A full triangle bag usually gets two zips on the non-drive side: a long one low down for tools and spares, a shorter one near the top for food and a phone. Keeping pulls on the non-drive side keeps them away from your leg, and zips that open towards the centre of the triangle are easier to reach while riding.

• Draw the zip lines on the pattern before cutting anything. Aim for an opening of at least 200mm — narrower and you'll be fishing for a tyre lever with two fingers.
• Fold the paper along each zip line to check the panels don't overlap when closed.
• Draw a side panel and taper it: roughly 45–60mm deep at the bottom bracket end, narrowing to 25–30mm at the head tube corner. A parallel-sided panel turns the bag into a cushion that rubs your knees.
• Tape the paper together, stuff it with newspaper and strap it into the frame. Sit on the bike and pedal.

Choose materials that hold their shape

• Outer: 500D coated nylon or a laminated ripstop. 500D is stiff enough to hold shape and still sews on a domestic machine; 1000D is tougher but a fight.
• Lining: 210D nylon in a bright colour, so you can find the small parts.
• Zips: a continuous coil zip, size 8 or 10. A size 5 will fail at the slider first. Cut longer than you need and trim after fitting.
• Stiffening: a 1mm sheet of HDPE or polypropylene slipped into a sleeve in the drive-side panel, or along the top edge, stops the bag ballooning when packed.
• Straps: 20–25mm webbing with hook-and-loop, or a daisy chain laced with shock cord. A full triangle bag needs five or six fixing points — two on the top tube, two on the down tube, one or two on the seat tube.
• Paint protection: closed-cell foam or strips of old inner tube under every strap and along the contact lines.

Fit, load, ride, revise

The mock-up ride is the cheap test. Strap the paper version in, sit on the bike, pedal out of the saddle and swing your knees. If it touches, trim the pattern now.

Once the bag is sewn, fit it empty and check the panels aren't bowed, then load it fully. A bag that only fits when empty will strain the zip and pull the straps loose. Ride it loaded on rough ground and look for rub marks, rattling pulls and slack straps; a short length of cord on each pull stops the rattle.

Mark the pattern with any adjustments — a millimetre off the head-tube corner, an extra strap at the bottom bracket — and keep it. Second versions are always better, and the pattern is the part worth keeping.