Designing and 3D printing a triathlon bike storage box
A DIY storage solution
An age-old problem in triathlon racing is finding a way to store things like nutrition and multitools on the bike. Road cyclists can typically store these things in their jersey pockets. While this is possible for triathletes too, it can be inconvenient because the swim comes before the bike leg of the race, and storing nutrition and bike tools in pockets can waste precious time while transitioning to the bike leg during a race.
Many triathletes opt to simply tape things directly to the top tube of the bike, but storage boxes (or “bento” boxes) like this one have gotten more popular over the last few years. Naturally, as the owner of a 3D printer, this seemed like a perfect use for 3D printing (as they say, if all you have is a hammer, everything looks like a nail), and I decided to design and print my own storage box instead of shelling out the $30+ required to buy one.
Designing & prototyping
I designed the storage box to be just under the width of my bike’s top tube (about 1 5/8 in), and long enough so it sits just behind the head tube, with enough space that it doesn’t interfere with steering. I added holes in the bottom (2.5 in apart) so the box attaches to the top tube with the standard M5 bolts that come with the bike. I also added a slight recessed area around each hole on the inside of the storage box to snugly fit the washers, so the box stays firmly in place. I also made the opening of the top of the box one long slit, with the idea that a TPU print would allow the box to easily be opened during a ride, but be firm enough to hold anything stored inside in place.
I printed a prototype of the box in PLA before trying to print with TPU, since PLA is cheaper and a bit more reliable to print. It came out nicely, but had a small imperfection towards the rear of the print where I had designed the model too thin. It printed beautifully without any supports, which I wanted to avoid because they might be difficult to remove from the inside of the print.
Assembly
Despite how firm and brittle PLA is, I actually managed to screw the prototype to the top tube of the bike with a hex key, through the slit opening of the box. It looked great, but PLA would be a bad choice of material for the real thing because it isn’t flexible and can warp when exposed to sunlight and heat.
TPU test print
Next, I did a test print with TPU, which is more flexible and much more durable than PLA. I decided to proceed with this despite the imperfection on the PLA prototype, just to see how it would print with TPU without any supports. The imperfection was a little more pronounced, but overall it printed nearly perfectly!
I was very satisfied with the stretchiness level. When attached the to the bike, it could be easily stretched open with one hand, but it was firm enough to resume its original shape at rest.
Improving the design
To fix the imperfection, I made some edits to the model. I added some extra thickness all around, especially to the area that was coming disconnected and leaving a hole during printing. I also took advantage of having to edit the design to make it a little taller and longer for a little more storage space. This new design printed perfectly, and attached to the top tube just as expected!
Testing on the road!
I took the storage box out for a test ride, and it did a perfect job keeping my multitool and a granola bar secure! Nothing fell out despite many bumps in the road. It rained a bit on this ride, but there didn’t seem to be any issues with the box getting wet (though obviously it doesn’t keep its contents dry).
Overall, I’m very happy with how this came out, and I’ll be testing it in a race soon!
Grab the file
Feel free to download my design from Thingiverse and print your own!
Let me know if you print one—I’d love to see how others use or remix the design!
Print Settings
- Printer: Creality Ender-3 V2 Neo
- Filament: TPU (Polymaker PolyFlex TPU95, orange)
- Supports: No
- Rafts: No