I picked up this saddle post hard shell box on the cheap. I wanted to try it out as I am not digging the Xlab mezzo bag under the Turbo wing. Got the box in yesterday and it fits really well around the saddle post. But the bottom part that lays against the back of the seat tube, is just a tad loose fitting. I imagine that if I went out for a ride right now, it would rattle against the seat tube. It does have two holes on each side where it looks like you can fit something to strap it down. But just don't know what to strap it down with. I thought about looking for a long thin O-ring and strapping it down with that. I was also looking for something like an elastic tie, but didn't see anything like that. The other thought I had was to glue some type of soft material inside that piece so that it then makes a tight fit against the seat tube. Anyone have any thoughts or ideas?

I like the look of that box. It fits nicely with the bike’s aerodynamics. I would bet the two holes you pointed out are specifically there for use in fastening around the front of the seat tube. I would try something like a rubber band, or a small piece of inner tube cute thin enough to fit through the hole(s) (make the holes bigger if necessary). Then, keep the band from going back through the hole with a small piece of dowel rod or wire. — Dan

What about really thin straps of Velcro? You should be able to find something in the craft section and it should be cheap enough to cut down to fit. At least it will give you an idea and time to come up with a more permanent solution.

There's always zip ties, bungee cords, and mini-ratchet straps. For one combination locking tool box on my bike with very heavy things I even used metal zip ties:
https://www.amazon.com/dp/B09MQQ1KMT

Attached using this tool:
https://www.amazon.com/dp/B08ML8QX1Y

Funny the $3.92 version shows some kind of "ties" included, can't quite tell what they are? - https://www.aliexpress.us/item/3256808347679402.html?

This is the version I bought. LOL. They are just zip ties. They are not long enough to fit around the seat tube. I am hesitant to use zip ties as I don't won't it to scratch up the paint. I might try some velcro straps, but really looking for an elastic band of some type that will work.

But if you go to the AliExpress link about and look at a closeup of the bag…those holes at the bottom of the bag on the seatpost side look more like slots rather than round holes. ..as if they’re intended purpose is for using the zip ties to secure it.



Dan

Correct, it does look like zip ties should fit in there. The zip ties that come with it aren't long enough for my bike. I might go to Home Depot or Lowes and see if I can find a really small flat bungee.

I got it figured out. I went and got some elastic from the arts/crafts area at Walmart. Also, got some black beads. I am using those to prevent the elastic from going back through the hole. I did a brick on Saturday and everything worked out well. It's a tight fight to get everything in the box (extra tube, bike tool, two tire tools, CO2 cartridge and attachment). It looks much better than the Xlab bag that was sagging underneath the turbo wing.
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Sounds like a job for Mr Inner Tube...