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The bicycle is a carbon fiber cross-country machine. It is from a local manufacturer, not a well known one.

Compared to other CF bikes but for more aggressive riding, when I knock on the tubes it feels that the wall thickness is half of the others! Nevertheless, it handles it's purpose well.

I am contemplating is it safe to add a triangle bag with a multitool, tube, oil, rag. <TODO: I have the bag, just equip it and weigh it> <TODO: add picture> Intended application: cross country with rock gardens and drops below one meter. My worry is that the bag is going to load the top tube radially. And the end strap is at the middle of the tube where it's certainly weakest.

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    @MaplePanda I am worried because the loading of "drops and stuff" is axial on all tubes. The bag would be a radial load and I've heard CF is non-istropic. Now thinking of it, the very shape of the top tube is intended to stand axial loads. – Vorac Feb 15 at 6:56
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    @MaplePanda Vorac is right, the direction and location of the force has a strong influence on how much force can be endured without breaking. Especially a perpendicular force right in the middle of the tube has the potential to provide the additional bending that's needed to break the tube under compression. I have no experience with carbon frames, so I won't answer, but the worry is very well justified. – cmaster - reinstate monica Feb 15 at 8:53
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    A not unknown accident on an XC bike ... youtube.com/watch?v=glU-ZoJssjA - no frame manufacturer would ship a frame that failed under this loading. A tube bag is minor in comparison!!! – mattnz Feb 15 at 9:10
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    I would be more worried about the straps rubbing and essentially sawing through the carbon with so much vibrations more than the overall force. – abdnChap Feb 15 at 9:27
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    @MaplePanda I carry oil in my road toolkit, which I also use for long MTB rides. The oil is decanted into a 5ml dropper bottle (cheap on eBay). That's enough for 2-3 chains; the other main use is if cleats start to feel stiff. But (on road) it's not unknown for me to ride 300km in almost unbroken rain – Chris H Feb 15 at 11:55
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Opinion, but a frame bag won't cause any problem for a normal bike frame. If it were an ultralight hillclimbing bike with no paint or something specialist, then I'd worry.

If you're concerned about fretting of straps on the clear coat, get some of those clear frame-protection stickers and apply to the frame under any retention straps for your bag. Also cinch velcro straps down firmly.

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    Agree completely. I'll add a recommendation to get generic 3M "clear helicopter tape" for the frame protection as you'll be able to purchase 10x the material for 0.5x the price compared to something branded for cycling. – Paul H Feb 15 at 16:24
  • Clear frame protection is expensive, just use duct tape. – mattnz Feb 15 at 19:18
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    @mattnz $10 will cover your entire frame, and the loss in resale value you get by slapping duct tape on your frame is worth much more than that. – MaplePanda Feb 15 at 19:39
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    @ChrisH I prefer a small frame bag, mounted in the nose of the front triangle, because it moves weight forward (helps me on climbs) and I can access it while riding (carefully). – Criggie Feb 15 at 22:01
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    @MaplePanda If you ever intend to sell your bike. There is also extra value in a low resale value: It reduces the likelihood of theft. If you do not intend to sell your bike ever, you are free to slap on any amount of duct tape, to customize it any way you want, and enjoy your bike for a longer time. Of course, that requires that you yourself don't fall for the looks of a shiny bike... – cmaster - reinstate monica Feb 16 at 21:43

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