I've a vitus substance Alu gravel bike and was idly wondering if I could add 2 rivnuts to the top tube for a bag?
Any issue or just don't do it?
Sounds fine to me, as long as you're competent enough with the tools
Drill, deburr, check carefully for cracks/chips/damage round the holes, make good if there is any (little round file or something), anticorrosion paint, fit rivnut.
Obvs. use the sharpest drill bit you've got!
I personally would cock it up and have that niggle that the frame would fail, so would just stick with velcro...
Google FEA analysis bicycle frame stress (or similar). Avoid the worst bits
Check out 76Projects, they have some great adhesive solutions.
Ortlieb and tailfin TT bags use a rubberized foot, reinforced body of the bag, and stretchy rubber straps that mean bolt-on bags have little use. They also negate the need for a steerer strap. I wouldn't be drilling a frame for this particular application personally, based on alternative options and potential for damage.
My dad did this on his bike and put the holes offcentre, it made my teeth itch every time I saw it. But the frame never snapped.