I didn't realise this bike had a second set of drink bottle bolt holes on vertical length of the front triangle, they're stopping the seat post getting as low as I would like it.

If I drill the rivnuts out there's going to be a hole in the frame directly over the bottom bracket, what're the options for sealing the hole up? Are there any special considerations for drilling the nut out of a carbon frame?

Additionally does anyone know an internally routed dropper with 27.2mm diameter that has 150mm of travel?

Bike: 2021 Polygon Syncline C2 - Medium Frame https://www.polygonbikes.com/product/mountain/syncline-c2/

enter image description here

  • 4
    Special considerations - 'don't' comes to mind. You will weaken the frame, enough to cause failure, who knows. You will also void any warranty. Consider a shorter dropper or selling the bike and buying one suitable for 150mm dropper.
    – mattnz
    Commented Jul 8, 2021 at 2:09
  • 3
    If you unscrew the bolts from the rivnuts, does that help get the dropper post any lower?
    – Criggie
    Commented Jul 8, 2021 at 2:14
  • 1
    @mattnz How is it going to weaken the frame? If it's done correctly no carbon should be touched. The dropper pictured is 105mm
    – Kieran
    Commented Jul 8, 2021 at 2:16
  • 1
    It may be worth asking Polygon directly - they may have a dropper post idea that fits better without this change.
    – Criggie
    Commented Jul 8, 2021 at 3:31
  • 1
    What is your target seat height? Commented Jul 8, 2021 at 3:59

1 Answer 1


In a cycle shop, it is not uncommon for people with carbon or aluminium frames to come in with the problem that one of the bottle cage bolts has corroded and become stuck in the rivnut, or crossthreaded and stuck so they both turn together.

In this instance, the shop does what it can to remove the bolt (this is often time consuming) before drilling out the rivnut and fitting a new one.

What you are proposing to do is much less damaging to the frame than removing a stuck bottle cage bolt. It is unlikely that you will make a problem if you do this carefully. A shop would have insurance against a faulty repair but if you choose to do this yourself, you are on your own regarding safety.

Holes can be covered by vinyl stickers.

Have fun, but think carefully what you are doing before committing.

  • 1
    I wonder if there's a hollow rivet that could be inserted to protect the edges, something like an eyelet for a sail, aka a grommet or grommit. But not deep enough to interfere with OP's seatpost.
    – Criggie
    Commented Jul 10, 2021 at 5:15
  • 2
    If it's a concern, epoxy resin could be used to ensure that no loose strands of carbon get tweaked out of position @Criggie . Often (usually) the post slides right up against the inside of the tube so an eyelet would still interfere.
    – Noise
    Commented Jul 10, 2021 at 6:43
  • 1
    good point - perhaps the dropper should be greased/lubed and then used as a backer while adding "something" to fill in the hole. That should stop it sticking, while still proving enough room for the dropper.
    – Criggie
    Commented Jul 10, 2021 at 6:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.