After some research I did not find similar photos/examples to mine so decided to ask.

Recently I have bought used aluminum road bike. I did check all other parts and they are in good condition, but forgot to flip it and when I did I found this:

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So my questions are:

  1. How bad is this?
  2. Can I stop it from spreading?

1 Answer 1


It’s not bad, it’s cosmetic only. It’s just surface corrosion that’s got under the clear coat. Do you live in area where salt is used on the roads? Perhaps the previous owner was not good about cleaning under the bottom bracket shell.

You can halt this by making sure to thoroughly clean the bike regularly and use something like WD40 in vulnerable area to displace water and provide a protective film.

  • Storing the bike inside helps as well, to reduce this Aluminium Oxide forming.
    – Criggie
    Oct 25, 2020 at 12:31
  • If the cosmetics don’t bother you, pop off the cable guide and lightly hand sand the affected area to remove the corrosion. I live near the sea and need to periodically kill off a similar corrosion. Oct 25, 2020 at 17:23
  • @WarrenBurton the trouble with this is you will remove the clear coat making further corrosion more likely Oct 25, 2020 at 17:45
  • @ArgentiApparatus Im cutting paint back to raw metal which is a permanent fix for me. Repainting just invites new corrosion , so I let the inherent coating take care of things. Oct 25, 2020 at 18:27
  • Thank you all for answers. They were very helpful. 1) yes, sometimes there is salt on roads but not that often. 2) will try WD40. 3) will keep it inside that for sure. 4) not sure will I try removal, but will have it in mind.
    – Vasyl
    Oct 26, 2020 at 9:20

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