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(Noob here.) I have a Trek Madone 2.1 2014 (Aluminum body, Carbon fork), and while upgrading the front brakes, some stuff got stuck and I damaged the fork. I got a fork from ebay that seemed to match. There's a difference however in the way the fork sits at the bottom of the headset:

two forks one bearing

In the old fork (right), the bearing was sitting directly on the fork, snugly. On the new one (left), it can sit there, but it does not seem correct: it is not hugging the fork as it was on the old one.

Question: What kind of adapter is required for that connection here, if this is possible at all?

Thanks!

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The new fork requires a crown race.

The old one had this integrated.

Measure the diameter of the flat sides where the crown race will sit. You will have to order a suitable replacement but they are quite easy to find and moderately universal...

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  • Thanks a bunch! These flat sides are at 43.78mm, while the inner diameter of the bearing is 39.85mm (if that's relevant). The diameter of the tube is 30mm. I can't seem to find a 44/30 crown race (if I'm reading what these numbers mean correctly). Am I to get a 42/30 and hammer it in somehow? Cheers!
    – Michaël
    Commented Aug 1 at 19:55
  • @Michaël The lower headset bearing spec should be IS52/40 but I am not sure why your crown race area is measuring so much over 40mm. I don't have a spec for this.
    – Noise
    Commented Aug 1 at 22:18
  • If you have a trek dealer nearby, they can identify the parts with "Dexter" if it's not possible to work it out here.
    – Noise
    Commented Aug 1 at 22:20
  • Thanks! I'll go see my local Trek dealer tomorrow and report. FWIW, this reddit thread seems to have a fork that looks very similar, and they seem to say that it has an integrated crown race. Maybe this fork is simply not compatible with the bearing/headset I have? Oof. Cheers!
    – Michaël
    Commented Aug 1 at 22:34
  • The Trek dealer didn't have the fork in their system; they say that any part of a bike pre 2019 is not listed separately, and that I'd need the exact bike model of the new fork for them to fetch info—as the fork is an eBay buy, no luck there. They helped, however: the new fork has an integrated crown race; the best guessed solution the tech could give is that I should try a 36° bearing with the same specs as my previous 45° bearing. Will report if it worked!
    – Michaël
    Commented Aug 2 at 16:23

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