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I have a split crown race on my carbon bike but that has a tapered steerer so wasn't sure the same principle would apply in this instance. I've just taken the fork out and the measured the crown width with some digital calibers and its coming in around 26.2mm so I'm short by .2mm.
Took a couple of pics of the fork crown with and without the 'race' on it. Also sat the bearing on the crown race and there is a small gap between them.
Seeing as this is a £100 headset I'm not that keen on cutting it up which is why I'm leaning more towards trying the coke shim or even giving this "Sellotape" method a try!
3 Attachments
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motman
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Seeing as this is a £100 headset I'm not that keen on cutting it up
Invest £5* in a split crown race with the correct chamfer (36° or 45°, if it's not marked on the bearing ask innicycle to confirm)
Or invest in a new fork, which should have the correct diameter to press on the bearing seat and also won't come with that nasty pitting which is where the crack that eventually snaps the fork will start.
*£4 if you just want a solid 26.4mm×45° one from my parts bin which you'll have to split yourself, $35 shipped for a spare from Innicycle
gbj_tester
Google "split crown race". Loads of cartridge bearing headsets come with split crown races, the chamfer transfers axial load into radial compression of the "race" (collet) so the higher the axial load, the tighter the collet grips the steerer. This is also how the preload adjuster at the top solves the issue of the upper bearing collet not being a press fit on the steerer.
The simple machine which does this is called a wedge (in this case wrapped into a cone)
Of course, you could be right, if the difference between the diameters is so great that the bearing bottoms out on the flat face of the seat before the collet has shrunk enough to grip the steerer. You'll be able to predict this by taking appropriate measurements (will probably require a feeler gauge to check the clearance between the bearing and the flat face of the seat) and using trigonometry.