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I need to find a replacement headset for an integrated system "IS". I can get the required dimensions by removing the fork and taking headtube and steerer tube measurements by using a digital caliper. I then compare what I get to possible values listed in this Cane Creek diagram from their excellent Everything you need to know about Headsets:

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I figured out that I need a replacement for a IS42/28.6 | IS52/40 but what about the bearings angle? Is there many possibilities for a given SHIS? If the angle is written on the old bearing that is fine, but what if it is not? And what if you do not have access to the old bearings?

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    I like to confirm against manufacturer specifications. Even if you successfully measure the bearings (of find a useful part number on the bearings) you are replacing, do you have certainty they ones you are replacing are the correct bearings (e.g. I have repaired wheels that turned out to have had wrong sized bearings installed)
    – mattnz
    May 2 at 22:30
  • @mattnz wow really? You mean the wrong size of loose ball bearings?
    – olliebulle
    May 6 at 15:56

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I think this angle is called a chamfer. The picture depicts a chamfer on the outer race. However, the inner races are chamfered as well - I think the inners are always chamfered.

Based on this 2021 Cyclingtips article by Dave Rome (metered paywall, also accessible through incognito window, site now under purview of Outside Inc. and not all images may display in future), the angles are usually 36 or 45 degrees. For the inner race, you can simply stick a business card into the bearing. There'll be a gap between the chamfer and the card stock if the chamfer angle is 36 deg, and no gap if it's 45 deg.

Rome reported that most of the outer races are 45 degree chamfers. There's not a super convenient way to confirm this. If you had access to a spare bearing whose outer race was chamfered at 45 deg (and you were sure of this), then you could just hold the chamfers against each other - the bearings will form a 90 degree angle if the unknown chamfer is 45 degrees. Otherwise, you need a protractor and a good eye, or a more specialist tool.

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    The inner angle is most important (and the one that varies btw 36° or 45°), because it has to match the angle of compression/centering sleeve on top and crown race at the bottom. Most cartridge bearings have the size and angles (inner x outer) laser etched on the outer circumference. Keep in mind that most headsets come with everything included for a perfect match. Check with bike manufacturer (Owners Manual generally has this info) for the IS spec angle (usually 45°), while pressed cups included with a headset will match included bearing
    – Jeff
    May 4 at 12:34
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Just discovered some nice tools from FSA to figure out all sorts of headset dimensions, including angles. They could be useful if one is doing lots of headset replacements. Still, I think the tips in Weiwen's answer (and Jeff's comment) would go a long way.

Headtube Guide for 1" and 1-1/8":

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Headtube Guide for 1 1/4" and 1.5":

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