Need Help Determining Replacement Headset Bearings

Related to my other post inquiring about how to remove headset spacers, how do I determine which replacement bearings fit my bike?

It is a 2010 Motobecane Immortal Pro. The upper bearing is labeled FSA IS-2. I easily found replacement bearings and thought I was good until I came across a Park Tool site that talks about two different standards for IS-2. I suspect the actual dimensions are printed on the bearing, but I can’t get to it right now due to the stuck spacers and really want to have everything on hand when I tear apart my front end.

The “IS” system is considered the most common. The name Integrated System is not a registered trade name. The system uses the 45-degree bearing contact in the frame. The bearings for the 1-1/8 inch steering columns use a 41mm outside diameter with a 45-degree bearing contact in the frame. The bearing may be marked “36-45.” The first number refers to the inside bearing contact with the headset race or centering cone. The second number refers to the frame contact.

The less common 36-degree angular contact standard uses a bearing for the 1-1/8 inch steering columns with a 41.5mm outside diameter. The bearings may be marked “36-36.” The IS frame standard of 36-degrees is now considered obsolete.

Also, how do I determine the size of the lower bearing? The fork is described as “AeroCarbon SL High Modulus Monocoque Carbon Fiber with Carbon Crown + Aluminum Steerer 1.125 inch.” The fork sits flush with the bike frame at the lower bearing. This Bike Radar site has a bunch of tables but I don’t know where to find what my bike needs.

Thanks for the help!


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OK, that didn’t format as I expected….

Go to the site, and then headsets. The PDF is their explainer for headsets. In my experience they make good stuff