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3 comments
In my experience with Genesis customer service (admittedly a few years old) they are completely useless and you can safely ignore whatever they say.
https://www.parktool.com/blog/repair-help/standardized-headset-identific...
ZS means the headset would be a cup that presses into the frame headtube, but is internal (so barely an edge of metal headset cup visible from the outside when assembled)
IS means the frame has the bearing seats (cups) machined into the frame so the headset doesn't have its own cups - it's basically just a bearing. If you look down the headtube of the frame you will be able to tell whether it is IS or ZS.
For ZS the headtube internal surface will be straight through. For IS you will clearly see some tapered machined surfaces close to the top/bottom edge of the headtube.
The bike shop should be able to confirm whether each cup is IS or ZS just with a visual check if you don't feel confident visually identifying it yourself. Have the bike shop seen the frame? If they are competent and have physically seem the frame, I would take their word for it rather than Genesis records which may or may not be accurate.
I would think it would be rather bizarre to have one cup ZS and one cup IS. But then bike manufacturers do odd things.
Thanks for the reply! It is odd to be honest. The original images of the complete bike you can clearly see the ZS cups just under the FSA top cone. However the frame 100% has the tapered edges for IS.
FSA has responded to me now recommending an alternative to the one listed on the complete bike from 2016. They say the original was an OEM part that is no longer available. It is IS so hopefully that will do the trick.
Thanks again for taking time to explain. 👍🏻