Replacing headset on 2018 Cannondale Synapse

[Onno]

I had my Synapse for 2 years, and I like it a lot. From the beginning, though, I've had to really crank down on stem cap bolt to keep the headset from clicking. A friend who worked at a Cannondale dealer told me that the headset bearings on these bikes are a weak point--they are low-end FSA bearings. I thought it might be a fun self-isolation project to replace the bearings with something better, but I'm having a hard time figuring out what will fit.

The owner's manual lists the specs as:
the upper bearing:
ACB 45/45, 41.8 O.D. with 45mm offset and 54mm crown diameter
the lower bearing:
ACB 36x45, 48.9 O.D. with 45 mm offset and 54 mm crown diameter

I've been trying to match these numbers with what I see on offer on Chris King and Cane Creek, but I don't know enough about what the numbers mean on any of the websites to find a match.

Can anyone with a bit of time or a lot of knowledge help me out here?

Many thanks, as usual,
Onno

[ultraman6970]

U have to measure the O.D at the frame. That will tell you what to get, because if the bearing doesnt fir in the hole then wont work, if bearing is too small the headset will get lose all the time. Measure the OD of that front tube.

[yinzerniner]

I had my Synapse for 2 years, and I like it a lot. From the beginning, though, I've had to really crank down on stem cap bolt to keep the headset from clicking. A friend who worked at a Cannondale dealer told me that the headset bearings on these bikes are a weak point--they are low-end FSA bearings. I thought it might be a fun self-isolation project to replace the bearings with something better, but I'm having a hard time figuring out what will fit.

The owner's manual lists the specs as:
the upper bearing:
ACB 45/45, 41.8 O.D. with 45mm offset and 54mm crown diameter
the lower bearing:
ACB 36x45, 48.9 O.D. with 45 mm offset and 54 mm crown diameter

I've been trying to match these numbers with what I see on offer on Chris King and Cane Creek, but I don't know enough about what the numbers mean on any of the websites to find a match.

Can anyone with a bit of time or a lot of knowledge help me out here?

Many thanks, as usual,
Onno

So after spending WAY too much time trying to find a low stack headset for synapse disc project bike, I think I might have the answer.

First thing is - what year and size is the Synapse? Different years use different specs of headsets, and for the more modern bikes the different sizes use different forks with different headsets.
https://www.cannondalespares.com/Cannondale-Supersix-EVO-Neo--Synapse-Carbon-Disc-%282018%2B%29-Headset-%28No-Crown-Race%29--K35018--K35028--K35038/product_detail/3-43244

Second, based on your measurements (they seemingly are more for the fork than for the headsets) from the SHIS manual, it looks like you're going with:
Upper: IS42 (outer)/ 28.6mm inner or 1-1/8" Campy with 45/45 contact bearings
Lower: IS49 (outer)/ 36/37mm inner or 1-3/8" with 36/45 contact bearings
See poster here (low def, but bottom table shows sizings)
http://www.canecreek.com/wp-content/uploads/2018/02/canecreek-shis-poster.pdf
Also a good chart is on the Ceramic Speed site:
https://www.ceramicspeed.com/en/cycling/support/ceramicspeed-headset-shis/

Also another weak point of the Cannondale headsets is their expander, which could lead to a loose headset and fork. It's very lightweight, but also absurdly flimsy. Suggest going with the Specialized expander plug, which is moderately lightweight (~20g) but very strong and will not slip when installed correctly.
https://cdn.bike24.net/i/mb/a1/5f/18/191236-00-d-354082.jpg

[Onno]

Thanks for the info.

My bike is a 2018 (Carbon DA version), size 58, so I think that the numbers and sites you are listing work for my bike.