How can I install a 1 1/8" to 1 3/8" Synapse fork onto a 44 mm headtube? I know you get headset questions all the time, hopefully this one mixes things up a bit. I recently acquired a 2015 litespeed CX frame, which has a 44 mm head tube. It is listed as having a height of 12 cm. I picked up a fork, from a Cannondale Synapse 2018, size 58. To my great surprise, the fork is listed as having a 1 1/8" to 1 3/8" tapered steerer. The headset on the Synapse is listed as a "Synapse Si". Most sites I have found are about trying to fit an alternate fork into a Cannondale headtube, as opposed to the other way around. I have found the following webpages: < < Is there any way to get this fork onto my 44 mm headtube? Thank you!

A lower akin to an EC44/40 could be made to do this, but it doesn't exist commercially. In other words it would be an EC44 frame interface and take the sort of bearing that goes in IS49, whereas EC44/40 does the same but with IS52. This hypothetical lower can't be described in SHIS because Cannondale 1-3/8 forks all have integrated crown races.

So yes, but it would have to be a custom made cup, i.e. turned out on a lathe just for the purpose. Using EC44 on a bike intended for ZS like this will of course slacken the geometry.