Someone recommend some good headsets! I have heard of chris king but get quite lost in what I am looking for. I am riding a standard aluminum cannondale synapse. I was professionally fit and just talked to the fitter again today and was encouraged to slam the stem as I am flexible.

FORK
SYNAPSE SAVE, CARBON BLADES, 1-1/8"
HEADSET
SYNAPSE SI, 25MM TOP CAP

It's not like you have much of a choice. A Synapse should use an integrated headset. C'dale used the Campagnolo standard dimensions for many years, but I haven't kept up well enough to know if that's changed.

If you want low bars, then the Synapse frame was really the wrong choice, with it's 20mm taller head tube. The first step in lowering the bars should be a -17 degree stem, so the extension is horizontal. After that, you may be able to find a headset top section that's in the 8-10mm range to lower the bars further.

You don't really need an entire headset, just a new bearing dust cap. I have one of these on my caad10 and they're said to work on synapses as well.
https://metallicpoutine.com/headset-b...-covers/v-1-1/

Awesome Nagrom!!!
Yes Dave, the synapse was a bad pick but its easier to replace a headset than a frame. Caad10/supersix in my future!

Shipping is pretty quick too. Only took a couple days.

Looks like the synapse is a perfect fit according to the site! So, when installing is it a simple swap of parts and do I need to re-grease the area? I am assuming I can place my stem right on top of it or maybe use a spacer?

Are you cutting your fork down? Because otherwise you will need spacers on top of your stem to make up the difference in stack heights.

I will cut the fork in a few weeks once I find the adjusted height comfortable.

If you install that short top section and cut the steering tube as short as possible, you may reduce your chances of reselling the bike, with the limited handlebar height adjustment. That's why I suggested using a -17 (73) degree stem first. If the bars are still too high, then change the headset top section.

It really depends on how long the OP intends to keep the bike. That's going to be the cheapest way to get by on a temporary basis, but a -17 stem on a tall head tube with spacers under it is going to look absolutely horrible. Part of the fun of a slammed stem is doing away with the slop that comes from having spacers under the stem.

There's a new uncut 2011 black Synapse fork on ebay right now for $100 BIN. Buy cheap fork and shorter bearing cover. Enjoy slammed stem. Put original stuff back on when it's time to sell.

Yeah, its a simple swap. You may need a microspacer if it makes contact with your headtube, but it shouldn't. And if it does, its a simple fix.

Most carbon fork manufacturers spec a 5mm-10mm spacer above and below the stem. It's up to you if you want to abide by that, as many don't.

If all that's used is the stock 25mm headset top, then there will be no spacers. When I wanted 2cm more handlebar drop, from 9cm to 11cm, I swapped my 84 degree stem for a 73 degree and it looks just fine with the standard 15mm headset top section and one 5mm spacer. The stem extension is horizontal, just like all stems used to be, before threadless headsets.