How to Choose Headset Bearings - Transition from Straight Steerer to Tapered Steerer

Question

I am upgrading the forks on my wife's Cannondale Althea 4 hybrid bike. The new forks have a tapered steerer instead of the straight one on the old Suntour forks, therefore I need to change the headset bearings. The current ones are just the caged ball bearing type. I had planned to just transfer all the bearings from old fork to the new but due to the new forks having the tapered steerer, I need to change something. The Cannondale website says the frame has a 1-1/2" to 1-1/8" tapered headtube Is this all I need to know in order to order replacement bearings? I took measurements of the outside of the head tube and got 56.9mm at the bottom and 46.6mm at the top. Obviously, the wall thickness would affect the final bearing size but I'm not sure how to choose, without hammering out the old bearing cups (not sure if that is the right word?).

Answer 1

There is some Cannondale weirdness here that, unless you're into the study of bicycle headset standards and the way they're contorted and mutated for the purpose of finding new ways to make OEM parts be as cheap as possible, may not bear a full explanation.

You have this headset. It is an oddball. It goes into an IS52 headtube lower, which in almost every bike that has it would take an integrated headset cartridge instead of a pressed-in cup with a looseball assembly. It then has a kind of odd, looseball reducer crown race.

(The above says 2019 and I know your bike is newer, but it's the kind of thing where the product data was probably first created for the first generation of the bike that used this and hasn't been updated to reflect that now it applies to more model years).

You are going to remove at least the lower cup from the frame completely. The right tool to remove it is going to be a little bit of a choose your own adventure. A punch would probably work. You'll be working in the vicinity of the area where your new integrated headset bearing is going to sit, so you have to be careful. A normal rocket ship type tool may or may not work.

The good news is that you can replace it with a normal headset. You could do just the lower, or the whole thing. If you do the lower you are buying an IS52/40 lower, which is one of the most common types available today and should be easy to find. If instead you want to replace the whole thing and also go higher quality (probably a good idea if this is a bike heavily ridden enough to need a fork), you are getting an IS42/52 for a 40mm crown, which again is the most common type of integrated headset.

To be clear, what you have now is an integrated headtube with a weirdo mutant looseball-for-integrated-headtubes headset in it that looks from the outside like a ZS type headset, but it's not one that conforms to any ZS standard. If you decide to get it done at a shop etc, most will not be familiar with what this bike has going on, so you could show them this and they should understand.

The reason for this headset is probably that the frames for the whole series of bikes was designed around a particular headtube. That isn't necessarily easy to change on a per-model basis because of all the hydroformed and tapered tubes, etc. There can be impetus to keep the same frame, even if it's for a low-end model that's getting a straight fork. At that point you still really want to spec a headset that's cheaper than a normal IS model with a reducer crown race. Apparently this headset was either available because enough other brands had found themselves in the same spot, or potentially the economies of scale lined up such that they just had it made. And thus an outlier headache compatibility situation is born.