The great Headset Debate

I have bikes with both headset types, they all work just fine, and they play no role in my bike decisions.

Voted cups because it simplifies frame manufacturing and gives you some recourse if you end up running a loose headset and beating up your bearing.seats, but agree with the above...both work fine its not a purchasing decision.

Whatever standard allows me to use angle adjustable headsets if I ever wanted to. That's the standard I would want. Otherwise, I never think about my headsets.

What ever style distributes the stress over the largest area, is adjustable and also the standard that is not smoking crack

It wouldn’t affect my buying decision.

If I get to choose when designing a frame I prefer IS. Here are some factors I consider when choosing for a frame:

IS head tubes have existed for about 20 years I’ve never seen a cracked one, whereas I have seen cracked press fit head tubes. This seems more important than angleset compatibility especially if I get to design the HT angle.

This crack resistance is because with IS the highest stresses areas are recessed inboard from the head tube opening*, and there’s no press-fit-hoop-stress**.

Both IS and ZS allow the down and top tubes to be better separated than EC; and the head tube to be longer for equivalent stack (this is particularly important for small frames with 29” wheel and long travel forks).

For welded frames the 46ish millimeter OD of an IS head tube typically delivers a nice long welds*** as the DT and TT  junctions wrap almost 180 degrees around the HT.

For carbon frames ZS can be the better choice because often an IS frame insert negates the , * and ** advantages, and there are no welds to envelop the head tube.

Head tube surfaces really don’t wear, but if the head tube wore with IS, simply retensioning the headset would move the bearing deeper into its conical bore. With ZS or EC a wallowed out head tube is hard to fix (probably it’s a sign that it’s time to retire a frame). 

I see all this as a big downgrade in products in recent years, I have a Santa Cruz V10 2024 and I haven't had any problems yet, but I've seen many friends with the parts causing looseness and noises in the parts that fit with looseness, and not with pressure. I've seen the same thing a lot in the Canyons Sender.

For me the average rider, if the bars turn, there is no creaking and i only need to regrease every year or so i couldn't care less what it is.  Don;t overthink it. Very few of us actually benefit greatly from top end tech. Waste of money

I had zero stack headsets for years and years and still have a pile of them in my bike bin, but I've been on IS on my Santa Cruz bikes for the last 5 years. I've never had a problem with an IS headset so far, but they scare the hell out of me and given the choice I'd take a press-in ZS headset 7 days a week.

First, it seems to me the IS headset requires waaaaaay higher manufacturing tolerances. Again, I've never had a problem with this on my Santa Cruz CC frames (disclaimer: SCB sponsored rider), but I can imagine this being a problem in an industry that has a mixed track record of delivering on tight tolerances.

Second, shipping! Whenever I packed my frame up for shipping in a standard bike box, I prayed to God the bike would arrive with a functional head tube. The thinnest part of the head tube, the outer lip of the IS interface, is the part that's exposed against the top and side of a cardboard bike box. YIKES. My best idea was to ship the frame with the headset bearings and top cap in the frame, and to use zip ties on both sides to try to keep the bearings in place in the IS cups, but this solution sucks. With ZS cups press-fit into the frame, there's a much more substantial structure to reinforce and protect this vulnerable spot on the frame.

Lastly, maintenance and problem sleuthing. If I have any issues whatsoever with a ZS headset, I can knock out the cups and start from scratch. If I have problems with my IS, if I pulled and cleaned everything and regreased it before assembly and still have problems, I have to worry about my head tube now? That's crazy. Who wants to have "check to make sure your front triangle isn't ruined" as part of their standard headset checklist?

I'm guessing the aluminum ZS cups weigh 20-40 grams more. Yeah, I'm cool with that.

Regarding wallowing out from excessive/careless headset installation or removal, I've done horrible things to ZS headtubes and never had a problem. Lots of "here's your new team frame the night before a race" headset installs with wooden blocks, mallets, etc and never had a problem. Not saying you can't wallow out a headtube, just saying I've never seen it. A robust ZS headtube is made out of very thick aluminum or carbon. It's not a pop can.

And regarding impacts, I can't imagine an impact that would ovalize or crack a robust ZS headtube and not crack or wallow out an IS. But I don't build bikes for a living like Digitbikes, so I accept that I'm just another idiot with an opinion. 

Both type of headsets are fine and have their positives and negatives.

The main reason i would say cups are far superior, is that it allows oversized/oval headtubes for reach adjust and angle sets. (you can do it with IS headsets but its less common). 

But IS on a XC bike would be my preffered, and cups with reach adjust on a DH bike. 

Press in cups for me. The surface only has to be a tiny bit worn or out of shape to cuse all kinds of creaking and lossening problems. Even a slighlty loose headset will start to wear the bearing surface quickly, and a lot of people don't preload headset bearings enough (as evidenced by the wear marks from the collet eating in to the steerer) so once its started the frame is pretty much ruined. Some companies are a lot better - Santa Cruz, as mentioned really knows how to design an interface like that strong enough and with decent tolerances that its unlikely to be a problem. 

Wouldn't change my bike purchasing though - IS is too common that you would be cutting out a huge chunk of options if I decided it must be ZS

Another vote here for cups due to the ease of adjustability regarding reach and angle.  

However, my number one criteria is that cartridge bearing headsets have split or slotted crown races.  I have several from FSA, Hope and Works Components...haven't found a downside yet.

9point8 released an adjustable head angle kit for IS style bikes

The integrated headset on my Propain Hugene lasted less than 2 months before destroying itself. I took the fork off chasing a creak and inner race and bearings came out with the fork. Getting the outer bearing race out without damaging the carbon head tube took a lot of creativity and swearing. 

There is a greater chance of damage to the frame with an integrated headset if something goes wrong. 

It's not a factor in my buying decision though. 

I'm  not rich enough for a nice modern bike  so a few years ago I bought a Cannondale Prophet frame and began building it up. (See my bike check) I modernized it and with its 1.5 headtube I'm able to run a modern tapered fork. I couldn't do thar with an IS headset. 

Did they? I can't find it on their website or their IG page. Asking because that sounds super sketchy (lots of leverage in a very shallow IS cup) and I wanted to see how they did it. Can't find any evidence.

While the idea is great, buddy has one installed on his SC nomad and bottom cup always rotates over time (over time not as in months, but rather few bike park days at best). At least it doesn't creak, but it's not perfect.

Funny you should mention Santa Cruz and IS-headsets. On my Tallboy V5 CC, the lower bearing seat cracked after less than 6 months of riding. That was the most scary mechanical failure I ever had on a bike - the kind that could end you up in the hospital if you don't notice it in time. Generally, since owning that Tallboy, I'm very much over Santa Cruz.

Regarding IS vs ZS: I don't really care. Like others have stated, having either wouldn't influence my purchasing decisions. For me, the specific type of headset is way down the list of priorities. 

Though I think we'll see more brands move to fully integrated or even proprietary headsets, as built-in reach- and angle-adjust mechanisms are becoming more widespread (eg: Specialized Stumpjumper, Giant Trance X, Canyon Strive, Trek Fuel EX, etc.)

Ever so slight off-topic:

My new bike came with adjustable head angle via headset cup, sounded great! But it also comes with headset routing, luckily not the worst implementation and can mostly be ignored. Except of course if you would like to rotate those fancy headset cups, suddenly I need to take out all my cables and disconnect my brake lever. Maybe there is a fancy tool and procedure that doesn't require dismantling all my components, but it certainly seems like those "convenient" headset cups are never realistically getting flipped.