Here's some stuff I have kinda taken as scripture since 2005 when I first ran an internal headset. (not integrated) It's kinda lengthy, but explains the difference between an integrated vs. internal "cup type" zero stack.
Worth the read
Integrated Headsets Explained
This article is an overview of the differences between "integrated" and conventional headsets. It is not intended as an engineering paper but as a plain language explanation of this often discussed but mostly misunderstood new bicycle option.
When you call King Cycle Group, you talk to a person, not a machine. Maybe that's why so many people call us with their questions and comments. Because of this we usually a have a good feel for the 'pulse' of the bike shops and riders in the US. We also have learned to identify trends in the kinds of questions people ask when they call. We are not some big company where the engineering and customer service departments don't talk to each other. Engineering gets to hear it all. That's why we wrote this bulletin.
We have gotten an enormous number of calls about "integrated" headsets:
* "What is an integrated headset?"
* "Can I buy one from you?",
* "Is this a good thing for my new bike to have?"
* "When are you guys going to make them?"
We also hear plenty of complaints about the "integrated" headset. Most people think that if we get enough complaints about it, King will start making "integrated" headsets. For as much confusion as there is out there, and as many frame builders using them, and as much marketing hype as is being pumped out there about this, there is no real explanation of what "integrated" is. And certainly nobody is going to tell you why this is a bad direction for the bike industry to go in, and a bad choice for your next bike. Somebody needed to say something about this.
So here we are, saying something about it.
What is an "Integrated" headset?
It is a bicycle frame, fork and bearing system designed to eliminate the humble headset cup. To integrate means to combine and hopefully to simplify. What has been "integrated" by the integrated headset? The bearings now rest inside the frame instead of inside pressed-in cups. All of this trouble and confusion is to remove two 12 gram headset cups from the front of your bicycle. True, an integrated headset can give the bike a nice, smooth looking front end, but the consequences of this change to your bicycle are significant. Simply put, the performance and lifetime that you expect from your new bicycle will be reduced, most severely in aluminum mountain bikes.
All bicycle frames that use integrated headsets will ultimately have substantial performance and reliability problems due to the inherent flaws in this design. The largest flaw is a bearing system that does not positively attach the bearing to the frame, leaving the bearing to "float" resulting in wear and impact damage to the frame. As an additional complication, each manufacturer seems to be doing their own thing, with no real standardization to date. As a result, there are multiple bearing types and sizes (some of which have been discontinued with no replacement options) and the frame builders and bearing makers are not all working from the same drawings.
Lack of standardization is a bad thing for everyone. It means that you may not be able to get replacement headset bearings for your bike, and you will need them.
The Conventional Headset:
Below, you see the plain old, everyday headset. The little picture underneath is a close-up of the cup and bearing area. This is what it would look like if you split your bike right down the middle. The bearing is press fit into the cup (it won't come out and it doesn't move around in the cup), then the cup is pressed into the frame. The whole thing is trapped by the bearing cap and the crown race on the fork. Only the inner part of the bearings can move, the outer race is fixed to the frame. As you ride your bike the forces being applied (hitting rocks and bumps) are trying to shift the whole assembly around. Other than when you are turning the bars to steer, there are only 2 places where the assembly can shift (because the cups and bearings are all securely pressed together into the head tube):
1)Between the lower bearing and the base plate and
2) Between the upper bearing and the bearing cap.
These areas are called "dynamic surfaces", they move all the time (see the appendix page for the details).
Check out the Bearing Cap Picture below. The aluminum bearing cap on the left is a new one, the one on the right is a year old. This is perfectly normal wear and tear. This wear is right at one of the dynamic surfaces. Remember, we have headsets out there that are 25 years old, we have learned a lot about headset wear.
This wear is because the bearings and fork are always moving. They move even when the headset bearings are firmly attached to the head tube, like in a conventional headset. The part of the fork that goes through the frame is called the steerer tube. The steerer tube is always flexing around, whenever you brake, turn, shift your weight or hit something, the steerer tube is simply not staying straight. And the bearings themselves have some play in them that can't be adjusted out.
All of these factors together explain the movement and corresponding wear on the Bearing Cap Picture. Incidentally, a new bearing cap from us will cost you a big $18 and you can replace it in 2 minutes flat using one 5mm allen key.
The "Integrated" Headset:
Now lets apply this knowledge to the "integrated" system (shown at below). Notice how there are no headset cups. Instead of a positive connection between the bearings and the head tube, this design allows the bearings to "float". Without any press fit, the bearings are free to move about on those ledges because, unlike a normal headset, they are not actually attached to anything. Because the bearings are not securely pressed into anything, they will move around even if your headset is properly adjusted. The amount of movement (in an integrated system) will be much larger than a conventional headset would experience. In addition to the two dynamic surfaces that you have in a conventional headset, you add two more: the two interfaces between the bearings and the frame.
Now the wear that you see in our Bearing Cap Picture is not only going to happen to an inexpensive part, it is also going to be your expensive frame taking the abuse. (See the Appendix for a good picture of this).
OK, enough techno-babble, what can you do to really see what is going on? Try this: You know how you can see your fork flex backward when you are braking really hard? Under this kind of braking, the front of the lower "integrated" bearing is moving down and the rear is moving up, like an airplane in a nosedive. When you let off the brake, the front comes back up and "levels off" to where it started. Enough repetitions of this and your headset will creak and click. Replacing the bearings will maybe help for a little while, but that creak will be back, louder than before. Add a little dirt and water into the bearing area (on your first wet ride, guaranteed), and that inevitable bearing movement is going to have some abrasives to help grind away your frame. This is going to be considered "normal wear and tear" by your frame maker. When your headset starts to creak, you will need to start regularly packing your "easy to service" integrated headset area with grease just to keep it quiet. This will not be a permanent solution though. Pretty soon, no amount of grease will allow you to silence the creaking and a perfectly good frame will be ruined.
The "Internal" Headset, yet another twist:
An "Internal" headset (also known as "semi-integrated", for maximum confusion) is yet another headset type that places the bearings within the head tube (rather than outside the head tube, like a conventional headset does). The key difference between an integrated and internal is THE BEARINGS DO NOT TOUCH THE FRAME with an internal headset. They are contained either by a cup or an aluminum or plastic shim assembly which is pressed into the headtube.
One example is the Zero-Stack™ headset. It is an "internal" headset that uses the exact same bearings as an integrated headset. The important difference is that in a Zero-Stack™ headset, a cup is first pressed into the frame, then the bearing is placed in the cup. The bearing still floats around in the cup, and it will eventually trash the cup. This is absolutely superior to an integrated headset because you can replace the cup. The frame will never be damaged by the bearing. Another example is the Columbus-type internal headset. It actually presses a bearing directly into the bike frame.
The difference is that the Columbus system utilizes a very thin sleeve to take up the gaps between the bearing and the frame. This is certainly better than a bearing rubbing around loose in the frame, but this system again relies on the frame builder to make that head tube perfectly. We manufacture our headset cups to within .0005" accuracy in order to correctly control the bearing's location and press fit. Frame builders typically hold about .005" accuracy at best. This is 10 times less accurate than a conventional headset cup and while it is perfectly fine for building a frame, it just is not close enough for holding a bearing in place properly. Result? The bearing could be held in the frame way too tightly, or much too loose. Either way, the headset will wear out faster and the frame will likely be damaged.
Important Facts to Realize:
Your frame has been designed for a specific headset type. You can't convert an integrated headset frame to use an internal headset. The frames are too different. Just like you can't convert an integrated headset frame to use a conventional headset. Internal or "semi-integrated" headsets offer basically no structural advantage over the conventional headset. Sure they may be radially stronger, but this isn't really a weakness of the conventional design.
Conventional Headset Frame Preparation:
Proper frame preparation is critical for a good headset installation. A quality bike shop will always perform 2 steps:
1) Ream the head tube. This makes the holes in the frame nice and round, the right size, the correct depth and in line with each other.
2) Face the head tube. This makes the ends of the head tube flat and parallel to each other.
Frame paint can be pretty thick, especially powder coat. Many times, frame preparation just gets the frame paint out of the way so that you can get a good metal-to-metal connection. These steps insure that once the headset is installed, the bearings are nicely lined up with each other. If the bearings aren't lined up very well, all sorts of things can happen. The first one is that you may not be able to get a good headset adjustment, it may come loose all the time, might have a tight spots, and it will probably creak. Second, you can be sure that your headset won't last as long if your frame isn't properly prepared. BUT ONLY YOUR HEADSET WILL BE DAMAGED. AND IT IS EASILY REPLACED.
"Integrated" Headset Frame Preparation:
Although the people that make "integrated" headsets might tell you that they have a "self-aligning feature", the fact of the matter is that frame preparation is just as critical as with a conventional headset. Since frame manufacturers have traditionally had a hard time making the conventional head tube accurately, should we believe that making the integrated head tube is going to be any easier? The roundness and alignment of those little angled ledges is very important. And your shop can't fix it. Your shop doesn't and hopefully won't ever have the ability to cut or re-cut that ledge in your head tube. Even if they could, you wouldn't want your bike shop cutting away the inside of your integrated head tube. They could easily cut too deep and pierce your head tube, or cut the ledge deep enough that the top of the fork would hit the frame. That level of damage is nearly impossible to do with a conventional headset setup. What are you going to do with this frame when you have a problem? Warranty or the trash heap. What a waste.