MCHardmanUK
08-27-2006, 02:26 PM
Originally posted by Chris King Cycle Group.
Headsets in General
There are three types of headset used in the BMX industr, there are from left to right:
Conventional
Intergrated
Internal
[/URL]
The Conventional Headset
At right, 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):
Between the lower bearing and the base plate and
Between the upper bearing and the bearing cap.
] (http://www.chrisking.com/tech/int_headsets_explained/int_hds_frames.html)
(http://www.chrisking.com/tech/int_headsets_explained/large_conventionalHS.html)
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.
The "Integrated" Headset
Now lets apply this knowledge to the "integrated" system. 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.
(http://www.chrisking.com/tech/int_headsets_explained/large_bearingcap.html)
(http://www.chrisking.com/tech/int_headsets_explained/large_integratedHS.html)
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
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.
[URL="http://www.chrisking.com/tech/int_headsets_explained/large_internalHS.html"]
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.
Whats the best type of headset?
There is no 'best' headset type, they are all equally as strong and reliable, the only difference is how there design effects the stress transfered through the frame they have been designed to work with and how the design of a frame is affected dpending of what type of headset it is designed for. All this is explained above and it makes for interesting reading, so I'll let you the reader decide what type of headset is best.
Headsets in General
There are three types of headset used in the BMX industr, there are from left to right:
Conventional
Intergrated
Internal
[/URL]
The Conventional Headset
At right, 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):
Between the lower bearing and the base plate and
Between the upper bearing and the bearing cap.
] (http://www.chrisking.com/tech/int_headsets_explained/int_hds_frames.html)
(http://www.chrisking.com/tech/int_headsets_explained/large_conventionalHS.html)
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.
The "Integrated" Headset
Now lets apply this knowledge to the "integrated" system. 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.
(http://www.chrisking.com/tech/int_headsets_explained/large_bearingcap.html)
(http://www.chrisking.com/tech/int_headsets_explained/large_integratedHS.html)
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
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.
[URL="http://www.chrisking.com/tech/int_headsets_explained/large_internalHS.html"]
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.
Whats the best type of headset?
There is no 'best' headset type, they are all equally as strong and reliable, the only difference is how there design effects the stress transfered through the frame they have been designed to work with and how the design of a frame is affected dpending of what type of headset it is designed for. All this is explained above and it makes for interesting reading, so I'll let you the reader decide what type of headset is best.