It also maintains preload on the system. With the forces from a long travel fork, the axial strength of a crown and stem clamped to then steerer is exceeded and they will slip.Originally posted by novice
What a sec. Stress on the star nut?
If I remember correctly, the only thing the star-nut/top cap was for was preloading the headset. In fact I am sure you can take the top cap/bolt off after the headset is properly loaded. One just needs the stem to be torqued down properly. I know this is true for single crown forks, but don't see how it could be different on dual crown forks. Because once the stem is tighten down, the stress of keeping the headset preloaded is the burden of the stem. This is because in order for the top cap to recieve any stress, the stem must first slip. So the strength of the star fangled nut only really needs to be strong enough to preload the bearings, it is not designed to take additional stresses.
check this out:
http://www.canecreek.com/site/product/headset/info/faq.html#Anchor-H7
If the clamped interface of the stem and crown to the steerer tube could handle the axial forces dished out by a long-travel fork this would be true. However headsets use a cone to center the steerer in the bearing system. This means a good component of the massive radial forces are transferred axially. This is often enough to cause the clamp to slip. A headlock insures this won't happen in addition to provided more consistent preload that a SFN, with which there is some flex in the star leaves.Originally posted by novice
the top cap doesn't maintain the preload once the stem is tightened.
Novice WAS correct until the advent of long-travel forks. It used to be that no fork/headset combination could produce enough upward force on the stem stack to cause it to slip. That is no longer true.Originally posted by kitchenware
Novice is correct.
The star nuts job is done once everything is pulled tight and is torqued correctly. If you are pulling star nuts, then something is set up wrong, i.e. torques, tightening patterns or contact surfaces.
jim
Well... I've never had a problem with it, so I see no need.Originally posted by ohio
Novice WAS correct until the advent of long-travel forks. It used to be that no fork/headset combination could produce enough upward force on the stem stack to cause it to slip. That is no longer true.
Reread my posts. I explained how a component of the radial force is transferred axially through the compression ring and/or bearing cone.Originally posted by novice
how does a long travel fork produce/cause more upward force than a shorter travel fork? The only force that increases is on the headtube, and that is a torque trying to rip the headtube from the top tube and crush the down tube. This is because of hte increase in axel to crown length of fork, thereby increasing the lever arm of any force experienced by the wheel.
Originally posted by novice
yeah, I get that. What I don't get is how long travel forks produce more upward force than non-long travel forks. I can ride a long travle fork, then a non-long travel fork, the forces don't change. The spring rate is lower on the long travel fork because it compress farther. Hell, with a long travel fork I'll put less force on it because it jacks the front of the bike up, effectively loading more of my mass onto the rear wheel.
Originally posted by ohio
The same forces exist in a single crown system, the magnitude is just much greater from a long travel fork. For example take a cartridge style headset and assume the compression ring is at a 30 degree bevel from parallel with the steerer. That means, in a well-greased system, that for every radial force on the headset, there is a force of half that magnitude pushing up on the crown, stem and preloading device. This can exceed the frictional force of a stem clamped to a steerer. Since a SFN is much more flexible, it offers little support in addition to the preload force to prevent the stem from moving. A headlock is a much more rigid system (which actually makes it harder to adjust proper preload), and does a much better job of preventing slippage along the axis of the steerer tube.
However, the usual culprits for a headset that consistently loosens are poorly faced headtube or poorly installed HS cups, as I mentioned before.
Um, not to be a jerk, but apparently you don't. I explained how radial forces can be transferred axially. Radial forces on the headset result from lateral and fore-aft forces at the dropouts. The further the droupouts are from the headset the greater the moment on the headset, the greater the radial forces are on the headset. Therefore long travel forks are more likely to cause a loosening headset. In most cases a star nut and the stem and upper crown are sufficient retention. In some cases (usually exaggerated by some other aspect of the setup) it is not.Originally posted by novice
yeah, I get that.