what is star nut for?

danlightbulb

I know this may be a stupid question, but is the star nut on a fork simply to hold on the top cap? Or does it have some other function i.e holding the forks onto the headset somehow.

thanks

cooldad

Tensioning the headset bearings. Tighten it up, then tighten up the stem bolts, which in turn hold the forks on.

marksimon69

As above, but don't over tighten it or it will break the star nut and cause you a lot of grief.

cooldad

I wouldn't worry about the starnut - overtighten it and the forks don't turn, should be just enough to remove the play, but still leave the steering nice and smooth.

nicklouse

It is actually just a means for holding a nut in a tube.

It is then used as a means to apply preload the the headset bearings via th top cap and top cap bolt.

Another option is to use a headloc this uses a plate over the lowerend of the steerer tube to be the anchor point to allow the preload to be applied.

Once the headset has been preloaded and b stem tightened in place the preload assembly is redundant and could reply be removed as it has done what I was needed for. But in 99.9% of th times it is left where it is.

Some road bikes don't actually have an means of supplying preload to the bearings other than buy hand.

What were you really needing to know?

danlightbulb

I was just interested, learning for the future you might say.

Anyway, I can't see how tightening a nut located in the top couple of cms of steerer tube can effect the bearings located in the headset itself, unless I'm mistaking how it works. It doens't go all the way through to the bottom of the steerer tube does it?

Along the same lines, can you explain what the different types of headset mean. Integrated, semi integrated, threadless, aheadset etc.

Thanks

nicklouse

It does not need to as it is pressing the bearings together via the steerer an the top cap with the frame between.

danlightbulb

Sorry I must be being thick. The star nut is located in the top few cm of steerer tube, so any compression between the star nut and top cap would only act on that short top section of tube? And why doesn't the star nut simply pull back up the tube as the bolt is tightened?

Unless you are saying that the position of the star nut is inside the head tube, between the two bearings, which would make it deeper in the steerer tube than a couple of cm.

nicklouse

danlightbulb wrote:

Sorry I must be being thick. The star nut is located in the top few cm of steerer tube, so any compression between the star nut and top cap would only act on that short top section of tube? And why doesn't the star nut simply pull back up the tube as the bolt is tightened?

Err so in your world what happens to the bottom part of the steerer it stays still? In that case it has to split in two parts.

What happens to the steerer if you pull it? The top cap bolt does the same. Are you missing the fact that the top cap presses on the bearing?

danlightbulb

Obviously the system works, I'm just trying to understand it. Not trying to disprove the laws of physics!

If you were to pull the steerer tube, you would need to brace yourself against the frame to do so. But the position of the star nut seems to imply that it is above the head tube, i.e not between the top and bottom bearings. If this is the case, what is the star nut pulling against?

nicklouse

danlightbulb wrote:

Obviously the system works, I'm just trying to understand it. Not trying to disprove the laws of physics!

If you were to pull the steerer tube, you would need to brace yourself against the frame to do so. But the position of the star nut seems to imply that it is above the head tube, i.e not between the top and bottom bearings. If this is the case, what is the star nut pulling against?

The star nut is doing nothing. See my first words.

It is a means to hold a nut in a tube.

That is it.

The bolt of the top cap pulls the steerer up into the headset via the star nut. If there was no star nut you need a very long bolt and a plater to go over the bottom of the steerer ( called a head lock). Or some other mans to pull the steerer up.

danlightbulb

nicklouse wrote:

The bolt of the top cap pulls the steerer up into the headset via the star nut. If there was no star nut you need a very long bolt and a plater to go over the bottom of the steerer ( called a head lock). Or some other mans to pull the steerer up.

Thanks I understand now. The force created by the tension between the star nut and the top cap is transmitted back down through the stem clamp into the top bearing, and because the bottom bearing can't move anywhere this causes compression between the two bearings.

I didn't realise that the top cap also covered the outer diameter of the stem clamp and compressed it down, thought the stem clamp was just a means of fixing the bars on.

Just wanted to understand the mechanism, thanks.

Twelly

I tend to pull things apart and have a look if I want to know how something works. Undo your top cap and stem and have a look at what is going on.

cooldad

Easier to see