Threadless steerer question

Why is the top cap on a threadless headset used to maintain pressure
on the bearings? It seems the bolts that hold the stem in place
should be plenty adequate to do that. Is there a good reason (other
than having to buy spacers) that a top cap must be used?

If a quill stem is adequate on most bikes, surely the clamping of the
stem to the steerer tube is at least as strong as that...

My cannondale MTB does not use a top cap because the shock absorber is
built into the head tube. The only thing that maintains bearing
pressure and keeps the fork from falling out are the bolts on the
stem.

What's the deal?

Thanks,

TD

On Fri, 05 Aug 2005 20:46:18 -0500, hmmmm hmmmm wrote:

Why is the top cap on a threadless headset used to maintain pressure
on the bearings? It seems the bolts that hold the stem in place
should be plenty adequate to do that. Is there a good reason (other
than having to buy spacers) that a top cap must be used?

If a quill stem is adequate on most bikes, surely the clamping of the
stem to the steerer tube is at least as strong as that...

My cannondale MTB does not use a top cap because the shock absorber is
built into the head tube. The only thing that maintains bearing
pressure and keeps the fork from falling out are the bolts on the
stem.

What's the deal?

My understanding is that the cap just makes it easy to dial in some preload and
take up the slack. You don't need the cap, it just makes adjustment much easier.

I'm sure Sheldon has a page.

BTW, which Cannon have you got and how cool is that fork?

Ron

someone writes:

Why is the top cap on a threadless headset used to maintain pressure
on the bearings? It seems the bolts that hold the stem in place
should be plenty adequate to do that. Is there a good reason (other
than having to buy spacers) that a top cap must be used?

Because ball bearing adjustment is a relatively precise process,
having a screw to bring the preload into the correct range is
desirable. You don't need to use it but I recommend it. I find this
feature convenient and useful for my use.

If a quill stem is adequate on most bikes, surely the clamping of the
stem to the steerer tube is at least as strong as that...

http://www.sheldonbrown.com/brandt/t...s-headset.html

My Cannondale MTB does not use a top cap because the shock absorber is
built into the head tube. The only thing that maintains bearing
pressure and keeps the fork from falling out are the bolts on the
stem.

That's after the correct play has been adjusted. A little preload is
desirable.

What's the deal?

The moving force behind the threadless steertube was the broad handled
MTB bars that in some cases cause stem failure and obviously flexed
the stem from side-to-side. For those who have not had a stem
failure, this doesn't seem to pose a threat but as a manufacturer, I
would prefer not to expose my brand to that possibility, one that has
occurred.

Jobst Brandt

hmmmm wrote:
Why is the top cap on a threadless headset used to maintain pressure
on the bearings? It seems the bolts that hold the stem in place
should be plenty adequate to do that. Is there a good reason (other
than having to buy spacers) that a top cap must be used?

If a quill stem is adequate on most bikes, surely the clamping of the
stem to the steerer tube is at least as strong as that...

My cannondale MTB does not use a top cap because the shock absorber is
built into the head tube. The only thing that maintains bearing
pressure and keeps the fork from falling out are the bolts on the
stem.

What's the deal?

Thanks,

TD

it doesn't maintain the pressure. it helps
to set the pressure. the stem (bolts) keep
the pressure in tact.
e-RICHIE

hmmmm Wrote:
Why is the top cap on a threadless headset used to maintain pressure
on the bearings? It seems the bolts that hold the stem in place
should be plenty adequate to do that. Is there a good reason (other
than having to buy spacers) that a top cap must be used?

If a quill stem is adequate on most bikes, surely the clamping of the
stem to the steerer tube is at least as strong as that...

My cannondale MTB does not use a top cap because the shock absorber is
built into the head tube. The only thing that maintains bearing
pressure and keeps the fork from falling out are the bolts on the
stem.

What's the deal?

Thanks,

TD

That Cannondale headset is an entirely different animal. Take the ste
off, and the fork will stay put. It is pressed into the bearings, an
must be driven out to remove it.
Don't try it without the proper tools and instruction though.
Da

--
Dan Burkhart

On Fri, 05 Aug 2005 20:46:18 -0500, hmmmm hmmmm wrote:

Why is the top cap on a threadless headset used to maintain pressure
on the bearings?

It isn't. It sets the initial location of the stem relative to the
top of the steerer, which will also put the initial load on the
headset bearings if everything has been done correctly. Once the stem
clamp is tight, the top cap has no further structural function and
could be removed without effect.

It seems the bolts that hold the stem in place
should be plenty adequate to do that.

The stem clamp is adequate to keep the stem from moving on the steerer
tube, but the clamp does not have any axial motion mechanism in its
design; thus, it isn't capable of setting the initial position;
something must push it into place.

Is there a good reason (other
than having to buy spacers) that a top cap must be used?

As stated above, yes, until the clamp is tight.

If a quill stem is adequate on most bikes, surely the clamping of the
stem to the steerer tube is at least as strong as that...

Different situation there; the quill stem is used with a threaded
headset whose upper nut obviates the need for any other form of
headset bearing retention or tensioning mechanism.

My cannondale MTB does not use a top cap because the shock absorber is
built into the head tube. The only thing that maintains bearing
pressure and keeps the fork from falling out are the bolts on the
stem.

What's the deal?

Read the tech details for the HeadShok steerer and the diference
should be obvious. That type of steerer does not use the same kind of
headset as a conventional threadless steerer. Even more than with the
apples-and-oranges comparison of the threaded vs threadless steerers
above, the headshok vs threadless comparison is apples and grapes.
Those two types of setup have even less in common than threadless vs
threaded.
--
Typoes are a feature, not a bug.
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My understanding is that the cap just makes it easy to dial in some preload and
take up the slack. You don't need the cap, it just makes adjustment much easier.

I'm sure Sheldon has a page.

He does. I found it a little after posting my original message. His
page confirmed what I found by playing with a stem and fork in my
garage. A clamp pushed down tight to the headset shim will do the
job. Too bad the steerer tube isn't finished. I'll have to paint it
to make it look a little better.


BTW, which Cannon have you got and how cool is that fork?

Its a 96 vintage Super V1000 with a Fatty SL fork. 70 mm travel,
air/oil, adjustable rebound damping (with the knob located on the top
of the steerer tube, prompting my original question). I like the fork
a lot. It is light and there is no twist at all like you can get with
forks where the shock elements are in the stanchions. Lock-out would
be nice, but I can live with it without.

Thanks

TD

That Cannondale headset is an entirely different animal. Take the stem
off, and the fork will stay put. It is pressed into the bearings, and
must be driven out to remove it.
Don't try it without the proper tools and instruction though.
Dan

I don't know... I swapped the original elastomer fork for the air/oil
fork that's in there now and when I took off the stem, the fork
dropped right out. The new fork went right in with no detectable play
in the bearings, even after many miles of off-road riding.

Thanks,

TD

Thanks to everyone who replied. I believe I have the answer I was
seeking.

TD

On Fri, 05 Aug 2005 23:56:34 -0500, hmmmm hmmmm wrote:


My understanding is that the cap just makes it easy to dial in some preload and
take up the slack. You don't need the cap, it just makes adjustment much easier.

I'm sure Sheldon has a page.

He does. I found it a little after posting my original message. His
page confirmed what I found by playing with a stem and fork in my
garage. A clamp pushed down tight to the headset shim will do the
job. Too bad the steerer tube isn't finished. I'll have to paint it
to make it look a little better.

Sheldon always has a page. It's one of those things I'm beginning to learn to
count on, like "google will answer most questions."

BTW, which Cannon have you got and how cool is that fork?

Its a 96 vintage Super V1000 with a Fatty SL fork. 70 mm travel,
air/oil, adjustable rebound damping (with the knob located on the top
of the steerer tube, prompting my original question). I like the fork
a lot. It is light and there is no twist at all like you can get with
forks where the shock elements are in the stanchions. Lock-out would
be nice, but I can live with it without.

I'm doing preliminary shopping on a XC bike and keep coming across the
Cannondales and their odd forks and wanted some real world feed back. It looks
like it could be the way to go for that type bike where the fork is really just
asked to take the edge off the roots, steer well, not weigh much and otherwise
stay out of the way.

Thanks,
Ron