Tall threadless steer tube or tall stem? (engineering question)

For all the engineers out there-

Is there a difference in force applied to the fork column (at the point it enters the compression
ring at the top of a threadless headset) between-

A flat stem with more spacers, vs

A steeply-angled stem mounted closer to the base?

The actual location of the handlebar is to be the same in either case (same distance forward
and height).

The reason this comes up is because we often get customers who want very tall fork columns, in order
to get their handlebars relatively high. However, many manufacturers spec a maximum amount of spacer
height under the stem. I'm not sure why, on a conventional (non-carbon) fork column it makes a big
difference whether the leverage applied comes from a very tall stem or a long fork column.

Thanks for any enlightenment-

--Mike-- Chain Reaction Bicycles http://www.ChainReaction.com

 

On Tue, 21 Jan 2003, Mike Jacoubowsky wrote:

>For all the engineers out there-
>
>Is there a difference in force applied to the fork column (at the point it enters the compression
>ring at the top of a threadless headset) between-
>
>A flat stem with more spacers, vs
>
>A steeply-angled stem mounted closer to the base?
>
>The actual location of the handlebar is to be the same in either case (same distance forward
>and height).
>
>The reason this comes up is because we often get customers who want very tall fork columns, in
>order to get their handlebars relatively high. However, many manufacturers spec a maximum amount of
>spacer height under the stem. I'm not sure why, on a conventional (non-carbon) fork column it makes
>a big difference whether the leverage applied comes from a very tall stem or a long fork column.

My non-engineer opinion would be that the setup with fewer spacers and steeply angled stem would be
the better solution. Putting a lot of spacers and then a flat stem would put more stress on the
column where it meets the headset. This would be increased by the fact that the stem length needs to
be longer to get the same reach, as the slope of the head tube is moving it back horizontally. This
would also result in a slightly heaver setup than a shorter column with an angled stem as there is
less material.

Look at it this way. As you've alluded, the carbon steerer have a maximum spacer stack that is
sometimes pretty short. There must be a sound reason for needing such a low stack. I imagine that it
is because the carbon steer can not hold up to the stress between the higher mounting point and the
angular forces being applied where the headset goes into the head tube. The total overall force on
the steerer is probably essentially the same, but it is focused in different parts of the assembly.

>
>Thanks for any enlightenment-
>
>--Mike-- Chain Reaction Bicycles http://www.ChainReaction.com
>
>
>

From: John B. Rees [email protected] http://www.jrees.net/

 

RE/
>The actual location of the handlebar is to be the same in either case (same distance forward
>and height).

Unencumbered by any engineering knowledge whatsoever, I would observe that if the steering tube
brakes, somebody might sue the steering tube manufacturer. OTOH, if the stem breaks, somebody would
tend to sue the stem manufacturer.

If I were making forks, I'd want to encourage situation #2.

OTOOH, the steering tube is only so wide and so thick. "One size fits all", so-to-speak. Whereas a
stem could be engineered according to it's length/angle. Thicker walls for longer lengths...

Intuitively, I'd opt for respecting the fork maker's specs.
-----------------------
Pete Cresswell

 

"Mike Jacoubowsky" <[email protected]> wrote in message
news:[email protected]...

> For all the engineers out there-
>
> Is there a difference in force applied to the fork column (at the point it enters the compression
> ring at the top of a threadless headset) between-
>
> A flat stem with more spacers, vs
>
> A steeply-angled stem mounted closer to the base?
>
> The actual location of the handlebar is to be the same in either case
(same
> distance forward and height).
>
> The reason this comes up is because we often get customers who want very tall fork columns, in
> order to get their handlebars relatively high. However, many manufacturers spec a maximum amount
> of spacer height under
the
> stem. I'm not sure why, on a conventional (non-carbon) fork column it
makes
> a big difference whether the leverage applied comes from a very tall stem
or
> a long fork column.

A short steerer and tall stem is inherently better. The reason is that a long steerer tube will bend
more along its whole length, above and below the top headset bearing, causing misalignment of the
bearings and spacers, maybe an "indexed" headset, etc. A shorter length of steerer won't bend as
far, because shorter spans are stiffer. If the stem bends it doesn't matter as much, plus it's not
constrained by headset dimensions, so it could be fatter/stiffer/stronger if necessary.

I feel your pain -- it's really hard to find long *and* high-rise threadless stems. It's a
shame, too, because the newer easy-swap stem designs should make fit adjustments easier than
ever, but unfortunately the range of available sizes has shrunk. This has been one of my pet
peeves for awhile.

Matt O.

 

"Mike Jacoubowsky" <[email protected]> wrote:
>
> Is there a difference in force applied to the fork column (at the point it enters the compression
> ring at the top of a threadless headset) between-
>
> A flat stem with more spacers, vs
>
> A steeply-angled stem mounted closer to the base?
>
> The actual location of the handlebar is to be the same in either case (same distance forward and
> height).

I have faced this dilemma a few times, and this is my line of thinking:

I borrow the extension I need from whichever component is sturdier. If I'm dealing with a tubular
aluminum stem and a 1 1/8" steel steerer, then I leave the steerer long. For an aluminum steerer or
a 1" steerer, it can work out the other way depending on the stem.

There is the issue of stem availability-- high-rise stems are neither as high nor as common as
during the time of the 1" MTB.

To hedge my bets when putting a lot of spacer under the stem, I make a very close-fitting (slip fit
with some friction) single tube as a spacer. I reckon that this stiffens the steerer a bit and
allows bearing loads to be transmitted more evenly than if the spacers were loose on the steerer.

Chalo Colina

 

(Rusty civil engineering education jumping into action here...) I suspect the less spacer option is
the superior option, from the fork manufacturer's point of view. Think of the fork as a spoke in a
vise: the more unsupported spoke protruding from the jaws of the vise means more flex and more
chance at fatigue for a given force. The spacers do not effectively support the steerer as well as
the compression fitting/bearing do, although they might support it somewhat. So by making the stem
as close as possible to that "fixed" bearing, you're minimizing the flex and chances of
fatigue/breaking. As far as the stem goes, I'm not sure that it's any more difficult to produce a
stem that is designed to accept the forces involved with both rise and extension and it's been
designed precisely for that (we hope). So the fork guy is passing the buck to the stem guy to build
the stem correctly for the application.

Having said all that, I doubt a steel steerer (or aluminum for that matter) would ever break with a
bunch of spacers..they're pretty beefy items. But I don't know the whole story (have any data) to
support that conclusion.

My $0.02CDN worth,

Scott..
--
Scott Anderson

"John Rees" <[email protected]> wrote in message
news[email protected]...
> On Tue, 21 Jan 2003, Mike Jacoubowsky wrote:
>
>
> My non-engineer opinion would be that the setup with fewer spacers and
steeply
> angled stem would be the better solution. Putting a lot of spacers and
then a
> flat stem would put more stress on the column where it meets the headset.
This
> would be increased by the fact that the stem length needs to be longer to
get
> the same reach, as the slope of the head tube is moving it back
horizontally.
> This would also result in a slightly heaver setup than a shorter column
with an
> angled stem as there is less material.
>
> Look at it this way. As you've alluded, the carbon steerer have a maximum spacer stack that is
> sometimes pretty short. There must be a sound reason for needing such a low stack. I imagine that
> it is because the carbon
steer
> can not hold up to the stress between the higher mounting point and the
angular
> forces being applied where the headset goes into the head tube. The total overall force on the
> steerer is probably essentially the same, but it is
focused
> in different parts of the assembly.
>
>
>
> From: John B. Rees [email protected] http://www.jrees.net/

 

> "Mike Jacoubowsky" <[email protected]> wrote in message
> news:[email protected]...
>
> > For all the engineers out there-
> >
> > Is there a difference in force applied to the fork column (at the point it enters the
> > compression ring at the top of a threadless headset) between-
> >
> > A flat stem with more spacers, vs
> >
> > A steeply-angled stem mounted closer to the base?
> >
> > The actual location of the handlebar is to be the same in either case
> (same
> > distance forward and height).
> >
> > The reason this comes up is because we often get customers who want very tall fork columns, in
> > order to get their handlebars relatively high. However, many manufacturers spec a maximum amount
> > of spacer height under
> the
> > stem. I'm not sure why, on a conventional (non-carbon) fork column it
> makes
> > a big difference whether the leverage applied comes from a very tall stem
> or
> > a long fork column.
>

In my most recent CO Cyclist and Excel Sports catalogs, most of the complete bikes have a
considerable number of spacers between the headset and stem. What's that all about?

Ken

 

There are plenty of nice stems with +17 degree rise out there. ;-)

"Matt O'Toole" <[email protected]> wrote in message
news:[email protected]...
>
> "Mike Jacoubowsky" <[email protected]> wrote in message
> news:[email protected]...
>
> > For all the engineers out there-
> >
> > Is there a difference in force applied to the fork column (at the point
it
> > enters the compression ring at the top of a threadless headset) between-
> >
> > A flat stem with more spacers, vs
> >
> > A steeply-angled stem mounted closer to the base?
> >
> > The actual location of the handlebar is to be the same in either case
> (same
> > distance forward and height).
> >
> > The reason this comes up is because we often get customers who want very tall fork columns, in
> > order to get their handlebars relatively high. However, many manufacturers spec a maximum amount
> > of spacer height under
> the
> > stem. I'm not sure why, on a conventional (non-carbon) fork column it
> makes
> > a big difference whether the leverage applied comes from a very tall
stem
> or
> > a long fork column.
>
> A short steerer and tall stem is inherently better. The reason is that a long steerer tube will
> bend more along its whole length, above and below
the
> top headset bearing, causing misalignment of the bearings and spacers,
maybe
> an "indexed" headset, etc. A shorter length of steerer won't bend as far, because shorter spans
> are stiffer. If the stem bends it doesn't matter as much, plus it's not constrained by headset
> dimensions, so it could be fatter/stiffer/stronger if necessary.
>
> I feel your pain -- it's really hard to find long *and* high-rise
threadless
> stems. It's a shame, too, because the newer easy-swap stem designs should make fit adjustments
> easier than ever, but unfortunately the range of available sizes has shrunk. This has been one of
> my pet peeves for
awhile.
>
> Matt O.

 

> fatigue/breaking. As far as the stem goes, I'm not sure that it's any
more
> difficult to produce a stem that is designed to accept the forces involved with both rise and
> extension and it's been designed precisely for that (we hope). So the fork guy is passing the buck
> to the stem guy to build the stem correctly for the application.

This is beginning to make some sense. Essentially we're producing a stronger stem to take the place
of a weaker fork. Sort of. We may be saving the extended portion of the fork column from trouble,
but I would think that the forces at work at the base of the fork column (where it exits the
headset) would be the same, whether you had a tall fork/short stem or short fork/tall stem.

If we extrapolate out to the absurd, we could have a two-foot fork column that would be flexy as all
get out, vs a super-heavy-duty two-foot-tall stem that connects at the base. My guess is that the
two-foot fork column would be awful to ride, flexing all over the place. On the other hand, I'd be
scared to death the amount of leverage the two-foot-stem exerts might cause the fork column to snap
off (even though it would be considerably stiffer).

--Mike-- Chain Reaction Bicycles http://www.ChainReaction.com

 

> There are plenty of nice stems with +17 degree rise out there. ;-)

That's true, and we have lots of them. But once in a while you get somebody who wants something
*way* up there, and requests a tall steer tube with many spacers. We do have extensions that work
nicely, but look, well, not that nice.

--Mike-- Chain Reaction Bicycles http://www.ChainReactionBicycles.com

"KBH" <[email protected]> wrote in message news:[email protected]...
> There are plenty of nice stems with +17 degree rise out there. ;-)
>
>
> "Matt O'Toole" <[email protected]> wrote in message
> news:[email protected]...
> >
> > "Mike Jacoubowsky" <[email protected]> wrote in message
> > news:[email protected]...
> >
> > > For all the engineers out there-
> > >
> > > Is there a difference in force applied to the fork column (at the
point
> it
> > > enters the compression ring at the top of a threadless headset)
between-
> > >
> > > A flat stem with more spacers, vs
> > >
> > > A steeply-angled stem mounted closer to the base?
> > >
> > > The actual location of the handlebar is to be the same in either case
> > (same
> > > distance forward and height).
> > >
> > > The reason this comes up is because we often get customers who want
very
> > > tall fork columns, in order to get their handlebars relatively high. However, many
> > > manufacturers spec a maximum amount of spacer height
under
> > the
> > > stem. I'm not sure why, on a conventional (non-carbon) fork column it
> > makes
> > > a big difference whether the leverage applied comes from a very tall
> stem
> > or
> > > a long fork column.
> >
> > A short steerer and tall stem is inherently better. The reason is that
a
> > long steerer tube will bend more along its whole length, above and below
> the
> > top headset bearing, causing misalignment of the bearings and spacers,
> maybe
> > an "indexed" headset, etc. A shorter length of steerer won't bend as fa
r,
> > because shorter spans are stiffer. If the stem bends it doesn't matter
as
> > much, plus it's not constrained by headset dimensions, so it could be fatter/stiffer/stronger if
> > necessary.
> >
> > I feel your pain -- it's really hard to find long *and* high-rise
> threadless
> > stems. It's a shame, too, because the newer easy-swap stem designs
should
> > make fit adjustments easier than ever, but unfortunately the range of available sizes has
> > shrunk. This has been one of my pet peeves for
> awhile.
> >
> > Matt O.
> >
>

 

-snip fork- "kwalters" <[email protected]> wrote in message news:[email protected]...
> In my most recent CO Cyclist and Excel Sports catalogs, most of the
complete
> bikes have a considerable number of spacers between the headset and stem. What's that all about?

Perhaps they have discovered that, for the bulk of riders, AheadSet stems are woefully low. When a
customer is looking at a factory-assembled bike in my store I'm pressured to give him another,
longer, fork which is of course a PITA. Bicycle designers apparently feel that the low "racing" look
is a valuable marketing feature. It's cost is borne by bicycle retailers who have to either swap the
fork, add a severely angled stem or a clubby adapter ( on our dime, too!) When we assemble a bicycle
from a frameset we leave an ample number of spacers. The relative merits of quill/ahead have been
beaten to death here, but suffice it to say that no one told my customers that they aren't supposed
to want their bars higher!

Since the big catalog stores have more control of their product then we do, perhaps they have also
now tired of exchanging forks? As the carpenters say, you can't cut it longer.

--
Andrew Muzi http://www.yellowjersey.org Open every day since 1 April 1971

 

"KBH" <[email protected]> wrote in message news:[email protected]...

> There are plenty of nice stems with +17 degree rise out there. ;-)

That gives you less than an inch over a typical 5 deg stem. Look here:

http://www.habcycles.com/fitting.html

Matt O.

 

Yep, I think that's about it. The forces are probably very close, but the short steerer is better
able to counter-act them (from the fork designer's point of view) and the stem designer (knowing the
fork designer's limitations) can design a stem that will definitively handle the stress because it
is non-adjustable (mostly). The fork designer doesn't want to leave the door open to your 2' crazy
steerer length but the stem guy may decide that it's ok to do this, knowing the short steerer can
take the load.

Cheers,

Scott..
--
Scott Anderson

"Mike Jacoubowsky" <[email protected]> wrote in message
news:[email protected]...
>
> This is beginning to make some sense. Essentially we're producing a stronger stem to take the
> place of a weaker fork. Sort of. We may be saving the extended portion of the fork column from
> trouble, but I would think that the forces at work at the base of the fork column (where it
exits
> the headset) would be the same, whether you had a tall fork/short stem or short fork/tall stem.
>
> If we extrapolate out to the absurd, we could have a two-foot fork column that would be flexy as
> all get out, vs a super-heavy-duty two-foot-tall
stem
> that connects at the base. My guess is that the two-foot fork column
would
> be awful to ride, flexing all over the place. On the other hand, I'd be scared to death the amount
> of leverage the two-foot-stem exerts might
cause
> the fork column to snap off (even though it would be considerably
stiffer).
>
> --Mike-- Chain Reaction Bicycles http://www.ChainReaction.com