stem length

In January of 2006 there was a discussion of stem length here on
rec.bicycles.tech:

***************
Michael Press wrote:

But since wheel size and fork offset are not scaled up, I
think a longer torso should be accommodated with a longer
top tube.

There's a good reason that the stems get longer on big bikes, rather
than everyone riding a 10cm stem on every size bike.

The "cockpit length" (top tube plus stem horizontal distance) can be
reached with a variety of approaches (56cm top tube and 11cm stem
yields the same cockpit length as a 52cm top tube and 15cm stem).
Either produces precisely the same "fit" and comfort, but obviously,
most bikes with a 52cm top tube will not handle properly with a 15cm
stem.

The handling issue isn't about where the bars are relative to the head
tube, or to the saddle, but to the front tire's contact patch. Make
the fore/aft position too far forward relative to the patch, and the
handling degrades. Move it too far back, ditto.

As the head tube gets longer, the stem has to "start futher back"
relative to the front tire's contact patch. Hence, a taller bike
needs a longer stem to get the bars back into the proper relationship
with the front tires's contact patch.

Mark Hickey
*******************

I read this again while considering changing a bike to a shorter stem,
but now don't understand the last paragraph at all. If the top tube gets
longer, but the fork angle stays the same, it seems to me that the stem
will still start at the same position relative to the contact patch of
the front tire. What am I missing?

Thanks for your comments.

Ned

Op vrijdag 20 april 2012 09:16:23 UTC+2 schreef Ned Mantei het volgende:
In January of 2006 there was a discussion of stem length here on
rec.bicycles.tech:

***************
Michael Press wrote:

But since wheel size and fork offset are not scaled up, I
think a longer torso should be accommodated with a longer
top tube.

There's a good reason that the stems get longer on big bikes, rather
than everyone riding a 10cm stem on every size bike.

The "cockpit length" (top tube plus stem horizontal distance) can be
reached with a variety of approaches (56cm top tube and 11cm stem
yields the same cockpit length as a 52cm top tube and 15cm stem).
Either produces precisely the same "fit" and comfort, but obviously,
most bikes with a 52cm top tube will not handle properly with a 15cm
stem.

The handling issue isn't about where the bars are relative to the head
tube, or to the saddle, but to the front tire's contact patch. Make
the fore/aft position too far forward relative to the patch, and the
handling degrades. Move it too far back, ditto.

As the head tube gets longer, the stem has to "start futher back"
relative to the front tire's contact patch. Hence, a taller bike
needs a longer stem to get the bars back into the proper relationship
with the front tires's contact patch.

Mark Hickey
*******************

I read this again while considering changing a bike to a shorter stem,
but now don't understand the last paragraph at all. If the top tube gets
longer, but the fork angle stays the same, it seems to me that the stem
will still start at the same position relative to the contact patch of
the front tire. What am I missing?

Thanks for your comments.

Ned

Make a drawing a see what happens when you vary things.

Lou

Ned Mantei writes:

In January of 2006 there was a discussion of stem length here on
rec.bicycles.tech:

***************
Michael Press wrote:

But since wheel size and fork offset are not scaled up, I
think a longer torso should be accommodated with a longer
top tube.

There's a good reason that the stems get longer on big bikes, rather
than everyone riding a 10cm stem on every size bike.

The "cockpit length" (top tube plus stem horizontal distance) can be
reached with a variety of approaches (56cm top tube and 11cm stem
yields the same cockpit length as a 52cm top tube and 15cm stem).
Either produces precisely the same "fit" and comfort, but obviously,
most bikes with a 52cm top tube will not handle properly with a 15cm
stem.

The handling issue isn't about where the bars are relative to the head
tube, or to the saddle, but to the front tire's contact patch. Make
the fore/aft position too far forward relative to the patch, and the
handling degrades. Move it too far back, ditto.

As the head tube gets longer, the stem has to "start futher back"
relative to the front tire's contact patch. Hence, a taller bike
needs a longer stem to get the bars back into the proper relationship
with the front tires's contact patch.

Mark Hickey
*******************

I read this again while considering changing a bike to a shorter stem,
but now don't understand the last paragraph at all. If the top tube gets
longer, but the fork angle stays the same, it seems to me that the stem
will still start at the same position relative to the contact patch of
the front tire. What am I missing?

Thanks for your comments.

Consider a *very* tall head tube. Eventually the top of it will
be behind the rear wheel (which will make mounting the bike a challenge).


--
Joe Riel

In article , Joe Riel
wrote:

Ned Mantei writes:

In January of 2006 there was a discussion of stem length here on
rec.bicycles.tech:

***************
Michael Press wrote:

But since wheel size and fork offset are not scaled up, I
think a longer torso should be accommodated with a longer
top tube.

There's a good reason that the stems get longer on big bikes, rather
than everyone riding a 10cm stem on every size bike.

The "cockpit length" (top tube plus stem horizontal distance) can be
reached with a variety of approaches (56cm top tube and 11cm stem
yields the same cockpit length as a 52cm top tube and 15cm stem).
Either produces precisely the same "fit" and comfort, but obviously,
most bikes with a 52cm top tube will not handle properly with a 15cm
stem.

The handling issue isn't about where the bars are relative to the head
tube, or to the saddle, but to the front tire's contact patch. Make
the fore/aft position too far forward relative to the patch, and the
handling degrades. Move it too far back, ditto.

As the head tube gets longer, the stem has to "start futher back"
relative to the front tire's contact patch. Hence, a taller bike
needs a longer stem to get the bars back into the proper relationship
with the front tires's contact patch.

Mark Hickey
*******************

I read this again while considering changing a bike to a shorter stem,
but now don't understand the last paragraph at all. If the top tube gets
longer, but the fork angle stays the same, it seems to me that the stem
will still start at the same position relative to the contact patch of
the front tire. What am I missing?

Thanks for your comments.

Consider a *very* tall head tube. Eventually the top of it will
be behind the rear wheel (which will make mounting the bike a challenge).


Oops, I missed the switch from top tube length in the first paragraph to
head tube length in the 3rd paragraph. All clear now! Thanks.

Ned

Ned Mantei wrote:
In January of 2006 there was a discussion of stem length here on
rec.bicycles.tech:


As the head tube gets longer, the stem has to "start futher back"
relative to the front tire's contact patch. Hence, a taller bike
needs a longer stem to get the bars back into the proper relationship
with the front tires's contact patch.

Mark Hickey
*******************

I read this again while considering changing a bike to a shorter stem,
but now don't understand the last paragraph at all. If the top tube gets
longer, but the fork angle stays the same, it seems to me that the stem
will still start at the same position relative to the contact patch of
the front tire. What am I missing?

You can visualize the effect by just imagining a standard quill stem
moving from its lowest to its highest possible position. It doesn't
move straight up; it moves up and back, so the handlebars move up and
back. A longer head tube has the same effect: moving the handlebars up
and back.

From https://www.rivbike.com/kb_results.asp?ID=41

"-- As the bar gets higher, it also retreats toward you. How much? On a
bike with a 73.5-degree head tube, raising it 4cm brings it back 1.5cm."


--
- Frank Krygowski

On Apr 20, 4:29*pm, Frank Krygowski
wrote:
Ned Mantei wrote:
In January of 2006 there was a discussion of stem length here on
rec.bicycles.tech:

As the head tube gets longer, the stem has to "start futher back"
relative to the front tire's contact patch. *Hence, a taller bike
needs a longer stem to get the bars back into the proper relationship
with the front tires's contact patch.

Mark Hickey
*******************

I read this again while considering changing a bike to a shorter stem,
but now don't understand the last paragraph at all. If the top tube gets
longer, but the fork angle stays the same, it seems to me that the stem
will still start at the same position relative to the contact patch of
the front tire. What am I missing?

You can visualize the effect by just imagining a standard quill stem
moving from its lowest to its highest possible position. *It doesn't
move straight up; it moves up and back, so the handlebars move up and
back. *A longer head tube has the same effect: moving the handlebars up
and back.

*Fromhttps://www.rivbike.com/kb_results.asp?ID=41

"-- As the bar gets higher, it also retreats toward you. How much? On a
bike with a 73.5-degree head tube, raising it 4cm brings it back 1.5cm."


When I'd given up on racing I was going to revert to my original 11cm
stem, but found with the higher position that the 13cm I'd originally
swapped in after 16 months of riding was also suitable for a
higher,less agressive position. It's a cinelli 1A stem I took from
lowest position to the max line showing just above the headset
locknut. That might be 5cm with a 74deg steer-axis.

RETREATS ? angles forward at a bend ?

seams like yawl need ruly expert and chronically unavailable advice here subbed only with riding experience.

to wit: on developing stand up,and power skills, power out of turn skills, plain drive ahead with a burst of power, the rider should reconsider stem length and position without hopefully screwing up his learned style.

My courses on the west coast are overrun with aluminum panneared BMW chain, shaft 4's and 6: underfoot. Software ? oil fields ?

I wonder what they are doing. Traveling so fast that surly they cannot see or understand the scenery.