2 bolt vs 4 bolt stems

[G.T.]

I'm shopping for a road stem to use on a 'cross bike and haven't found a
definitive answer regarding the benefits/liabilities of the two styles with
regards to stem and bar longevity.

From searching I see the tide leaning towards 2 bolt for the steerer clamp,
4 bolt for the face plate, and forged rather than machined. I assume forged
and a 2 bolt steerer clamp is definitely the way to go but how about the
number of bolts holding the faceplate on?

Thanks,
Greg

[Werehatrack]

Post by G.T.
I'm shopping for a road stem to use on a 'cross bike and haven't found a
definitive answer regarding the benefits/liabilities of the two styles with
regards to stem and bar longevity.
From searching I see the tide leaning towards 2 bolt for the steerer clamp,
4 bolt for the face plate, and forged rather than machined. I assume forged
and a 2 bolt steerer clamp is definitely the way to go but how about the
number of bolts holding the faceplate on?

Due to a number of issues, many feel that a two-bolt clamp on the bar
is inadequate. My own opinion leans strongly toward agreement with
that contention. From what I have seen, using four bolts on the bar
clamp not only provides redundancy but also greatly reduces the
tendency for uneven bar loading to cause the clamp to flex open and
place undue strain on the fastener threads. The steerer clamp is
generally a more robust design that doesn't use a separate cap; as
such, two bolts is plenty for that location.

[Lou Holtman]

Post by Werehatrack

Post by G.T.
I'm shopping for a road stem to use on a 'cross bike and haven't found a
definitive answer regarding the benefits/liabilities of the two styles with
regards to stem and bar longevity.
From searching I see the tide leaning towards 2 bolt for the steerer clamp,
4 bolt for the face plate, and forged rather than machined. I assume forged
and a 2 bolt steerer clamp is definitely the way to go but how about the
number of bolts holding the faceplate on?

Due to a number of issues, many feel that a two-bolt clamp on the bar
is inadequate. My own opinion leans strongly toward agreement with
that contention. From what I have seen, using four bolts on the bar
clamp not only provides redundancy but also greatly reduces the
tendency for uneven bar loading to cause the clamp to flex open and
place undue strain on the fastener threads. The steerer clamp is
generally a more robust design that doesn't use a separate cap; as
such, two bolts is plenty for that location.

I read an article (TOUR magazin?) where they adviced that on lightweight
aluminium bars and carbon bars to use a 4 bolt clamp only if that clamp
consists of two seperate clamps like the new Ritchey WCS because of the
danger of uneven load on the bar with a one piece clamp and 4 bolts.

Lou

[Werehatrack]

On Wed, 21 Dec 2005 12:11:49 +0100, "Lou Holtman"

Post by Lou Holtman

Post by Werehatrack
Due to a number of issues, many feel that a two-bolt clamp on the bar
is inadequate. My own opinion leans strongly toward agreement with
that contention. From what I have seen, using four bolts on the bar
clamp not only provides redundancy but also greatly reduces the
tendency for uneven bar loading to cause the clamp to flex open and
place undue strain on the fastener threads. The steerer clamp is
generally a more robust design that doesn't use a separate cap; as
such, two bolts is plenty for that location.

I read an article (TOUR magazin?) where they adviced that on lightweight
aluminium bars and carbon bars to use a 4 bolt clamp only if that clamp
consists of two seperate clamps like the new Ritchey WCS because of the
danger of uneven load on the bar with a one piece clamp and 4 bolts.

IMO, a bar so dainty that it would be endangered by the use of a
single four-bolt clamp (or any other properly-designed clamp) is not a
bar that I'd want to use anyway...and a properly designed single cap
using four bolts will have a good chance of spreading the compression
over a larger area of the bar than two smaller clamps. I think the
writer was reaching for a justification to recommend the New Thing, as
is often the case when a specialist mag covers a design change.

[bobv]

Post by Werehatrack
On Wed, 21 Dec 2005 12:11:49 +0100, "Lou Holtman"

Post by Lou Holtman

Post by Werehatrack
Due to a number of issues, many feel that a two-bolt clamp on the bar
is inadequate. My own opinion leans strongly toward agreement with
that contention. From what I have seen, using four bolts on the bar
clamp not only provides redundancy but also greatly reduces the
tendency for uneven bar loading to cause the clamp to flex open and
place undue strain on the fastener threads. The steerer clamp is
generally a more robust design that doesn't use a separate cap; as
such, two bolts is plenty for that location.

I read an article (TOUR magazin?) where they adviced that on lightweight
aluminium bars and carbon bars to use a 4 bolt clamp only if that clamp
consists of two seperate clamps like the new Ritchey WCS because of the
danger of uneven load on the bar with a one piece clamp and 4 bolts.

IMO, a bar so dainty that it would be endangered by the use of a
single four-bolt clamp (or any other properly-designed clamp) is not a
bar that I'd want to use anyway...and a properly designed single cap
using four bolts will have a good chance of spreading the compression
over a larger area of the bar than two smaller clamps. I think the
writer was reaching for a justification to recommend the New Thing, as
is often the case when a specialist mag covers a design change.

Actually my new Easton EC90 Equipe carbon bar came with instructions to not use
it with a 4 bolt clamp. Doesn't make a lot of sense to me. It seems to me the
width of the clamp would be at least as important as the number of bolts. I
will however use it with a 2 bolt stem.

[Alex Rodriguez]

In article <***@4ax.com>, ***@comcast.net
says...

Post by bobv
Actually my new Easton EC90 Equipe carbon bar came with instructions to not use
it with a 4 bolt clamp. Doesn't make a lot of sense to me. It seems to me the
width of the clamp would be at least as important as the number of bolts. I
will however use it with a 2 bolt stem.

The reason for the Easton warning is very simple. Easton only sells two bolt
stems. They want you to use their stems.
-------------
Alex

[Neil Brooks]

Post by Alex Rodriguez
says...

Post by bobv
Actually my new Easton EC90 Equipe carbon bar came with instructions to not

use

Post by bobv
it with a 4 bolt clamp. Doesn't make a lot of sense to me. It seems to me

the

Post by bobv
width of the clamp would be at least as important as the number of bolts. I
will however use it with a 2 bolt stem.

The reason for the Easton warning is very simple. Easton only sells two bolt
stems. They want you to use their stems.

Here's their "logic."

Forgive me if this was already posted in this thread....

http://nbeener.com/EASTON_TWO_BOLTS_vs_FOUR.pdf

[b***@mambo.ucolick.org]

Post by Werehatrack
Due to a number of issues, many feel that a two-bolt clamp on the bar
is inadequate. My own opinion leans strongly toward agreement with
that contention. From what I have seen, using four bolts on the bar
clamp not only provides redundancy but also greatly reduces the
tendency for uneven bar loading to cause the clamp to flex open and
place undue strain on the fastener threads. The steerer clamp is
generally a more robust design that doesn't use a separate cap; as
such, two bolts is plenty for that location.

4 bolt clamps typically use smaller bolts than 2 bolt clamps
(5mm vs 6mm). Nominally, the 4 bolts are stronger anyway,
but not twice as much. While there is some redundancy in
a 4 bolt clamp, I would not like to rely on it very strongly.

With a four bolt clamp, it is possible to tighten the bolts to
quite different torques and still clamp the bar. If this happens,
under loading the load is not evenly distributed, and effectively
carried by fewer than four bolts. Also the looser bolts might
become unloaded and gradually work free. So be careful
to get all the bolts to similar torques. This isn't a fatal weakness,
just an example of "don't install improperly." But it is a type of
improper installation that used not to exist, so not everyone
is looking out for it.

[Phil, Squid-in-Training]

Post by b***@mambo.ucolick.org
With a four bolt clamp, it is possible to tighten the bolts to
quite different torques and still clamp the bar.

Tighten in a star (box) pattern...

[j***@stanfordalumni.org]

Post by G.T.
I'm shopping for a road stem to use on a 'cross bike and haven't
found a definitive answer regarding the benefits/liabilities of the
two styles with regards to stem and bar longevity.
From searching I see the tide leaning toward 2 bolt for the steerer
clamp, 4 bolt for the face plate, and forged rather than machined.
I assume forged and a 2 bolt steerer clamp is definitely the way to
go but how about the number of bolts holding the faceplate on?

For those of us who have had various stem bolt failures on quill
stems, there is a definite preference for redundancy in a system in
which clamp failure means the bars fall off as with a threadless
steertube. With a quill (Cinelli) stem at least the hardware didn't
fall off but got loose. For that reason, for me two clamp bolts on the
steerer and two pairs of clamp bolts for the bars is a must.

Jobst Brandt

[Matt O'Toole]

Post by G.T.
I'm shopping for a road stem to use on a 'cross bike and haven't found a
definitive answer regarding the benefits/liabilities of the two styles
with regards to stem and bar longevity.
From searching I see the tide leaning toward 2 bolt for the steerer
clamp, 4 bolt for the face plate, and forged rather than machined. I
assume forged and a 2 bolt steerer clamp is definitely the way to go but
how about the number of bolts holding the faceplate on?

For those of us who have had various stem bolt failures on quill stems,
there is a definite preference for redundancy in a system in which clamp
failure means the bars fall off as with a threadless steertube. With a
quill (Cinelli) stem at least the hardware didn't fall off but got loose.
For that reason, for me two clamp bolts on the steerer and two pairs of
clamp bolts for the bars is a must.

I agree, but stems like this are hard to find. And if you do find one,
there's no telling how good the rest of it is. That is, it may have
four bolts, but will the welds crack, or will a machined body (with tool
marks) hold up as well as a forged one?

Also, what about hinged bar clamps, with a hinge on top and two bolts on
the bottom? These seem pretty good to me too.

Matt O.

[j***@stanfordalumni.org]

Post by Matt O'Toole

Post by j***@stanfordalumni.org

Post by G.T.
I'm shopping for a road stem to use on a 'cross bike and haven't
found a definitive answer regarding the benefits/liabilities of
the two styles with regards to stem and bar longevity.
From searching I see the tide leaning toward 2 bolt for the
steerer clamp, 4 bolt for the face plate, and forged rather than
machined. I assume forged and a 2 bolt steerer clamp is definitely
the way to go but how about the number of bolts holding the
faceplate on?

For those of us who have had various stem bolt failures on quill
stems, there is a definite preference for redundancy in a system in
which clamp failure means the bars fall off as with a threadless
steertube. With a quill (Cinelli) stem at least the hardware
didn't fall off but got loose. For that reason, for me two clamp
bolts on the steerer and two pairs of clamp bolts for the bars is a
must.

I agree, but stems like this are hard to find. And if you do find
one, there's no telling how good the rest of it is. That is, it may
have four bolts, but will the welds crack, or will a machined body
(with tool marks) hold up as well as a forged one?

How about these:

http://www.ritcheylogic.com/
http://www.ritcheylogic.com/stems.htm

Post by Matt O'Toole
Also, what about hinged bar clamps, with a hinge on top and two
bolts on the bottom? These seem pretty good to me too.

That is if they have two screws clamping the steertube.

Jobst Brandt

[Jeff Starr]

Post by j***@stanfordalumni.org
http://www.ritcheylogic.com/
http://www.ritcheylogic.com/stems.htm

Post by Matt O'Toole
Also, what about hinged bar clamps, with a hinge on top and two
bolts on the bottom? These seem pretty good to me too.

That is if they have two screws clamping the steertube.
Jobst Brandt

I use a Ritchey WCS with a set of Easton CF drop bars. After seeing
that stem testing article, I was reassured that I made a good choice.

I use a 100mm in length and I sure didn't notice any stiffness
differences between the 4 bolt plate and the generic 2 -bolt face
plate stem, that I had been using. I choose the WCS because of
recommendations from I believe Peter and I liked the appearance. I
also got it for less than full price.


Life is Good!
Jeff

[j***@stanfordalumni.org]

http://www.ritcheylogic.com/
http://www.ritcheylogic.com/stems.htm

Post by j***@stanfordalumni.org

Post by Matt O'Toole
Also, what about hinged bar clamps, with a hinge on top and two
bolts on the bottom? These seem pretty good to me too.

That is if they have two screws clamping the steertube.

I use a Ritchey WCS with a set of Easton CF drop bars. After seeing
that stem testing article, I was reassured that I made a good
choice.
I use a 100mm in length and I sure didn't notice any stiffness
differences between the 4 bolt plate and the generic 2 -bolt face
plate stem, that I had been using. I choose the WCS because of
recommendations from I believe Peter and I liked the appearance. I
also got it for less than full price.

There is no difference between number of screws that you can feel
because that would require that the clamp was loose for there to be
relative motion (something you can feel). Safety is entire
difference. Screws can fail for one reason or another, such as threads
pulling out of the aluminum or a crack in the screw itself.

Because these stems work the way they do, no single screw should alone
be be able to release the bar from the bicycle. That is why I believe
in two bolt clamping to the steer tube and four for the bar clamp.
That way there is a redundancy.

Jobst Brandt

[Mike DeMicco]

Post by j***@stanfordalumni.org
There is no difference between number of screws that you can feel
because that would require that the clamp was loose for there to be
relative motion (something you can feel). Safety is entire
difference. Screws can fail for one reason or another, such as threads
pulling out of the aluminum or a crack in the screw itself.
Because these stems work the way they do, no single screw should alone
be be able to release the bar from the bicycle. That is why I believe
in two bolt clamping to the steer tube and four for the bar clamp.
That way there is a redundancy.

I'm trying to understand why failure of one bolt on a 2-bolt bar clamp
would automatically cause the bars to release. How do you know the bar
will release? I removed one of the bolts from my bar clamp of my
Bontrager mountain bike stem and, while the joint was a little loose, the
bars did not fall out nor did it seem like it would do so if it happened
out on a ride.

Only once did I see a bar release when the stem bolt broke. This was on a
stem which had one bolt to clamp the handlebar, and the clamp itself was
hinged at the top. The bolt itself was loaded in bending and it was made
of aluminum. The stem was subsequently recalled. It was a Trek Icon stem.

I once had a Softride stem break at the handlebar clamp. This had a
conventional attachment like a quill stem normally has. Luckily it broke
on a climb when I was seated. The attachment was so loose that I believe
the bars would have released on a descent.

As evidenced by the article at
http://nbeener.com/EASTON_TWO_BOLTS_vs_FOUR.pdf it would seem that a 4
bolt clamp has more of a potential to damage the handlebars due to
overtightening (according to the article, it's easily done), that could
cause the bars to break, so we may be trading one failure mode for
another.

[j***@stanfordalumni.org]

Post by Mike DeMicco

Post by j***@stanfordalumni.org
There is no difference between number of screws that you can feel
because that would require that the clamp was loose for there to be
relative motion (something you can feel). Safety is entire
difference. Screws can fail for one reason or another, such as
threads pulling out of the aluminum or a crack in the screw itself.
Because these stems work the way they do, no single screw should
alone be be able to release the bar from the bicycle. That is why
I believe in two bolt clamping to the steer tube and four for the
bar clamp. That way there is a redundancy.

I'm trying to understand why failure of one bolt on a 2-bolt bar
clamp would automatically cause the bars to release. How do you
know the bar will release? I removed one of the bolts from my bar
clamp of my Bontrager mountain bike stem and, while the joint was a
little loose, the bars did not fall out nor did it seem like it
would do so if it happened out on a ride.

First, the bar would become loose immediately and on the next pull
would bend open the cover plate that is now attached only on one end.

Post by Mike DeMicco
Only once did I see a bar release when the stem bolt broke. This
was on a stem which had one bolt to clamp the handlebar, and the
clamp itself was hinged at the top. The bolt itself was loaded in
bending and it was made of aluminum. The stem was subsequently
recalled. It was a Trek Icon stem.
I once had a Softride stem break at the handlebar clamp. This had a
conventional attachment like a quill stem normally has. Luckily it broke
on a climb when I was seated. The attachment was so loose that I believe
the bars would have released on a descent.
As evidenced by the article at

http://nbeener.com/EASTON_TWO_BOLTS_vs_FOUR.pdf

Post by Mike DeMicco
it would seem that a 4 bolt clamp has more of a potential to damage
the handlebars due to overtightening (according to the article, it's
easily done), that could cause the bars to break, so we may be
trading one failure mode for another.

I don't understand why the concept of redundancy for safety is so
obscure. The stem pictured at that URL would release the bar if one
screw stripped out or broke for some reason. Attributing the design
to fashion is silly.

As for denting the bar, the both stem and cap have a circular contour
that matches the bar diameter and will not damage the bar unless it is
too weak as a handlebar anyway. Handlebar forces are large enough to
readily approach tube deformation more sooner than clamp forces would
because they are canting forces. For this reason a bar clamp should
be at least a bar diameter wide, which two bolt clamps generally are
not.

Jobst Brandt

[Sandy]

Post by j***@stanfordalumni.org

Post by Mike DeMicco

Post by j***@stanfordalumni.org
There is no difference between number of screws that you can feel
because that would require that the clamp was loose for there to be
relative motion (something you can feel). Safety is entire
difference. Screws can fail for one reason or another, such as
threads pulling out of the aluminum or a crack in the screw itself.
Because these stems work the way they do, no single screw should
alone be be able to release the bar from the bicycle. That is why
I believe in two bolt clamping to the steer tube and four for the
bar clamp. That way there is a redundancy.

I'm trying to understand why failure of one bolt on a 2-bolt bar
clamp would automatically cause the bars to release. How do you
know the bar will release? I removed one of the bolts from my bar
clamp of my Bontrager mountain bike stem and, while the joint was a
little loose, the bars did not fall out nor did it seem like it
would do so if it happened out on a ride.

First, the bar would become loose immediately and on the next pull
would bend open the cover plate that is now attached only on one end.

Post by Mike DeMicco
Only once did I see a bar release when the stem bolt broke. This
was on a stem which had one bolt to clamp the handlebar, and the
clamp itself was hinged at the top. The bolt itself was loaded in
bending and it was made of aluminum. The stem was subsequently
recalled. It was a Trek Icon stem.
I once had a Softride stem break at the handlebar clamp. This had a
conventional attachment like a quill stem normally has. Luckily it
broke on a climb when I was seated. The attachment was so loose
that I believe the bars would have released on a descent.
As evidenced by the article at

http://nbeener.com/EASTON_TWO_BOLTS_vs_FOUR.pdf

Post by Mike DeMicco
it would seem that a 4 bolt clamp has more of a potential to damage
the handlebars due to overtightening (according to the article, it's
easily done), that could cause the bars to break, so we may be
trading one failure mode for another.

I don't understand why the concept of redundancy for safety is so
obscure. The stem pictured at that URL would release the bar if one
screw stripped out or broke for some reason. Attributing the design
to fashion is silly.
As for denting the bar, the both stem and cap have a circular contour
that matches the bar diameter and will not damage the bar unless it is
too weak as a handlebar anyway. Handlebar forces are large enough to
readily approach tube deformation more sooner than clamp forces would
because they are canting forces. For this reason a bar clamp should
be at least a bar diameter wide, which two bolt clamps generally are
not.
Jobst Brandt

I *completely* agree with you, except for more sooner. I don't see a good
reason for having split caps, in contrast with a single cap.

[RonSonic]

Post by Mike DeMicco

Post by j***@stanfordalumni.org
There is no difference between number of screws that you can feel
because that would require that the clamp was loose for there to be
relative motion (something you can feel). Safety is entire
difference. Screws can fail for one reason or another, such as threads
pulling out of the aluminum or a crack in the screw itself.
Because these stems work the way they do, no single screw should alone
be be able to release the bar from the bicycle. That is why I believe
in two bolt clamping to the steer tube and four for the bar clamp.
That way there is a redundancy.

I'm trying to understand why failure of one bolt on a 2-bolt bar clamp
would automatically cause the bars to release. How do you know the bar
will release? I removed one of the bolts from my bar clamp of my
Bontrager mountain bike stem and, while the joint was a little loose, the
bars did not fall out nor did it seem like it would do so if it happened
out on a ride.

On a road bike it's a bit more of a problem, even a riser bar is more or less in
line with the mounting, a drop bar is cantilevered out in front of the stem and
will put you flat on your face if it's even loose. Ask how I know....

Post by Mike DeMicco
Only once did I see a bar release when the stem bolt broke. This was on a
stem which had one bolt to clamp the handlebar, and the clamp itself was
hinged at the top. The bolt itself was loaded in bending and it was made
of aluminum. The stem was subsequently recalled. It was a Trek Icon stem.

I have an Icon in a special section of my bike junk box called "stems that scare
me."

Ron

Post by Mike DeMicco
I once had a Softride stem break at the handlebar clamp. This had a
conventional attachment like a quill stem normally has. Luckily it broke
on a climb when I was seated. The attachment was so loose that I believe
the bars would have released on a descent.
As evidenced by the article at
http://nbeener.com/EASTON_TWO_BOLTS_vs_FOUR.pdf it would seem that a 4
bolt clamp has more of a potential to damage the handlebars due to
overtightening (according to the article, it's easily done), that could
cause the bars to break, so we may be trading one failure mode for
another.

[Sheldon Brown]

Post by Mike DeMicco
I'm trying to understand why failure of one bolt on a 2-bolt bar clamp
would automatically cause the bars to release. How do you know the bar
will release? I removed one of the bolts from my bar clamp of my
Bontrager mountain bike stem and, while the joint was a little loose, the
bars did not fall out nor did it seem like it would do so if it happened
out on a ride.

Breakage of a single bolt would not cause the bar to "fall off" but
could permit it to rotate on the pitch axis. If you are holding the bar
itself, this is not liable to cause a loss of control, but if you're
riding on the brake lever hoods, sudden rotation of the bars could cause
your hands to lose contact, possibly causing a FDGB.

Post by Mike DeMicco
I once had a Softride stem break at the handlebar clamp. This had a
conventional attachment like a quill stem normally has. Luckily it broke
on a climb when I was seated. The attachment was so loose that I believe
the bars would have released on a descent.

This is not entirely due to "luck." The greatest stress on a bar/stem
is generally when you're climbing, because that's when you are going to
be pulling hard on it. (Landing from a jump can also be an issue. The
only time I ever broke a handlebar was going down a curb. Fortunately I
wasn't going fast, and didn't crash.

Sheldon "Ouch!" Brown
+-------------------------------------------------+
| Search the Quality Bicycle Products Catalog |
| and order on line: |
| http://sheldonbrown.com/quality |
+-------------------------------------------------+
Harris Cyclery, West Newton, Massachusetts
Phone [phone] FAX [phone]
http://harriscyclery.com
Hard-to-find parts shipped Worldwide
http://captainbike.com http://sheldonbrown.com

[Phil, Squid-in-Training]

Post by G.T.
I'm shopping for a road stem to use on a 'cross bike and haven't
found a definitive answer regarding the benefits/liabilities of the
two styles with regards to stem and bar longevity.
From searching I see the tide leaning towards 2 bolt for the steerer
clamp, 4 bolt for the face plate, and forged rather than machined. I
assume forged and a 2 bolt steerer clamp is definitely the way to go
but how about the number of bolts holding the faceplate on?
Thanks,
Greg

Don't even think about less than four for the faceplate. You'll wonder why
the bike is noodly and may not pinpoint the stem as being the culprit. The
30-gram weight savings is piddling compared to the difference in stiffness.

On that note, I've never heard of a stem bolt failure but I know others on
the NG have, personally, too. I've only seen fractures around the bolt
eyelets, mostly due to uneven loading.

[j***@stanfordalumni.org]

Post by Phil, Squid-in-Training

Post by G.T.
I'm shopping for a road stem to use on a 'cross bike and haven't
found a definitive answer regarding the benefits/liabilities of the
two styles with regards to stem and bar longevity.
From searching I see the tide leaning towards 2 bolt for the
steerer clamp, 4 bolt for the face plate, and forged rather than
machined. I assume forged and a 2 bolt steerer clamp is definitely
the way to go but how about the number of bolts holding the
faceplate on?

Don't even think about less than four for the faceplate. You'll
wonder why the bike is noodly and may not pinpoint the stem as being
the culprit. The 30-gram weight savings is piddling compared to the
difference in stiffness.

The quill stem gets most of its flexing from not being clamped at the
top of the steertube and fro its slender forward reach that acts as a
torsion bar. You won't find either of these 1/10 as great with any
threadless steer tube stem. The diameter of the reach is about twice
a s large and the attachment to the steer tube must be solid or the
stem would walk right off the top of the steertube, something you
would notice with a decidedly loose head bearing before separation.

The issue is fail-safe operation and that is why double clamping is
essential. It is not a matter of performance.

Post by Phil, Squid-in-Training
On that note, I've never heard of a stem bolt failure but I know
others on the NG have, personally, too. I've only seen fractures
around the bolt eyelets, mostly due to uneven loading.

I have had a stem expander fail. Stem bolts on quill stems with the
slant wedge expanders unscrew under heavy climbing forces. I had
handlebar free rotation on climbs and had to stop to tighten the
expander bolt. Bar clamps on (typically Cinelli) quill stems are only
lightly loaded and don't fail and cannot release the bar even on
failure while the ones on threadless stems will release the bars
completely if there is no redundancy.

Jobst Brandt

[James Scott]

Post by Phil, Squid-in-Training
Don't even think about less than four for the faceplate. You'll wonder why
the bike is noodly and may not pinpoint the stem as being the culprit. The
30-gram weight savings is piddling compared to the difference in stiffness.

Seems like stiffness is going to be more proportional to the stem
extension diameter, and the properties of the handlebar, than the
number of bolts on the bar clamp.

Post by Phil, Squid-in-Training
On that note, I've never heard of a stem bolt failure but I know others on
the NG have, personally, too. I've only seen fractures around the bolt
eyelets, mostly due to uneven loading.

Just to inject some test data into the discussion:
http://www.biketechreview.com/stems/index.htm

Briefly, the welded stems tended to fail at the welds and one-piece
stems tended to fail at tool marks or wall thickness transitions in the
extension. Many of the 10 stems tested exhibited wear at the bar clamp,
but only one (a two-bolt design) failed there. One of the fixing bolts
was undersize and the stem was designed with insufficient thread
engagement, leading to stripped threads.

Based on this test, I'd be more wary of undersized hardware and shallow
thread engagement than the number of bolts on the bar clamp.

JLS

[Phil, Squid-in-Training]

Post by James Scott

Post by Phil, Squid-in-Training
Don't even think about less than four for the faceplate. You'll
wonder why the bike is noodly and may not pinpoint the stem as being
the culprit. The 30-gram weight savings is piddling compared to the
difference in stiffness.

Seems like stiffness is going to be more proportional to the stem
extension diameter, and the properties of the handlebar, than the
number of bolts on the bar clamp.

It was very obvious when riding my roommate's bike that there was visible
deflection of the faceplate *at the clamp*.

When you have a narrow faceplate/clamp, and only two bolts, that means you
have no torsional rigidity. Think about it: the next time you get Chinese,
take 6 chopsticks and a friend. Take one horizontally; that is the
handlebar. Take two more chopsticks and have your friend hold them on top
of and below the handlebar chopstick, touching. This is a 2-bolt clamp.
How hard is it to rotate the chopstick (like a propeller)? Totally easy...
your friend/2 chopsticks would never have the strength to hold it in place.
Now, use the other remaining 2 chopsticks, and place them as how they would
be in a 4-bolt faceplate. How hard is it to rotate now? Much harder.

Post by James Scott

Post by Phil, Squid-in-Training
On that note, I've never heard of a stem bolt failure but I know
others on the NG have, personally, too. I've only seen fractures
around the bolt eyelets, mostly due to uneven loading.

http://www.biketechreview.com/stems/index.htm
Briefly, the welded stems tended to fail at the welds and one-piece
stems tended to fail at tool marks or wall thickness transitions in
the extension. Many of the 10 stems tested exhibited wear at the bar
clamp, but only one (a two-bolt design) failed there. One of the
fixing bolts was undersize and the stem was designed with
insufficient thread engagement, leading to stripped threads.
Based on this test, I'd be more wary of undersized hardware and
shallow thread engagement than the number of bolts on the bar clamp.

My OP was about flex, not failure. Shallow thread engagement also worries
me, though. Once I was building a BMX bike and the stem had 2.5 threads
engaged. Thankfully, it stripped upon bike build-up and not use.

[j***@stanfordalumni.org]

Post by James Scott

Post by Phil, Squid-in-Training
Don't even think about less than four for the faceplate. You'll
wonder why the bike is noodly and may not pinpoint the stem as
being the culprit. The 30-gram weight savings is piddling
compared to the difference in stiffness.

Seems like stiffness is going to be more proportional to the stem
extension diameter, and the properties of the handlebar, than the
number of bolts on the bar clamp.

It was obvious when riding my roommate's bike that there was visible
deflection of the faceplate *at the clamp*.

That's a basically bad design in which extended screws are loaded in
bending. Screws are tension elements and don't work in the bending
mode as we see on pedals that auger into the face of cranks because
they are always moving... until the crank breaks off. Two screws can
be made to work well if the clamp is designed to not load the screws
in bending. However, that does not address the fail safe aspect of
such stems.

Unfortunately components are not generally designed by engineers who
understand the concepts or work under a manager who does. The logo of
a well known brand is no guarantee of proper designed. For example
some major blunders such as Shimano Octalink or Campagnolo Delta brake
as examples, both of which went through two versions while not
recognizing why the design was basically flawed. There have been
others, such as the Cinelli fork crown or the quill stem, both of
which produced predictable failures. Another was Specialized Umma
Gumma brown tire tread that caused 7-11 team riders in Europe to crash
for lack wet traction because there was no carbon in the tread rubber.

Jobst Brandt

[(PeteCresswell)]

Post by j***@stanfordalumni.org
blunders such as Shimano Octalink

?

[Ryan Cousineau]

Post by j***@stanfordalumni.org
blunders such as Shimano Octalink

?

http://draco.acs.uci.edu/rbfaq/FAQ/8f.20.html

In short, Jobst has identified a failure mode in which back torque can
be a big problem, causing loosening of the crank bolts.

I run a set of these doomed cranks, but I have a few things going for
me: I'm light, I don't descend right foot forward, and they were so
cheap I won't lose any sleep if I only get a few years out of the crank
and BB.

[j***@stanfordalumni.org]

Post by Ryan Cousineau

...blunders such as Shimano Octalink?

http://draco.acs.uci.edu/rbfaq/FAQ/8f.20.html

Post by Ryan Cousineau
In short, Jobst has identified a failure mode in which back torque
can be a big problem, causing loosening of the crank bolts.

What was sad to see is that Shimano thought the failures were caused
by insufficient spline length and came out with a second version of
the Octalink before realizing that it worked no better than the first
one. I'm not sure they understand what caused the failure, only that
the design didn't work. I've seen such things in industry a few
times, where the failure of a design was never understood and it was
left behind for another solution.

At least the new design has redundancy in that it used two pinch
bolts. Shimano may not have done that for safety but rather to get a
more elegant profile with two smaller screws instead of one large one.

Post by Ryan Cousineau
I run a set of these doomed cranks, but I have a few things going
for me: I'm light, I don't descend right foot forward, and they were
so cheap I won't lose any sleep if I only get a few years out of the
crank and BB.

This has nothing to do with rider weight. Not being goofy-footed is
the main benefit. Many riders insisted that the failures were due to
faulty installation because it never happened to them. In fact it had
nothing to do with that. Most people naturally lead with their left
foot, dancing as well as on surf, snow and skate boards and when they
approach a stair.

Jobst Brandt

[RonSonic]

Post by Ryan Cousineau

Post by Ryan Cousineau

...blunders such as Shimano Octalink?

http://draco.acs.uci.edu/rbfaq/FAQ/8f.20.html

Post by Ryan Cousineau
In short, Jobst has identified a failure mode in which back torque
can be a big problem, causing loosening of the crank bolts.

What was sad to see is that Shimano thought the failures were caused
by insufficient spline length and came out with a second version of
the Octalink before realizing that it worked no better than the first
one. I'm not sure they understand what caused the failure, only that
the design didn't work. I've seen such things in industry a few
times, where the failure of a design was never understood and it was
left behind for another solution.
At least the new design has redundancy in that it used two pinch
bolts. Shimano may not have done that for safety but rather to get a
more elegant profile with two smaller screws instead of one large one.

Post by Ryan Cousineau
I run a set of these doomed cranks, but I have a few things going
for me: I'm light, I don't descend right foot forward, and they were
so cheap I won't lose any sleep if I only get a few years out of the
crank and BB.

This has nothing to do with rider weight. Not being goofy-footed is
the main benefit. Many riders insisted that the failures were due to
faulty installation because it never happened to them. In fact it had
nothing to do with that. Most people naturally lead with their left
foot, dancing as well as on surf, snow and skate boards and when they
approach a stair.

In my off road riding I've been trying to train myself to lead with the foot
that goes down next. In other words if the trail goes left I've got my right
foot forward, if the next corner is a right turn then I'm left first. At my
otherwise inept level of bike handling it doesn't make a lot of difference
except in wear and tear on my right hip. This way both legs get the same amount
of work.

I use ISIS on my main MTB.

Ron

[(PeteCresswell)]

Post by Ryan Cousineau
I won't lose any sleep if I only get a few years out of the crank
and BB.

On one hand, after reading Jobst's explanation, it seems like as long as we
apply a torque wrench periodically there's not going to be a problem.

On the other hand, I'd definitely lose sleep over the prospect of a crank
failing under load. Been there done that with a chain lunging up a hill. It
definitely smarts - and with the chain, at least the foot stays on the pedal.

I'd think a crank arm parting under that kind of load could be catastrophic to
the rider - especially if there are moving motor vehicles in the vicinity.

[j***@stanfordalumni.org]

Post by (PeteCresswell)

Post by Ryan Cousineau
I won't lose any sleep if I only get a few years out of the crank
and BB.

On one hand, after reading Jobst's explanation, it seems like as
long as we apply a torque wrench periodically there's not going to
be a problem.

I think you misunderstand. This is a problem that, in the course of
one ride, can loosen the retaining bolt far enough that the ends of
the spline in the aluminum crank shear off (the common mode of failure
for this system).

Post by (PeteCresswell)
On the other hand, I'd definitely lose sleep over the prospect of a
crank failing under load. Been there done that with a chain lunging
up a hill. It definitely smarts - and with the chain, at least the
foot stays on the pedal.

I haven't experienced it but I suspect it is a mushy failure in which
the ends of the aluminum spline are sheared off.

Post by (PeteCresswell)
I'd think a crank arm parting under that kind of load could be
catastrophic to the rider - especially if there are moving motor
vehicles in the vicinity.

I don't know, I've never met anyone who had such a failure. I only
saw the results in the bicycle shop and pictures here in wreck.bike.

Jobst Brandt

[Phil]

Post by j***@stanfordalumni.org
I think you misunderstand. This is a problem that, in the course of
one ride, can loosen the retaining bolt far enough that the ends of
the spline in the aluminum crank shear off (the common mode of failure
for this system).

Perhaps they were not installed with the correct torque?

I have been running XT octalink v2 cranks (M751 and M752) for five
years on my MTBs. I pop them off routinely to change the rings and
when I replace the BB (every year or so as preventative maintenance).

I always install the cranks using a torque wrench, and I always
recheck after the first few rides. Only once do I recall a crank bolt
that loosened slightly after the install (I don't remember if that was
within a few rides of a re-install or just during normal use).

I frequent one of the best shops in my area, and am always surprised
when they "laugh off" the need to use a torque wrench. For that
reason, I try to never let them get near my stems...

[j***@stanfordalumni.org]

Post by Phil

Post by j***@stanfordalumni.org
I think you misunderstand. This is a problem that, in the course
of one ride, can loosen the retaining bolt far enough that the ends
of the spline in the aluminum crank shear off (the common mode of
failure for this system).

Perhaps they were not installed with the correct torque?

Aaargh! You seem to have missed the earlier part of this thread or
any of the similar ones that preceded it. The failure mode occurs
with "goofy footed" riders, ones who stand on their pedals with the
right foot forward. You are apparently not one of these and should
have no problem. That is why Shimano couldn't discover what caused
the failures. They did not recognize this effect even though it had
been discussed on this forum often.

Post by Phil
I have been running XT Octalink v2 cranks (M751 and M752) for five
years on my MTBs. I pop them off routinely to change the rings and
when I replace the BB (every year or so as preventative
maintenance).

It makes no difference how tight you make the retaining bolt. It will
unscrew if you stand on your pedals when coasting downhill or jumping
over bumps.

Post by Phil
I always install the cranks using a torque wrench, and I always
recheck after the first few rides. Only once do I recall a crank
bolt that loosened slightly after the install (I don't remember if
that was within a few rides of a re-install or just during normal
use).
I frequent one of the best shops in my area, and am always surprised
when they "laugh off" the need to use a torque wrench. For that
reason, I try to never let them get near my stems...

Oh how nice of you, but they are right about that. Torque has no
effect on loosening of the retaining bolt. To be repetitive:

I think you misunderstand.

Jobst Brandt

[Phil]

Post by j***@stanfordalumni.org
Aaargh! You seem to have missed the earlier part of this thread or
any of the similar ones that preceded it. The failure mode occurs
with "goofy footed" riders, ones who stand on their pedals with the
right foot forward. You are apparently not one of these and should
have no problem. That is why Shimano couldn't discover what caused
the failures. They did not recognize this effect even though it had
been discussed on this forum often.
It makes no difference how tight you make the retaining bolt. It will
unscrew if you stand on your pedals when coasting downhill or jumping
over bumps.
Oh how nice of you, but they are right about that. Torque has no
I think you misunderstand.

Thanks for taking the time to post the explanation again. Maybe I
did/do misunderstand, but I did read all of the posts in this thread
as well as your comments in the FAQ (link provided by Ryan Cousineau
above). In the FAQ, you describe a reverse torque effect (that I
interpret as a backwards ratcheting effect) that only occurs when the
rider stands on the pedals with right foot forward.

Well, I did mention in my post that I never had an octalink v2 crank
bolt loosen significantly during a ride, but I failed to mention that
I always stand on the pedals when riding over technical terrain, and
usually with my right foot forward (i dunno why my right foot likes to
be forward, it just does). I think that makes me "goofy footed". I've
been bouncing down the trails this way for five years now...

Ok, so if proper torque has no effect, and I am not sure that I
believe that yet, but if so, then the only other thing I can think of
is that maybe my light weight (around 125 lbs) limits the extent of
reverse ratcheting that I can produce?

[j***@stanfordalumni.org]

Post by Phil

Post by j***@stanfordalumni.org
Aaargh! You seem to have missed the earlier part of this thread or
any of the similar ones that preceded it. The failure mode occurs
with "goofy footed" riders, ones who stand on their pedals with the
right foot forward. You are apparently not one of these and should
have no problem. That is why Shimano couldn't discover what caused
the failures. They did not recognize this effect even though it
had been discussed on this forum often.
It makes no difference how tight you make the retaining bolt. It
will unscrew if you stand on your pedals when coasting downhill or
jumping over bumps.
Oh how nice of you, but they are right about that. Torque has no
I think you misunderstand.

Thanks for taking the time to post the explanation again. Maybe I
did/do misunderstand, but I did read all of the posts in this thread
as well as your comments in the FAQ (link provided by Ryan Cousineau
above). In the FAQ, you describe a reverse torque effect (that I
interpret as a backward ratcheting effect) that only occurs when the
rider stands on the pedals with right foot forward.
Well, I did mention in my post that I never had an Octalink v2 crank
bolt loosen significantly during a ride, but I failed to mention
that I always stand on the pedals when riding over technical
terrain, and usually with my right foot forward (i dunno why my
right foot likes to be forward, it just does). I think that makes
me "goofy footed". I've been bouncing down the trails this way for
five years now...
OK, so if proper torque has no effect, and I am not sure that I
believe that yet, but if so, then the only other thing I can think
of is that maybe my light weight (around 125 lbs) limits the extent
of reverse ratcheting that I can produce?

I find that interesting, because the spline has backlash. In use,
while the retaining screw is backing out, cranks show no looseness
because they are on a slight taper on the tubular spindle. Friction
will not prevent the that backlash from being taken up when reverse
torque occurs from standing on the left crank in the rearward
position. Similarly pedal attachments move with every hard pedaling
stroke even tough the pedal has been tightened as much as is possible.
Left pedals have left hand threads because they always move.

That your crank, with right foot forward riding, did not loosen means
either that you tightened it often enough (it creeps only a fraction
of a degree for many load changes) at which time you should have
noticed that the retaining bolt could be tightened. I cannot imagine
operating these cranks for any longer period, right foot forward
standing, without unscrewing one or both the retaining screws.

In any event, the Octalink failed often enough under these
circumstances that Shimano first tried to fix it by a lengthening the
spline, not having understood the cause of failure, and then finally
giving up on the concept.

Jobst Brandt