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Re: On the virtue of traditional wheels when racing Paris-Roubaix
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GYXU > Cycling > Re: On the virtue of traditional wheels when racing Paris-Roubaix 20 April 2008 18:49:37
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Re: On the virtue of traditional wheels when racing Paris-Roubaix

Tom Sherman 20 April 2008 18:49:37
 Ryan Cousineau wrote:
[...]
Also, and never underestimate this factor, CX bikes with Zipp 404s look
way cool.
Does that opinion have the Fabrizio Mazzoleni seal of approval?

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful
Add comment
Guest 15 April 2008 20:17:18 [ permanent link ]
 On Tue, 15 Apr 2008 04:11:46 GMT, Ryan Cousineau <rcousine@gmail.com­> wrote:

In article
<e58771fb-c5c7-4a3­1-b5a9-fba6484015aa@­q10g2000prf.googlegr­oups.com>,
"joseph.santaniello­@gmail.com" <joseph.santaniello­@gmail.com> wrote:
On Apr 14, 6:27pm, unforgive...@juno.c­om wrote:
On Apr 14, 8:35 am, "joseph.santanie...­@gmail.com"
<joseph.santanie...­@gmail.com> wrote:
On Apr 14, 1:17 pm, phs...@gmail.com wrote:
I think it's just a matter of time before one of the wheel
manufacturers comes up with a batch of Roubaix special carbon wheels.
There's no reason why those deep carbon rims can't be strong enough to
handle the cobbles if enough material is added, and in a race where a
I agree. And with all the special one-off bikes that are used, I'm
surprised the wheel manufacturers haven't already.
46 ring is "small" the extra weight won't be an issue. In addition to
aerodynamics, tall rims don't get sucked into deep mud as hard as box
sections.
Is that why those wheels are used so often in cyclo-cross? I often
wondered why they are so prevalent.
I believe that's the theory, yes. After all, the aero considerations are
low, and the weight can't be any better than that of the best
low-profile rims.
Also, and never underestimate this factor, CX bikes with Zipp 404s look
way cool.

The aero and semi-aero rims shed mud well and are also stiffer and more rugged.
I'm thinking they don't get used in P-R as a concession to rider comfort.

Ron
Add comment
Tim McNamara 15 April 2008 23:27:28 [ permanent link ]
 In article <t4l904p023r4g9g1aq­l63ojurrhjn75kes@4ax­.com>,
Hobbes@spnb&s.com wrote:

The aero and semi-aero rims shed mud well and are also stiffer and
more rugged. I'm thinking they don't get used in P-R as a concession
to rider comfort.

Oy. Umm, how much more "shock absorption" do you think box section rims
provide compared to an "aero" rim?
Add comment
Guest 16 April 2008 03:23:25 [ permanent link ]
 On Tue, 15 Apr 2008 14:27:28 -0500, Tim McNamara <timmcn@bitstream.n­et> wrote:

In article <t4l904p023r4g9g1aq­l63ojurrhjn75kes@4ax­.com>,
Hobbes@spnb&s.com wrote:
The aero and semi-aero rims shed mud well and are also stiffer and
more rugged. I'm thinking they don't get used in P-R as a concession
to rider comfort.
Oy. Umm, how much more "shock absorption" do you think box section rims
provide compared to an "aero" rim?

Don't know. They are certainly much more flexible. Are you presuming that it
couldn't make a difference?
Add comment
Jobst Brandt 16 April 2008 04:04:08 [ permanent link ]
 Anthony DeLorenzo wrote:

The aero and semi-aero rims shed mud well and are also stiffer
and more rugged. I'm thinking they don't get used in P-R as a
concession to rider comfort.

Oy. Umm, how much more "shock absorption" do you think box
section rims provide compared to an "aero" rim?

Don't know. They are certainly much more flexible. Are you
presuming that it couldn't make a difference?

Probably not as much difference as those air-filled rubber shock
absorbers that are wrapped around the rims, aka the tires.

That's not the problem but rather how malleable the rim is so that it
doesn't fracture when a tire bottoms on a road hazard. A thin rim
wall that retains the tire can either bend a little or crack and let
the tire blow out. Therein lies the difference. The aluminum rim can
be repaired using a small crescent wrench to straighten the bead.
There is nothing you can do for Carbon fiber composite.

Jobst Brandt
Add comment
Tim McNamara 16 April 2008 07:13:21 [ permanent link ]
 In article <sqda04tjq6t4uge56d­5skjbd20ultt4dkl@4ax­.com>,
Hobbes@spnb&s.com wrote:

On Tue, 15 Apr 2008 14:27:28 -0500, Tim McNamara
<timmcn@bitstream.n­et> wrote:
In article <t4l904p023r4g9g1aq­l63ojurrhjn75kes@4ax­.com>,
Hobbes@spnb&s.com wrote:
The aero and semi-aero rims shed mud well and are also stiffer and
more rugged. I'm thinking they don't get used in P-R as a
concession to rider comfort.
Oy. Umm, how much more "shock absorption" do you think box section
rims provide compared to an "aero" rim?
Don't know. They are certainly much more flexible. Are you presuming
that it couldn't make a difference?

No, I'm going by published finite element analysis, which shows that
"low profile" box section rims flex about .001 inches when built into a
wheel and loaded. How much comfort do you think that adds? Besides,
there is a tire between the rim and the ground that is several orders of
magnitude more flexible.

I think that the answer is that pro teams don't want to beat up their
thousand dollar wheelsets on the cobbles.
Add comment
Ryan Cousineau 16 April 2008 09:05:16 [ permanent link ]
 In article <timmcn-76FD05.2213­2115042008@news.ipho­use.com>,
Tim McNamara <timmcn@bitstream.n­et> wrote:

In article <sqda04tjq6t4uge56d­5skjbd20ultt4dkl@4ax­.com>,
Hobbes@spnb&s.com wrote:
On Tue, 15 Apr 2008 14:27:28 -0500, Tim McNamara
<timmcn@bitstream.n­et> wrote:
In article <t4l904p023r4g9g1aq­l63ojurrhjn75kes@4ax­.com>,
Hobbes@spnb&s.com wrote:
The aero and semi-aero rims shed mud well and are also stiffer and
more rugged. I'm thinking they don't get used in P-R as a
concession to rider comfort.
Oy. Umm, how much more "shock absorption" do you think box section
rims provide compared to an "aero" rim?
Don't know. They are certainly much more flexible. Are you presuming
that it couldn't make a difference?
No, I'm going by published finite element analysis, which shows that
"low profile" box section rims flex about .001 inches when built into a
wheel and loaded. How much comfort do you think that adds? Besides,
there is a tire between the rim and the ground that is several orders of
magnitude more flexible.
I think that the answer is that pro teams don't want to beat up their
thousand dollar wheelsets on the cobbles.

I think that pro teams get those wheels for cheaper than free, and Zipp,
Hed, Bontrager etc. would prefer they used their product during the most
famous one-day road race of all.

At least among teams with a wheel sponsor (most, if not all the P-R
teams), they're paying for the non-sponsor wheels they use out of their
own pockets, and in many cases those rims are oddball stuff that is no
longer made, on tires that were never sold to the public, and weirder
stuff yet. In other words, it almost certainly costs more money to ride
low-profile Ambrosio tubulars (a fairly common choice) than it does to
ride your sponsor's deep-section stuff.

James Huang at Cyclingnews.com has done some great P-R tech reporting,
including details of exactly what wheels went on the key riders' race
and spare bikes (frequently very different) and even the story of
Pozzato, whose race plan was to ride the cobble-free first 100 km on his
regular race bike with deep-section wheels, followed by a bike change
for the cobbles.

http://www.cyclingn­ews.com/road/2008/ap­r08/roubaix08/tech.p­hp?id=/tech/20
08/features/boonen_­roubaix08

Huang also frequently points out when a bike shows evidence of
sponsor-cheating, or just camouflage of non-sponsor equipment, or other
equipment mods (everything from cyclocross levers to a hose-clamp
deployed to prevent seatpost slippage).

The photos and captions are a rich mine for those interested in P-R tech.

I think this year's race was influenced by the clear, dry conditions,
which led many of the mud-centric frame setups (often custom cx-like
rigs including canti brakes) to stay on the team cars as spare bikes
that day.

--
Ryan Cousineau rcousine@gmail.com http://www.wiredcol­a.com/
"In other newsgroups, they killfile trolls."
"In rec.bicycles.racing­, we coach them."
Add comment
Ryan Cousineau 16 April 2008 18:23:21 [ permanent link ]
 In article
<0cb5bcb2-3bda-43bd­-b5f9-83b9d18ddf80@m­36g2000hse.googlegro­ups.com>,
unforgiven99@juno.c­om wrote:

On Apr 15, 8:04 pm, jobst.bra...@stanfo­rdalumni.org wrote:
Anthony DeLorenzo wrote:
The aero and semi-aero rims shed mud well and are also stiffer
and more rugged. I'm thinking they don't get used in P-R as a
concession to rider comfort.
Oy. Umm, how much more "shock absorption" do you think box
section rims provide compared to an "aero" rim?
Don't know. They are certainly much more flexible. Are you
presuming that it couldn't make a difference?
Probably not as much difference as those air-filled rubber shock
absorbers that are wrapped around the rims, aka the tires.
That's not the problem but rather how malleable the rim is so that it
doesn't fracture when a tire bottoms on a road hazard. A thin rim
wall that retains the tire can either bend a little or crack and let
the tire blow out. Therein lies the difference. The aluminum rim can
be repaired using a small crescent wrench to straighten the bead.
There is nothing you can do for Carbon fiber composite.
Jobst Brandt
That's an interesting point, but in the racing world broken is
broken. A tire blowout costs you as much time as a cracked rim, and a
bent aluminum rim is not going to be repaired and put back into
service. The issue becomes whether or not there is a magnitude of
impact that would fracture a carbon rim but would only bend an
aluminum one without a tire blowout. Seeing how there are people out
there racing cylclocross on Lightweights, I think bottoming out the
tire is not an instant catastrophe for a carbon rim. It seems like
the ideal wheel would be something like the Flashpoint in a tubular.
Even if rim plasticity isn't an issue, aluminum still brakes better
when wet.

I think that bottoming out in deep mud is less problematic than on
cobbles. And there are very few cobblestones in most world-class CX
races.

--
Ryan Cousineau rcousine@gmail.com http://www.wiredcol­a.com/
"In other newsgroups, they killfile trolls."
"In rec.bicycles.racing­, we coach them."
Add comment
Guest 16 April 2008 19:02:56 [ permanent link ]
 On Tue, 15 Apr 2008 16:55:07 -0700 (PDT), Anthony DeLorenzo
<anthony.delorenzo@­gmail.com> wrote:

On Apr 15, 4:23 pm, Hobbes@spnb&s.com wrote:
The aero and semi-aero rims shed mud well and are also stiffer and
more rugged. I'm thinking they don't get used in P-R as a concession
to rider comfort.
Oy. Umm, how much more "shock absorption" do you think box section rims
provide compared to an "aero" rim?
Don't know. They are certainly much more flexible. Are you presuming that it
couldn't make a difference?
Probably not as much difference as those air-filled rubber shock
absorbers that are wrapped around the rims, aka the tires.

Not as much ain't the same thing as doesn't.

How much travel is available from the tires? Maximum is going to be about 20mm -
24mm sewup minus radius of the tire bed of the rim - minus thickness of rubber
latex and casing. That's brave low pressure for a race without a pit every half
mile so let's get some safety margin and not wallow around and pump it up hard
enough for only 15mm of compliance. Since so many of the obstacles are
relatively sharp edged you might want even more pressure to make sure. Still, 15
stinking millimeters, maximum and that's with sewups.

So how much does a box section rim on a 32 spoke wheel give when a 170 pound guy
with a bike hits rocks at 25per? That's a harder question. But I'll bet real
cash the answer is not insubstantial compared to the mere 15mm we're allowing
from the tire.

Hey, how do I submit a proposal for a steam-punkish, Fogel-project to measure
this?
Add comment
Guest 16 April 2008 19:09:42 [ permanent link ]
 On Tue, 15 Apr 2008 22:13:21 -0500, Tim McNamara <timmcn@bitstream.n­et> wrote:

In article <sqda04tjq6t4uge56d­5skjbd20ultt4dkl@4ax­.com>,
Hobbes@spnb&s.com wrote:
On Tue, 15 Apr 2008 14:27:28 -0500, Tim McNamara
<timmcn@bitstream.n­et> wrote:
In article <t4l904p023r4g9g1aq­l63ojurrhjn75kes@4ax­.com>,
Hobbes@spnb&s.com wrote:
The aero and semi-aero rims shed mud well and are also stiffer and
more rugged. I'm thinking they don't get used in P-R as a
concession to rider comfort.
Oy. Umm, how much more "shock absorption" do you think box section
rims provide compared to an "aero" rim?
Don't know. They are certainly much more flexible. Are you presuming
that it couldn't make a difference?
No, I'm going by published finite element analysis, which shows that
"low profile" box section rims flex about .001 inches when built into a
wheel and loaded.

That's the static load. What's the deflection between a hard man and a rock when
making a selection on the cobbles.

How much comfort do you think that adds?

None, because you're just sitting on the bike at that point. Now go hit
something and see if it adds comfort. The lack of rebound doesn't mean there
isn't any compliance.

Besides,
there is a tire between the rim and the ground that is several orders of
magnitude more flexible.

The tire is only as flexible as you want it to be. Or more important only as
flexible as it needs to be to prevent flatting and bottoming out.

I think that the answer is that pro teams don't want to beat up their
thousand dollar wheelsets on the cobbles.

So they waste days of mechanic time and inventory space and many hundreds of
dollars on special wheels?
Add comment
Jobst Brandt 16 April 2008 20:10:00 [ permanent link ]
 Tim McNamara wrote:

The aero and semi-aero rims shed mud well and are also stiffer
and more rugged. I'm thinking they don't get used in P-R as a
concession to rider comfort.

Oy. Umm, how much more "shock absorption" do you think box
section rims provide compared to an "aero" rim?

Don't know. They are certainly much more flexible. Are you
presuming that it couldn't make a difference?

No, I'm going by published finite element analysis, which shows that
"low profile" box section rims flex about .001 inches when built
into a wheel and loaded. How much comfort do you think that adds?
Besides, there is a tire between the rim and the ground that is
several orders of magnitude more flexible.

I think that the answer is that pro teams don't want to beat up
their thousand dollar wheelsets on the cobbles.

As I have mentioned on such "ride comfort issues", the difference is
like riding over a sheet of printer paper (0.003") lying on the road.
I don't believe we have anyone who can discern a sheet of paper even
riding on a glass-smooth surface.

Jobst Brandt
Add comment
Guest 16 April 2008 22:34:29 [ permanent link ]
 On Wed, 16 Apr 2008 11:02:56 -0400, Hobbes@spnb&s.com wrote:

On Tue, 15 Apr 2008 16:55:07 -0700 (PDT), Anthony DeLorenzo
<anthony.delorenzo­@gmail.com> wrote:
On Apr 15, 4:23 pm, Hobbes@spnb&s.com wrote:
The aero and semi-aero rims shed mud well and are also stiffer and
more rugged. I'm thinking they don't get used in P-R as a concession
to rider comfort.
Oy. Umm, how much more "shock absorption" do you think box section rims
provide compared to an "aero" rim?
Don't know. They are certainly much more flexible. Are you presuming that it
couldn't make a difference?
Probably not as much difference as those air-filled rubber shock
absorbers that are wrapped around the rims, aka the tires.
Not as much ain't the same thing as doesn't.
How much travel is available from the tires? Maximum is going to be about 20mm -
24mm sewup minus radius of the tire bed of the rim - minus thickness of rubber
latex and casing. That's brave low pressure for a race without a pit every half
mile so let's get some safety margin and not wallow around and pump it up hard
enough for only 15mm of compliance. Since so many of the obstacles are
relatively sharp edged you might want even more pressure to make sure. Still, 15
stinking millimeters, maximum and that's with sewups.
So how much does a box section rim on a 32 spoke wheel give when a 170 pound guy
with a bike hits rocks at 25per? That's a harder question. But I'll bet real
cash the answer is not insubstantial compared to the mere 15mm we're allowing
from the tire.
Hey, how do I submit a proposal for a steam-punkish, Fogel-project to measure
this?

Dear Hobbes,

Just rolling under the hub on smooth pavement, a rim deflects only a
thousandth of an inch or so.

That's obviously imperceptible.

But some riders occasionally notice spokes rattling when they hit
things hard. The rattling means that the rim deflected enough to lose
all its tension. That's around 3 to 5 mm, depending on initial
tension, spoke length, and spoke gauge.

That's getting close to snake-bite territory, where the tire is mashed
flat against the rim. (For an impact flat, a tire already mashed flat
against the rim must be given a good whack to split the rubber tube
pinched between the rim and the road.)

So what you're really wondering is how much impact is needed to mash a
rim to spoke-rattle depth for deep carbon versus metal box rim.

If the deep carbon rim flattened only half as much as the metal box
rim, the suspension travel difference would be only half of 3 to 5 mm.

Maybe someone can calculate the theoretical difference for a deep
carbon versus a metal box rim, but I suspect that difference will
remain more theoretical than noticeable to a rider.

Cheers,

Carl Fogel
Add comment
Jobst Brandt 16 April 2008 23:11:14 [ permanent link ]
 Carl Fogel wrote:

The aero and semi-aero rims shed mud well and are also stiffer
and more rugged. I'm thinking they don't get used in P-R as a
concession to rider comfort.

Oy. Umm, how much more "shock absorption" do you think box
section rims provide compared to an "aero" rim?

Don't know. They are certainly much more flexible. Are you
presuming that it couldn't make a difference?

Probably not as much difference as those air-filled rubber shock
absorbers that are wrapped around the rims, aka the tires.

Not as much ain't the same thing as doesn't.

How much travel is available from the tires? Maximum is going to
be about 20mm - 24mm sewup minus radius of the tire bed of the rim
- minus thickness of rubber latex and casing. That's brave low
pressure for a race without a pit every half mile so let's get some
safety margin and not wallow around and pump it up hard enough for
only 15mm of compliance. Since so many of the obstacles are
relatively sharp edged you might want even more pressure to make
sure. Still, 15 stinking millimeters, maximum and that's with
sewups. So how much does a box section rim on a 32 spoke wheel
give when a 170 pound guy with a bike hits rocks at 25per? That's
a harder question. But I'll bet real cash the answer is not
insubstantial compared to the mere 15mm we're allowing from the
tire. Hey, how do I submit a proposal for a steam-punkish,
Fogel-project to measure this?

Just rolling under the hub on smooth pavement, a rim deflects only a
thousandth of an inch or so.

That's obviously imperceptible.

But some riders occasionally notice spokes rattling when they hit
things hard. The rattling means that the rim deflected enough to
lose all its tension. That's around 3 to 5 mm, depending on initial
tension, spoke length, and spoke gauge.

Unless the wheel is under tensioned, spokes do not rattle. Spokes
that become slack under shock load, if they make any sound, make a
sharp non-reverberating twang. This is especially so for interleaved
and properly tensioned wheels.

That's getting close to snake-bite territory, where the tire is
mashed flat against the rim. (For an impact flat, a tire already
mashed flat against the rim must be given a good whack to split the
rubber tube pinched between the rim and the road.)

Snake bites occur from short length obstacles in contrast to spoke
slackening that occurs typically from road washboard, for instance.
In that event the contact length is sufficient to prevent bottoming
the tire while slackening spokes.

So what you're really wondering is how much impact is needed to mash
a rim to spoke-rattle depth for deep carbon versus metal box rim.

That requires striking a rock or root less than 100mm length in the
direction of travel.

If the deep carbon rim flattened only half as much as the metal box
rim, the suspension travel difference would be only half of 3 to 5
mm.

That is not the issue. Damaging the bead is a fracture with
composites and a mild ding for aluminum. The first one releases the
tire the other usually doesn't. I have repaired enough metal rims
while having seen failed composite rims at the LBS.

Maybe someone can calculate the theoretical difference for a deep
carbon versus a metal box rim, but I suspect that difference will
remain more theoretical than noticeable to a rider.

Leave it to theory!

Jobst Brandt
Add comment
Guest 16 April 2008 23:42:32 [ permanent link ]
 On 16 Apr 2008 19:11:14 GMT, jobst.brandt@stanfo­rdalumni.org wrote:

Carl Fogel wrote:

[snip quibbles]

If the deep carbon rim flattened only half as much as the metal box
rim, the suspension travel difference would be only half of 3 to 5
mm.
That is not the issue. Damaging the bead is a fracture with
composites and a mild ding for aluminum. The first one releases the
tire the other usually doesn't. I have repaired enough metal rims
while having seen failed composite rims at the LBS.

[snip]

Dear Jobst,

The post to which I replied was specifically about the shock absorbing
ability of deep carbon versus box metal rims.

If you want to address a different issue, feel free to do so.

Cheers,

Carl Fogel
Add comment
Tim McNamara 17 April 2008 02:52:21 [ permanent link ]
 In article <ub5c04t999u9mbtm1n­u2q5vs4bn01e9tat@4ax­.com>,
Hobbes@spnb&s.com wrote:

On Tue, 15 Apr 2008 22:13:21 -0500, Tim McNamara
<timmcn@bitstream.n­et> wrote:
In article <sqda04tjq6t4uge56d­5skjbd20ultt4dkl@4ax­.com>,
Hobbes@spnb&s.com wrote:
On Tue, 15 Apr 2008 14:27:28 -0500, Tim McNamara
<timmcn@bitstream.n­et> wrote:
In article <t4l904p023r4g9g1aq­l63ojurrhjn75kes@4ax­.com>,
Hobbes@spnb&s.com wrote:
The aero and semi-aero rims shed mud well and are also stiffer
and more rugged. I'm thinking they don't get used in P-R as a
concession to rider comfort.
Oy. Umm, how much more "shock absorption" do you think box
section rims provide compared to an "aero" rim?
Don't know. They are certainly much more flexible. Are you
presuming that it couldn't make a difference?
No, I'm going by published finite element analysis, which shows that
"low profile" box section rims flex about .001 inches when built
into a wheel and loaded.
That's the static load. What's the deflection between a hard man and
a rock when making a selection on the cobbles.

How about a soft man? Humans really aren't all that hard. In fact they
are pretty much gelatinous with an articulated endoskeleton. Even the
Belgians. And what's with the Freudian imagery in cycling, anyway?

How much comfort do you think that adds?
None, because you're just sitting on the bike at that point. Now go
hit something and see if it adds comfort. The lack of rebound doesn't
mean there isn't any compliance.

That doesn't make a lot of sense. If there's no rebound, then the wheel
is just bent. Plastic deformation could be called "compliance" but it's
not repeatable and hence, in the case of wheels, not useful.

So, let's see you demonstrate it. Find a photo from P-R showing a wheel
riding over some obstacle like a cobble with the rim deflecting visibly,
say 5mm, and which continued to be ridable. I'm always open to proof.

Besides, there is a tire between the rim and the ground that is
several orders of magnitude more flexible.
The tire is only as flexible as you want it to be. Or more important
only as flexible as it needs to be to prevent flatting and bottoming
out.

No matter how hard the tire is pumped, it can always be pinch-flatted.
The tire is more flexible than you want it to be for this particular
issue, and probably not as flexible as you want it to be for comfort and
rolling resistance.

I think that the answer is that pro teams don't want to beat up
their thousand dollar wheelsets on the cobbles.
So they waste days of mechanic time and inventory space and many
hundreds of dollars on special wheels?

Wheels that they probably already have, because they don't usually use
the high-bling carbon wheels for training. They just ride their normal
training wheels in this particular race. And the teams that normally
ride clinchers ride tubulars for this one for the pinch flat reduction.
Add comment
Guest 17 April 2008 03:46:34 [ permanent link ]
 On Wed, 16 Apr 2008 12:34:29 -0600, carlfogel@comcast.n­et wrote:

Dear Hobbes,
Just rolling under the hub on smooth pavement, a rim deflects only a
thousandth of an inch or so.
That's obviously imperceptible.
But some riders occasionally notice spokes rattling when they hit
things hard. The rattling means that the rim deflected enough to lose
all its tension. That's around 3 to 5 mm, depending on initial
tension, spoke length, and spoke gauge.
That's getting close to snake-bite territory, where the tire is mashed
flat against the rim. (For an impact flat, a tire already mashed flat
against the rim must be given a good whack to split the rubber tube
pinched between the rim and the road.)
So what you're really wondering is how much impact is needed to mash a
rim to spoke-rattle depth for deep carbon versus metal box rim.
If the deep carbon rim flattened only half as much as the metal box
rim, the suspension travel difference would be only half of 3 to 5 mm.
Maybe someone can calculate the theoretical difference for a deep
carbon versus a metal box rim, but I suspect that difference will
remain more theoretical than noticeable to a rider.
Cheers,
Carl Fogel

Ron Ruff just posted his estimate of only 1 mm of stretch for a thin
spoke (1.5 mm), 290 mm long, 1250 N tension.

That roused me to check the equations sections at the end of Jobst's
book.

Sure enough, Jobst's calculations, corrected in the 3rd edition,
worked out to 0.75 mm stretch for a bit less tension (1000 N) on a bit
thicker spoke (1.8 mm).

In other words, the 3~5 mm estimate that I carelessly accepted was
about five times too large.

So a metal box rim will lose spoke tension and twang or rattle the
spokes if it mashes a millimeter or less under impact. Even an
infinitely stiff rim would lose only a millimeter of its shock
absorbing travel on an impressively severe impact, and a carbon rim
would lose even less than a millimeter.

Less than a millimeter difference in shock travel is unlikely to be
noticeable to a rider.

Cheers,

Carl Fogel
Add comment
Guest 17 April 2008 03:49:11 [ permanent link ]
 On Wed, 16 Apr 2008 15:04:29 -0700 (PDT), Ron Ruff
<rruffrruff@yahoo.c­om> wrote:

On Apr 16, 9:52am, unforgive...@juno.c­om wrote:
Back of the envelope says that a straight 14ga spoke of 280mm length
and 110kgf tension goes slack at 5mm of rim deflection, so that's the
practical limit of compliance.
The back of my envelope gives 1mm of length change per 1250N force for
a 290mm 1.5mm dia spoke. So I'd say the practical limit is ~1mm.

Dear Ron,

Thanks--you're right. I should have checked that figure.

Jobst's 3rd edition calculates 0.75 mm stretch for 1000 N on a 1.8 mm
spoke, so your envelope looks right.

Cheers,

Carl Fogel
Add comment
Ryan Cousineau 17 April 2008 05:46:48 [ permanent link ]
 In article <timmcn-E88F07.1752­2116042008@news.ipho­use.com>,
Tim McNamara <timmcn@bitstream.n­et> wrote:

In article <ub5c04t999u9mbtm1n­u2q5vs4bn01e9tat@4ax­.com>,
Hobbes@spnb&s.com wrote:
On Tue, 15 Apr 2008 22:13:21 -0500, Tim McNamara
<timmcn@bitstream.n­et> wrote:
In article <sqda04tjq6t4uge56d­5skjbd20ultt4dkl@4ax­.com>,
Hobbes@spnb&s.com wrote:
On Tue, 15 Apr 2008 14:27:28 -0500, Tim McNamara
<timmcn@bitstream.n­et> wrote:
In article <t4l904p023r4g9g1aq­l63ojurrhjn75kes@4ax­.com>,
Hobbes@spnb&s.com wrote:

[special traditional-type wheels for P-R]

So they waste days of mechanic time and inventory space and many
hundreds of dollars on special wheels?
Wheels that they probably already have, because they don't usually use
the high-bling carbon wheels for training. They just ride their normal
training wheels in this particular race. And the teams that normally
ride clinchers ride tubulars for this one for the pinch flat reduction.

That's simply not correct. The stuff that gets broken out for P-R is
often not only lower-profile stuff than they generally use for training,
it's often wheel sets using parts that are no longer even available new:

<http://www.cycling­news.com/road/2008/a­pr08/wevelgem08/tech­.php?id=/photo
s/2008/tech/feature­s/wevelgem_tech208/C­aisse_dEpargne_Campy­_rim>

<http://www.cycling­news.com/road/2008/a­pr08/rvv08/tech.php?­id=/photos/200
8/tech/features/fla­nders_tech108/Saunie­r_Duval-Scott_rims2>­

Here's a team caught by a canny tech writer putting their sponsor's
stickers on someone else's rim:

<http://www.cycling­news.com/road/2008/a­pr08/rvv08/tech.php?­id=/photos/200
8/tech/features/fla­nders_tech108/Quick-­Step_rims>

Oh, and for those wondering at the logic behind P-R wheel choices, I
present this photo:

<http://www.cycling­news.com/road/2008/a­pr08/roubaix08/tech.­php?id=/photos
/2008/tech/features­/paris_roubaix08/Agr­itubel_Kuota_KOM_Ber­ges_tied>

Note that several of those photos are from other classics leading up to
P-R. In some cases, the races are a test-bed for P-R equipment, or may
have equipment choices completely unrelated to the team's P-R choices.

--
Ryan Cousineau rcousine@gmail.com http://www.wiredcol­a.com/
"In other newsgroups, they killfile trolls."
"In rec.bicycles.racing­, we coach them."
Add comment
Guest 17 April 2008 19:36:03 [ permanent link ]
 On Wed, 16 Apr 2008 08:52:08 -0700 (PDT), unforgiven99@juno.c­om wrote:

On Apr 16, 11:02 am, Hobbes@spnb&s.com wrote:
On Tue, 15 Apr 2008 16:55:07 -0700 (PDT), Anthony DeLorenzo
<anthony.delore...@­gmail.com> wrote:
On Apr 15, 4:23 pm, Hobbes@spnb&s.com wrote:
The aero and semi-aero rims shed mud well and are also stiffer and
more rugged. I'm thinking they don't get used in P-R as a concession
to rider comfort.
Oy. Umm, how much more "shock absorption" do you think box section rims
provide compared to an "aero" rim?
Don't know. They are certainly much more flexible. Are you presuming that it
couldn't make a difference?
Probably not as much difference as those air-filled rubber shock
absorbers that are wrapped around the rims, aka the tires.
Not as much ain't the same thing as doesn't.
How much travel is available from the tires? Maximum is going to be about 20mm -
24mm sewup minus radius of the tire bed of the rim - minus thickness of rubber
latex and casing. That's brave low pressure for a race without a pit every half
mile so let's get some safety margin and not wallow around and pump it up hard
enough for only 15mm of compliance. Since so many of the obstacles are
relatively sharp edged you might want even more pressure to make sure. Still, 15
stinking millimeters, maximum and that's with sewups.
So how much does a box section rim on a 32 spoke wheel give when a 170 pound guy
with a bike hits rocks at 25per? That's a harder question. But I'll bet real
cash the answer is not insubstantial compared to the mere 15mm we're allowing
from the tire.
Hey, how do I submit a proposal for a steam-punkish, Fogel-project to measure
this?
Back of the envelope says that a straight 14ga spoke of 280mm length
and 110kgf tension goes slack at 5mm of rim deflection, so that's the
practical limit of compliance.

That's the maximum compliance you'd want to design for. But there is still
plenty of compliance beyond that point.

Funny you should mention not having a pit every half mile. The
cobbled sectors in Paris Roubaix run up to 3.7km, are narrow, and are
closed to team cars. I think that overriding any theoretical
assessment of comfort is the realization that every piece of equipment
that rolls up to that start line is going to get crashed at least
once. Crash survival probably gets much more consideration than
comfort for a lot of parts.

I wouldn't be surprised if the box section rim recovers better from the
overexcursions than a more rigid deep section rim. But, yep, not breaking is
priority one.
Add comment
Guest 17 April 2008 19:40:30 [ permanent link ]
 On 16 Apr 2008 19:11:14 GMT, jobst.brandt@stanfo­rdalumni.org wrote:

Carl Fogel wrote:
The aero and semi-aero rims shed mud well and are also stiffer
and more rugged. I'm thinking they don't get used in P-R as a
concession to rider comfort.
Oy. Umm, how much more "shock absorption" do you think box
section rims provide compared to an "aero" rim?
Don't know. They are certainly much more flexible. Are you
presuming that it couldn't make a difference?
Probably not as much difference as those air-filled rubber shock
absorbers that are wrapped around the rims, aka the tires.
Not as much ain't the same thing as doesn't.
How much travel is available from the tires? Maximum is going to
be about 20mm - 24mm sewup minus radius of the tire bed of the rim
- minus thickness of rubber latex and casing. That's brave low
pressure for a race without a pit every half mile so let's get some
safety margin and not wallow around and pump it up hard enough for
only 15mm of compliance. Since so many of the obstacles are
relatively sharp edged you might want even more pressure to make
sure. Still, 15 stinking millimeters, maximum and that's with
sewups. So how much does a box section rim on a 32 spoke wheel
give when a 170 pound guy with a bike hits rocks at 25per? That's
a harder question. But I'll bet real cash the answer is not
insubstantial compared to the mere 15mm we're allowing from the
tire. Hey, how do I submit a proposal for a steam-punkish,
Fogel-project to measure this?
Just rolling under the hub on smooth pavement, a rim deflects only a
thousandth of an inch or so.
That's obviously imperceptible.
But some riders occasionally notice spokes rattling when they hit
things hard. The rattling means that the rim deflected enough to
lose all its tension. That's around 3 to 5 mm, depending on initial
tension, spoke length, and spoke gauge.
Unless the wheel is under tensioned, spokes do not rattle. Spokes
that become slack under shock load, if they make any sound, make a
sharp non-reverberating twang. This is especially so for interleaved
and properly tensioned wheels.
That's getting close to snake-bite territory, where the tire is
mashed flat against the rim. (For an impact flat, a tire already
mashed flat against the rim must be given a good whack to split the
rubber tube pinched between the rim and the road.)
Snake bites occur from short length obstacles in contrast to spoke
slackening that occurs typically from road washboard, for instance.
In that event the contact length is sufficient to prevent bottoming
the tire while slackening spokes.
So what you're really wondering is how much impact is needed to mash
a rim to spoke-rattle depth for deep carbon versus metal box rim.
That requires striking a rock or root less than 100mm length in the
direction of travel.
If the deep carbon rim flattened only half as much as the metal box
rim, the suspension travel difference would be only half of 3 to 5
mm.
That is not the issue. Damaging the bead is a fracture with
composites and a mild ding for aluminum. The first one releases the
tire the other usually doesn't. I have repaired enough metal rims
while having seen failed composite rims at the LBS.

Here we're talking almost entirely about tubulars. God pity the man trying to
keep clinchers alive at P-R.

Maybe someone can calculate the theoretical difference for a deep
carbon versus a metal box rim, but I suspect that difference will
remain more theoretical than noticeable to a rider.
Leave it to theory!

Just a reminder, things happen whether or not there is a theory to explain it. I
know you grasp that, but some people here don't.
Add comment
Guest 17 April 2008 19:49:21 [ permanent link ]
 On Wed, 16 Apr 2008 17:46:34 -0600, carlfogel@comcast.n­et wrote:

On Wed, 16 Apr 2008 12:34:29 -0600, carlfogel@comcast.n­et wrote:
Dear Hobbes,
Just rolling under the hub on smooth pavement, a rim deflects only a
thousandth of an inch or so.
That's obviously imperceptible.
But some riders occasionally notice spokes rattling when they hit
things hard. The rattling means that the rim deflected enough to lose
all its tension. That's around 3 to 5 mm, depending on initial
tension, spoke length, and spoke gauge.
That's getting close to snake-bite territory, where the tire is mashed
flat against the rim. (For an impact flat, a tire already mashed flat
against the rim must be given a good whack to split the rubber tube
pinched between the rim and the road.)
So what you're really wondering is how much impact is needed to mash a
rim to spoke-rattle depth for deep carbon versus metal box rim.
If the deep carbon rim flattened only half as much as the metal box
rim, the suspension travel difference would be only half of 3 to 5 mm.
Maybe someone can calculate the theoretical difference for a deep
carbon versus a metal box rim, but I suspect that difference will
remain more theoretical than noticeable to a rider.
Cheers,
Carl Fogel
Ron Ruff just posted his estimate of only 1 mm of stretch for a thin
spoke (1.5 mm), 290 mm long, 1250 N tension.
That roused me to check the equations sections at the end of Jobst's
book.
Sure enough, Jobst's calculations, corrected in the 3rd edition,
worked out to 0.75 mm stretch for a bit less tension (1000 N) on a bit
thicker spoke (1.8 mm).
In other words, the 3~5 mm estimate that I carelessly accepted was
about five times too large.
So a metal box rim will lose spoke tension and twang or rattle the
spokes if it mashes a millimeter or less under impact. Even an
infinitely stiff rim would lose only a millimeter of its shock
absorbing travel on an impressively severe impact, and a carbon rim
would lose even less than a millimeter.
Less than a millimeter difference in shock travel is unlikely to be
noticeable to a rider.


Losing spoke tension does not stop a rim from deflecting or consequently
absorbing road shock. In fact it becomes more compliant.

These are not rigid spokes bound to the rim, they rest in sockets in the rim.
Bend the rim enough to remove the tension and there's nothing to stop it from
moving further. In fact the release of tension at the flattened part of the rim
will reduce tension on the rest of the spokes making the assembly more
compliant.

As for this 1mm business, how much spoke thread do you use when tensioning a
wheel from the point that the nipples are seated on the rim and the wheel is up
to tension. A hell of a lot more than 1mm.

I'll agree that my premise that a box section rim is more compliant and therefor
more comfortable under extreme conditions may be wrong. But the arguments
against have been counter to simple observation.
Add comment


Guest 17 April 2008 19:53:08 [ permanent link ]
 On Wed, 16 Apr 2008 14:55:26 -0700 (PDT), Ron Ruff <rruffrruff@yahoo.c­om> wrote:

On Apr 16, 9:02am, Hobbes@spnb&s.com wrote:
So how much does a box section rim on a 32 spoke wheel give when a 170 pound guy
with a bike hits rocks at 25per? That's a harder question. But I'll bet real
cash the answer is not insubstantial compared to the mere 15mm we're allowing
from the tire.
I'll take that bet.

Cool, I'm going to have to work out how to test. Ne