On the virtue of traditional wheels when racing Paris-Roubaix

Ryan Cousineau

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."

Hobbes@spnb&s.com

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?

unforgiven99@juno.com

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.
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.

carlfogel@comcast.net

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

jobst.brandt@stanfordalumni.org

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

carlfogel@comcast.net

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

Ron Ruff

On Apr 15, 6:04*pm, jobst.bra...@stanfordalumni.org wrote:
> 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.

This is it. A shallow aluminum rim will flex first and then dent...
but you can still ride it. The deep carbon rim is vertically very
rigid, so on a sharp impact it will crack... and if it cracks badly
enough it falls to pieces.

Deep rims would be nice on a solo escape at the end, but they are
simply a poor choice for all those cobbled sections.

Ron Ruff

On Apr 16, 9:02*am, 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.

Ron Ruff

On Apr 16, 9:52*am, 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.

carlfogel@comcast.net

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

carlfogel@comcast.net

On Wed, 16 Apr 2008 15:04:29 -0700 (PDT), Ron Ruff
<rruffrruff@yahoo.com> wrote:

>On Apr 16, 9:52*am, 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

Ryan Cousineau

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/200...h.php?id=/photo
s/2008/tech/features/wevelgem_tech208/Caisse_dEpargne_Campy_rim>

<http://www.cyclingnews.com/road/200...?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/200...?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/200....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."

Ron Ruff

Ryan Cousineau wrote:
> Oh, and for those wondering at the logic behind P-R wheel choices, I
> present this photo:
>
> <http://www.cyclingnews.com/road/200....php?id=/photos
> /2008/tech/features/paris_roubaix08/Agritubel_Kuota_KOM_Berges_tied>

Yup... it is an extreme circumstance that calls for extreme measures.
Best not to have a busted spoke flapping around.

Hobbes@spnb&s.com

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.