From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.racing
Subject: Re: Clinchers vs. Tubulars
Date: 1 Dec 1996 03:36:51 GMT

Mark Hickey writes:

> Something to consider about your misfortune.... The ability
> to ride on a flat tubular may have saved your butt, even if
> it did prematurely end your ride. 

You say that as if you can't ride a clincher that's flat.  I've had
that opportunity for a sizable distance when the rim got smashed
beyond holding the bead.  I rode that thing to shreds where I could
get a ride after about 20 miles.  The tire stayed right in place being
a wire bead tire,

Jobst Brandt      <jbrandt@hpl.hp.com> 

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.racing
Subject: Re: Clinchers vs. Tubulars
Date: 1 Dec 1996 03:46:11 GMT

M Haldy (who?) writes:

> I believe that tubulars are far superior to clinchers for racing and
> some training. They handle better and tend to ride more comfortably.

Well, that's what we are all lead to believe because everyone repeats
it like a mantra.  I for one don't believe it from any measurements I
can make.  Often unequal tires are compared for pinch flats or rolling
resistance.  It's like comparing hand made 250g tubulars with machine
made 400g tubulars that hang stiff and flat in the hook.  The weight
of the tire says a lot about its damping and rolling losses.  With
every bit of weight you gain some hysteresis through more cords and
inter cord rubber that all builds up to losses and a dead sound when
they roll.

I liked the ride of tubulars but I won't put up with all their
problems, especially their temperature sensitivity when descending
mountain roads with series of hairpins where they liquefy the glue and
eat away the base tape through rim friction.  Don't tell me to use
another glue.  I've used enough and when they get to 250 deg F they
melt.

Jobst Brandt      <jbrandt@hpl.hp.com> 

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.racing
Subject: Re: Clinchers vs. Tubulars
Date: 2 Dec 1996 18:35:46 GMT

Mark Hickey writes:

>>> Something to consider about your misfortune.... The ability to
>>> ride on a flat tubular may have saved your butt, even if it did
>>> prematurely end your ride.

>> You say that as if you can't ride a clincher that's flat.  I've had
>> that opportunity for a sizable distance when the rim got smashed
>> beyond holding the bead.  I rode that thing to shreds where I could
>> get a ride after about 20 miles.  The tire stayed right in place
>> being a wire bead tire,

> Actually, I don't have any problem believing you can ride a clincher
> (very carefully) for long distances. 

What's this "very carefully".  As I said, I have had the opportunity
to ride on a flat clincher for a long distance and plenty fast.  I
have also done so on tubulars and don't know that one was particularly
better than the other.

> But if I knew I was going to have a catastrophic blowout on a fast
> downhill, and I had my choice, I'd certainly go with a tubie. 

"If I was going to" implies that you are hypothesizing.  I assure you
that you are imagining results that are not borne out in practice.
If you are leaning into a curve when it happens, you crash.  So it
doesn't make any difference in that case.

> My reasoning would be that it would be relatively easy to force the
> clincher tire away from one side of the rim, leaving a rim to
> asphalt connection (not a good thing for staying upright if you need
> to make a steering correction).  It would be much more difficult to
> force a tubie so far off the rim that you'd touch rim to road.  I've
> also seen wire beaded clinchers that are *very* easy to remove from
> the rim.

This in contrast to tubulars that are hot from descending and are
seated on liquefied glue.

Jobst Brandt      <jbrandt@hpl.hp.com> 

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.misc
Subject: Re: Sew-ups slipping on long descent???
Date: 6 Aug 1997 15:47:28 GMT

Marnu Who? writes:

> All these many years I've ridden tubulars and have climbed hundreds
> of thousands of feet on windy mountain roads, I'm always a little
> wary of those long descents.  No, I've never rolled a tire.  But,
> the front tire (which gets most of the braking forces) slips
> somewhat on the rim in such a way that the valve stem begins to
> point to the front of the bike (when it's at the bottom of the
> revolution).

This is a major headache with tubulars and is one of their great
failings.  It doesn't take hot weather either, if you ride down
classic alpine roads that have a hairpin turn every 200m on a 10%+
grade.  Temperature sensitivity is a characteristic common to any
pressure sensitive adhesive, so don't let anyone tell you that there
is a glue that doesn't melt.  If it no longer melts, it doesn't stick
(as you found out).  I fought melting adhesive for years and developed
a glued insulator strip between rim and tire.

I used 5/8" wide cotton webbing sewn into a closed loop (with a stem
hole) to fit the rim.  I applied rim glue to the rim as if I were
mounting a tire and mounted the epoxy soaked cloth strip on the rim.
Then I laid a six inch wide 0.020" thick plastic sheet over the
strip, mounted a new tire and inflated it so that the epoxy cloth
strip was firmly formed onto the rim.  When the epoxy was stiff but
not hard, I removed the tire and plastic and trimmed the flash with a
knife and cleaned up the exposed surfaces of the rim of epoxy.

The rigid epoxy strip is locked into the sockets of the rim and cannot
creep because the whole strip would have to move at once.  A flexible
strip will not work because it is no better than the tire in staying
put.

Melting rim glue is another good reason to use clinchers.  As soon as
a durable clincher came along, I stopped using tubulars for this and
other good reasons.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Higher priced tubulars worth it?
Date: 30 Aug 1997 23:03:50 GMT

Diane Benham writes:

> I just recently acquired a set of tubulars and have noticed that the
> price range between high and low tends to be very large.  Are the
> higher-end tubies *that* much better that I should spend $50 more
> per tire for them?   If they're much more puncture resistant, I would
> be more than happy to pay the extra money since gluing tires every
> week doesn't sound like much fun.

The way you state that, I wonder why you are riding tubulars.  It
can't be for puncture resistance or low cost.  High priced tubulars
are like high priced steel frames that are fillet brazed by hand, are
light, yet durable and reliable.  If you compare the casing fabric of
high and low priced tubulars, you should see the difference right
away.  Good tubulars are hand made and can be easily detected because
they don't fold flat.

Nick Lynch, a former bike shop proprietor, used to say "don't buy flat
tires", referring to machine made tubulars that hang on the wall flat
as a pancake.  Hand made silks, and better cotton tubulars, are made
inflated and remain round.  They have fine casings of 120 threads per
inch or so, and have a latex glued tread and base tape. The thin
casing, tube and tread are flexible and give the lowest rolling
resistance of any tire available.  Not that RR is important to that
degree for road riding.  They are also easier to repair than flat
slugs made of "kite string".

In the days of yore, road tubulars had latex covered base tapes to
accept road rim glue that remains tacky because road tires were
formerly changed during a race in the event of a flat, as they are on
training rides today.  Track tires used hard glue (and for this reason
had bare cloth base tapes) because hard glue had no rolling resistance
as pressure sensitive road glue does.  However, hard glue (shellac)
can not be changed, because once cured it is no longer sticky.

In my experience, the reason for track glue was not understood by the
racing community when tubulars were the mainstay.  That road glue had
substantial rolling resistance, became apparent to me years later when
performing RR tests on high performance clinchers, using tubulars as a
base line.  Then I finally understood what all this shellac track glue
was about.

The road glue we used gave the tubulars poorer rolling than equivalent
clinchers, even though the tubulars were lighter and had thinner tubes
in them.  In a 1000m or 4000m TT, 1/100 of a second counts, and track
glue will give much more than that to the top racers.  It has nothing
to do with rolling tires off the rim, as we were told by those who had
no reasonable explanation, but felt they should know.  When in doubt,
make up an answer, never say "I don't know".

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Sewups losing air
Date: 8 Sep 1997 22:49:49 GMT

Vincent Huang writes:

> Do sewups lose pressure after a few days?  My Vittorias go flat in
> about 3 days.  They are brand new and have been ridden about 8
> times.

A good tubular tire needs to be pumped every day in warm weather if it
is a high performance tire.  These tires have latex tubes that have
low rolling losses but don't hold air well and must be pumped daily.
Less expensive and lower performance tubulars use thin butyl tubes
that hold air longer than latex tubes although they are thinner than
butyl tubes used in clinchers.

The tubular can use a thinner tube than will work reliably in a
clincher because the tube is protected from any rim to tire
discontinuities that might pinch or chafe the tube.  Using thinner
tubes in clinchers is not reliable although some riders do so.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Tire irons, was Re: Cornstarch vs. Talc
Date: 11 Nov 1997 17:22:44 GMT

Matt O'Toole writes:

> I'm aware of this, though it's never happened to me.  What is it about
> folding tires that you think makes them more susceptible to blowing off?

The flexibility of the bead makes it easier to locally dislodge it
from its clinch, both because the hoop is not rigid and because the
bead cross section can squirm and change shape, something a steel wire
bead cannot.  That is not to say that steel wire beads are immune to
blow-offs.

>>> Given the choice, I'd rather use tires that are really easy to get
>>> off and on.  I see no reason why all tires can't be made this way.

>> I haven't seen many road tires that do that.

> Neither have I, but the Specialized ones I used a few years ago were great.
> What I'm wondering, is why all tires can't be this easy to deal with.  I
> haven't owned a road bike in about five years, so I don't know what's
> available these days.

I run my tires hard and ride down some steep places where the rims get
extremely hot.  In fact, two summers ago I rode down a paved detour in
the mountains that went for several miles at more than 20% grade.  I
stopped twice to cool the rims because they were so hot that you could
feel the heat without touching them.  I was relieved to not have had a
blowout when I got to the bottom.

It is for these circumstances that I prefer to have the best
protection.  I became aware of the heat problem when we all rode
tubulars, because I often melted the tires off the rim on many of the
steep descents around here and in the Alps.  I equipped all my tubular
rims with insulator bands to prevent rolling a tire or shearing the
stem off.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Tire irons, was Re: Cornstarch vs. Talc
Date: 12 Nov 1997 02:20:44 GMT

Jeb (who?) writes:

> Having never heard of this before, could you describe these
> insulator bands in a little more detail, particularly how they are
> attached to the rim/tire? ( or are they attached at all? )

Using 5/8" wide cotton webbing with a valve stem hole, sewn into a
belt to fit the circumference of the rim soaked in Hysol 0151 epoxy,
Position the belt on a conventionally glue covered rim.  Lay a thick
sheet of plastic around the combination, mount a tubular tire and
inflate it hard.  When the epoxy is no longer tacky, but still soft,
pull off the tire and plastic sheet and trim excess epoxy from the
edge of the rim and clean and smooth the strip with a rasp so that it
has no sharp edges.

The insulator cannot move because it is interlocked with the spoke
holes and cannot lift off because it is a hoop that is embedded in the
glue, even if the glue gets soft from heat.  Without the glue, the
epoxy bone fractures under thermal stress and the whole thing
separates from the rim with tire.  To replace a spoke nipple, drill a
3/16" hole at the appropriate place.  This will stop tire creep for
anything but long continuous heating.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: tubulars
Date: 12 Jan 1998 22:57:05 GMT

T. Holland writes:

> As others have stated, a loose tubular shrinks in (major) diameter
> as its inflated and its section (minor) diameter increases.  On
> mine, it shrunk enough to fall inside a tubular rim at about 90 psi.
> As it shrinks, it turns so the base tape is out.  The base tape, an
> axial ply bonded to the ID, has curly edges at this point -- it is
> under compression.

Therefore, you believe that the pressure that tries to expand the
minor diameter of the tire is held by the casing whose bias ply causes
constriction.

> Don't think your clinchers exhibit similar "chinese finger trap" behavior?

Why do you believe that the bias ply on a clincher does not have the
same effect?  Just because you cannot see it because you can't inflate
it without a rim.  If it has a wire bead, the bead supports that
constriction, it doesn't mean the force is not there.  With the tire,
on the rim, deflections are in the 1/1000" range, the effect of a
steel wire bead are mostly negated, the rim taking most of that load.

> I deflated a 2.1" knobby to <10 psi.  Stuck a strip of scotch tape
> around the narrow clincher rim and up each sidewall.  Pumped the
> tire to 75 psi and the tape peeled away from the rim at an angle,
> indicating that the beads moved to allow a more radial alignment of
> the casing threads.  Marked the tire at the edges of the tape,
> peeled it off and stuck it back down to verify the movement.  While
> the movement was very slight, it was visible, repeatable and in the
> right direction.

> Some conclusions:

> 1. Any contention that tubular tire adhesive is somehow in tension
>    and pulling the rim outward is pure bunk.  While the very edges
>    prestreching may see tension and unbond (turning a dirty gray)
>    with use, the bulk of the adhesive is loaded in shear and stays
>    put.

The dirty gray you see is not from lifting but proof that the tire
squirms on the rim with every loaded rotation of the wheel.  This is
why tubulars, mounted with pressure sensitive (not hard) glue, have
poorer rolling resistance than clinchers.  The work that goes into
this interface is clearly visible in the RR data of a wide range of
tires.

> 2. Base tape overlap is unnecessary to resist tension in use, only
>    during  and mounting.

Overlap is necessary to prevent exposure of the seam thread to the
rim.  A gap in the base tape can and has caused blowouts as the seam
thread was abraded by tire motion on the glue.

> 3. Increasing the pressure further will continue to decrease the
>    diameter and expand the section by bringing the bias toward
>    radial.  This will happen until burst pressure (lacking ear
>    protection and a Silca Pista, I didn't go there).  There is no
>    step-function.

The limit of constriction occurs when the cord angle is at 35.27 deg
as I mentioned before.  This is the angle when cord force in the
circumferential direction equals the inflation pressure times the area
of the minor diameter.  It does not continue to constrict farther than
this angle.  As I said, pressure hoses are woven at this angle.  The
derivation is shown in "the Bicycle Wheel".

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.racing
Subject: Re: sew-ups better than clinchers? if so, why?
Date: 13 Oct 1998 19:07:09 GMT

David L. Johnson writes:

> The latter may have been the case, but I think there is a developing
> mythology that tubulars have to be glued on something akin to the
> way linoleum is glued on a floor, which is just not true.  A small
> bead of fresh glue between each spoke before you install the tire
> will suffice.  There should be some beading of glue at the edge when
> you inflate the tire, but not copious amounts.  That way the tire
> will stay on (I've never rolled one, and never even seen it happen),
> and the tire can be pulled off in a few seconds once you get it
> started.

There is more to gluing on a tubular than keeping it from falling off.
Even a well glued tubular, on that isn't glued on with track glue,
moves around on the rim more than is good for the tire.  This motion
causes the black discoloration of the glue by aluminum oxide and it
wears out the base tape.  Once the base tape is worn through the casing
explodes because the next thing that wears through are casing cords.

> Two folded-up tubulars can be strapped comfortably under the seat
> with a toestrap (whatever that is...).  With clinchers, as far as I
> have seen, you not only need the tube, but the [tire irons] that go
> with it, and that seems to require some sort of case...

I carry my spare tube that makes a small package held by two newspaper
rubber bands that also hold two plastic tire irons.  This and a patch
> kit fit in my back pocket along with a plastic envelope with a Visa
card, cash, medical insurance card and business cards.  That's not too
much for me to carry.  The tubulars under the saddle is neat looking
but not what it appears to be.  More often than riders like to
remember, the tubular under the saddle had chafed through, or nearly
so, by the time it was needed.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech,rec.sport.triathlon
Subject: Re: Tubular v. Clincerh
Date: 11 Mar 1999 23:43:55 GMT

Achim Wilfried Heinle writes:

> Maybe it is something that just cannot be scientifically proven. The
> same way you cannot prove why something tastes better then something
> else. Personally I don't always need scientific prove to make decisions.
> I train on clinchers and race on tubulars and I feel the difference. I
> would suggest that you try to borrow some tubulars, ride them and then
> make a decision.

You speak as a true arts major, or at least what is characterized as
one.  The performance factors of the two type tires can be precisely
measured as well as the hazards that can be statistically classified.
I believe that most of the respondents to the subject are
hypothesizing rather than speaking from measured data or knowledge of
tire failures that cause serious injury.

Most advantages of tubulars can be gained without compromise on the
race track, however, drawbacks for the road are serious enough that
riders in general as well as many racers in the world classics choose
not to ride them on certain stages.  The stages they don't care about
what tires they use make little difference.  Melting glue and rolled
tires are a serious hazard descending mountains where repeated near
full stops at hairpin turns must be made.  Base tape wear and casing
failure is another undetectable problem that can cause total failure
unless a new tire is mounted for every stage.

As you might deduce, the threat of serious injury is a strong
incentive to not use tubulars in the Alps where braking is a major
problem.  The tubular's light weight an advantage but not much.  That
is why we see them in hill climbs and then again not on road stages
over similar roads where a subsequent descent follows.  If you rule
out using them these climbs, the the benefit of the tubular vanishes.
On average terrain, the increased weight of the clincher is no more
important than a couple of gulps of water from the bottle, the actual
weight difference.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Spare Tire (sewup) Valve Stem Corrosion
Date: 29 Mar 1999 21:36:54 GMT

Jay Beattie writes:

> Somewhat off point, but I was riding in Jobst's 'hood many years ago
> down Page Mill on a hot day, and my tire started to shift on the
> base tape (but did not come off).  I noticed this when I stopped
> after running over a squirrel at high speed (It lived, but is now
> receiving Social Security Disability).  I think it was a Clement 50.
> I assume that I was not imagining this (I do <not> want to be
> accused of starting an urban myth).  Can a sew up, regardless of how
> well it is affixed to the rim, slide off the base tape?

Clement tires had their base tape affixed with latex solution so that
would most likely not be affected by braking heat.  The main thermal
problem is the base tape to rim bond that is generally made with
pressure sensitive adhesive.  The reason for the pressure sensitive
qualification is that these glues all have a thermal characteristic
that operates near "room temperature".  That is, they are near liquid
and become so when heated, some more easily than others.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.misc,rec.bicycles.tech
Subject: Re: tubular or clincher for race wheels?
Date: 6 Aug 1999 16:07:16 GMT

That tubulars get fewer pinch flats than clinchers has its origin in
tubulars of long ago when mainly racers here rode tubulars, tubulars
with condom-thin latex tubes and fine (high TPI) weave casings, the
best tubulars available.  Such tires are more resistant to pinch flats
because the fine mesh casings are smoother so that individual pressure
points against the tube are lower and because latex can stretch
several times more than butyl rubber, whose design feature is holding
air rather than stretching.  A pinch compresses a sheet of rubber so
that it tries to escape laterally from the pressure point, stretching
the rubber in that area.  It is not the pressure on the rubber itself
that causes the perforation but rather the tesnsion caused by
displacing the rubber out of the pressure zone.

The reason for not using them is that air diffuses through latex tubes
fast enough that tires must be inflated daily, which was is not a
problem for professional racers.  In the "tubular days" it was common
to put multiple dents a rim a on rough road without getting a flat.
On the other hand, pinch flats that occurred caused such small holes
that they were often hard to find, or at least that there were two
holes, one smaller than the other.  It was this feature for which I
coined the term "snake bite" for the wednesdy evening tubular patch
sessions I held for the bikies of the 1960's who spent the evening
sewing and telling tall tales of bicycling adventure.

from the FAQ:
---------------------------------------------------------------------

Subject: 8.41  Tubular Tire Repair
From: Jobst Brandt <jbrandt@hpl.hp.com>

Opening the Tire

The tire casing must be opened to gain access to patch the tube.  To
do this, open the casing by peeling the base tape back and unstitching
the seam.  If this is a seamless tire, chuck it.  There are two types
of seams, zipper stitch (using one thread) and two thread stitch.  The
zipper stitch is identified by having only one thread.  It appears to
make a pattern of slanted arrows that point in the direction in which
it can be 'unzipped'.

Never open more tire than is necessary to pull the tube out of the
casing.  Remember, the tube is elastic and can be pulled a long way
from a three cm long opening.  Even if there are two punctures not too
far apart, the tube can be pulled out of a nearby opening.  However,
to insert a boot requires an opening of about 6 to 10 cm at the
location of the cut or rupture, about the length of the boot (at least
10cm) and a couple of cm more.

Base Tape

Never cut the base tape because it cannot be butt joined.  Always pull
it to one side or separate it where it is overlapped.  Do not cut the
stitching, because it takes more time to pull out the cut thread than
to pull it out in one piece.  When working on the stem, only unstitch
on one side of the stem, preferably the side where machine finished.
Use latex to glue down loose threads on a sidewall cut.  Paint the
exposed casing zone that is to be covered by the base tape and the
tape with latex emulsion, allow to partially dry and put the tape in
place.  Put the tire on a rim and inflate hard.

Seam Ripper and Triangular Needle

A convenient tool, available in the sewing department at most
department and sewing specialty stores is a seam ripper.  This and the
triangular sewing needle from a Velox patch kit are two highly useful
tools for tubular repair, scissors and razor blades being common
household items.

Zipper Stitch

Cut the thread at some convenient place at the upstream end of the
intended opening and with a blunt awl, like a knitting needle, pull
out several stitches in the direction the stitch pattern points.  When
enough thread is free to pull on, the stitching can be opened like a
zipper.  When enough seam is open, thread the loose end through the
last loop and pull tight, to lock the zipper.  Don't cut off the free
end because it is often good enough to re-sew the seam.

Two Thread Stitch

One of the threads makes a zig zag as it locks the other thread where
it penetrates the tire casing.  Cut both threads near the middle of
the opening and, with a blunt awl like a knitting needle, pull out
only the locking thread in both directions, stitch at a time.  The
locking thread is the one that is easier to pull out.  Remove as many
stitches as the opening requires.  The other thread pulls out like a
zipper.  Tie a square knot with the loose ends at both ends of the
opening and cut off the rest.

Patching

Patch butyl (black) tubes using patches from a bicycle patch kit.

To patch a latex tube, make fully rounded patches, just large
enough to cover the hole plus five mm, from an old latex tube.  For
instance, a thorn hole takes a 10 mm diameter patch.  Use Pastali rim
glue (tire patch glue also works but not as well) wiped thinly onto
the patch with your finger.  Place the patch on the tube immediately
and press flat.  Latex will pass the volatile solvent allowing the
glue to cure rapidly with good adhesion to the tube.

Casing Repair

Repairing tubular tires requires latex emulsion.  You can get it from
carpet layers, who usually have it in bulk.  You must have a container
and beg for a serving.  If you are repairing a tubular you probably
ride them, and therefore, will have dead ones lying around.  The best
tubulars generally furnish the best repair material.

Most cuts of more than a few cords, like a glass cut, require a
structural boot.  With thin latex tubes, uncovered casing cuts will
soon nibble through the tube and cause another flat.  For boot
material, pull the tread off a silk sprint tire, unstitch it and cut
off the bead at the edge of the fold.  Now you have a long ribbon of
fine boot material.  Cut off a 10cm long piece and trim it to a width
that just fits inside the casing of the tire to be booted from inside
edge of the bead (the folded part) to the other edge.

The boot must be trimmed using a razor blade to a thin feathered edge
so that the tube is not exposed to a step at the boot's edge,
otherwise this will wear pinholes in a thin latex tube.  Apply latex
to the cleaner side of the boot and the area inside the tire,
preferably so the boot cords are 90 degrees from the facing tire
cords.

Insert the boot and press it into place, preferably in the natural
curve of the tire.  This makes the the boot the principal structural
support when the tire is again inflated, after the boot cures.  If the
casing is flat when the boot is glued, it will stretch the casing more
than the boot upon inflation.  After the boot dries, and this goes
rapidly, sew the tire.

Valve Stem Replacement

This depends on the type of tube.  Latex tubes and some of the others
have a screwed in stem that has a mushroomed end on the inside and a
washer and nut on the outside.  These are easily replaced from another
tire whose tube is shot.  Open the old ruined tire at the stem, loosen
the nut, lift the washer and pull out the stem.

Open the tire to be repaired on one side of the stem, preferably the
side where sewing ended, the messier side, and loosen the base nut,
lift the washer, wet the stem at the tube opening with saliva and
twist it until it turns freely.  Pull it out carefully and insert the
replacement stem after wetting its mushroom with saliva.  Tire
stores have a soapy mixture called "Ru-glide" or the like to do the
wetting but it cost a lot more than spit and doesn't work any better.

Tube Replacement

To replace the entire tube, open the tire on one side of the stem, the
side that seems to be easier to re-sew after the repair.  Open about
eight to ten cm the usual way, so that the old tube can be pulled out
by the stem.  Cut the tube and attach a strong cord to the loose end
of the tube to be pulled through the casing by the old tube as you
pull it out.

Cut the "new" latex tube about 8-10 cm away from the stem, tie the
cord onto the loose end and pull it gently into the casing.  Dumping
some talc into the casing and putting talc onto the tube helps get the
tube into place.  With the tube in place, pull enough of it out by
stretching it, to splice the ends together.

Splicing the Tube

This procedure works only with latex tubes.  Overlap the tube ends so
the free end goes about one cm inside the end with the stem.  With the
tube overlapped, use a toothpick to wipe Pastali rim cement into the
interface.  The reason this MUST be done in place is that the solvent
will curl the rubber into an unmanageable mess if you try this in free
space.  Carefully glue the entire circumference and press the joint
together by pressing the tube flat in opposing directions.  Wait a
minute and then gently inflate to check the results.  More glue can be
inserted if necessary if you do not wait too long.

Sewing the Tire

Sewing machines make holes through the bead that are straight across
at a regular stitch interval.  For best results, use the original
stitch holes when re-sewing.  Use a strong thread (one that you cannot
tear by hand) and a (triangular) needle from a Velox tubular patch kit
(yes I know they are scarce).  Make the first stitch about one stitch
behind the last remaining machine stitch and tie it off with a noose
knot.

With the beads of the tire pressed against each other so that the old
holes are exactly aligned, sew using a loop stitch pulling each stitch
tight, going forward two holes then back one, forward two, back one,
until the seam is closed.  This is a balanced stitch that uses one
thread and can stretch longitudinally.

Gluing Tire to Rim

For road tires, that are intended to be manually mounted and replaced
on the road, tires with a rubberized base tape are preferred because
these are easily and securely mounted by applying a coating of glue to
the rim, allowing it to harden and mounting the tire to be inflated
hard so that it will sink in and set.

Because road tires are intended to be changed on the road, they use a
glue that does not completely harden and allows reuse for mounting a
spare.

Track tires, in contrast can be mounted using hardening glue such as
shellac or bicycle tire track glue.  This glue is best suited for base
tapes that are "dry" cloth.  The tire is mounted either with a light
coating of track glue on the base tape or un-glued onto a good base of
track glue whose last coat is still soft on the rim, into which the
tire will set when inflated upon mounting.  Hard glue prevents rolling
resistance otherwise generated by the gummy road glue.  Track glue is
primarily useful for record attempts where every effort is needed.

Mounting a Tubular

The most effective and fastest way to mount a tubular is to place the
rim upright on the ground, stem hole up; insert the valve stem of the
tire and with both hands stretch the tire with downward force to
either side, working the hands downward to the bottom of the rim
without allowing the tire to slacken.  Try this before applying rim
glue on a dry rim and inflate the tire hard so that afterward,
mounting is easier on the glued rim.

Note that inflation pressure causes the tire to constrict until the
cord plies are at about 35 degrees.  This effect helps retain the tire
on the rim in use.  Therefore, do not inflate a tire to mount it.
Tubulars should generally not be inflated off a rim because this
deforms the tire and base tape adversely, possibly shearing the
inter-ply adhesion and loosening the base tape and stitching.

Now that you know everything there is to know about this, get some
practice.  It works, I did it for years.
------------------------------


Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Lateral Loads on Bicycle Wheels
Date: 13 Feb 2000 04:05:02 GMT

Warren (who?) writes:

> What kind of forces are at work trying to roll my tubular tire off
> the rim while cornering? How about when I'm cornering in the rain
> and my wheels slide out from under me? Does the wet road create
> lateral forces or just make them more obvious? I've also noticed
> that when very strong sprinters are coming down the finish straight
> they seem to have a hard time keeping their wheels from hopping
> around from side to side about a foot or so.

A simple static test will best explain that.  If you slid just a
little bit on some bad traction, or under inflate your tire, it will
distort laterally just enough to put the center of pressure over the
edge of the rim and it can roll off.  However, you might want to try
this statically and see that even an unglued tire is not easily
dislodged when inflated.  I've seen enough tires that had been ridden
that had as good as no glue on them and they stayed on.  The center of
pressure of a tubular at 45 degrees lean is still within the width of
the rim.  That would be 0.707 of the distance between the central
plane of the tire and the cross sectional diameter.  For a 22mm tire,
that's 7.777mm on a 20mm wide rim or 10-7.777=2.223mm inside the edge
of the rim.  This is not a good practice without glue but it explains
why there it doesn't take a large disturbing load to roll the tire.

Jobst Brandt      <jbrandt@hpl.hp.com>