Heat resistant tubular glue?

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[email protected] wrote:

<snip>

> > I don't have anything to back this up, but I suspect that
> > temperatures must be much higher to blow clinchers off the rim than
> > to melt glue. But this is something I will certainly think about
> > before I think I am home free with clinchers.
>
> You can say that with grate assurance. We don't blow tires off rims
> but rarely, but creeping tubulars and subsequent stem failures were
> relatively common. I would not have spent time installing insulator
> strips on my tubular rims otherwise. These were entirely effective
> and also protected the tubular base tape from rim chafing.

</snip>

I know! It is my recollection of my melt problems that is keeping me
from getting a set of tubulars today. I like the ride of tubulars, and
otherwise have no complaints about the maintenace issues. If I didn't
weigh so much, I would not hesitate to use tubulars again today.


> > In normal riding my braking acceleration isn't anywhere near as hard
> > as these examples, but the heating is the same for changing speeds
> > (discounting cooling effects while actually braking) and even around
> > here where it is only rolling hills, I hardly ever have a day where
> > I don't go 60+ at least once, so those few days in the mountains
> > will certainly see so higher speeds than that. If I tried to
> > routinely brake with 97% weight transfer, I think my helmet would
> > get a good work-out! I do ride front-brake endos on my MTB to
> > entertain my 6 year old son...
>
> Don't worry about how hard you brake, the energy is dissipated into the
> rim at any rate and the energy will go into the rim.
>
> Jobst Brandt

That observation about not worrying about how hard one brakes got me
thinking.

Riders go down twisty descents more or less the same speed regardless
of their size. They both have to dissipate energy in the form of heat
to keep speed down. Both riders have the same capacity to dissipate
heat since both have the same size rims, and the same amount of cool
air blowing over those rims, yet the capacity to generate heat is not
the same. The heavy rider has to dissipate lots more energy. Where does
this extra energy go? It goes into the glue and/or tire. This is
evident by the fact that at the end of a descent even a light rider has
hot rims and tires. Even the light rider is not able to dissipate all
their energy to the air. To get down the hill at any given speed each
rider has to dissipate a given amount of energy. This energy can be
dissipated in big chunks by braking hard occasionally, or moderately
for longer periods. The key is what is the specific heat of glue and
rubber, and what is the cooling capacity of glue and rubber. The
glue/rubber has less propensity to absorb, and likewise dissipate
energy than the rim. We know from experience that riding the brakes
causes problems, but short hard braking causes less problems. Short
hard braking generates higher temperatures, but due to the specific
heat of the glue, not much heat is transferred to the glue before the
rim is cooled by the air. But what heat is there remains longer than in
the rim because it has fewer options to escape. The next hard brake
application adds some more heat to the glue in the same way. For a
lighter rider this all remains within a margin of safety. Larger riders
toe the line on the margin of safety. But if we look at "riding" the
brakes, the total amount of energy dissipated is the same, but the
longer period that the rim is hot (although at a lower temp than short
hard braking) combined with less cooling from the air due to slower
airspeed means more heat makes it's way into the glue (or clincher),
due to the glue's specific heat being more conducive to absorbing heat
over longer periods. And the glue has more or less only the rim to
dissipate it's energy to, so it never gets a chance due too the rim not
getting a chance to cool. So it just gets hotter and hotter until it
blows or melts. Clinchers proably blow less often than tubulars melt
due to mechanical restraints of the bead, as well as the cooling
capacity of a tire exposed to the air, as opposed to glue not exposed
to the air.

I'll bet rims on their own cool quite quickly, so any residual heat
felt from rims after a descent is not heat from the rim that has not
been yet dissipated but rather is heat that has actually been trapped
in the glue/tire and is finally able to escape to the rim once the rim
temperature stabilizes.

Joseph

 

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[email protected] wrote:

> Quantitatively these assumptions could make huge differences, but not
> qualitatively. What I am trying to demonstrate is that the conventional
> braking system of road bikes with tubulars is of an appropriate spec
> for avergae sized riders, and has sufficiant braking power and cooling
> to do the job. This is evident by the fact that no normal people
> complain of lack of braking power or overheating issues.

So what does social adjustment have to do with it?

> I contend that
> rim brakes and tubulars is an underspec'd solution for heavier riders,
> due to the cooling issue. The question is what is the threshold for
> this to become apparent.
> I think the threshold for tubular creep is below what I am likely to
> encounter, while clincher blow-offs is above that threshold. That
> threshold is defined by how much heat gets transferred from the rim to
> the tire/tube/glue and what temperature is required for the failure to
> occur.
>
> I'm pretty sure clinchers will work fine withour resorting to letting
> air out. As it is I run low pressures, so there should be plenty of
> reserve.

I just talked to a long-time riding companion, just to check the foggy
memory. Yes, we had tires creep while riding on flat roads in the
Midwest. Like, _flat_: tallest elevations visible for miles were the
highway overpasses. Happened during the heat of the summer, especially
on fresh glue jobs, using Clement Red, the cement of choice; although
I'm sure we might have used other brands, too. I've had tubulars creep
on cool roads, too-- the comparatively easy descents around Aspen,
Colorado (Rt. 82, down from Independence Pass, and other), and at body
weights of 165lbs (and up <g>). Being aware of the phenomenom,
especially after seeing it as a regular problem, I/we certainly did not
ride the brakes coming down hills.

If the Vittoria Mastik cement solves the creep problem, fine. "Awaiting
report". I glued a tire on, a few months ago, with this cement and
found it set up quickly when applied to rim/tire for installation, and
quickly gave a strong bond (rideable immediately, if with caution). The
bond was strong a month or three later when I peeled the tire off to
give to a friend; an ideal (YMMV) strength where I was thinking about
getting a tool but managed to get the glue "started" without destroying
the tire after a few minutes' worth of poking and prodding. "Good
stuff" at least from one use. I didn't see any creep, btw, but these
tires were used on my fixed gear bike, which I usually ride pretty
conservatively.

The problem with sewups IMHO is the unreliability of
(especiallybutnotlimitedto) old cement. I've never rolled a tire,
myself, but have seen people do so with glue jobs of various reported
ages, with plenty of glue residue on tire and rim. This is something
you don't have to think about with clinchers. Not to mention having to
run for your spare at a race when the moonlighting blacksmith (hired by
an opposing team that is promoting the event) peels your rear tubular
tire off the rim during the pre-race ceremonies*.

*Fessing up: Actually, it was my club, and we used a carpenter. --D-y

 

[[email protected]]

[email protected] wrote:
> I think the threshold for tubular creep is below what I am likely to
> encounter, while clincher blow-offs is above that threshold. That
> threshold is defined by how much heat gets transferred from the rim to
> the tire/tube/glue and what temperature is required for the failure to
> occur.

See, this is where I think you may be wrong. Your problems with tire
creep were observed with 3M which has about half the bond strength and
deteriorates more noticeably with heating than Vittoria. I think that
based on your experience as described here the change in glue just
might make the difference. Conversely, the extreme examples that seem
like they might cause a problem with Vittoria glue seem like the very
same type of rim heating that might cause a blowout. But it's your skin
on the line and your decision.

It seems to be that at 100kg lowering the tire pressure enough could
make pinch flats more likely.

 

[[email protected]]

[email protected] wrote:
> [email protected] wrote:
> > I think the threshold for tubular creep is below what I am likely to
> > encounter, while clincher blow-offs is above that threshold. That
> > threshold is defined by how much heat gets transferred from the rim to
> > the tire/tube/glue and what temperature is required for the failure to
> > occur.
>
> See, this is where I think you may be wrong. Your problems with tire
> creep were observed with 3M which has about half the bond strength and
> deteriorates more noticeably with heating than Vittoria. I think that
> based on your experience as described here the change in glue just
> might make the difference. Conversely, the extreme examples that seem
> like they might cause a problem with Vittoria glue seem like the very
> same type of rim heating that might cause a blowout. But it's your skin
> on the line and your decision.

That's the funny thing. With 3M, the problem all but disappeared! I
don't recall having creep with 3M, but rather with all other sorts of
glues I used, including Vittoria. Maybe 3M has a lower failure temp,
but a higher resistance to getting warm. Or perhaps a more of an
all-or-nothing type of release, while the other glues let go more
gradually. The problem with the 3M was the solvent (I guess) made the
base-tape of the tire separate from the tire a bit, more or less
ruining it in a short period.

> It seems to be that at 100kg lowering the tire pressure enough could
> make pinch flats more likely.

That's why I need 25mm or greater tires. (See the other threads going
on now...)

Joseph

 

[[email protected]]

[email protected] wrote:
> Riders go down twisty descents more or less the same speed regardless
> of their size. They both have to dissipate energy in the form of heat
> to keep speed down. Both riders have the same capacity to dissipate
> heat since both have the same size rims, and the same amount of cool
> air blowing over those rims, yet the capacity to generate heat is not
> the same. The heavy rider has to dissipate lots more energy. Where does
> this extra energy go? It goes into the glue and/or tire.

Not exactly. Because air resistance increases exponentially with speed,
the effect of air braking becomes more pronounced with speed, and we're
talking significant speed here, hence major air resistance. Higher
descending speeds will cause less rim heating because less total energy
is left to be dealt with by the brakes. Coasting between braking leaves
less energy to dissapated. It is significant that Brandt previously
talked about unpaved roads and constant braking, or his scenario of
constant braking at 10mph. Air resistance shares much less of the
braking duty in these situations. So the total amount of energy
dissipated by constant braking is not the same as that dissipated by
hard braking and coasting in between. Obviously, aerodynamics plays a
significant role in the air braking effect.

 

[[email protected]]

[email protected] wrote:
> That's the funny thing. With 3M, the problem all but disappeared! I
> don't recall having creep with 3M, but rather with all other sorts of
> glues I used, including Vittoria.

There are two types of Vittoria glue. Maybe you were using the other
type?

> Maybe 3M has a lower failure temp,
> but a higher resistance to getting warm.

The researchers found both a lower resistance to getting warm and less
strength once it got warm. They didn't really come to any conclusions
about an absolute failure temperature, just the relative strength of
the bonds at an increased temperature.

 

[dvt]

[email protected] wrote:
> Not to mention having to
> run for your spare at a race when the moonlighting blacksmith (hired by
> an opposing team that is promoting the event) peels your rear tubular
> tire off the rim during the pre-race ceremonies*.
>
> *Fessing up: Actually, it was my club, and we used a carpenter. --D-y

Say what? That sounds like an interesting story, but I didn't quite get
it the first time.

--
Dave
dvt at psu dot edu

 

[[email protected]]

anonymous snipes:

>> I think you don't grasp the concept of descending rate and brake
>> heating power. Maybe you have not observed trucks descending steep
>> grades, but they do that at 10-15mph at times.

> Christ. Yes, of course, but they don't do it by riding the brakes,
> they use engine compression braking with a (very) low gear. Surely
> you knew that!

Let's not introduce religion into this thread. So if it is the
compression brake, why do they descend so slowly? You must be aware
that the compression brake does not have enough power dissipation to
avoid using wheel brakes.

Jobst Brandt

 

[[email protected]]

[email protected] wrote:
> anonymous snipes:
>
> >> I think you don't grasp the concept of descending rate and brake
> >> heating power. Maybe you have not observed trucks descending steep
> >> grades, but they do that at 10-15mph at times.
>
> > Christ. Yes, of course, but they don't do it by riding the brakes,
> > they use engine compression braking with a (very) low gear. Surely
> > you knew that!
>
> Let's not introduce religion into this thread. So if it is the
> compression brake, why do they descend so slowly? You must be aware
> that the compression brake does not have enough power dissipation to
> avoid using wheel brakes.

Christ, again. I didn't say they didn't use the brakes, I said they
didn't *ride* the brakes.