A customer brought in a Cosmic SL for service.
It's a wheel that was marketed as Cosmic Carbon SL,
but apart from cosmetic rim differences, it's essentially the same as
this generation's Cosmic SL model.
Anyway, the customer had been riding this wheel with Michelin Pro 3 Race tires,
when they noticed the front tire bulging inward
as if it had been hit by Hokuto Shinken
and quickly let air out. But after riding a bit more,
the tire exploded. At least it didn't happen on a descent.
Michelin tires have a tendency for the rubber to melt and stick to the rim
at the point directly below the valve hole
(though this seems to have disappeared with endurance models—either the manufacturing changed or the OEM source shifted),
but on this wheel it had happened all around the rim.
Even though only about 2,000 km had been ridden on it,
over a year had passed since the tire was mounted,
and a combination of bad conditions—brake heat from descents and the poor weather resistance of red sidewalls—added up.
↑Near the valve hole on the front wheel
This much is still pretty common, but...
the melted rubber had spread over the rim tape and
deep into the bead hook interior.
I
wiped it with acetone and
cleaned it up.
I'm writing this simply, but it was actually quite a struggle.
↑This is near the valve hole on the rear wheel.
The outer perimeter of the bead hook cleaned up relatively easily.
I replaced the rim tape on both wheels.
On a different note, Continental makes a model called "Attack & Force,"
where Attack is a front-specific tread and width design,
and Force is rear-specific. They come in tubular and clincher versions, but the following is about clinchers.
The Attack II & Force II successors came with Attack at 22C and Force at 24C,
and until recently, the best rolling efficiency setup I could comfortably use with clincher tires
was a 22C Attack up front and—not a 24C Force but—a 23C Grand Prix 4000 S II out back,
or if you didn't mind about tire life and puncture risk, a 23C Grand Prix TT.
But the current models are Attack III & Force III, which are 1C wider at 23C and 25C respectively,
and since the Grand Prix 5000 clincher is excellent for rolling efficiency,
there's no more reason to run a front-only 23C Attack III.
The Attack II is already discontinued,
but I was selling final warehouse stock at special prices—"was" being the key word in past tense.
Yes, my apologies. All of them sold out because of this incident.
I fitted a 25C Goodyear Eagle Sport to the rear wheel, but
since the rim has a narrow internal width (thick bead hooks measuring 13.5mm actual),
even at 8 bar it measures just under 23mm.
↑The front tire wasn't on the wheel when the customer brought it in,
so this is the tire that was on the rear, but
the rubber directly below the valve hole melted, exposing the casing.
From the inside too
↑it had worn pretty thin.
This is a separate case—an old photo for a previous article—
a black Lition from the same era as the Pro 3 Race.
While it happens less with color tires,
you see the same symptom with black tires too.
Actually, the Cosmic SL was the day before yesterday,
and then today I replaced tires on 3 more wheel sets.
All of them were the same Pro 3 Race red 23C tires.
↑The timeline jumps around, but these are the removed tires.
Well, once you lose trust or have a bad experience,
you naturally want to replace things.
Among these tires, none had casing exposed from the inside
below the valve hole like the first one did.
This is a Campagnolo Bullet Ultra,
with a wider internal rim width than the Cosmic Carbon at the start—
measuring 15.8mm actual.
The tire is claimed to be 23C, but
actually measures 25.4mm.Exactly one inch.
Michelin tires run wide to begin with, but
it's clear they've also expanded with age.
The same wheel fitted with a 25C Eagle Sport
(this model has no 23C option) measured
23.7mm at 7 bar.
Since 2020, the ETRTO standard for road bike tire widths has changed to accommodate the reality of wider rims.
According to the new standard, 22-24C tires are designed for 17mm internal rim width,
and 25-28C tires for 19mm internal rim width.
That means with the new standard, a 25C tire won't actually measure 25C at proper pressure unless mounted on a 19mm internal rim.
Vittoria has stated they're already following this,
but Goodyear's compliance is unclear.
I've confirmed that on an AL22W rim with measured 19.2mm internal width,
Goodyear's claimed 25C tires do measure about as marked,
so Goodyear may also be complying with the new ETRTO.
↑This is a Vision wheel, and
the area below the valve hole had melted.
This much is pretty common to see.
Even so, the casing on the inside hadn't been exposed.
Not just at the valve point but across the tire,
the rubber had migrated onto the bead,
so it may well have been a candidate for explosion.
It's a wheel that was marketed as Cosmic Carbon SL,
but apart from cosmetic rim differences, it's essentially the same as
this generation's Cosmic SL model.
Anyway, the customer had been riding this wheel with Michelin Pro 3 Race tires,
when they noticed the front tire bulging inward
and quickly let air out. But after riding a bit more,
the tire exploded. At least it didn't happen on a descent.
Michelin tires have a tendency for the rubber to melt and stick to the rim
at the point directly below the valve hole
(though this seems to have disappeared with endurance models—either the manufacturing changed or the OEM source shifted),
but on this wheel it had happened all around the rim.
Even though only about 2,000 km had been ridden on it,
over a year had passed since the tire was mounted,
and a combination of bad conditions—brake heat from descents and the poor weather resistance of red sidewalls—added up.
↑Near the valve hole on the front wheel
This much is still pretty common, but...
the melted rubber had spread over the rim tape and
deep into the bead hook interior.
I
wiped it with acetone and
cleaned it up.
I'm writing this simply, but it was actually quite a struggle.
↑This is near the valve hole on the rear wheel.
The outer perimeter of the bead hook cleaned up relatively easily.
I replaced the rim tape on both wheels.
On a different note, Continental makes a model called "Attack & Force,"
where Attack is a front-specific tread and width design,
and Force is rear-specific. They come in tubular and clincher versions, but the following is about clinchers.
The Attack II & Force II successors came with Attack at 22C and Force at 24C,
and until recently, the best rolling efficiency setup I could comfortably use with clincher tires
was a 22C Attack up front and—not a 24C Force but—a 23C Grand Prix 4000 S II out back,
or if you didn't mind about tire life and puncture risk, a 23C Grand Prix TT.
But the current models are Attack III & Force III, which are 1C wider at 23C and 25C respectively,
and since the Grand Prix 5000 clincher is excellent for rolling efficiency,
there's no more reason to run a front-only 23C Attack III.
The Attack II is already discontinued,
but I was selling final warehouse stock at special prices—"was" being the key word in past tense.
Yes, my apologies. All of them sold out because of this incident.
I fitted a 25C Goodyear Eagle Sport to the rear wheel, but
since the rim has a narrow internal width (thick bead hooks measuring 13.5mm actual),
even at 8 bar it measures just under 23mm.
↑The front tire wasn't on the wheel when the customer brought it in,
so this is the tire that was on the rear, but
the rubber directly below the valve hole melted, exposing the casing.
From the inside too
↑it had worn pretty thin.
This is a separate case—an old photo for a previous article—
a black Lition from the same era as the Pro 3 Race.
While it happens less with color tires,
you see the same symptom with black tires too.
Actually, the Cosmic SL was the day before yesterday,
and then today I replaced tires on 3 more wheel sets.
All of them were the same Pro 3 Race red 23C tires.
↑The timeline jumps around, but these are the removed tires.
Well, once you lose trust or have a bad experience,
you naturally want to replace things.
Among these tires, none had casing exposed from the inside
below the valve hole like the first one did.
This is a Campagnolo Bullet Ultra,
with a wider internal rim width than the Cosmic Carbon at the start—
measuring 15.8mm actual.
The tire is claimed to be 23C, but
actually measures 25.4mm.
Michelin tires run wide to begin with, but
it's clear they've also expanded with age.
The same wheel fitted with a 25C Eagle Sport
(this model has no 23C option) measured
23.7mm at 7 bar.
Since 2020, the ETRTO standard for road bike tire widths has changed to accommodate the reality of wider rims.
According to the new standard, 22-24C tires are designed for 17mm internal rim width,
and 25-28C tires for 19mm internal rim width.
That means with the new standard, a 25C tire won't actually measure 25C at proper pressure unless mounted on a 19mm internal rim.
Vittoria has stated they're already following this,
but Goodyear's compliance is unclear.
I've confirmed that on an AL22W rim with measured 19.2mm internal width,
Goodyear's claimed 25C tires do measure about as marked,
so Goodyear may also be complying with the new ETRTO.
↑This is a Vision wheel, and
the area below the valve hole had melted.
This much is pretty common to see.
Even so, the casing on the inside hadn't been exposed.
Not just at the valve point but across the tire,
the rubber had migrated onto the bead,
so it may well have been a candidate for explosion.