The day has finally come to write this.
I've been holding onto a front wheel WH-7900-C24-TL from a customer for some time now.
Since Shimano wouldn't offer a free replacement
(well, it's their prerogative to make that call, so that part is what it is),
the customer asked if I could at least pull out the front hub, and it's been years—
I asked the customer to hold off on taking the wheel apart until I wrote this article.
You can already see something's wrong in the image above, but
one of the rim holes has blown out.
↑Normally it looks like this, but
↑it looks like this.
Now, regarding the vulnerability of the C24's TL (tubeless) rim.
I wanted to call this a "defect" from the start, both in the title and in text,
but for various reasons I gave up on that.
The diagram above shows the C24's CL (clincher) rim, but
the aluminum/carbon hybrid rim is supposed to be
lighter than full aluminum and stronger than full carbon—
a "best of both worlds" rim, as the pitch goes.
The outer edge of the rim has spoke holes for nipples,
and it requires rim tape as part of its design.
Early versions of the 7850-C24-CL came with a spoke hole plug part
that was like a velociped plug to seal the rim holes,
but when it turned out there was a high risk of punctures,
Shimano started offering replacement rim tape for free.
After that, rim tape became standard equipment on Shimano CL rims.
Here's what's important: the CL rim receives spoke tension
through the root aluminum rim section.
You might think that's obvious, but
actually, the TL rim doesn't work that way.
On the TL rim, the spoke holes on the outer edge are sealed (except the valve hole),
so you either have to cut threads on the inner side for the nipple
or, like Fulcrum, use magnets to call the nipple.
In the latter case, the rim holes don't need threads.
Mavic's aluminum/carbon rim for Zygrals—
the WO version of the first-gen Cosmic Carbone 40C (→here) comes to mind,
and that one has threads cut directly into the aluminum rim section
(the tubular version has rim holes on the outside and uses standard nipples,
so it's a pretty ordinary wheel structure).
But with Shimano's aluminum/carbon TL rim,
the threaded section is glued to the aluminum rim from the outside,
and then carbon is layered over it.
Aside from the adhesive force, the root aluminum rim section
isn't bearing the spoke tension at all.
It's a structure that strains credulity. How is one not supposed to call this a defect—
I mean, a vulnerability?
There's also a problem with the adhesive surface area—
contact only happens at the green section shown in the diagram above.
I couldn't find primary sources for this, which was also one reason
this article took so long to write,
but Shimano made remarks about Company M's (of course, Mavic) Zygral spokes,
saying the aluminum section recessed inside the rim was
unnecessarily heavy,
and boasted about the weight advantage of their own aluminum/carbon TL rim.
I've definitely seen this material with my own eyes.
It was rare for Shimano to pit themselves against another company, even with the name obscured,
and I remember thinking that clearly.
I went searching everywhere for this material and even visited distributors who handle Shimano
to have them let me flip through past catalogs,
but I never found it.
That leaves only one possibility: I must have seen it
on a slide from a photo-restricted training session (technical seminar).
I prepared a cut sample of the rim from Company M's K wheel.
The Zygral hole
looks like this from the inside.
As far as I know, this section hasn't failed and pulled inward
from spoke tension, but when it comes to Shimano's TL rim
where the threaded section has blown out (pulled inward), I know of at least three cases,
including hearsay—so this structure is clearly not a weight waste, which means
it serves a purpose.
↑This is the rim hole of the TL rim.
No matter how I look at it, the thickness suggests a structurally def—
I mean, vulnerable design.
This is the threaded insert part of the TL rim.
Because the threads are long, most of the section recessed into the rim
isn't involved in the adhesive surface area.
They apparently thought the face-to-face adhesion of the flange section would be enough.
The inner wall thickness of Company M's Model K rim looks substantial,
but that's only because it's right below a rim hole—
in the section between rim holes
it thins out.
This K rim is slightly heavier than the C24-CL rim,
but clearly lighter than the C24-TL rim,
and in terms of strength and spoke-tension resistance,
it's far superior to either C24 rim.
The C24 front wheel is a lightweight, low-profile rim with a ridiculous 16 spokes,
so the rim holes get pulled alternately left and right by spoke tension,
deforming the rim and creating a slight lateral wobble in the finished state—
but the K doesn't do that.
There's also a Fulcrum Racing 3 front wheel with 16 spokes and steel spokes,
and it doesn't have rim wobble either.
That's because the rim is considerably heavier than the K or C24.
As for the carbon section, when I showed it to someone knowledgeable about carbon,
they said "the thickness is way too thin."
I received a more detailed explanation about thickness,
where they described it using a unit of measurement
the way you'd count squid by cups or tansu chests by poles,
but that seems like their trade secret, so I can't go into detail.
But even to an amateur's eye, it's clear the thickness isn't
adequate for structural strength (and indeed, it's blown out).
That the TL rim doesn't receive spoke tension through the aluminum rim section
isn't something Shimano is hiding—
they just nonchalantly put it in the catalog (though the official diagram
does show a small adhesive area).
Of course, they don't explicitly write "this rim doesn't receive spoke tension
through the aluminum rim section," but still.
I found this while searching for materials comparing to Company M,
and the image above explains the "T-nut structure,"
a design detail about tubeless rims near the spoke holes.
This catalog only describes it as "reinforcement around the nipple where strength is needed,"
so I can't tell what material this rim is made from, but
going back further in year, there's a note mentioning "brazed welding."
This means it's referring to the structure of the scandium rim models
like the WH-7801SL, Shimano's first road tubeless wheel,
and aluminum rims like the WH-6700/6800.
Separately from that, this cross-section diagram of the aluminum/carbon rim
is actually from a CL rim, not a TL rim, but
they're applying these two images to the aluminum/carbon TL rim.
This is clearly a lie
(depending on the catalog year, sometimes the CL rim image is here instead,
but either way, the T-nut structure explanation is false).
So I sent this blown-out wheel to Shimano's customer service
after informing them in advance that I was sending it,
expecting (in my own mind) a free replacement—
but they just sent it back as-is.
The stated reason was that, based on the purchase date the customer honestly disclosed,
the warranty had expired just over six months ago.
They applied this rule rigidly,
so I called back a few days later and pushed the issue,
arguing that given the abnormal nature of the failure,
they should make an exception and replace it—but no luck.
So Shimano's position is that this damage isn't exceptional.
I'm not going to say "you should do it because I would,"
but if this were a Nomunlab wheel, we'd do a free replacement.
Setting aside the question of whether there's a sincere willingness to respond to complaints,
these days when incidents like this (along with the response, or lack thereof) spread
on social media and such, you have to consider the potential economic damage.
Replacing one front wheel is far cheaper than that.
Also, personally speaking, as a "lesson fee" for keeping the broken wheel on hand
to understand how it broke, giving a replacement wheel would be on the cheap side.
Whichever way you look at it, I can't arrive at the conclusion
of not doing a free replacement.
If this kind of failure happened in 1 in 100 wheels, it would be more widely known,
so I suspect the rate is considerably lower than that.
But at that rate, they might as well replace it.
If the same failure happened to another user, then for the second and subsequent cases,
you could argue "your usage was at fault"—
but not for the first time.
When I made that follow-up call, the person on the other end seemed to be
playing a game of "we won't cave to unreasonable complaints"
and was just committed to not replacing it,
so there was no way to get through to them.
One thing I remember clearly: I said something like
"The customer didn't notice until the wheel was sitting there and it had blown out,"
and they responded with
"Well, if you leave a wheel in a hot car or something, the adhesive can fail."
Wait, who said anything about a hot car?
Don't make up scenarios that work in your favor.
When I said "sitting there," I meant
I was glad the wheel didn't blow out while riding
and the customer didn't get seriously hurt as a result.
I couldn't help but laugh at how desperately they were trying not to replace it.
The customer is someone I know well, and in summer,
there's no situation where they'd leave a wheel in a hot car.
They rarely ride routes over mountain passes from within Osaka Prefecture,
meaning they're also rarely braking downhill in ways that generate brake heat.
If the blow-out were caused by the customer's usage or frequency,
wheels in the hands of racers would fail dozens of times more often.
Seeing that this doesn't happen makes me think
the customer bears no fault—but I couldn't even discuss this reasonably.
By saying the adhesive fails in hot cars, they were indicating they think
the aluminum/carbon TL rim is sensitive to heat.
But that was just idle talk from a phone operator,
and I don't consider it an official statement from Shimano.
I said I know of three blow-out cases, and they were all front wheels.
This is probably not unrelated to the ridiculous 16-spoke count,
and I suspect the failure rate would drop significantly with 20 spokes
(assuming we're comparing front wheels finished to similar tension).
Whether to offer a free replacement, whether within warranty or as an exception,
is entirely the manufacturer's or distributor's call.
So once they say no, there's no point in pushing further.
Some readers might think the rabid anti-Shimano Nomunlab got
the brush-off because of who we are.
I can't completely deny that possibility, but
I do think Shimano treated me fairly on this point.
This is a WH-9000-C24-TL front wheel (or what's left of it),
and when we first took it in, it still looked like a front wheel,
but after pulling spokes for repairs to the customer's other front wheel,
it became just a rim sample.
The bead hook has blown out.
The situation was that the wheel was being used for cyclocross,
and although it was eventually run at under 2 psi,
when they pumped it up to just over 3 psi to seat the tubeless tire bead,
it blew out at that point.
Again, I'm glad it didn't blow during a ride.
The brake zone shows a wedge-shaped wear pattern at its center—
apparently because the cantilever brake lever arc was set so the shoe edge was hitting—
and this probably wasn't unrelated to the failure.
So it's fair to say the customer wasn't entirely without fault,
but they also didn't get a free replacement.
This one wasn't sent from our shop, though.
Since it was within the warranty period, maybe they found some angle
(possibly that brake wear mark) to justify their "we won't be bullied by unreasonable complaints" stance.
If they're firm on this one, I understand their stance on the first case too.
On a different note: starting with the R9100 series,
Shimano's C24 wheels come only in clincher (CL) models.
The tubeless (TL) version is gone. Did something happen?
I've been holding onto a front wheel WH-7900-C24-TL from a customer for some time now.
Since Shimano wouldn't offer a free replacement
(well, it's their prerogative to make that call, so that part is what it is),
the customer asked if I could at least pull out the front hub, and it's been years—
I asked the customer to hold off on taking the wheel apart until I wrote this article.
You can already see something's wrong in the image above, but
one of the rim holes has blown out.
↑Normally it looks like this, but
↑it looks like this.
Now, regarding the vulnerability of the C24's TL (tubeless) rim.
I wanted to call this a "defect" from the start, both in the title and in text,
but for various reasons I gave up on that.
The diagram above shows the C24's CL (clincher) rim, but
the aluminum/carbon hybrid rim is supposed to be
lighter than full aluminum and stronger than full carbon—
a "best of both worlds" rim, as the pitch goes.
The outer edge of the rim has spoke holes for nipples,
and it requires rim tape as part of its design.
Early versions of the 7850-C24-CL came with a spoke hole plug part
that was like a velociped plug to seal the rim holes,
but when it turned out there was a high risk of punctures,
Shimano started offering replacement rim tape for free.
After that, rim tape became standard equipment on Shimano CL rims.
Here's what's important: the CL rim receives spoke tension
through the root aluminum rim section.
You might think that's obvious, but
actually, the TL rim doesn't work that way.
On the TL rim, the spoke holes on the outer edge are sealed (except the valve hole),
so you either have to cut threads on the inner side for the nipple
or, like Fulcrum, use magnets to call the nipple.
In the latter case, the rim holes don't need threads.
Mavic's aluminum/carbon rim for Zygrals—
the WO version of the first-gen Cosmic Carbone 40C (→here) comes to mind,
and that one has threads cut directly into the aluminum rim section
(the tubular version has rim holes on the outside and uses standard nipples,
so it's a pretty ordinary wheel structure).
But with Shimano's aluminum/carbon TL rim,
the threaded section is glued to the aluminum rim from the outside,
and then carbon is layered over it.
Aside from the adhesive force, the root aluminum rim section
isn't bearing the spoke tension at all.
It's a structure that strains credulity. How is one not supposed to call this a defect—
I mean, a vulnerability?
There's also a problem with the adhesive surface area—
contact only happens at the green section shown in the diagram above.
I couldn't find primary sources for this, which was also one reason
this article took so long to write,
but Shimano made remarks about Company M's (of course, Mavic) Zygral spokes,
saying the aluminum section recessed inside the rim was
unnecessarily heavy,
and boasted about the weight advantage of their own aluminum/carbon TL rim.
I've definitely seen this material with my own eyes.
It was rare for Shimano to pit themselves against another company, even with the name obscured,
and I remember thinking that clearly.
I went searching everywhere for this material and even visited distributors who handle Shimano
to have them let me flip through past catalogs,
but I never found it.
That leaves only one possibility: I must have seen it
on a slide from a photo-restricted training session (technical seminar).
I prepared a cut sample of the rim from Company M's K wheel.
The Zygral hole
looks like this from the inside.
As far as I know, this section hasn't failed and pulled inward
from spoke tension, but when it comes to Shimano's TL rim
where the threaded section has blown out (pulled inward), I know of at least three cases,
including hearsay—so this structure is clearly not a weight waste, which means
it serves a purpose.
↑This is the rim hole of the TL rim.
No matter how I look at it, the thickness suggests a structurally def—
I mean, vulnerable design.
This is the threaded insert part of the TL rim.
Because the threads are long, most of the section recessed into the rim
isn't involved in the adhesive surface area.
They apparently thought the face-to-face adhesion of the flange section would be enough.
The inner wall thickness of Company M's Model K rim looks substantial,
but that's only because it's right below a rim hole—
in the section between rim holes
it thins out.
This K rim is slightly heavier than the C24-CL rim,
but clearly lighter than the C24-TL rim,
and in terms of strength and spoke-tension resistance,
it's far superior to either C24 rim.
The C24 front wheel is a lightweight, low-profile rim with a ridiculous 16 spokes,
so the rim holes get pulled alternately left and right by spoke tension,
deforming the rim and creating a slight lateral wobble in the finished state—
but the K doesn't do that.
There's also a Fulcrum Racing 3 front wheel with 16 spokes and steel spokes,
and it doesn't have rim wobble either.
That's because the rim is considerably heavier than the K or C24.
As for the carbon section, when I showed it to someone knowledgeable about carbon,
they said "the thickness is way too thin."
I received a more detailed explanation about thickness,
where they described it using a unit of measurement
the way you'd count squid by cups or tansu chests by poles,
but that seems like their trade secret, so I can't go into detail.
But even to an amateur's eye, it's clear the thickness isn't
adequate for structural strength (and indeed, it's blown out).
That the TL rim doesn't receive spoke tension through the aluminum rim section
isn't something Shimano is hiding—
they just nonchalantly put it in the catalog (though the official diagram
does show a small adhesive area).
Of course, they don't explicitly write "this rim doesn't receive spoke tension
through the aluminum rim section," but still.
I found this while searching for materials comparing to Company M,
and the image above explains the "T-nut structure,"
a design detail about tubeless rims near the spoke holes.
This catalog only describes it as "reinforcement around the nipple where strength is needed,"
so I can't tell what material this rim is made from, but
going back further in year, there's a note mentioning "brazed welding."
This means it's referring to the structure of the scandium rim models
like the WH-7801SL, Shimano's first road tubeless wheel,
and aluminum rims like the WH-6700/6800.
Separately from that, this cross-section diagram of the aluminum/carbon rim
is actually from a CL rim, not a TL rim, but
they're applying these two images to the aluminum/carbon TL rim.
This is clearly a lie
(depending on the catalog year, sometimes the CL rim image is here instead,
but either way, the T-nut structure explanation is false).
So I sent this blown-out wheel to Shimano's customer service
after informing them in advance that I was sending it,
expecting (in my own mind) a free replacement—
but they just sent it back as-is.
The stated reason was that, based on the purchase date the customer honestly disclosed,
the warranty had expired just over six months ago.
They applied this rule rigidly,
so I called back a few days later and pushed the issue,
arguing that given the abnormal nature of the failure,
they should make an exception and replace it—but no luck.
So Shimano's position is that this damage isn't exceptional.
I'm not going to say "you should do it because I would,"
but if this were a Nomunlab wheel, we'd do a free replacement.
Setting aside the question of whether there's a sincere willingness to respond to complaints,
these days when incidents like this (along with the response, or lack thereof) spread
on social media and such, you have to consider the potential economic damage.
Replacing one front wheel is far cheaper than that.
Also, personally speaking, as a "lesson fee" for keeping the broken wheel on hand
to understand how it broke, giving a replacement wheel would be on the cheap side.
Whichever way you look at it, I can't arrive at the conclusion
of not doing a free replacement.
If this kind of failure happened in 1 in 100 wheels, it would be more widely known,
so I suspect the rate is considerably lower than that.
But at that rate, they might as well replace it.
If the same failure happened to another user, then for the second and subsequent cases,
you could argue "your usage was at fault"—
but not for the first time.
When I made that follow-up call, the person on the other end seemed to be
playing a game of "we won't cave to unreasonable complaints"
and was just committed to not replacing it,
so there was no way to get through to them.
One thing I remember clearly: I said something like
"The customer didn't notice until the wheel was sitting there and it had blown out,"
and they responded with
"Well, if you leave a wheel in a hot car or something, the adhesive can fail."
Wait, who said anything about a hot car?
Don't make up scenarios that work in your favor.
When I said "sitting there," I meant
I was glad the wheel didn't blow out while riding
and the customer didn't get seriously hurt as a result.
I couldn't help but laugh at how desperately they were trying not to replace it.
The customer is someone I know well, and in summer,
there's no situation where they'd leave a wheel in a hot car.
They rarely ride routes over mountain passes from within Osaka Prefecture,
meaning they're also rarely braking downhill in ways that generate brake heat.
If the blow-out were caused by the customer's usage or frequency,
wheels in the hands of racers would fail dozens of times more often.
Seeing that this doesn't happen makes me think
the customer bears no fault—but I couldn't even discuss this reasonably.
By saying the adhesive fails in hot cars, they were indicating they think
the aluminum/carbon TL rim is sensitive to heat.
But that was just idle talk from a phone operator,
and I don't consider it an official statement from Shimano.
I said I know of three blow-out cases, and they were all front wheels.
This is probably not unrelated to the ridiculous 16-spoke count,
and I suspect the failure rate would drop significantly with 20 spokes
(assuming we're comparing front wheels finished to similar tension).
Whether to offer a free replacement, whether within warranty or as an exception,
is entirely the manufacturer's or distributor's call.
So once they say no, there's no point in pushing further.
Some readers might think the rabid anti-Shimano Nomunlab got
the brush-off because of who we are.
I can't completely deny that possibility, but
I do think Shimano treated me fairly on this point.
This is a WH-9000-C24-TL front wheel (or what's left of it),
and when we first took it in, it still looked like a front wheel,
but after pulling spokes for repairs to the customer's other front wheel,
it became just a rim sample.
The bead hook has blown out.
The situation was that the wheel was being used for cyclocross,
and although it was eventually run at under 2 psi,
when they pumped it up to just over 3 psi to seat the tubeless tire bead,
it blew out at that point.
Again, I'm glad it didn't blow during a ride.
The brake zone shows a wedge-shaped wear pattern at its center—
apparently because the cantilever brake lever arc was set so the shoe edge was hitting—
and this probably wasn't unrelated to the failure.
So it's fair to say the customer wasn't entirely without fault,
but they also didn't get a free replacement.
This one wasn't sent from our shop, though.
Since it was within the warranty period, maybe they found some angle
(possibly that brake wear mark) to justify their "we won't be bullied by unreasonable complaints" stance.
If they're firm on this one, I understand their stance on the first case too.
On a different note: starting with the R9100 series,
Shimano's C24 wheels come only in clincher (CL) models.
The tubeless (TL) version is gone. Did something happen?