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Hunt carbon rim exploded while inflating

Old 12-09-23, 12:51 PM
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Originally Posted by Kai Winters
At least the OP wasn't just calling out Hunt for a bad wheel when it does appear the OP blew it...literally and figuratively.
Glad that Hunt send the OP a replacement rim...they just could have said 'sucks for you, next time read the owners manual' or some such wording.
Love the stories about 'asplosions'...keep them coming.
The OP didn't blow anything. The OP was following SOP in using overpressure to seat the bead on a tubeless tire. Everyone does this. If these Hunt rims assplode before you can even get the bead to seat, then this is entirely a problem with Hunt.

My guess is that Hunt has to make the shelf area tighter than normal, because there is no bead to keep the tire from lifting off. That bead has to be tight against the rim shelf to prevent air pressure from prying underneath the tire bead. This tight construction, in turn means you need much higher pressure to seat the bead. But the weak hookless sidewall cannot stand the higher pressure. So now you have a death spiral.
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Old 12-09-23, 12:58 PM
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Yep, hoop stresses. I spread a double-walled aluminum rim that way once.
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Old 12-09-23, 01:02 PM
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Originally Posted by Jughed
Not all of us are luddites.

I ride all three types of bikes - carbon, aluminum and steel.

I have aluminum and CF wheels.

I have rim and disc brakes, and I like the discs better.

Assploding CF is the only thing thatís put me in the hospital.

So Iím cautious about what parts and the type of parts I ride, pain will do that to you.

Oh and yes, my high end steel bike is awesome.
No CF rims thus far, and no hospital - not that carelessness couldnít land me in a hospital with Al rims. I guess I became cautious through learning other peopleís mishaps.

Some people have a tendency to go to extremes in their hope to substantiate their argument but end up comparing proverbial oranges and apples. Use of CF in jets produced for our war department was thrown in by someone as the proof of materialís reliability - Iím not sure that the level of testing and quality control applied by bicycle companies will approach that of leading aerospace and war industry, such as Lockheed Martin etc. Of course, this is just a guess, may be bicycle industry perfected the technology and Lockheed Martin copied it. 😉

I have good quality frames made from steel, titanium, aluminum, and yes CF. They all work satisfactorily and admirably well for the purpose they were made and built up.
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Old 12-09-23, 01:41 PM
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A quick defense of Hunt carbon rims since they all don’t explode. Have had a pair of 60 mms for two years and have put on three sets of tires - using a compressor to seat the them. Don’t know the pressure used, but enough to get them in place, and never an issue.
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Old 12-09-23, 02:12 PM
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Originally Posted by Jughed
I have zero concerns with CF parts that come from a well known source. I ride Roval C38 wheels .
Got any pics of their factory floor or location?
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Old 12-09-23, 02:18 PM
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Originally Posted by terrymorse
Reason #3: metal fatigue, which will happen on any Al rim with enough stress cycles.
Improper spoke tension is the main cause of metal fatigue on alloy rims...A properly built wheel especially if it's a disc wheel where brake track wear isn't an issue will last forever, unless it is crashed badly or seriously abused.
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Old 12-09-23, 02:36 PM
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Originally Posted by wolfchild
A properly built [aluminum alloy] wheel especially if it's a disc wheel where brake track wear isn't an issue will last forever, unless it is crashed badly or seriously abused.
Everything we know about material science says that is untrue. Use an aluminum rim long enough, it will eventually fail from fatigue.
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Old 12-09-23, 03:24 PM
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Originally Posted by wolfchild
There are only two reasons why alloy rims fail. Those two reasons are worn out braking track or improper and inconsistent spoke tension. Both of these problems are easily preventable,
Stanís rims are frequently rated at lower PSI than their counterparts. I like their wheels and have several of them. They are noticeably thinner (and lighter) than typical aluminum rims. You absolutely can blow the sidewall out.

So there is that.
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Old 12-09-23, 03:35 PM
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Originally Posted by sweeks
My experience agrees with this with the exception of several 20" (406) aluminum rims on the rear wheel of my folding commuter bike which failed along the center plane. I originally thought these were brake track wear failures which propagated into the rim. Eventually I showed these to Bill Mould, and was told these were more likely caused by high pressure (60psi) in wide (47mm) tires on relatively narrow rims. These were Kinetix rims, and while I can't say the rims were the problem, I did solve the problem by changing to Sun Ringle rims which are slightly wider.
For reference, I weigh about 215 pounds.


Rim failure from hoop stress. Brake tracks were about 1mm thick.



Rear brake was thumping when applied.



Another rim with hoop stress failure.
Originally Posted by wolfchild
There are only two reasons why alloy rims fail. Those two reasons are worn out braking track or improper and inconsistent spoke tension. Both of these problems are easily preventable,
Brake wear or inconsistent spoke tension? Which is this?
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Old 12-09-23, 03:47 PM
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Originally Posted by 79pmooney
Brake wear or inconsistent spoke tension? Which is this?
Brake tracks were at least 1.0mm thick, and spoke tensions were all within 20% of the mean tension (at the time of building). I initially thought this was brake track wear that spread inward, but the rims weren't very worn and Bill Mould knows more about rims than I do, so I'm willing to accept that interpretation. In any case, the problem is licked.
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Old 12-09-23, 03:53 PM
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Originally Posted by sweeks
Brake tracks were at least 1.0mm thick, and spoke tensions were all within 20% of the mean tension (at the time of building). I initially thought this was brake track wear that spread inward, but the rims weren't very worn and Bill Mould knows more about rims than I do, so I'm willing to accept that interpretation. In any case, the problem is licked.
This was directed at wolfchild who stated explicitly that only brake track wear and uneven spoke tensions can cause aluminum rim failure, not you. You posted evidence against. Thank you.
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Old 12-09-23, 03:54 PM
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Well, folks - it’s really not rocket-surgery (=rocket science + neurosurgery). All materials yield to pressure/force. The thinner the material, greater likelihood of failure, all else being equal.
The only reason my Al wheels seem indestructible is because I start with a slightly heavier rim of high quality, build it myself quite well using a sturdy set of hubs, 32H laced 2-cross with double butted SS spokes - and most importantly, even (very close to equal) tension on all spokes. One can easily true a wheel without equal tension on spokes but they will not stay true for very long.

I’m sure that if I have someone weighing twice as much as I do, the bike and the wheels will survive… for a while, but wouldn’t prove indestructible in the long-run.

Im sure very similar principles apply to CF rims/wheels.

Given enough time, everything gets weaker and eventually fails. Things that built well will last a life-time of a person but it doesn’t mean they will never fail.
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Old 12-09-23, 04:12 PM
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Some years back I learned the hard way that a larger cross-section on a tire increases stress on the rim,
when I cracked the sidewall of an aluminum rim...twice.
I broke the first rim, moved the hub & spokes to a new rim, then that one broke a couple months later.
Failure was where the bead of the rim met the inner rim wall, pressure was at max rating of a 1.9" tire.

So I did some digging. (PDF)
Understanding the Influence of Pressure and Radial Loads on Stress and Displacement Response of a Rotating Body: The Automobile Wheel

See page 3, Section "2.2. Influence of tire air pressure".
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Old 12-09-23, 04:22 PM
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Originally Posted by 79pmooney
This was directed at wolfchild who stated explicitly that only brake track wear and uneven spoke tensions can cause aluminum rim failure, not you. You posted evidence against. Thank you.
My pleasure. I just thought the extra information would help.
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Old 12-09-23, 06:08 PM
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So I find this thread enlightening.

Ive been on bikes in a semi serious to way too serious capacity since the early 90ís.

In that time, this simply has never come up for me. To be fair, my super serious years were spent on 20 and 23c tires, often glued on. So a totally different story.

Still, Iíve got a load of gravel and mountain bikes now. All tubeless. I would have never thought that the lower of either the rim max pressure or tire max pressure could destroy a rim, based on tire size. Seems like a more detailed rim sticker would be an easy fix.

I think Iím probably like most of us, itís never happened to me before only because my tires feel pretty firm around 40-45psi. Not because I knew any better.
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Old 12-09-23, 07:25 PM
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Originally Posted by 79pmooney
This was directed at wolfchild who stated explicitly that only brake track wear and uneven spoke tensions can cause aluminum rim failure, not you. You posted evidence against. Thank you.
He trolls by intentionally posting inaccurate information.

Either that, or heís clueless.
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Old 12-09-23, 08:25 PM
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Originally Posted by indyfabz
He trolls by intentionally posting inaccurate information.

Either that, or he’s clueless.
It doesn't have to be an either / or situation.

Last edited by tomato coupe; 12-09-23 at 10:29 PM. Reason: typo
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Old 12-10-23, 08:34 AM
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Damn, I mounted my hunt wheels the other day. I have never set up tubeless before and watched a bunch of youtube videos on it. The one thing I never saw was how to install the valve stem correctly. The videos just showed inserting and hand tight the little nut. So thatís what I did. 6 co2 cartridges later I couldnít get the bead to set fully. Gave up and took it to the shop to install.

Something that took me hours, took my buddy 5 mins.
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Old 12-10-23, 08:45 AM
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Should clarify, I did not push the valve stem in place while tightening the nut. I got 70 percent the tire to set but couldnít get the rest of it.
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Old 12-10-23, 10:43 AM
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Originally Posted by bampilot06
Should clarify, I did not push the valve stem in place while tightening the nut. I got 70 percent the tire to set but couldnít get the rest of it.
was the air leaking out? Or did the air stay inside the tire, but the bead refused to pop?
the valve stem should definitely be pushed down firmly while you tighten the ring nut.
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Old 12-10-23, 01:25 PM
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Originally Posted by icemilkcoffee
was the air leaking out? Or did the air stay inside the tire, but the bead refused to pop?
the valve stem should definitely be pushed down firmly while you tighten the ring nut.

Air leaked out of the drain hole and the valve stem.
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Old 12-10-23, 08:10 PM
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Originally Posted by tomato coupe
It doesn't have to be an either / or situation.
True.
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Old 12-10-23, 10:29 PM
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I find this conversation to be very informative as I'd always assumed that 100psi is a 100psi and if that's what a rim is rated for than why would the tire matter. Still not fully getting it as the amount of material in contact with the rim would seem to be the same regardless of the tire size, either way its the same amount of tire contact at the bead as well as the same amount of pressure contained within the system, So is it ultimately a leverage situation? The way the tire expands pushes out on the rim differently effecting how the stress of holding the tire is placed on the rim? Cause I read the amount of area being an issue but I don't see how a larger tire has any more area in contact with the rim. The larger tire has a larger cross section obviously but it would seem to me that there can't be any additional amount air in contact with the rim as the bigger tire does nothing to change the amount of surface area of the rim the tire/tube/air can act upon. How can any size tire with a 100psi apply more pressure than 100psi onto the rim other than by increasing the load on the tire?

Originally Posted by wolfchild
There are only two reasons why alloy rims fail. Those two reasons are worn out braking track or improper and inconsistent spoke tension. Both of these problems are easily preventable,
I've seen aluminum rims in cross races shattered, a lady walked off the course with her rim cracked into 4 separate pieces and rims split width wise from trick riding, so there's plenty of ways an alloy rim could fail.
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Old 12-10-23, 11:09 PM
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Originally Posted by Russ Roth
I find this conversation to be very informative as I'd always assumed that 100psi is a 100psi and if that's what a rim is rated for than why would the tire matter. Still not fully getting it as the amount of material in contact with the rim would seem to be the same regardless of the tire size, either way its the same amount of tire contact at the bead as well as the same amount of pressure contained within the system, So is it ultimately a leverage situation? The way the tire expands pushes out on the rim differently effecting how the stress of holding the tire is placed on the rim? Cause I read the amount of area being an issue but I don't see how a larger tire has any more area in contact with the rim. The larger tire has a larger cross section obviously but it would seem to me that there can't be any additional amount air in contact with the rim as the bigger tire does nothing to change the amount of surface area of the rim the tire/tube/air can act upon. How can any size tire with a 100psi apply more pressure than 100psi onto the rim other than by increasing the load on the tire?
Ideal gas law: P V = n R T [Pressure x Volume = number of moles of gas x R (ideal gas constant) x Pressure]

What is the ideal gas law? (article) | Khan Academy

A wider tire has greater Volume (than a narrower tire). Thus, at the same Pressure and Temperature, the wider tire also contains a greater number of moles (i.e., amount) of air than a narrower tire.

All of the air within the tire exerts a force against the sidewalls of the wheel via the tire, not just the air at the boundary of the tire and wheel. If you don't believe me, you can do this experiment: Mount a 700x25c tire and a 700x32c tire to the same wheel and inflate each to the same pressure, and see which tire feels firmer?

This is confirmed by the Hoop Stress formula: Pressure Vessel, Thin Wall Hoop and Longitudinal Stresses Equation and Calculator (engineersedge.com)

... which shows that at the same Pressure, Hoop Stress increases with the cross-sectional diameter of the tire, which is proportional to Volume.
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Old 12-10-23, 11:40 PM
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Originally Posted by Russ Roth
IStill not fully getting it as the amount of material in contact with the rim would seem to be the same regardless of the tire size, either way its the same amount of tire contact at the bead as well as the same amount of pressure contained within the system, So is it ultimately a leverage situation? The way the tire expands pushes out on the rim differently effecting how the stress of holding the tire is placed on the rim? Cause I read the amount of area being an issue but I don't see how a larger tire has any more area in contact with the rim. The larger tire has a larger cross section obviously but it would seem to me that there can't be any additional amount air in contact with the rim as the bigger tire does nothing to change the amount of surface area of the rim the tire/tube/air can act upon. How can any size tire with a 100psi apply more pressure than 100psi onto the rim other than by increasing the load on the tire?
.
See post 88;
All explained on page 3 of that document.
Look at Figure 4 and Equation 5.
"a" is the overall radius of the tread of the inflated tire.
"rf" is the radius of the rim at the inner surface of the bead.
Assuming the tire has a round cross-section when inflated: a - rf = <width of tire>
Now think about varying "a" by changing tire width;
As "a" becomes closer to "rf" (narrower tire), the lateral force on the rim decreases.
As "a" becomes further from "rf" (wider tire), the lateral force on the rim increases.
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