Hunt carbon rim exploded while inflating
#1
Hunt carbon rim exploded while inflating
Was setting up some Panaracer 38c tires on Hunt Carbon 30 rims and the rim exploded at about 80psi when I was trying to get the bead to set. Reached out to Hunt, noting that the max PSI on the rim was 100, and got this reply.
Hi Kent
Thanks for getting back to me with the information.
There is one point that you make that I must correct you on, in that the tyre size has no impact on the rim's maximum pressure rating, this is incorrect, the tyres size and volume is the biggest factor of all with regards to the pressure that a bicycle rim can handle, hence why you always work to the rim's maximum pressure and not the tyres.
Exponentially as the tyre size and most importantly the tyres volume increases, the pressure that the tyres bead will place on the rim increases significantly, this is why rim manufactures scale the maximum pressure ratings dependant on the tyre size being fitted.
As from the information listed on our site, the max pressure for the Hunt 30 Carbon Gravel Disc rim with a 38c tyre is 40 psi, when fitting the tyre you went to double (and potentially higher) than that of the rims max pressure rating, in addition you also went to 20 psi above the tyres max pressure rating of 60 psi. For future tyre fits on our and other manufactures wheelsets, please work to the max rim / tyre pressure and work to the lower of the two units when fitting your tubeless tyres.
As a company we will always do what we can to assist riders, in this instance we would offer the rider a crash replacement discounted rim to replace the damaged unit, however I can offer you a replacement rim as a 'free of charge - goodwill gesture' that you can get the wheel rebuilt with at your local bike store. At present we we will have replacement rims back into stock for December week 2.
Curious if the volume not psi argument is legit.
Thanks,
Kent
Hi Kent
Thanks for getting back to me with the information.
There is one point that you make that I must correct you on, in that the tyre size has no impact on the rim's maximum pressure rating, this is incorrect, the tyres size and volume is the biggest factor of all with regards to the pressure that a bicycle rim can handle, hence why you always work to the rim's maximum pressure and not the tyres.
Exponentially as the tyre size and most importantly the tyres volume increases, the pressure that the tyres bead will place on the rim increases significantly, this is why rim manufactures scale the maximum pressure ratings dependant on the tyre size being fitted.
As from the information listed on our site, the max pressure for the Hunt 30 Carbon Gravel Disc rim with a 38c tyre is 40 psi, when fitting the tyre you went to double (and potentially higher) than that of the rims max pressure rating, in addition you also went to 20 psi above the tyres max pressure rating of 60 psi. For future tyre fits on our and other manufactures wheelsets, please work to the max rim / tyre pressure and work to the lower of the two units when fitting your tubeless tyres.
As a company we will always do what we can to assist riders, in this instance we would offer the rider a crash replacement discounted rim to replace the damaged unit, however I can offer you a replacement rim as a 'free of charge - goodwill gesture' that you can get the wheel rebuilt with at your local bike store. At present we we will have replacement rims back into stock for December week 2.
Curious if the volume not psi argument is legit.
Thanks,
Kent
#3
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As from the information listed on our site, the max pressure for the Hunt 30 Carbon Gravel Disc rim with a 38c tyre is 40 psi, when fitting the tyre you went to double (and potentially higher) than that of the rims max pressure rating, in addition you also went to 20 psi above the tyres max pressure rating of 60 psi. For future tyre fits on our and other manufactures wheelsets, please work to the max rim / tyre pressure and work to the lower of the two units when fitting your tubeless tyres.
Maximum tire pressure for this rim is 100psi when used with 25-28mm tires. 100 psi is more than enough for any rider on road. Click here to listen to a podcast exploring the science of why lower pressures were found to be faster by pro teams. Maximum tire pressures for other tyre sizes: 30mm - 32mm do not exceed 70psi, 33mm do not exceed 50psi, 35-45mm do not exceed 45psi, 45-50mm do not exceed 40psi. Please do not exceed the maximum pressure stated on your tire. Suitable for tires from 23mm up to 50mm wide.
...at the same time, I ride 43mm tires on my gravel bike and have 0 interest in running them under 45psi. I am 220# and 45psi is right at what I set my tires at because anything lower makes them sometimes feel sluggish or wobbly in random moments of riding.
Also, every tubeless tire I have seated has required a shot of air that well exceeds the psi I will actually use for riding. The burst seats the tire. Apparently these Hunt rims, which are hooked, cant handle a burst to seat the tire?
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Well they are right as far as I can tell. I have a basic understanding of the physics here. There is psi which is the pressure being exerted inside the tire and rim against the walls of the space created. There is also (separately) the force that the bead of the tire is exerting on the rim preventing it from being blown off. The higher the volume of the tire but at the same psi the higher the force that the bead is exerting on the rim becomes. At least that is how I understand things. I'm happy to be corrected by someone more in tune with the math. I'm an engineering major but my discipline is Civil.
Not sure why you aren't buying it. They sound entirely reasonable in their communications to you and you are coming out ahead anyway. Sounds like customer service above and beyond.
I am currently riding 38mm tires (Pathfinder Pro's) on my carbon rims (25mm internal width). I usually ride at between 34 - 42 psi depending on the surface my route will take me on. When seating a tire I might go barely up to 60 psi to make sure its seated (if its stubborn - usually its well seated by about 50 psi) but there is no way I would ever go beyond that.
Not sure why you aren't buying it. They sound entirely reasonable in their communications to you and you are coming out ahead anyway. Sounds like customer service above and beyond.
I am currently riding 38mm tires (Pathfinder Pro's) on my carbon rims (25mm internal width). I usually ride at between 34 - 42 psi depending on the surface my route will take me on. When seating a tire I might go barely up to 60 psi to make sure its seated (if its stubborn - usually its well seated by about 50 psi) but there is no way I would ever go beyond that.
Last edited by KJ43; 12-07-23 at 04:23 PM.
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Well they are right as far as I can tell. I have a basic understanding of the physics here. There is psi which is the pressure being exerted inside the tire and rim against the walls of the space created. There is also (separately) the force that the bead of the tire is exerting on the rim preventing it from being blown off. The higher the volume of the tire but at the same pressure the higher the force that the bead is exerting on the rim becomes. At least that is how I understand things. I'm happy to be corrected by someone more in tune with the math. I'm an engineering major but my discipline is Civil.
Pressure = Force / Area. So as you increase the tyre sidewall area, the tensile force also increases at a constant pressure.
This is the same reason why you need less tyre pressure to support your weight with a wider tyre.
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I think this issue was less about the pressure and more about how the tires were mounted. If you don't inflate gradually and check that the bead is aligning correctly, the inflating tube can force a bulge in the tire that eventually forces the bead off the rim explosively. And yes this can cause rim damage.
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I think this issue was less about the pressure and more about how the tires were mounted. If you don't inflate gradually and check that the bead is aligning correctly, the inflating tube can force a bulge in the tire that eventually forces the bead off the rim explosively. And yes this can cause rim damage.
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On my list "Stuff that might happen" this does not make even page 3. Good to know, if disconcerting.
The Park Tool mounting a tubeless tire videos are complicated enough--don't recall them mentioning 'sploding rims.
The Park Tool mounting a tubeless tire videos are complicated enough--don't recall them mentioning 'sploding rims.
#14
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#15
Well I guess he only used double the maximum rated pressure for the rim with that tyre width. How would you split the liability?
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Pressure x area. A big tire has more area so the total force exerted on the rim goes up.
Sorry you blew up your rim. Hunt is being more than fair. Charitable, even.
Sorry you blew up your rim. Hunt is being more than fair. Charitable, even.
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I shouldn't have to "make myself more visible;" Drivers should just stop running people over.
Car dependency is a tax.
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An easy way to get around this issue entirely is to just back up 5 decades. To sewups aka tubulars. Now tire pressure and size have absolutely no effect on the rim sidewall. None. You do have to embrace a 120 year old technology. Accept being totally self-sufficient since no one is going to have spares. Accept that you have to glue your tires on like your life might depend on that glue.
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When you go above the pressure rating for the tire as well as the rim, you are playing a dangerous game. They were quite nice in offering a new rim. Kudos to Hunt for really helping their customers.
#20
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Actually, the rim has no clue as to the tire size (or the pressure). All it knows is how large a force is being applied to the rim wall. When that force exceeds what it is made to handle, it fails. The force the tire applies is a product of the pressure and the tire size. (This was an engineering question I may have answered correctly a million years ago but I cannot remember the answer. Is it pressure times sectional area or pressure times circumference? The test question context had nothing to do with bicycle tires. If it had, I'd remember to this day!).
Hoop stress is proportional to the diameter of the cylinder, so doubling the diameter doubles the stress. Or doubling the tire width doubles the stress on the rim.
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I inflate my Barlow Pass rear tire to about 50psi, consistent with their guidelines.
https://www.renehersecycles.com/tire...re-calculator/
If my rims said 100 psi max, I wouldn't think twice about pumping my tires up to 50 psi. If Hunt Rims really can't handle going over 40 psi for what is considered a thin gravel or standard all-road tire, then they really need to re-think that 100 psi max label on a gravel rim. Nobody rides 26 mm tires on gravel rims.
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The term you are looking for is “hoop stress”. It’s something that was worked out after cylindrical boilers in ships were exploding.
Hoop stress is proportional to the diameter of the cylinder, so doubling the diameter doubles the stress. Or doubling the tire width doubles the stress on the rim.
Hoop stress is proportional to the diameter of the cylinder, so doubling the diameter doubles the stress. Or doubling the tire width doubles the stress on the rim.
Last edited by 79pmooney; 12-08-23 at 12:27 AM.
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The webpage for my Gravel wheels (Roval Terra CL) says:
- Tire Size: 28mm - 47mm - Max Pressure: 28c-32c: 80psi, 33c – 36c: 65psi, 37c- 47c: 60psi