Catastrophic Wheel Failure Analysis!
06-06-06, 01:08 AM
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Catastrophic Wheel Failure Analysis!
Hypothesis:
The catastrophic wheel failure shown in this thread:
https://www.bikeforums.net/bicycle-mechanics/201510-catastrophic-wheel-failure-why.html
was caused by a tire too large for the rim.
Supporting Information:
1. Mavic recommends tires between 19 and 28 mm for the CXP33 rim - at the time of failure, 37c tires were fitted to the rim.
2. On the day of the failure, the 37c tires were inflated at or below the recommended sidewall pressure of 85 psig (verified by "thumb test" before the ride and by visual observation during the ride that the rear tire was "pooching out" from the rim edges more than usual).
3. At the time of the failure, I had just "sat up" on the seat, putting all of my 275 pounds on the rear tire.
4. The rim shows cracking between multiple spoke-holes in the "V" of the rim (consistent with outward forces from the tire pulling the mounting lips of the rim apart).
5. The vector of force on the actual rim lips would point increasingly outward from the rim lips rather than in line with the rim walls as the tire spread more.
6. The rim probably (further hypothesis) sustained the "tear fracture" (radial) while the wheel was still rotating and the rim was splitting into two halves. The axial failure probably happened when the wheel was stationary and I came down on the seat. The wheel, no longer supported by the spokes, cracked in the direction of vertical stress as I landed on the seat.
Summary:
This failure was not caused by a manufacturing defect - the rim was designed properly for the tire sizes recommended by the manufacturer.
This failure was not caused by the wheel builder - the wheel was properly trued and tensioned.
This failure was caused by installing a tire that was too wide for the rim and that (subsequently) caused the rim to split in half. The situation was worsened by low tire pressure that caused stresses on the rim not anticipated in the rim design.
If the 37c tires had been maintained at 15 psig above recommended sidewall pressure, this failure might have never happened (and it still might have, eventually). This is conjecture is pure speculation...
Lessons Learned:
1. Use equipment within the recommendations of the manufacturer.
If anyone has reason to disagree with this analysis, I'd be interested to hear your thoughts. This is the best scenario I can think of that fits the facts.
The catastrophic wheel failure shown in this thread:
https://www.bikeforums.net/bicycle-mechanics/201510-catastrophic-wheel-failure-why.html
was caused by a tire too large for the rim.
Supporting Information:
1. Mavic recommends tires between 19 and 28 mm for the CXP33 rim - at the time of failure, 37c tires were fitted to the rim.
2. On the day of the failure, the 37c tires were inflated at or below the recommended sidewall pressure of 85 psig (verified by "thumb test" before the ride and by visual observation during the ride that the rear tire was "pooching out" from the rim edges more than usual).
3. At the time of the failure, I had just "sat up" on the seat, putting all of my 275 pounds on the rear tire.
4. The rim shows cracking between multiple spoke-holes in the "V" of the rim (consistent with outward forces from the tire pulling the mounting lips of the rim apart).
5. The vector of force on the actual rim lips would point increasingly outward from the rim lips rather than in line with the rim walls as the tire spread more.
6. The rim probably (further hypothesis) sustained the "tear fracture" (radial) while the wheel was still rotating and the rim was splitting into two halves. The axial failure probably happened when the wheel was stationary and I came down on the seat. The wheel, no longer supported by the spokes, cracked in the direction of vertical stress as I landed on the seat.
Summary:
This failure was not caused by a manufacturing defect - the rim was designed properly for the tire sizes recommended by the manufacturer.
This failure was not caused by the wheel builder - the wheel was properly trued and tensioned.
This failure was caused by installing a tire that was too wide for the rim and that (subsequently) caused the rim to split in half. The situation was worsened by low tire pressure that caused stresses on the rim not anticipated in the rim design.
If the 37c tires had been maintained at 15 psig above recommended sidewall pressure, this failure might have never happened (and it still might have, eventually). This is conjecture is pure speculation...
Lessons Learned:
1. Use equipment within the recommendations of the manufacturer.
If anyone has reason to disagree with this analysis, I'd be interested to hear your thoughts. This is the best scenario I can think of that fits the facts.
06-06-06, 02:19 AM
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Not plausible to me. Whatever shape and size the tyre is, 85 psi just won't tear a good rim apart. Looks like a defective rim to me, combined with your bodyweight. How's the warranty situation?
06-06-06, 02:36 AM
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Wouldn't a too large tyre simply blow off the rim instead of splitting it open?
I seem to recall having read about people experiencing spontaneous "de-tyring" when inflating a large tyre too much.
I seem to recall having read about people experiencing spontaneous "de-tyring" when inflating a large tyre too much.
06-06-06, 05:31 AM
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Originally Posted by CdCf
Wouldn't a too large tyre simply blow off the rim instead of splitting it open?
The rim failed first because of outward pressure on the hook of the rim. Once the rim began center-cracking and separating, THEN (and only then) did the tube fail.
06-06-06, 05:33 AM
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"Oversize" tires are routinely fitted to narrow road rims for cyclocross use. Open Pro rims equipped with 35 or 37 mm Cyclocross tires are very common.
06-06-06, 06:56 AM
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Yeah, doesn't sound plausible to me - simply because it's so common in the cyclocross world (and to a lesser extent the winter-commuter world) and nobody here seems to have seen this before. Could well be a contributing factor in slvoid's deep-scratch theory, though - which is my vote for winner.
06-06-06, 07:27 AM
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Hmmm. We have run some big tires on cyclocross bikes on these same rims with no failure. And some huge tires on narrow MTB rims. I can see a big enough tire loading the bead funny but it seems like it would just flare the rim. I really want to see the area that is folded in and back on the drive side, from the drive side. It looks like the rim on that side broke free and grabbed the brake shearing the rim apart on that side and then splitting it like a wishbone 180 opposite.
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06-06-06, 07:51 AM
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If the rim failed from too large a tire, why did BOTH sides of the rim bend INWARD at the "tear" break? What if a crack started at one of the spoke holes, and then propagated down the centerline of the rim? This crack meant that the two sides of the rim were no longer tied together, so that entire portion of the rim buckled. If you notice, the spokes on either side of the break do pull it in that fashion. I would guess the "clean" failure is a secondary failure caused by the other one. I have no guess as to WHY a crack started at the spoke hole. You might want to look at the other spoke holes to see if there are other small cracks.
This is all a guess, so take it or leave it.
God bless!
Wayne J.
This is all a guess, so take it or leave it.
God bless!
Wayne J.
06-06-06, 08:21 AM
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Originally Posted by FarHorizon
Hypothesis:
This failure was not caused by a manufacturing defect
This failure was not caused by a manufacturing defect
06-06-06, 09:26 AM
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Originally Posted by BostonFixed
*****ty wheelbuild.
I can be the jury if you want...
06-06-06, 09:35 AM
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Originally Posted by aadhils
Rev. Chuckie built the wheel I can be the jury if you want...
I can be the jury if you want...
06-06-06, 09:38 AM
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Originally Posted by FarHorizon
The tube blowout was NOT the cause of the rim failure. The rim failure was the cause of the tube blowout.
The rim failed first because of outward pressure on the hook of the rim. Once the rim began center-cracking and separating, THEN (and only then) did the tube fail.
The rim failed first because of outward pressure on the hook of the rim. Once the rim began center-cracking and separating, THEN (and only then) did the tube fail.
06-06-06, 10:31 AM
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From Sheldon Brown's website:
https://sheldonbrown.com/tire-sizing.html
https://sheldonbrown.com/tire-sizing.html
Width Considerations
Although you can use practically any tire/rim combination that shares the same bead seat diameter, it is unwise to use widely disparate sizes.
If you use a very narrow tire on a wide rim, you risk pinch flats and rim damage from road hazards.
If you use a very wide tire on a narrow rim, you risk sidewall or rim failure. This combination causes very sloppy handling at low speeds. Unfortunately, current mountain-bike fashion pushes the edge of this. In the interest of weight saving, most current mountain bikes have excessively narrow rims. Such narrow rims work very poorly with wide tires, unless the tires are overinflated...but that defeats the purpose of wide tires, and puts undue stress on the rim sidewalls.
Although you can use practically any tire/rim combination that shares the same bead seat diameter, it is unwise to use widely disparate sizes.
If you use a very narrow tire on a wide rim, you risk pinch flats and rim damage from road hazards.
If you use a very wide tire on a narrow rim, you risk sidewall or rim failure. This combination causes very sloppy handling at low speeds. Unfortunately, current mountain-bike fashion pushes the edge of this. In the interest of weight saving, most current mountain bikes have excessively narrow rims. Such narrow rims work very poorly with wide tires, unless the tires are overinflated...but that defeats the purpose of wide tires, and puts undue stress on the rim sidewalls.
Last edited by NoRacer; 06-06-06 at 12:13 PM.
06-06-06, 12:49 PM
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Rev.Chuck,
you mentioned in the other thread that you had some properly built (and tensioned) Mavic rims cracking. May I ask where they cracked?
FarHorizon,
I don't think that your tire choice caused the fracture. However, it might have made things worse and lead to a complete collaps.
Looking at the first picture and the pattern the spokes are bent (especially around the valve), I think the wheel is still in the position as when it finally collapsed.
I think the crack might have been started on the inside of the rim (actually at the spoke hole of the last spoke of the upper part of the rim (second picture)), possibly when that part was at the bottom of the rotation. Further I think it propagated along the inside of the rim (this crack growth might also have happened over time) until it weakend the rim sufficiantly enough to be spread apart by the pressure from the tire/tube (this would probably have happened even with recommended tire/tube/pressure combinations). It subsequently would collapse in the rear and leave the sidewalls pointing inward.
I think the fracture in the third picture is only a result of the other fracture and the wheel loosing it's integrety. An open/broken rim would collapse and most probably break in the middle through bending. (I think there might be some buckling on the inside of the rim in the third picture, which would support a bending fracture. But it is hard to see).
In short, I would think the collaps was started by crack initiation on the rim which should not happen and not by your tire choice.
This is only my personal opinion.
you mentioned in the other thread that you had some properly built (and tensioned) Mavic rims cracking. May I ask where they cracked?
FarHorizon,
I don't think that your tire choice caused the fracture. However, it might have made things worse and lead to a complete collaps.
Looking at the first picture and the pattern the spokes are bent (especially around the valve), I think the wheel is still in the position as when it finally collapsed.
I think the crack might have been started on the inside of the rim (actually at the spoke hole of the last spoke of the upper part of the rim (second picture)), possibly when that part was at the bottom of the rotation. Further I think it propagated along the inside of the rim (this crack growth might also have happened over time) until it weakend the rim sufficiantly enough to be spread apart by the pressure from the tire/tube (this would probably have happened even with recommended tire/tube/pressure combinations). It subsequently would collapse in the rear and leave the sidewalls pointing inward.
I think the fracture in the third picture is only a result of the other fracture and the wheel loosing it's integrety. An open/broken rim would collapse and most probably break in the middle through bending. (I think there might be some buckling on the inside of the rim in the third picture, which would support a bending fracture. But it is hard to see).
In short, I would think the collaps was started by crack initiation on the rim which should not happen and not by your tire choice.
This is only my personal opinion.
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06-06-06, 01:16 PM
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The 26" Ritchey rims on my mountain bike are extremely narrow compared to the 2"/50cm wide tires for which they are designed. I have put well over 5k miles on them without incident.
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06-06-06, 03:01 PM
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I have hadReflex(the tubular rim) crack at the eyes under a big rider. But it took several thousand miles and they were small cracks with noticable untrueing well before a complete failure like this. I have seen many brands crack at the eyes with out this kind of failure. I had a Bontrager MTB wheel(About six years old),on a bike, in today, that the customer has been riding weekly with numerous cracks but no outright failure, the wheel is just out of true. Usually when they start cracking like this, the wheel goes out of true bad enough to get your notice long before there could a be a catastrophic failure.
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06-06-06, 03:08 PM
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I've had Mavic MA-40's 'delaminate' near a spoke hole, the crack look like the sidewall of the rim is pulling away from the spokehole face.
THAT, however ^^^^^^^ is some serious s*&!
THAT, however ^^^^^^^ is some serious s*&!
06-06-06, 06:10 PM
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Originally Posted by NoRacer
So, do we really have a mystery here?
06-06-06, 07:32 PM
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From the USENET rec.bicycles.tech in response to this link being posted there:
Hi Antti,
Don't forget that the force exerted by the tire on the rim scales with
the radius of the tire section (that is, with the surface area of the
casing). A wide tire at lowish pressure can exert more force at the
bead/rim interface than a 700x18 tire at 150 psi.
Hoop stress in a cylindrical pressure vessel is PR/T where P is
pressure, R is the cylinder radius and T is the thickness of the
material. Since we're concerned about force and not stress (which is
force/area), we can dispense with the denominator. This leaves us with
PR.
For an 18mm (0.009 m radius) tire pumped to 150 psi (1.03 megaPascals)
we get a force of 9270N per unit length*,
For a 37 mm (0.0185 m radius) tire pumped to 85 psi (0.59 MPa) we get a
force of 10,915N per unit length--obviously, a larger force.
When one considers a 23mm tire pumped to 115 psi (perhaps the most
common numbers), we get a result of 9118N per unit length.
This calculation incorporates a number of assumptions. I've assumed
that nominal tire width is actual width and that toroidal pressure
vessels (i.e., tires) operate exactly like cylindrical pressure
vessels. However, the forces I've listed should be pretty accurate on a
relative scale.
The point is that low-pressure fat tires can and do exert higher forces
on rims at the bead interface than do high-pressure skinny tires.
This is a very strange failure to me. I'll be interested to hear what
the cause was.
Cheers,
Jason
* N.B.: A Pascal is a unit of pressure, specifically, a force of one
Newton per square meter. Since P*R is (N/m^2)*m, the unit of radius
cancels with one of the units of area, yielding force (Newtons) per
meter.
Don't forget that the force exerted by the tire on the rim scales with
the radius of the tire section (that is, with the surface area of the
casing). A wide tire at lowish pressure can exert more force at the
bead/rim interface than a 700x18 tire at 150 psi.
Hoop stress in a cylindrical pressure vessel is PR/T where P is
pressure, R is the cylinder radius and T is the thickness of the
material. Since we're concerned about force and not stress (which is
force/area), we can dispense with the denominator. This leaves us with
PR.
For an 18mm (0.009 m radius) tire pumped to 150 psi (1.03 megaPascals)
we get a force of 9270N per unit length*,
For a 37 mm (0.0185 m radius) tire pumped to 85 psi (0.59 MPa) we get a
force of 10,915N per unit length--obviously, a larger force.
When one considers a 23mm tire pumped to 115 psi (perhaps the most
common numbers), we get a result of 9118N per unit length.
This calculation incorporates a number of assumptions. I've assumed
that nominal tire width is actual width and that toroidal pressure
vessels (i.e., tires) operate exactly like cylindrical pressure
vessels. However, the forces I've listed should be pretty accurate on a
relative scale.
The point is that low-pressure fat tires can and do exert higher forces
on rims at the bead interface than do high-pressure skinny tires.
This is a very strange failure to me. I'll be interested to hear what
the cause was.
Cheers,
Jason
* N.B.: A Pascal is a unit of pressure, specifically, a force of one
Newton per square meter. Since P*R is (N/m^2)*m, the unit of radius
cancels with one of the units of area, yielding force (Newtons) per
meter.
06-06-06, 07:36 PM
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Thanks, Denver, for keeping up to date with that thread for those of us who don't regularly read usenet! Interesting stuff...
06-06-06, 08:08 PM
#23
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Whatever it was, I don't think it's the tire since the safety factor is way over any screw up you're gonna subject the wheel too, unless you inflated the tire at like 200psi. Either a manufacturers defect (what you said isn't a defect, it just means it's spec'ed correctly but there could still be a random defect in manufacturing) or something put a stress riser in the rim during your first 500 miles.
06-06-06, 09:18 PM
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Originally Posted by FarHorizon
Hypothesis:
If the 37c tires had been maintained at 15 psig above recommended sidewall pressure, this failure might have never happened (and it still might have, eventually). This is conjecture is pure speculation...
If the 37c tires had been maintained at 15 psig above recommended sidewall pressure, this failure might have never happened (and it still might have, eventually). This is conjecture is pure speculation...
The quote from someone posted from sheldon brown supports this. he says that fat tires on skinny rims perform poorly unless they are overinflated which places undue stress on the rim.
06-07-06, 05:33 AM
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Originally Posted by alanbikehouston
The Mavic factory chart listed in your post says this rim was designed for a 19mm to 23mm tire. The tire mounted on it was a 37mm. The rider is as heavy as two of the guys in the Tour de France.
So, do we really have a mystery here?
So, do we really have a mystery here?