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FarHorizon 06-05-06 02:39 PM

catastrophic wheel failure - why?
Look at the photos below of what happened to my wheel today:

Facts are as follows:

This wheel was 36-spoke, 3-cross, custom built, tensioned, and true.
The wheel had about 500 miles on it when it detonated.
The tire was a WTB Slickisaurus 700x37c inflated to (Mfg. recommended) 85 psig.
The tube showed about a 9-inch-long smooth split on the spoke-side of the tube
The rim tape was not punctured
The wheel detonated with a bang on smooth pavement at about 19 mph
The rim did NOT fail at the weld - the weld is still intact.
The wheel bead showed no signs of damage other than where it was punctured by the broken rim
The LBS does NOT think this was caused by the bead coming loose from the rim (their opinion)


What caused this rim to fail?
What can I do to prevent this from happening again? (I'm lucky to be alive)
Does Mavic owe me another wheel?
I have three other wheels with the same rims - am I at risk from them too?

powers2b 06-05-06 02:42 PM

Missing mucho info.
What were you doing when the wheel broke?
What did you hit or what hit you?
Why does the wheel appear to be too big for the bike?
Why are you riding around without a seat?


FarHorizon 06-05-06 02:48 PM

What were you doing when the wheel broke?

I was riding on smooth pavement at 19mph. I was about 40 minutes into my daily ride. No potholes, no debris - smooth pavement.

What did you hit or what hit you?

No collision whatsoever. One moment everything was normal, the next, I was sliding down the road on my butt. I believe when the wheel detonated, I was thrown up. When I came down, the seatpost bolt broke and dumped me off the back of the bike. Luckily, I didn't land on the seatpost or the broken rim or I'd not be here now.

Why does the wheel appear to be too big for the bike?

Must be an artifact of the photo - the bike is a Klein Navigator touring frame made for (and with clearance for) the 700x37c tires that are on the bike.

top506 06-05-06 02:53 PM

IED maybe? Did you also draw sniper fire?:D
Seriously, boyo, you had enough good luck left to walk away.
I find the secondary faliure quite interesting, a fracture caused by the rapid de-tensioning of the rim.

FarHorizon 06-05-06 03:00 PM


Originally Posted by top506
...I find the secondary faliure quite interesting, a fracture caused by the rapid de-tensioning of the rim. Top

Hi Top - Do you think the tube just failed and that the rapid decompression caused the rim failure (in TWO places - 180 degrees apart)? My LBS says they've seen tube failures damage rims before but ONLY at pressures significantly above 100 psig. This tire was only at 85 psig! My LBS said they don't think the tube blowout is the cause of the rim failure (actually, they seem to think that the rim failure was the cause of the tube blowout). Do you disagree with them? If so, please expound - I REALLY want to get to the bottom of this so I can prevent it from happening again. Thanks for your input!

CHenry 06-05-06 03:03 PM

Interesting, as if your rim sheared in half once the tire-tube unit stopped rotating at the same rate as the rim and hub. That rim is a monocoque thin-wall design, not a "boxed" design, right?

mrhedges 06-05-06 03:07 PM

poorly built wheel?

CHenry 06-05-06 03:15 PM

The position of the tear in the rim makes sense--8 and 2 o'clock--which is close to the horizontal direction of movement of the bike with a slightly nose-down attitude, typical for the nose-down dive that takes place in an emergency braking, and with the center of mass--mostly you--above the line of shear. Did you leave rubber on the pavement?

CHenry 06-05-06 03:16 PM

The position of the tear in the rim makes sense--8 and 2 o'clock--which is close to the horizontal direction of movement of the bike with a slightly nose-down attitude, typical for the nose-down dive that takes place in an emergency braking, and with the center of mass--mostly you--above the line of shear. Did you leave rubber on the pavement?

rat_factory 06-05-06 03:33 PM

who built this timebomb? if your LBS did and it hasnt been too long since you've got it, they shouldn't give you much trouble. Mavic may have had some machining error, but I might try to get the wheelbuilder to give you a new one. you could have been seriously hurt.

spider-man 06-05-06 03:38 PM

No spokes broke? None were pulled through the rim? I wonder if it's not just a defective rim from Mavic.

top506 06-05-06 03:42 PM

I don't have a lot of experience with thin-wall rims (if that is indeed what you have), but 85 PSI doesn't seem to be enough pressure for that kind of damage at the primary break. The clean break was incured my the sudden stress loading that the first break caused in what remained (for milliseconds) a tensioned wheel.
If the tube went, the metal damage on the rim would be blown OUT, not folded inward as shown in the pics.
To quote one of my trainning offcers may years ago, "sure beats the hell out of me!"

CdCf 06-05-06 03:54 PM

A guess...

Maybe the wheel was stress-relieved by bending it, while holding on to the rim, and the builder used too much force, cracking the rim in the middle - i.e. in two places diametrically opposite.

Ray Dockrey 06-05-06 04:04 PM

Did the chain break? The rear part of the drivetrain doesn't look quite right.

Makeitso 06-05-06 04:07 PM

I have no idea what could have caused that but, I'm glad you're OK.

Never seen anything like it.

Chuckie J. 06-05-06 04:12 PM

I don't have any answers but am glad you are ok. It looks horrible! Yikes!

Looking at all the parts of the wheel there are certain places you can rule out: hub, spokes (none broke, tire (you mentioned no damage to the tire, right?), rim tape is intact.

Only the tube and the rim are damaged (and considerably).


LilSprocket 06-05-06 05:31 PM

HOLY CRAP! :eek:

The Great Stonk 06-05-06 05:54 PM

looking at the evidence the only conclusion i can come up with is that the rim was defective, that or it was tensioned way too high - not to put down your lbs.

Stevie47 06-05-06 06:10 PM

I've thought and thought about this one. I'd think you can pretty much rule out a material problem because of the dual failure. The only thing that makes sense to me is a poor wheel build. If a number of spokes 180 deg opposite from each other were way too tight, and the ones 90 deg out from these were then too loose it would cause rim forces much like if you were to push down on a hula hoop. Every revolution of the wheel would be the equivalent of pushing and letting up on the hoop. The aluminum would fatigue pretty quickly at the two sides where the spokes were loose. When the first side failed catastrophicaly that would send a shock wave around the rim causing the failure at the opposite side.

DieselDan 06-05-06 06:28 PM

Mavic has had quaility control problems as of late. My LBS is contemplating dropping them.

ozbiker 06-05-06 06:32 PM

This wheel has failed as I would have expected it to if it had an explosive decompression near the valve.

Look carefully. The wheel is in about the same position as when the accident occurred. Decompression near the valve (on the road at this time) causes a rapid destressing of the rim. The rim "springs out", and the elastic shock propogates (via the hub) to the top spokes (near the brake), pulling the rim down at the top. See how the top of the rim has been flattened, and at least one spoke head (near the label) is partially pulled out of the rim. The top spokes are already loaded at this time by the weight of the rider - remember, the bike hangs off the top spokes. The deformation (flattening) of the top half of the rim causes the rim to bulge out in the for/aft positions, ie. to make the rim elliptical. It is likely that at this time, the bottom half of the rim has elastically rebounded and is therefore contributing to the fore/aft elongation.

The result of this is a classical shear failure at the fore/aft positions as shown in the photo. We would expect a shear failure would be at about 45 degrees, which is exactly what we see. The initiator for the shear failures is, as expected, spoke holes, which are the local stress raisers.

I see no pre-existing contributor to this failure. It's just plain bad luck. You got an explosive blowout just at the point that the wheel contacted the ground and all the other dynamics were just not in your favour - saddle bouncing, slight road irregularities, pedal torque - it all came together at the wrong time.

I could be wrong and I only have the supplied photo to work from, however I am an engineer and have done this stuff before. Any other engineers care to comment on this failure - an ATSB accident investigator would be just dandy!!!

I am interested in what other have to say about this failure. I ride on Mavic wheels (MA40's and M193's), weigh 95kg, and have no interest in a set of circumstances that may result in the seatpost comming out my nostrils!!!

hope this helps,

ozbiker 06-05-06 06:43 PM

I've had another close look at the photo. The left hand side of the wheel certainly failed in sheer as expected. Clearly, the subsequent collapse of the wheel cause the failure of the right hand side of the wheel, which appears on closer inspection to have a brittle bending failure. See how the rim appears to have opened up from the outer side, the fracture propogating back towards the nipple hole. On the other side, a crack has run along the rim terminating in a shear failure out to the edge, just as expected for a failure in bending.

I think there is some possibility that this rim was overly brittle. How much does the rider weigh and how many miles on the wheel?? I would get the wheel to the metallurgical department of the local Uni and have it examined.

ozbiker 06-05-06 06:53 PM

I note that there are no ferrules in this rim. Each to his own, but I will not ride a rim without ferrules, or some other equivalent destressing arrangement.

caotropheus 06-05-06 07:36 PM

Three important issues not discussed here:

1. FarHorizon, how heavy are you and is there any specifications for maximum wheel weight?
2. Did you contact directly Mavic in the country where you live? if not, do it, Mavic engineers and developers would be most interested on checking that wheel, and certainly will replace you the wheel.
3. Was the tire width size within the limits for the rim specification?

Al1943 06-05-06 08:35 PM

Looks to me as if the wheel was dropped from the top of a 10 story building before it was installed on the frame.


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