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Old 08-03-13, 09:57 PM   #1
diabloridr
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Blowout post-mortum (feedback welcome)

Looking for insight into exactly how our rear tire failed today.

Background: Co-Motion speedster, Rolf Tandem wheels, 25mm Conti Gran Prix 4-Seasons tires, inflated to 120 PSI. Team + Bike weight ~ 300 pounds. Rear tire is relatively new, perhaps 200 miles of use. Good history with Gran Prix 4-Seasons for us, no known issue.

Failure reconstruction: We're riding a 1.5 mile stretch of freeway to get home. Good shoulder with moderate amount of debris. Rumble strip is present adjacent to traffic lane. Lots of traffic on the freeway. This segment starts downhill, then is flat to our exit. We're travelling 32.6 MPH when the rear tire blows. I hold the bike neutral and don't brake, but the rear wheel starts to come around to the right, causing the bike to start to move left. I know if we get into the rumble strip it's "game over", but I am able to steer the bike back to right and coast it to a stop on the shoulder. Stoker was super-smooth throughout the entire event - I wouldn't expect anything less from her though our adrenaline was pegged.

We were able to boot the tire and put a new tube in to get home. Inspecting at home we found the following:



I don't believe we hit anything, I certainly didn't feel any impact. My best assessment is the tube blew for unknown reasons and the force dislodged the circular portion of the tread (no damage to the cords existed at the time of the flat, the fraying seen was caused by the 10 mile ride home).

Open to alternate theories or experience.
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File Type: jpg DSC02648.jpg (95.0 KB, 94 views)
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Old 08-03-13, 11:17 PM   #2
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Never seen anything like it. So odd that the missing oval piece is nearly symmetrical about centerline, and has such a smooth edge. Not ragged. Looks cut, really. Hard to see how it could be a tire defect, but what else could it be? Obviously an almost new tire. My guess is that the rubber disappeared first, then you hit some small rock that punctured the cords. Such a neat hole in the tube.

Good job on getting it stopped upright! I would have braked the front. Do you think that would have been a mistake?
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Old 08-03-13, 11:55 PM   #3
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Good job on getting it stopped upright! I would have braked the front. Do you think that would have been a mistake?
Yes, that would have been a big mistake because the rear is essentially riding on the rim with little or no traction. When you apply braking force on the front, the rear will want to continue moving, causing a fish tailing effect.

Not good!
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Old 08-04-13, 01:29 AM   #4
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We have had a rear tyre blow out at around 35mph downhill. Stopped reasonably quickly on the front brake without problem. Couldn't really not use it as otherwise we would of kept accelerating!
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Old 08-04-13, 07:19 AM   #5
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It almost looks like you ran over something that was round and sharp enough to do a "cookie-cutter" on your tire's casing and when that happened, the tube pushed the rubber plug out of the way and the ulcerated casing was an easy mark for some other small piece of debris that punctured the tube with the resulting "blow-out".
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Old 08-04-13, 07:27 AM   #6
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It almost looks like you ran over something that was round and sharp enough to do a "cookie-cutter" on your tire's casing and when that happened, the tube pushed the rubber plug out of the way and the ulcerated casing was an easy mark for some other small piece of debris that punctured the tube with the resulting "blow-out".
^^^ Yep...What did the inside of the tire look like?
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Old 08-04-13, 11:09 AM   #7
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It reminds me of a tire that developed a bubble and then blew out. I suspect a defective tire, it looks like a drop of some foreign material was on the casing and the tread did not attach as it was supposed to.
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Old 08-04-13, 02:55 PM   #8
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What did the inside of the tire look like?
Here are some additional photos:



No damage was detected visually or by feel while repairing the tire, it's possible the damage seen in the photos is the result of riding the damaged tire for an additional 10 miles. I did slap a Park TB-2 tire boot inside the tire before installing the replacement tube.

The drill bit seen in the some of the photos is to show the location of a through-wall tear in the tire. That's a 1/16" bit, I'd estimate the length of the tear as ~ 1/8". The scuffing of the tire cords seen at the bit is definitely post-blowout damage, I'm sure it wasn't there when I repaired the tire.

I'm gonna shoot a note to Conti and see what response I get.
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File Type: jpg Conti Inner Surface.jpg (94.0 KB, 37 views)
File Type: jpg Conti Inner Surface with bit.jpg (71.1 KB, 35 views)
File Type: jpg Conti outer Surface with bit.jpg (82.0 KB, 43 views)
File Type: jpg Conti outer Surface with bit-1.jpg (83.8 KB, 40 views)
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Old 08-04-13, 03:05 PM   #9
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Old 08-04-13, 09:36 PM   #10
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Good eyes. Fits DubT's bubble/contamination theory. There should be a cut looking area and a hinge area.
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Old 08-05-13, 09:23 AM   #11
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Lots of sharp things out on the road. Looks clearly like a punched out cut. I do see the little torn area. Thank God you guys are safe and healthy..
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Old 08-07-13, 11:37 AM   #12
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If it were possibly from striking a smallish sharp piece of road debris, would a 28mm tire have had any better chance of surviving?
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Old 08-07-13, 01:23 PM   #13
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What about a screw that was stuck in asphalt. Would punch through then when pulled back tore the section out of the tire(or started it and the rest finished during the stop)(section of tire may have had a poor bond)? The reason I say this is that the hole through the tire would have gone through your tire even if the rubber was there to protect it. Just an idea outside the box.
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Old 08-08-13, 06:48 AM   #14
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Bottle top?
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Old 08-08-13, 09:36 AM   #15
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OK way out there. High pressure air from the tube went between layers of tire due to puncture and delaminated it enough to tear out the section during the stop from speed.

I do like the bottle cap though, how does the size compare?
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Old 08-08-13, 09:48 AM   #16
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Bottle top?
That's what I was thinking except I'd expect to see some serrations around the cut area.

There's a possibility that it was a manufacturing defect and Continental might want to see that tire.
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Old 08-09-13, 09:11 AM   #17
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Screw-on bottle tops don't have serrations and can be very sharp.
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Old 08-09-13, 09:28 AM   #18
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Screw-on bottle tops don't have serrations and can be very sharp.

That's exactly what I was thinking.
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Old 08-09-13, 09:28 AM   #19
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I'd say the cut came first, a bottle cap cut is as good a possibility as any. We've done 10's of thousands of miles on Conti 4 Season GP's on many nasty roads and never a slightest hint of a structural failure.....we're a 290 pound team on 28c's.
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Old 08-09-13, 11:13 AM   #20
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Bottle top?
In the interests of science, I measured 2 bottle caps:

1) Pelegrino mineral water screw-top = 33mm diameter

2) Firestone-Walker Wookie Jack Black Rye IPA cap = 28 mm diameter.

Area of missing tread on tire is an oval with length of 22mm and width of 11 mm.

I'm not sold on the bottle top theory.
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