First ride of season -- blowout! Why?

Dear group,

My first ride of the season turned out to be quite a disappointment, as I
only got about a mile out before experiencing a blowout. I would very much
appreciate it if you all would help me diagnose what happened, so I can
prevent it from happening again.

Observations:

- Blowout occurred on the front wheel, with a loud bang.

- I was going down a short hill, braking, going perhaps 15-20 MPH.

- Immediately before the blowout, the rolling resistance of the wheel
increased significantly (felt like the brakes suddenly got more draggy).
As soon as this occurred, I braked harder and wasn't going very fast when
the blowout happened.

- 4-5" of the tire was off the rim on one side.

- Right brake shoe was turned and in contact with the tire.

- Tire was a never-before-ridden Avocet FasGrip Duro Plus 700Cx32
(Measured width 30.5mm.)

- Tire was intermittently contacting my fender, but as far as I could
tell, just the manufacturing excess which would wear off presently.

- Tire was cool to the touch after blowout.

- Tires inflated to 90 PSI.

- Rim was Alexrims R450, 13.9mm internal width.

My two ideas for what happened are 1) the tires are too wide for the rim
(according to Sheldon Brown's website, a 32mm tire is one step too wide
for a 14mm rim), or 2) the brake shoe contacted the tire and pulled it off
the rim.

Thoughts?

Thanks very much,

Reid

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Reid Priedhorsky writes:

My first ride of the season turned out to be quite a disappointment,
as I only got about a mile out before experiencing a blowout. I
would very much appreciate it if you all would help me diagnose what
happened, so I can prevent it from happening again.

Observations:

- Blowout occurred on the front wheel, with a loud bang.

- I was going down a short hill, braking, going perhaps 15-20 MPH.

- Immediately before the blowout, the rolling resistance of the
wheel increased significantly (felt like the brakes suddenly got
more draggy). As soon as this occurred, I braked harder and
wasn't going very fast when the blowout happened.

- 4-5" of the tire was off the rim on one side.

- Right brake shoe was turned and in contact with the tire.

- Tire was a never-before-ridden Avocet FasGrip Duro Plus 700Cx32
(Measured width 30.5mm.)

- Tire was intermittently contacting my fender, but as far as I
could tell, just the manufacturing excess which would wear off
presently.

- Tire was cool to the touch after blowout.

- Tires inflated to 90 PSI.

- Rim was Alexrims R450, 13.9mm internal width.

My two ideas for what happened are 1) the tires are too wide for the
rim (according to Sheldon Brown's website, a 32mm tire is one step
too wide for a 14mm rim), or 2) the brake shoe contacted the tire
and pulled it off the rim.

I think part of your analysis is correct and that is that the barks
show contacted the tire. The brake pad was not secure and managed to
rotate crosswise to the brake track of the rim. This caused the (felt
like the brakes suddenly got more draggy). I think if you inspect the
tire you'll see that the brake abraded the tire. I'm surprised the
tire bead came off the rim. Usually such an incident will frazzle the
sidewall and cause a tire casing failure. In any case, the brake pad
could not have rotated had it been properly secured. I can't imagine
how its retaining but got loose but it could have been a brake
adjustment that never got completed.

I know how that goes from experience. I once got a new fork that was
about 8mm longer and transferred all parts to the new fork. On the
first curve on a swift descent I smelled the burning brake pad and
then came the bang and I was on the ground. Conveniently, one of my
friends had his touring bag on his bicycle and gave me a spare tire so
we could continue. Lesson learned. Always check brakes before you
need them after equipment changes.

On Mon, 28 Mar 2005 16:23:01 -0600, Reid Priedhorsky
may have said:

Observations:

- Blowout occurred on the front wheel, with a loud bang.

- I was going down a short hill, braking, going perhaps 15-20 MPH.

- Immediately before the blowout, the rolling resistance of the wheel
increased significantly (felt like the brakes suddenly got more draggy).
As soon as this occurred, I braked harder and wasn't going very fast when
the blowout happened.

Evenly dragging, without pulsations? That would be consistent with
the brake pad getting out of position as per the second observation
below.

- 4-5" of the tire was off the rim on one side.

Was the blowout in the tube at the same place as the unseating of the
tire?

- Right brake shoe was turned and in contact with the tire.

- Tire was a never-before-ridden Avocet FasGrip Duro Plus 700Cx32
(Measured width 30.5mm.)

- Tire was intermittently contacting my fender, but as far as I could
tell, just the manufacturing excess which would wear off presently.

This makes me think that the tire's bead may not have been properly
seated, or perhaps a small fold of the tube was between the bead and
the rim flange.

- Tire was cool to the touch after blowout.

- Tires inflated to 90 PSI.

- Rim was Alexrims R450, 13.9mm internal width.

My two ideas for what happened are 1) the tires are too wide for the rim
(according to Sheldon Brown's website, a 32mm tire is one step too wide
for a 14mm rim), or 2) the brake shoe contacted the tire and pulled it off
the rim.

Thoughts?

With the exception of the brake shoe rotation and the brake effect
going up, it sounds consistent with a tire that was not fully seated
on the rim, or a tube folded under the bead. I can't think of a
reason why a tube escaping from the bead would have been able to snag
and rotate the brake pad, though, and that's the phenomenon which
makes this a bit of a puzzle. Is it possible that the brake shoe was
positioned to ride close enough to the tire that the unseating bead
might have brushed it and swung it out of position just prior to
coming far enough past the rim flange to allow the tube to blow out?
Putting together the pieces of this one without haivng it in front of
me is a matter of guesswork at best, but that's the closest I can come
to a plausible (just barely!) scenario which explains all of the
effects reported.

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On Mon, 28 Mar 2005 22:47:29 +0000, jobst.brandt wrote:

Reid Priedhorsky writes:

My first ride of the season turned out to be quite a disappointment,
as I only got about a mile out before experiencing a blowout.

My two ideas for what happened are 1) the tires are too wide for the
rim (according to Sheldon Brown's website, a 32mm tire is one step
too wide for a 14mm rim), or 2) the brake shoe contacted the tire
and pulled it off the rim.

I think part of your analysis is correct and that is that the barks
show contacted the tire. The brake pad was not secure and managed to
rotate crosswise to the brake track of the rim. This caused the (felt
like the brakes suddenly got more draggy). I think if you inspect the
tire you'll see that the brake abraded the tire.

I looked for this and didn't find anything that jumped out at me. I
thought there might be a faint line about where the brake shoe touched,
but I wasn't sure.

I'm surprised the tire bead came off the rim. Usually such an incident
will frazzle the sidewall and cause a tire casing failure.

Could this be because the tire is too large for the rim?

In any case, the brake pad could not have rotated had it been properly
secured. I can't imagine how its retaining but got loose but it could
have been a brake adjustment that never got completed.

It was my fault. I don't think I tightened the brake shoes enough. (Or
should I be using loctite on these threads?)

Lesson learned. Always check brakes before you need them after equipment
changes.

Indeed! I'm glad I was able to stop the bike without crashing.

Thanks much,

Reid

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Please do not CC me on replies to my USENET or mailing list posts.

On Mon, 28 Mar 2005 19:44:22 -0600, Werehatrack wrote:

On Mon, 28 Mar 2005 16:23:01 -0600, Reid Priedhorsky
may have said:


- Immediately before the blowout, the rolling resistance of the wheel
increased significantly (felt like the brakes suddenly got more draggy).
As soon as this occurred, I braked harder and wasn't going very fast when
the blowout happened.

Evenly dragging, without pulsations? That would be consistent with
the brake pad getting out of position as per the second observation
below.

As far as I can recall, yes, without pulsations.

- 4-5" of the tire was off the rim on one side.

Was the blowout in the tube at the same place as the unseating of the
tire?

I don't know. I would assume so. Interestingly, I believe (not 100% sure)
the tire was unseated at the label.

- Tire was intermittently contacting my fender, but as far as I could
tell, just the manufacturing excess which would wear off presently.

This makes me think that the tire's bead may not have been properly
seated, or perhaps a small fold of the tube was between the bead and
the rim flange.

Well, the noise of contact correlated very strongly with how high the
manufacturing excess (a small, very thin flap of rubber sticking ~0-3mm
above the center of the rolling area of the tire and varying in height
about the tire). So, I don't this in itself was evidence for such a fold
of tube.

With the exception of the brake shoe rotation and the brake effect
going up, it sounds consistent with a tire that was not fully seated
on the rim, or a tube folded under the bead. I can't think of a
reason why a tube escaping from the bead would have been able to snag
and rotate the brake pad, though, and that's the phenomenon which
makes this a bit of a puzzle.

Seems like if this is what happened, the increased drag would have been
pulsating rather than smooth.

Is it possible that the brake shoe was positioned to ride close enough
to the tire that the unseating bead might have brushed it and swung it
out of position just prior to coming far enough past the rim flange to
allow the tube to blow out? Putting together the pieces of this one
without haivng it in front of me is a matter of guesswork at best, but
that's the closest I can come to a plausible (just barely!) scenario
which explains all of the effects reported.

It's possible, I suppose. This sounds a little farfetched, though.

Reid

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Please do not CC me on replies to my USENET or mailing list posts.

Reid Priedhorsky writes:

My first ride of the season turned out to be quite a
disappointment, as I only got about a mile out before experiencing
a blowout.

My two ideas for what happened are 1) the tires are too wide for
the rim (according to Sheldon Brown's website, a 32mm tire is one
step too wide for a 14mm rim), or 2) the brake shoe contacted the
tire and pulled it off the rim.

I think part of your analysis is correct and that is, that the
brake shoe contacted the tire. The brake pad was not secure and
managed to rotate crosswise to the brake track of the rim. This
caused the (felt like the brakes suddenly got more draggy). I
think if you inspect the tire you'll see that the brake abraded the
tire.

I looked for this and didn't find anything that jumped out at me.
I thought there might be a faint line about where the brake shoe
touched, but I wasn't sure.

I'm surprised the tire bead came off the rim. Usually such an
incident will frazzle the sidewall and cause a tire casing failure.

Could this be because the tire is too large for the rim?

I don't believe so. Such rins have been used effectively with 2" and
larger MTB tires.

In any case, the brake pad could not have rotated had it been
properly secured. I can't imagine how its retaining bolt got loose
but it could have been a brake adjustment that never got completed.

It was my fault. I don't think I tightened the brake shoes enough.
(Or should I be using loctite on these threads?)

No, that should not be necessary but from your description, I
visualize a brake pad turning crosswise to drag on the tire sidewall,
something you can reconstruct statically to see what effect that has.

Lesson learned. Always check brakes before you need them after
equipment changes.

Indeed! I'm glad I was able to stop the bike without crashing.

As I mentioned, I didn't, and took a dive with my misplaced brakes.

Reid Priedhorsky wrote in
news
- Tire was a never-before-ridden Avocet FasGrip Duro Plus 700Cx32
(Measured width 30.5mm.)

- Tire was intermittently contacting my fender, but as far as I could
tell, just the manufacturing excess which would wear off presently.

Was there any visibile damage to the tire? Serious fender or brake rub could
wear a hole in your tire and cause a blowout.

If not, most likely the tire was improperly installed. If the bead is not
fully seated, the tube will pop out and blow out.

On Mon, 28 Mar 2005 19:44:22 -0600, Werehatrack
wrote:

On Mon, 28 Mar 2005 16:23:01 -0600, Reid Priedhorsky
may have said:

Observations:

- Blowout occurred on the front wheel, with a loud bang.

- I was going down a short hill, braking, going perhaps 15-20 MPH.

- Immediately before the blowout, the rolling resistance of the wheel
increased significantly (felt like the brakes suddenly got more draggy).
As soon as this occurred, I braked harder and wasn't going very fast when
the blowout happened.

Evenly dragging, without pulsations? That would be consistent with
the brake pad getting out of position as per the second observation
below.

- 4-5" of the tire was off the rim on one side.

Was the blowout in the tube at the same place as the unseating of the
tire?

- Right brake shoe was turned and in contact with the tire.

- Tire was a never-before-ridden Avocet FasGrip Duro Plus 700Cx32
(Measured width 30.5mm.)

- Tire was intermittently contacting my fender, but as far as I could
tell, just the manufacturing excess which would wear off presently.

This makes me think that the tire's bead may not have been properly
seated, or perhaps a small fold of the tube was between the bead and
the rim flange.

- Tire was cool to the touch after blowout.

- Tires inflated to 90 PSI.

- Rim was Alexrims R450, 13.9mm internal width.

My two ideas for what happened are 1) the tires are too wide for the rim
(according to Sheldon Brown's website, a 32mm tire is one step too wide
for a 14mm rim), or 2) the brake shoe contacted the tire and pulled it off
the rim.

Thoughts?

With the exception of the brake shoe rotation and the brake effect
going up, it sounds consistent with a tire that was not fully seated
on the rim, or a tube folded under the bead. I can't think of a
reason why a tube escaping from the bead would have been able to snag
and rotate the brake pad, though, and that's the phenomenon which
makes this a bit of a puzzle. Is it possible that the brake shoe was
positioned to ride close enough to the tire that the unseating bead
might have brushed it and swung it out of position just prior to
coming far enough past the rim flange to allow the tube to blow out?
Putting together the pieces of this one without haivng it in front of
me is a matter of guesswork at best, but that's the closest I can come
to a plausible (just barely!) scenario which explains all of the
effects reported.

Ya know, if that pad came loose first, and then rotated forward with the rear
portion of the pad going up as it would want to, it could catch the tire and cam
it up off the rim. Especially with a tire that is large for the rim as described
there'd be a lot of sidewall overhanging the rim for the pad to catch..

At least that's the mode I'll put my money on. Pad came loose, caught and lifted
tire enough for the tube to escape.

Ron

On Mon, 28 Mar 2005 16:23:01 +0000, Reid Priedhorsky wrote:

Dear group,

My first ride of the season turned out to be quite a disappointment, as I
only got about a mile out before experiencing a blowout. I would very much
appreciate it if you all would help me diagnose what happened, so I can
prevent it from happening again.

Observations:

- Blowout occurred on the front wheel, with a loud bang.

- I was going down a short hill, braking, going perhaps 15-20 MPH.

- Immediately before the blowout, the rolling resistance of the wheel
increased significantly (felt like the brakes suddenly got more draggy).
As soon as this occurred, I braked harder and wasn't going very fast when
the blowout happened.

- 4-5" of the tire was off the rim on one side.

- Right brake shoe was turned and in contact with the tire.

- Tire was a never-before-ridden Avocet FasGrip Duro Plus 700Cx32
(Measured width 30.5mm.)

- Tire was intermittently contacting my fender, but as far as I could
tell, just the manufacturing excess which would wear off presently.

- Tire was cool to the touch after blowout.

- Tires inflated to 90 PSI.

- Rim was Alexrims R450, 13.9mm internal width.

My two ideas for what happened are 1) the tires are too wide for the rim
(according to Sheldon Brown's website, a 32mm tire is one step too wide
for a 14mm rim), or 2) the brake shoe contacted the tire and pulled it off
the rim.

Thoughts?

Thanks very much,

Reid

Is it possible that 90 psi was just too much for 32C tires ? Most 32C
tires I've seen were rated closer to 70 psi max. Can anybody here report
from personal experience on what happens to an over-inflated tire ? Am I
being too simplistic ?

Jacques

On Tue, 29 Mar 2005 22:21:17 +0200, Jacques Moser wrote:

On Mon, 28 Mar 2005 16:23:01 +0000, Reid Priedhorsky wrote:

My first ride of the season turned out to be quite a disappointment, as I
only got about a mile out before experiencing a blowout. I would very much
appreciate it if you all would help me diagnose what happened, so I can
prevent it from happening again.

Is it possible that 90 psi was just too much for 32C tires ? Most 32C
tires I've seen were rated closer to 70 psi max. Can anybody here report
from personal experience on what happens to an over-inflated tire ? Am I
being too simplistic ?

I don't think so -- 90 psi is what's on the sidewall, and that's probably
fairly conservative for blowoff protection. It's also consistent with Mr.
Brown's recommendations on his website.

I've settled on the brake-shoe-rotation theory myself. I think the
geometry and observations of the incident are consistent with the
brake shoe lifting the tire off the rim, causing the blowout, and not
consistent with other theories I've considered.

Reid

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