Overinflation, rim splitting, rim damage again

Phil said:

Here are a series of pictures that show a Bontrager Valiant or
Mustang that had rim damage resulting in a locked rear wheel. Please
note that the tube did not pinch flat.

Whoops... the urls should be

http://plaza.ufl.edu/phillee/rbt/rim1.jpg
http://plaza.ufl.edu/phillee/rbt/rim2.jpg
http://plaza.ufl.edu/phillee/rbt/rim3.jpg
http://plaza.ufl.edu/phillee/rbt/rim4.jpg
http://plaza.ufl.edu/phillee/rbt/rim5.jpg
http://plaza.ufl.edu/phillee/rbt/rim6.jpg

--
Phil, Squid-in-Training

Squid-in-Training said:

Here are a series of pictures that show a Bontrager Valiant or Mustang that
had rim damage resulting in a locked rear wheel. Please note that the tube
did not pinch flat.

http://plaza.ufl.edu/phillee/rbt/rim1.jpg
http://plaza.ufl.edu/phillee/rbt/rim2.jpg
http://plaza.ufl.edu/phillee/rbt/rim3.jpg

[note the corrected URLs]

Over on mtbr, I found this in the reviews of the Bontrager Mustang:

Quoted message said:

Recently I hit a little stump sticking out of the ground almost exactly
as wide as the rim. I didn't see it coming and almost went over the
bars. I think the z2 saved me from that. After hitting it, the front
brakes were dragging badly in one spot. I thought I knocked the rim
way out of true. Upon later inspection, I found the rim to be
perfectly true, but folded down slightly and equally on both sides
where the tire bead sits. It was a fairly hard hit. I was impressed
that the wheel didn't need truing at all, but unimpressed that the
metal folded so easily at the edges. Later I was riding on the road
with higher tire pressures, and the rear tire blew off the rim. I
discovered two folds at the edge of the rim on the same side about
eight inches apart, which is how big the hole in my inner tube was. I
have no idea how long the rim was bent like that since it held fine at
normal off road tire pressures, and it was a one time road thing.
After the incident with the front rim I just bent it back into shape
and it seemed fine. I tried the same thing for the rear and the metal
braking surface started to rip just below the rim tape level. I made
it home just fine but I think it's the end of those rims.

The poster apparently felt that the bends were there first, and then
the tire failed, but now I'm starting to think that the failure method
proposed in the other recent thread may be on the right track. I will
admit that I've had bead blow-offs that never produced such flange
bends, but all of my bead blow-offs have been on bikes that had
street-profile tires on which there was little or no ballooning of the
sidewall. It's still hard to envision the tube not failing well
before this much bead had unseated, though.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Squid-in-Training said:

Phil said:

Here are a series of pictures that show a Bontrager Valiant or
Mustang that had rim damage resulting in a locked rear wheel. Please
note that the tube did not pinch flat.

Whoops... the urls should be

http://plaza.ufl.edu/phillee/rbt/rim1.jpg
http://plaza.ufl.edu/phillee/rbt/rim2.jpg
http://plaza.ufl.edu/phillee/rbt/rim3.jpg
http://plaza.ufl.edu/phillee/rbt/rim4.jpg
http://plaza.ufl.edu/phillee/rbt/rim5.jpg
http://plaza.ufl.edu/phillee/rbt/rim6.jpg

In photo 4, the bend looks asymmetric; is there another on the same
flange a short distance away which is approximately a mirror image of
that one?
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Werehatrack said:

Squid-in-Training said:

Phil said:

Here are a series of pictures that show a Bontrager Valiant or
Mustang that had rim damage resulting in a locked rear wheel.
Please note that the tube did not pinch flat.

Whoops... the urls should be

http://plaza.ufl.edu/phillee/rbt/rim1.jpg
http://plaza.ufl.edu/phillee/rbt/rim2.jpg
http://plaza.ufl.edu/phillee/rbt/rim3.jpg
http://plaza.ufl.edu/phillee/rbt/rim4.jpg
http://plaza.ufl.edu/phillee/rbt/rim5.jpg
http://plaza.ufl.edu/phillee/rbt/rim6.jpg

In photo 4, the bend looks asymmetric; is there another on the same
flange a short distance away which is approximately a mirror image of
that one?

There were so many pinch-flat flat spots on the rim because my friend had
been trying to learn bunnyhopping with curbs, all of which resulted in pinch
flats, but after replacing the tube, this one did not. I don't know if
there was an impact at this location before or not. I really should have
put this information in the first post.

As to if the one in the distance is puffing out a bit... it appears that it
did, but this was 2 years ago, so my memory is foggy, and my observational
skills mediocre.
--
Phil, Squid-in-Training

Squid-in-Training said:

There were so many pinch-flat flat spots on the rim because my friend had
been trying to learn bunnyhopping with curbs, all of which resulted in pinch
flats, but after replacing the tube, this one did not. I don't know if
there was an impact at this location before or not. I really should have
put this information in the first post.

Ah. That would explain the fact that the rim itself below the flange
also shows distortion consistent with impact damage.

Quoted message said:

As to if the one in the distance is puffing out a bit... it appears that it
did, but this was 2 years ago, so my memory is foggy, and my observational
skills mediocre.

Probably not important, given the added details. User error, pretty
clearly.

We now return to the regularly scheduled rantings....
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

Werehatrack said:

Squid-in-Training said:

There were so many pinch-flat flat spots on the rim because my
friend had been trying to learn bunnyhopping with curbs, all of
which resulted in pinch flats, but after replacing the tube, this
one did not. I don't know if there was an impact at this location
before or not. I really should have put this information in the
first post.

Ah. That would explain the fact that the rim itself below the flange
also shows distortion consistent with impact damage.

My subject is misleading. I suppose that this rim is fully a result of an
off-camber landing, not of overinflation. The fact that the rim landing was
due to a 120-lb girl hitting a curb means that the 2.1" tire pressure
probably wasn't anywhere above 40psi.

Quoted message said:

Quoted message said:

As to if the one in the distance is puffing out a bit... it appears
that it did, but this was 2 years ago, so my memory is foggy, and my
observational skills mediocre.

Probably not important, given the added details. User error, pretty
clearly.

We now return to the regularly scheduled rantings....

Actually my purpose in posting this was to show what actual impact damage
looks like, something that the two other posters assert could never be the
case. Whether or not they are correct is something I am not trying to
judge... I'm merely putting some comparison material up.

--
Phil, Squid-in-Training

Phil Lee said:

Actually my purpose in posting this was to show what actual impact
damage looks like, something that the two other posters assert could
never be the case. Whether or not they are correct is something I
am not trying to judge... I'm merely putting some comparison
material up.

I think that the picture:

http://plaza.ufl.edu/phillee/rbt/rim4.jpg

Is the most diagnostic of the set other than the vertical view that
shows that the other bead of the rim is also bent out slightly as is
the spot in the background of the present dent in another picture.

Did the tire come off the rim and was it flat. If so, would you
re-mount the tire with another tube and see if it stays on when
inflated? This may be redundant because I am not clear about the
surrounding circumstance of the wheel jamming in the brake. The
heading about overinflation introduces a subject that is not

In any case, I'll stay with my original assessment of such dings.
They are impact induced, not inflation related regardless of whether
the action caused the rim to crack or not. Not all rim dents cause
snake bites.

[email hidden]

Quoted message said:

Phil Lee said:

Actually my purpose in posting this was to show what actual impact
damage looks like, something that the two other posters assert could
never be the case. Whether or not they are correct is something I
am not trying to judge... I'm merely putting some comparison
material up.

I think that the picture:

http://plaza.ufl.edu/phillee/rbt/rim4.jpg

Is the most diagnostic of the set other than the vertical view that
shows that the other bead of the rim is also bent out slightly as is
the spot in the background of the present dent in another picture.

Did the tire come off the rim and was it flat.

I distinctly remember that the tire and tube did *not* come off the rim, and
except for the bent part, was properly seated.

Quoted message said:

If so, would you
re-mount the tire with another tube and see if it stays on when
inflated? This may be redundant because I am not clear about the
surrounding circumstance of the wheel jamming in the brake.

This was 2 years ago when I took these pictures. It wasn't until recently
that I realized it could be useful in our discussions here.

Quoted message said:

The
heading about overinflation introduces a subject that is not

Applicable? Yes, I apologize: overinflation has little to do with this
thread. I meant to relate this thread with the overinflation thread, but I
didn't do it properly.

Quoted message said:

In any case, I'll stay with my original assessment of such dings.
They are impact induced, not inflation related regardless of whether
the action caused the rim to crack or not. Not all rim dents cause
snake bites.

I'm straddling the fence on your first point.

--
Phil, Squid-in-Training

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Phil Lee said:

Actually my purpose in posting this was to show what actual impact
damage looks like, something that the two other posters assert could
never be the case. Whether or not they are correct is something I
am not trying to judge... I'm merely putting some comparison
material up.

I think that the picture:

http://plaza.ufl.edu/phillee/rbt/rim4.jpg

Is the most diagnostic of the set other than the vertical view that
shows that the other bead of the rim is also bent out slightly as is
the spot in the background of the present dent in another picture.

Did the tire come off the rim and was it flat. If so, would you
re-mount the tire with another tube and see if it stays on when
inflated? This may be redundant because I am not clear about the
surrounding circumstance of the wheel jamming in the brake. The
heading about overinflation introduces a subject that is not

In any case, I'll stay with my original assessment of such dings.
They are impact induced, not inflation related regardless of whether
the action caused the rim to crack or not. Not all rim dents cause
snake bites.

[email hidden]

The damage is so localized that it almost looks like compression buckling.
The rim is in compression and some outside influence - such as impact -
might induce buckling. Sort of like flange bucking in a beam.

Just a thought.

Dan

--
"Their rims were high and awesome" Ezekiel

Phil said:

Actually my purpose in posting this was to show what actual impact

damage

Quoted message said:

looks like, something that the two other posters assert could never

be the

Quoted message said:

case. Whether or not they are correct is something I am not trying

to

Quoted message said:

judge... I'm merely putting some comparison material up.

Phil, thanks so much for putting the pictures up, they help a lot, as I
don't have any examples of known inpact bends. These are perfect for
comparison.

After looking at these photos, looking at my photos, and finally,
looking at my rim again, I'm convinced that the small failure on my rim
was not from impact damage.

Perhaps it's not obvious from the pictures, but my "ding" shows
evidence of outward force but not downward force. The crack is opened
in mine, squeezed shut in yours. More revealing, if I put a
straightedge to the edge of my rim, I get < 1mm gap. If I put a
straightedge along the inside wall, I get a several (~6mm) gap. Also, I
notice, from the distortion of the braking scratches on your sidewall
that the whole sidewall and spoke bed seem to be bent, concrete
evidence of strong downward (radial) forces. I see no such distortion
on my wheel, the spokes in that region haven't lost any tension at all,
either.

My small failure:
http://home.comcast.net/~peter_cole/closeup.jpg

Phil's failure (one of known impact)
http://plaza.ufl.edu/phillee/rbt/rim3.jpg

Phil's, another angle, showing rim distortion
http://plaza.ufl.edu/phillee/rbt/rim6.jpg

DVT's failure:
http://home.comcast.net/~carlfogel/download/small_crack.JPG

I think the damage to DVT's and my rims were caused by the tire blowing
off and loading the rim via the bead with the tire's hoop forces. I
think close comparison of these pictures shows that none of the damage
could have been caused by impact. Impact damage looks different, and
those differences make sense intuitively.

"Phil, Squid-in-Training" <[email hidden]> wrote in
message news:[email hidden]...

Quoted message said:

Phil said:

Here are a series of pictures that show a Bontrager Valiant or
Mustang that had rim damage resulting in a locked rear wheel. Please
note that the tube did not pinch flat.

Whoops... the urls should be

http://plaza.ufl.edu/phillee/rbt/rim1.jpg
http://plaza.ufl.edu/phillee/rbt/rim2.jpg
http://plaza.ufl.edu/phillee/rbt/rim3.jpg
http://plaza.ufl.edu/phillee/rbt/rim4.jpg
http://plaza.ufl.edu/phillee/rbt/rim5.jpg
http://plaza.ufl.edu/phillee/rbt/rim6.jpg

I've got a question - what is that ding in the left side visible in
http://plaza.ufl.edu/phillee/rbt/rim3.jpg?

I run 60 psi and love it that hard but I've never had
that happen. Or maybe I don't use Trek Company stuff. That rim hit
something and lost the fight.

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

I run 60 psi and love it that hard but I've never had
that happen. Or maybe I don't use Trek Company stuff. That rim hit
something and lost the fight.

A curb @ low psi. It was no mystery. Any XC MTB rim would have done that.

--
Phil, Squid-in-Training

"Tom Kunich" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

"Phil, Squid-in-Training" <[email hidden]> wrote in
message news:[email hidden]...

Quoted message said:

Phil said:

Here are a series of pictures that show a Bontrager Valiant or
Mustang that had rim damage resulting in a locked rear wheel. Please
note that the tube did not pinch flat.

Whoops... the urls should be

http://plaza.ufl.edu/phillee/rbt/rim1.jpg
http://plaza.ufl.edu/phillee/rbt/rim2.jpg
http://plaza.ufl.edu/phillee/rbt/rim3.jpg
http://plaza.ufl.edu/phillee/rbt/rim4.jpg
http://plaza.ufl.edu/phillee/rbt/rim5.jpg
http://plaza.ufl.edu/phillee/rbt/rim6.jpg

I've got a question - what is that ding in the left side visible in
http://plaza.ufl.edu/phillee/rbt/rim3.jpg?

It is a previous rim dent from another impact that probably resulted in a
pinch flat. This is why I can't rule out the possibility that there might
have been a previous impact on the failure point on the right flange.

As a matter of technique, my friend was learning bunnyhops and probably hit
the rim 4 or 5 times before realizing it was causing damage.

--
Phil, Squid-in-Training

Phil said:

Quoted message said:

Quoted message said:

http://plaza.ufl.edu/phillee/rbt/rim1.jpg
http://plaza.ufl.edu/phillee/rbt/rim2.jpg
http://plaza.ufl.edu/phillee/rbt/rim3.jpg
http://plaza.ufl.edu/phillee/rbt/rim4.jpg
http://plaza.ufl.edu/phillee/rbt/rim5.jpg
http://plaza.ufl.edu/phillee/rbt/rim6.jpg

Useful photos. In particular, we see that although they are all from
impact damage, they are not all quite the same. Rim 4 is like the first
poster's (bends out all the way to the edge), rim 6 like PC's, although
not as severe. Some appear asymmetrical, others not. In other words,
exactly the direction of the hit combined with the local
characteristics of the rim determine the final outcome, surprise
surprise. And such dings do not always result in the tire blowing off.

Note that this rim does not appear to have a worn brake trake (the
machining marks are still there). Whether such impacts deform the rim
bed, as happened more or less here, or not, clearly depends on how
strong the hits had to be- with a worn out sidewall they would not have
to be so strong, and so would be less likely to deform the rim bed.
Also the construction and width of the rim would matter; a narrower
rim, like PC's, less likely to deform at the bed.

All in all they nicely confirm that the previous two posters' dings
were exactly that..

41 said:

Phil said:

Quoted message said:

> http://plaza.ufl.edu/phillee/rbt/rim1.jpg
> http://plaza.ufl.edu/phillee/rbt/rim2.jpg
> http://plaza.ufl.edu/phillee/rbt/rim3.jpg
> http://plaza.ufl.edu/phillee/rbt/rim4.jpg
> http://plaza.ufl.edu/phillee/rbt/rim5.jpg
> http://plaza.ufl.edu/phillee/rbt/rim6.jpg

Useful photos. In particular, we see that although they are all from
impact damage, they are not all quite the same. Rim 4 is like the
first poster's (bends out all the way to the edge), rim 6 like PC's,
although not as severe. Some appear asymmetrical, others not. In
other words, exactly the direction of the hit combined with the local
characteristics of the rim determine the final outcome, surprise
surprise. And such dings do not always result in the tire blowing off.

Note that this rim does not appear to have a worn brake trake (the
machining marks are still there). Whether such impacts deform the rim
bed, as happened more or less here, or not, clearly depends on how
strong the hits had to be- with a worn out sidewall they would not
have to be so strong, and so would be less likely to deform the rim
bed. Also the construction and width of the rim would matter; a
narrower rim, like PC's, less likely to deform at the bed.

All in all they nicely confirm that the previous two posters' dings
were exactly that..

They were all the exact same failure from 6 different angles, not 6 separate
failures.
--
Phil, Squid-in-Training

41 said:

Phil said:

Quoted message said:

> http://plaza.ufl.edu/phillee/rbt/rim1.jpg
> http://plaza.ufl.edu/phillee/rbt/rim2.jpg
> http://plaza.ufl.edu/phillee/rbt/rim3.jpg
> http://plaza.ufl.edu/phillee/rbt/rim4.jpg
> http://plaza.ufl.edu/phillee/rbt/rim5.jpg
> http://plaza.ufl.edu/phillee/rbt/rim6.jpg

Useful photos. In particular, we see that although they are all from
impact damage, they are not all quite the same. Rim 4 is like the

first

Quoted message said:

poster's (bends out all the way to the edge), rim 6 like PC's,

although

Quoted message said:

not as severe.

The forces that I am theorizing are applied by the transfer of hoop
forces from the tire casing to the bead, and from the bead to the rim
edge. If this mechanism is correct, the direction of the force should
be outward laterally and inward radially, with the lateral force
predominating. Impact forces, on the other hand, have to be almost
entirely inward radially, because they have to fully compress the tire
before the rim can be locally loaded.

The photos taken by the 3 posters who claim rim damage as a result of
tire blow off show clear evidence of outward lateral forces. All of the
cracks were spread open by these forces, which would not occur in a
simple buckle, as evidenced by the fact that there is no evidence of
cracks being spread open in the 6 impact pictures.

Tire pressure alone would not be sufficient to spread these cracks
open. Hoop forces (as estimated) of around 50 lb per inch would only
generate a modest force over cracks of this length, but if that force
is multiplied by the blow off length (as evidenced by the tube split)
the forces become large enough to crack and fold the rim at the point
of application. Additionally, the hoop force direction is tangential to
the sidewall, so while the bead is on the rim hook, or even slightly
disengaged, the hoop force wouldn't act to spread the crack open
(laterally), since it would be acting (mostly) upward radially. With
several inches of bead off the hook, the bead force is both outward
(laterally) and downward (radially). This is obvious to anyone who has
ever mounted a tire.

If impact force and inflation pressure force are ruled out as the means
of spreading the cracks outward in these photographs, then that outcome
must be from some other mechanism. There's a reason why all these
cracks are spread open, while none of the impact cracks are. The impact
damage is simple buckling.

All the photos are alike in so far as they show bent rims, that's about
where the similarities end.

Phil said:

41 said:

Phil said:

>> http://plaza.ufl.edu/phillee/rbt/rim1.jpg
>> http://plaza.ufl.edu/phillee/rbt/rim2.jpg
>> http://plaza.ufl.edu/phillee/rbt/rim3.jpg
>> http://plaza.ufl.edu/phillee/rbt/rim4.jpg
>> http://plaza.ufl.edu/phillee/rbt/rim5.jpg
>> http://plaza.ufl.edu/phillee/rbt/rim6.jpg

Useful photos. In particular, we see that although they are all

from

Quoted message said:

Quoted message said:

impact damage, they are not all quite the same. Rim 4 is like the
first poster's (bends out all the way to the edge), rim 6 like

PC's,

Quoted message said:

Quoted message said:

although not as severe. Some appear asymmetrical, others not. In
other words, exactly the direction of the hit combined with the

local

Quoted message said:

Quoted message said:

characteristics of th e rim determine the final outcome, surprise
surprise. And such dings do not always result in the tire blowing

off.

Quoted message said:

Quoted message said:

Note that this rim does not appear to have a worn brake trake (the
machining marks are still there). Whether such impacts de form the

rim

Quoted message said:

Quoted message said:

bed, as happened more or less here, or not, clearly depends on how
strong the hits had to be- with a worn out sidewall they would not
have to be so strong, and so would be less likely to deform the rim
bed. Also the constructi on and width of the rim would matter; a
narrower rim, like PC's, less likely to deform at the bed.

All in all they nicely confirm that the previous two posters' dings
were exactly that..

They were all the exact same failure from 6 different angles, not 6

separate

Quoted message said:

failures.

I stand corrected then.

Fortunately I qualified my response to "not quite the same", since the
differences as I saw them were not as dramatic as those between the two
incidents before. While I still think those incidents were different as
I described, I would say after this experience with the flash lighting
and perspective, since before I said both resulted from impact, but
just differed in execution, I would stick with the general point that
they were both impact dings, but be less willing to go into any more
detail about how exactly the impact formed them.

h

Peter Cole said:

The forces that I am theorizing are applied by the transfer of hoop
forces from the tire casing to the bead, and from the bead to the rim
edge.

You still have the rim. Why not just mount a new tire on it, leave a
section hanging out as you describe, start inflating, and see what
happens?

This would be on some virgin section of the rim (choose a weak one),
but you could also try seeing how the tire fits into the two defects
you have. Then send the pictures of the results and we will know.

Quoted message said:

The photos taken by the 3 posters who claim rim damage as a result of
tire blow off show clear evidence of outward lateral forces. All of

the

Quoted message said:

cracks were spread open by these forces, which would not occur in a
simple buckle, as evidenced by the fact that there is no evidence of
cracks being spread open in the 6 impact pictures.

Quoted message said:

There's a reason why all these
cracks are spread open, while none of the impact cracks are. The

impact

Quoted message said:

damage is simple buckling.

All the photos are alike in so far as they show bent rims, that's

about

Quoted message said:

where the similarities end.

As you can see from my experience perhaps such detail is too much to
extract from photos of curved metal with simple uni-directional flash
lighting. For example, I would not say that the crack is not spread
open on these pictures, certainly no different from what was shown in
the first poster's rim. Likewise, we cannot tell from the first
poster's pictures whether or not the sidewall/rim bed buckled down, as
is clear from these and as you say did not happen with yours. His rim
was equivalent to new while yours was old.

Do try hooking the tire as you described, pumping up, and seeing what
happens.

n