Starburst punctures near stem



G

G.T.

Guest
I've been having an inordinate number of starburst failures next to the
stem, this is with two different rims and a variety of tires and tubes. I
had originally thought it was from running tubes which are too small for the
tires but this latest one was with a 27" x 1 1/4" tire and a 700c/27" x 32mm
tube, the optimal tube for the tire.

I'm running Velox rim tape on both rims, wide Ritchey 700c 'cross rims from
about 8 years ago or 27" Sun M13IIs.

Nothing looks abnormal around the stem hole. What am I missing?

Greg
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R

Robert

Guest
G.T. wrote:
> I've been having an inordinate number of starburst failures next to the
> stem, this is with two different rims and a variety of tires and tubes. I
> had originally thought it was from running tubes which are too small for the
> tires but this latest one was with a 27" x 1 1/4" tire and a 700c/27" x 32mm
> tube, the optimal tube for the tire.
>
> I'm running Velox rim tape on both rims, wide Ritchey 700c 'cross rims from
> about 8 years ago or 27" Sun M13IIs.
>
> Nothing looks abnormal around the stem hole. What am I missing?
>
> Greg


Greg,

A good way to get more info would be to, on the next flat, when removing
tyre and tube, preserve the orientation of each. Locate position of tube
blowout in relation to tyre and rim, which may reduce your search area.

Or it could be as bizarre as a misaligned brake block touching the tyre
casing, causing small holes close to the bead. A wild guess but since
I've done some support vehicle work for races, I've seen it happen.

But you also say you use 27 in tyres on 700c rims. If that's true, then
you have a 630 tyre on a 622 rim, which kind of increases the risk for
the tube working its way between tyre and rim . . .

Let us know what it turned out to be.

/Robert
 
B

Bill Sornson

Guest
G.T. wrote:
> I've been having an inordinate number of starburst failures next to
> the stem, this is with two different rims and a variety of tires and
> tubes. I had originally thought it was from running tubes which are
> too small for the tires but this latest one was with a 27" x 1 1/4"
> tire and a 700c/27" x 32mm tube, the optimal tube for the tire.
>
> I'm running Velox rim tape on both rims, wide Ritchey 700c 'cross
> rims from about 8 years ago or 27" Sun M13IIs.
>
> Nothing looks abnormal around the stem hole. What am I missing?


Switch to Mentos.
 
P

Phil

Guest
G.T. wrote:
> I've been having an inordinate number of starburst failures next to
> the stem, this is with two different rims and a variety of tires and
> tubes. I had originally thought it was from running tubes which are
> too small for the tires but this latest one was with a 27" x 1 1/4"
> tire and a 700c/27" x 32mm tube, the optimal tube for the tire.
>
> I'm running Velox rim tape on both rims, wide Ritchey 700c 'cross
> rims from about 8 years ago or 27" Sun M13IIs.
>
> Nothing looks abnormal around the stem hole. What am I missing?
>
> Greg


I've started putting rubber washers around the stem. It seems that my rim
strip doesn't cover the abrasive edge of the valve stem hole.

--
Phil
 
G

G.T.

Guest
"Robert" <[email protected]> wrote in message
news:[email protected]
> G.T. wrote:
>> I've been having an inordinate number of starburst failures next to the
>> stem, this is with two different rims and a variety of tires and tubes.
>> I had originally thought it was from running tubes which are too small
>> for the tires but this latest one was with a 27" x 1 1/4" tire and a
>> 700c/27" x 32mm tube, the optimal tube for the tire.
>>
>> I'm running Velox rim tape on both rims, wide Ritchey 700c 'cross rims
>> from about 8 years ago or 27" Sun M13IIs.
>>
>> Nothing looks abnormal around the stem hole. What am I missing?
>>
>> Greg

>
> Greg,
>
> A good way to get more info would be to, on the next flat, when removing
> tyre and tube, preserve the orientation of each. Locate position of tube
> blowout in relation to tyre and rim, which may reduce your search area.
>


"next to the stem". There is no searching, the punctures are on each side
of the stem.

> Or it could be as bizarre as a misaligned brake block touching the tyre
> casing, causing small holes close to the bead. A wild guess but since I've
> done some support vehicle work for races, I've seen it happen.
>
> But you also say you use 27 in tyres on 700c rims. If that's true, then
> you have a 630 tyre on a 622 rim, which kind of increases the risk for the
> tube working its way between tyre and rim . . .
>


700c tires on 700c rims, 27" tires on 27" rims.

Greg
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G

G.T.

Guest
"Phil" <[email protected]> wrote in message
news:[email protected]
> G.T. wrote:
>> I've been having an inordinate number of starburst failures next to
>> the stem, this is with two different rims and a variety of tires and
>> tubes. I had originally thought it was from running tubes which are
>> too small for the tires but this latest one was with a 27" x 1 1/4"
>> tire and a 700c/27" x 32mm tube, the optimal tube for the tire.
>>
>> I'm running Velox rim tape on both rims, wide Ritchey 700c 'cross
>> rims from about 8 years ago or 27" Sun M13IIs.
>>
>> Nothing looks abnormal around the stem hole. What am I missing?
>>
>> Greg

>
> I've started putting rubber washers around the stem. It seems that my rim
> strip doesn't cover the abrasive edge of the valve stem hole.
>


Interesting. Any tips there? Do you make your own or are there some that
are ready-made?

Greg
--
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http://ticketmastersucks.org/tracker.html

Dethink to survive - Mclusky
 
Greg who? writes:

> I've been having an inordinate number of starburst failures next to
> the stem, this is with two different rims and a variety of tires and
> tubes. I had originally thought it was from running tubes which are
> too small for the tires but this latest one was with a 27" x 1 1/4"
> tire and a 700c/27" x 32mm tube, the optimal tube for the tire.


> I'm running Velox rim tape on both rims, wide Ritchey 700c 'cross
> rims from about 8 years ago or 27" Sun M13IIs.


> Nothing looks abnormal around the stem hole. What am I missing?


Star-burst holes mean the tube bubbles out spherically and burst. You
must have a hole in the casing that only opens under pressure. If it
is near the stem, you would probably have seen it when inflating the
tire if the wheel was oriented with the stem at the top.

Take a look.

Jobst Brandt
 
G

G.T.

Guest
<[email protected]> wrote in message
news:[email protected]
> Greg who? writes:
>
>> I've been having an inordinate number of starburst failures next to
>> the stem, this is with two different rims and a variety of tires and
>> tubes. I had originally thought it was from running tubes which are
>> too small for the tires but this latest one was with a 27" x 1 1/4"
>> tire and a 700c/27" x 32mm tube, the optimal tube for the tire.

>
>> I'm running Velox rim tape on both rims, wide Ritchey 700c 'cross
>> rims from about 8 years ago or 27" Sun M13IIs.

>
>> Nothing looks abnormal around the stem hole. What am I missing?

>
> Star-burst holes mean the tube bubbles out spherically and burst. You
> must have a hole in the casing that only opens under pressure. If it
> is near the stem, you would probably have seen it when inflating the
> tire if the wheel was oriented with the stem at the top.
>
> Take a look.


Sorry, I was unclear. They're on either side of the stem on the spoke bed
side of the tube and in line with the spoke bed, maybe a 1/4" from the stem.
One side will be burst and on the other side one can see where the tube was
probably bulging and ready to burst before the other side gave out first. I
can get photos later.

It seems to me to be roughness around the stem hole but it looks and feels
clean to me. And, as mentioned, this happens on two entirely different
pairs of rims.

Greg
--
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J

[email protected]umni.org

Guest
Greg who? writes:

>>> I've been having an inordinate number of starburst failures next
>>> to the stem, this is with two different rims and a variety of
>>> tires and tubes. I had originally thought it was from running
>>> tubes which are too small for the tires but this latest one was
>>> with a 27" x 1 1/4" tire and a 700c/27" x 32mm tube, the optimal
>>> tube for the tire.


>>> I'm running Velox rim tape on both rims, wide Ritchey 700c 'cross
>>> rims from about 8 years ago or 27" Sun M13IIs.


>>> Nothing looks abnormal around the stem hole. What am I missing?


>> Star-burst holes mean the tube bubbles out spherically and burst.
>> You must have a hole in the casing that only opens under pressure.
>> If it is near the stem, you would probably have seen it when
>> inflating the tire if the wheel was oriented with the stem at the
>> top.


>> Take a look.


> Sorry, I was unclear. They're on either side of the stem on the
> spoke bed side of the tube and in line with the spoke bed, maybe a
> 1/4" from the stem. One side will be burst and on the other side
> one can see where the tube was probably bulging and ready to burst
> before the other side gave out first. I can get photos later.


> It seems to me to be roughness around the stem hole but it looks and
> feels clean to me. And, as mentioned, this happens on two entirely
> different pairs of rims.


As I said, a star-burst break in a tube comes from a spherical tube
blister and that can only occur with an unsupported hole in the
enclosure, be that tire or rim. You can get such a burst from a stem
that does not fit in the stem hole and rides high in the tire instead
of seating flush against the rim floor.

Investigate ho much of the stem is exposed with the mounted tire and
compare with stem length. I think you'll find the stem jams in the
rim hole before bottoming against the rim floor.

Jobst Brandt
 
On Thu, 12 Jul 2007 17:46:32 -0700, "G.T." <[email protected]>
wrote:

>
><[email protected]> wrote in message
>news:[email protected]
>> Greg who? writes:
>>
>>> I've been having an inordinate number of starburst failures next to
>>> the stem, this is with two different rims and a variety of tires and
>>> tubes. I had originally thought it was from running tubes which are
>>> too small for the tires but this latest one was with a 27" x 1 1/4"
>>> tire and a 700c/27" x 32mm tube, the optimal tube for the tire.

>>
>>> I'm running Velox rim tape on both rims, wide Ritchey 700c 'cross
>>> rims from about 8 years ago or 27" Sun M13IIs.

>>
>>> Nothing looks abnormal around the stem hole. What am I missing?

>>
>> Star-burst holes mean the tube bubbles out spherically and burst. You
>> must have a hole in the casing that only opens under pressure. If it
>> is near the stem, you would probably have seen it when inflating the
>> tire if the wheel was oriented with the stem at the top.
>>
>> Take a look.

>
>Sorry, I was unclear. They're on either side of the stem on the spoke bed
>side of the tube and in line with the spoke bed, maybe a 1/4" from the stem.
>One side will be burst and on the other side one can see where the tube was
>probably bulging and ready to burst before the other side gave out first. I
>can get photos later.
>
>It seems to me to be roughness around the stem hole but it looks and feels
>clean to me. And, as mentioned, this happens on two entirely different
>pairs of rims.
>
>Greg


Dear Greg,

Possibly like this, only with a presta valve?

http://home.comcast.net/~carlfogel/download/tubebump2.jpg

http://home.comcast.net/~carlfogel/download/tubebump.jpg

Cheers,

Carl Fogel
 
G

G.T.

Guest
<[email protected]> wrote in message
news:[email protected]
> Greg who? writes:
>
>> Sorry, I was unclear. They're on either side of the stem on the
>> spoke bed side of the tube and in line with the spoke bed, maybe a
>> 1/4" from the stem. One side will be burst and on the other side
>> one can see where the tube was probably bulging and ready to burst
>> before the other side gave out first. I can get photos later.

>
>> It seems to me to be roughness around the stem hole but it looks and
>> feels clean to me. And, as mentioned, this happens on two entirely
>> different pairs of rims.

>
> As I said, a star-burst break in a tube comes from a spherical tube
> blister and that can only occur with an unsupported hole in the
> enclosure, be that tire or rim. You can get such a burst from a stem
> that does not fit in the stem hole and rides high in the tire instead
> of seating flush against the rim floor.
>
> Investigate ho much of the stem is exposed with the mounted tire and
> compare with stem length. I think you'll find the stem jams in the
> rim hole before bottoming against the rim floor.


Will do.

Greg Thomaswho?
 
G

G.T.

Guest
<[email protected]> wrote in message
news:nak[email protected]
> On Thu, 12 Jul 2007 17:46:32 -0700, "G.T." <[email protected]>
> wrote:
>
>>
>><[email protected]> wrote in message
>>news:[email protected]
>>> Greg who? writes:
>>>
>>>> I've been having an inordinate number of starburst failures next to
>>>> the stem, this is with two different rims and a variety of tires and
>>>> tubes. I had originally thought it was from running tubes which are
>>>> too small for the tires but this latest one was with a 27" x 1 1/4"
>>>> tire and a 700c/27" x 32mm tube, the optimal tube for the tire.
>>>
>>>> I'm running Velox rim tape on both rims, wide Ritchey 700c 'cross
>>>> rims from about 8 years ago or 27" Sun M13IIs.
>>>
>>>> Nothing looks abnormal around the stem hole. What am I missing?
>>>
>>> Star-burst holes mean the tube bubbles out spherically and burst. You
>>> must have a hole in the casing that only opens under pressure. If it
>>> is near the stem, you would probably have seen it when inflating the
>>> tire if the wheel was oriented with the stem at the top.
>>>
>>> Take a look.

>>
>>Sorry, I was unclear. They're on either side of the stem on the spoke bed
>>side of the tube and in line with the spoke bed, maybe a 1/4" from the
>>stem.
>>One side will be burst and on the other side one can see where the tube
>>was
>>probably bulging and ready to burst before the other side gave out first.
>>I
>>can get photos later.
>>
>>It seems to me to be roughness around the stem hole but it looks and feels
>>clean to me. And, as mentioned, this happens on two entirely different
>>pairs of rims.
>>
>>Greg

>
> Dear Greg,
>
> Possibly like this, only with a presta valve?
>
> http://home.comcast.net/~carlfogel/download/tubebump2.jpg
>
> http://home.comcast.net/~carlfogel/download/tubebump.jpg
>


Precisely. Especially like the ones next to the stem.

What caused the bumps on the one where they're not next to the stem???

Greg Thomaswho?
 
On Thu, 12 Jul 2007 18:43:34 -0700, "G.T." <[email protected]>
wrote:

>> Dear Greg,
>>
>> Possibly like this, only with a presta valve?
>>
>> http://home.comcast.net/~carlfogel/download/tubebump2.jpg
>>
>> http://home.comcast.net/~carlfogel/download/tubebump.jpg
>>

>
>Precisely. Especially like the ones next to the stem.
>
>What caused the bumps on the one where they're not next to the stem???
>
>Greg Thomas


Dear Greg,

I think that Dianne came up with the most likely explanation:

http://groups.google.com/group/rec.bicycles.tech/msg/70ec3cf61af0f653

Here's a lavish description:

http://groups.google.com/group/rec.bicycles.tech/msg/15b823be155e9e1f

Here's a shorter theory.

A jammed valve stem can hold the inner tube away from the rim, leaving
a tiny unsupported spot of inner tube being pushed outward at high
pressure against nothing but thin air:

valve
|
|
_________________|______________________rim bed____
'''''''.s.'''-. | .-'''.s.'''''''''''.s.''''''tube
*.|.'
/
!!!

'''''''''''''''''''''''''''''''''''''''''' tube

s = spoke heads denting the tube inward in my case
* = burst outward into void between valve base and rim

The rubber bulges out into the void, flexes a tiny bit, slowly deforms
permanently, eventually fatigues, and finally bursts on one side or
the other of the base of the valve.

The bigger the void, the sooner the tube bursts. Wide rims seem tobe
more prone to this odd failure.

Your rims probably have double walls with holes covered by rim tape
and no covered spoke heads pressing on the inner tube.

In my case, the bulge next to the valve was exaggerated by the nearby
spoke-head bulge. Elsewhere, the tube bulged and deformed over the
covered spoke-heads, but didn't burst because the pressure was the
same on the inside and the outside of the tube--no voids existed
except on either side of the base of the valve stem.

Cheers,

Carl Fogel
 
M

me

Guest
"G.T." <[email protected]> wrote in message
news:[email protected]
>
> <[email protected]> wrote in message
> news:[email protected]
>> On Thu, 12 Jul 2007 17:46:32 -0700, "G.T." <[email protected]>
>> wrote:
>>
>>>
>>><[email protected]> wrote in message
>>>news:[email protected]
>>>> Greg who? writes:
>>>>
>>>>> I've been having an inordinate number of starburst failures next to
>>>>> the stem, this is with two different rims and a variety of tires and
>>>>> tubes. I had originally thought it was from running tubes which are
>>>>> too small for the tires but this latest one was with a 27" x 1 1/4"
>>>>> tire and a 700c/27" x 32mm tube, the optimal tube for the tire.
>>>>
>>>>> I'm running Velox rim tape on both rims, wide Ritchey 700c 'cross
>>>>> rims from about 8 years ago or 27" Sun M13IIs.
>>>>
>>>>> Nothing looks abnormal around the stem hole. What am I missing?
>>>>
>>>> Star-burst holes mean the tube bubbles out spherically and burst. You
>>>> must have a hole in the casing that only opens under pressure. If it
>>>> is near the stem, you would probably have seen it when inflating the
>>>> tire if the wheel was oriented with the stem at the top.
>>>>
>>>> Take a look.
>>>
>>>Sorry, I was unclear. They're on either side of the stem on the spoke
>>>bed
>>>side of the tube and in line with the spoke bed, maybe a 1/4" from the
>>>stem.
>>>One side will be burst and on the other side one can see where the tube
>>>was
>>>probably bulging and ready to burst before the other side gave out first.
>>>I
>>>can get photos later.
>>>
>>>It seems to me to be roughness around the stem hole but it looks and
>>>feels
>>>clean to me. And, as mentioned, this happens on two entirely different
>>>pairs of rims.
>>>
>>>Greg

>>
>> Dear Greg,
>>
>> Possibly like this, only with a presta valve?
>>
>> http://home.comcast.net/~carlfogel/download/tubebump2.jpg
>>
>> http://home.comcast.net/~carlfogel/download/tubebump.jpg
>>

>
> Precisely. Especially like the ones next to the stem.
>
> What caused the bumps on the one where they're not next to the stem???
>
> Greg Thomaswho?
>


When you insert a tube into the tire, are you perhaps using a stem nut?
If so, are you tightening it before you get the bead of the tire over the
rim? You can trap a bit of the tube under the tire bead this way, leading
to a bubble of tube working its way out later and giving you the starburst
rupture.

Cal
 
P

Phil

Guest
G.T. wrote:
> "Phil" <[email protected]> wrote in message
> news:[email protected]
>> G.T. wrote:
>>> I've been having an inordinate number of starburst failures next to
>>> the stem, this is with two different rims and a variety of tires and
>>> tubes. I had originally thought it was from running tubes which are
>>> too small for the tires but this latest one was with a 27" x 1 1/4"
>>> tire and a 700c/27" x 32mm tube, the optimal tube for the tire.
>>>
>>> I'm running Velox rim tape on both rims, wide Ritchey 700c 'cross
>>> rims from about 8 years ago or 27" Sun M13IIs.
>>>
>>> Nothing looks abnormal around the stem hole. What am I missing?
>>>
>>> Greg

>>
>> I've started putting rubber washers around the stem. It seems that
>> my rim strip doesn't cover the abrasive edge of the valve stem hole.
>>

>
> Interesting. Any tips there? Do you make your own or are there some
> that are ready-made?
>
> Greg


Make. When I make them, I am actually producing the exact same pattern that
the tube made when it exploded. Take a bum tube, cut a 10-20mm square out
of it, and fold it in half. Use scissors to cut a ~5mm perpendicular across
the fold. Rotate the fold 90 degrees, then cut again. When unfolded, you
should have a cut in the shape of a cross. Repeat if desired at 45 degree
angles to get a starburst pattern.

Slip this small square over the tube you want to protect and install the
tube as usual. Presto, the tube is protected against valve hole abrasion,
especially because it's not under tension (air pressure).

--
Phil
 
B

Bob McFakename

Guest
On Thu, 12 Jul 2007 20:13:52 -0700, me wrote:

> "G.T." <[email protected]> wrote in message
> news:[email protected]
>>
>> <[email protected]> wrote in message
>> news:[email protected]
>>> On Thu, 12 Jul 2007 17:46:32 -0700, "G.T." <[email protected]>
>>> wrote:
>>>
>>>>
>>>><[email protected]> wrote in message
>>>>news:[email protected]
>>>>> Greg who? writes:
>>>>>
>>>>>> I've been having an inordinate number of starburst failures next to
>>>>>> the stem, this is with two different rims and a variety of tires and
>>>>>> tubes. I had originally thought it was from running tubes which are
>>>>>> too small for the tires but this latest one was with a 27" x 1 1/4"
>>>>>> tire and a 700c/27" x 32mm tube, the optimal tube for the tire.
>>>>>
>>>>>> I'm running Velox rim tape on both rims, wide Ritchey 700c 'cross
>>>>>> rims from about 8 years ago or 27" Sun M13IIs.
>>>>>
>>>>>> Nothing looks abnormal around the stem hole. What am I missing?
>>>>>
>>>>> Star-burst holes mean the tube bubbles out spherically and burst. You
>>>>> must have a hole in the casing that only opens under pressure. If it
>>>>> is near the stem, you would probably have seen it when inflating the
>>>>> tire if the wheel was oriented with the stem at the top.
>>>>>
>>>>> Take a look.
>>>>
>>>>Sorry, I was unclear. They're on either side of the stem on the spoke
>>>>bed
>>>>side of the tube and in line with the spoke bed, maybe a 1/4" from the
>>>>stem.
>>>>One side will be burst and on the other side one can see where the tube
>>>>was
>>>>probably bulging and ready to burst before the other side gave out first.
>>>>I
>>>>can get photos later.
>>>>
>>>>It seems to me to be roughness around the stem hole but it looks and
>>>>feels
>>>>clean to me. And, as mentioned, this happens on two entirely different
>>>>pairs of rims.
>>>>
>>>>Greg
>>>
>>> Dear Greg,
>>>
>>> Possibly like this, only with a presta valve?
>>>
>>> http://home.comcast.net/~carlfogel/download/tubebump2.jpg
>>>
>>> http://home.comcast.net/~carlfogel/download/tubebump.jpg
>>>

>>
>> Precisely. Especially like the ones next to the stem.
>>
>> What caused the bumps on the one where they're not next to the stem???
>>
>> Greg Thomaswho?
>>

>
> When you insert a tube into the tire, are you perhaps using a stem nut?
> [excised]


Come on guys, this is a family newsgroup.
 
G

G.T.

Guest
me wrote:
> "G.T." <[email protected]> wrote in message
> news:[email protected]
>> <[email protected]> wrote in message
>> news:[email protected]
>>> On Thu, 12 Jul 2007 17:46:32 -0700, "G.T." <[email protected]>
>>> wrote:
>>>
>>>> <[email protected]> wrote in message
>>>> news:[email protected]
>>>>> Greg who? writes:
>>>>>
>>>>>> I've been having an inordinate number of starburst failures next to
>>>>>> the stem, this is with two different rims and a variety of tires and
>>>>>> tubes. I had originally thought it was from running tubes which are
>>>>>> too small for the tires but this latest one was with a 27" x 1 1/4"
>>>>>> tire and a 700c/27" x 32mm tube, the optimal tube for the tire.
>>>>>> I'm running Velox rim tape on both rims, wide Ritchey 700c 'cross
>>>>>> rims from about 8 years ago or 27" Sun M13IIs.
>>>>>> Nothing looks abnormal around the stem hole. What am I missing?
>>>>> Star-burst holes mean the tube bubbles out spherically and burst. You
>>>>> must have a hole in the casing that only opens under pressure. If it
>>>>> is near the stem, you would probably have seen it when inflating the
>>>>> tire if the wheel was oriented with the stem at the top.
>>>>>
>>>>> Take a look.
>>>> Sorry, I was unclear. They're on either side of the stem on the spoke
>>>> bed
>>>> side of the tube and in line with the spoke bed, maybe a 1/4" from the
>>>> stem.
>>>> One side will be burst and on the other side one can see where the tube
>>>> was
>>>> probably bulging and ready to burst before the other side gave out first.
>>>> I
>>>> can get photos later.
>>>>
>>>> It seems to me to be roughness around the stem hole but it looks and
>>>> feels
>>>> clean to me. And, as mentioned, this happens on two entirely different
>>>> pairs of rims.
>>>>
>>>> Greg
>>> Dear Greg,
>>>
>>> Possibly like this, only with a presta valve?
>>>
>>> http://home.comcast.net/~carlfogel/download/tubebump2.jpg
>>>
>>> http://home.comcast.net/~carlfogel/download/tubebump.jpg
>>>

>> Precisely. Especially like the ones next to the stem.
>>
>> What caused the bumps on the one where they're not next to the stem???
>>
>> Greg Thomaswho?
>>

>
> When you insert a tube into the tire, are you perhaps using a stem nut?
> If so, are you tightening it before you get the bead of the tire over the
> rim? You can trap a bit of the tube under the tire bead this way, leading
> to a bubble of tube working its way out later and giving you the starburst
> rupture.


No, I got into the habit of not using a stem nut at all on my mtn bike
tires. But that brings up the point that in haste I probably am not
pulling the stem all the way through the rim before I inflate the tube.
I will be conscious of this now and will probably start using the stem
nuts on my skinny tired wheels.

Greg
 
G

G.T.

Guest
Phil wrote:
> G.T. wrote:
>> "Phil" <[email protected]> wrote in message
>> news:[email protected]
>>> G.T. wrote:
>>>> I've been having an inordinate number of starburst failures next to
>>>> the stem, this is with two different rims and a variety of tires and
>>>> tubes. I had originally thought it was from running tubes which are
>>>> too small for the tires but this latest one was with a 27" x 1 1/4"
>>>> tire and a 700c/27" x 32mm tube, the optimal tube for the tire.
>>>>
>>>> I'm running Velox rim tape on both rims, wide Ritchey 700c 'cross
>>>> rims from about 8 years ago or 27" Sun M13IIs.
>>>>
>>>> Nothing looks abnormal around the stem hole. What am I missing?
>>>>
>>>> Greg
>>> I've started putting rubber washers around the stem. It seems that
>>> my rim strip doesn't cover the abrasive edge of the valve stem hole.
>>>

>> Interesting. Any tips there? Do you make your own or are there some
>> that are ready-made?
>>
>> Greg

>
> Make. When I make them, I am actually producing the exact same pattern that
> the tube made when it exploded. Take a bum tube, cut a 10-20mm square out
> of it, and fold it in half. Use scissors to cut a ~5mm perpendicular across
> the fold. Rotate the fold 90 degrees, then cut again. When unfolded, you
> should have a cut in the shape of a cross. Repeat if desired at 45 degree
> angles to get a starburst pattern.
>
> Slip this small square over the tube you want to protect and install the
> tube as usual. Presto, the tube is protected against valve hole abrasion,
> especially because it's not under tension (air pressure).


Cool, I think I'll start making some.

Greg
 
M

Michael Press

Guest
In article <[email protected]>,
"G.T." <[email protected]> wrote:

> me wrote:
> > "G.T." <[email protected]> wrote in message
> > news:[email protected]
> >> <[email protected]> wrote in message
> >> news:[email protected]
> >>> On Thu, 12 Jul 2007 17:46:32 -0700, "G.T." <[email protected]>
> >>> wrote:
> >>>
> >>>> <[email protected]> wrote in message
> >>>> news:[email protected]
> >>>>> Greg who? writes:
> >>>>>
> >>>>>> I've been having an inordinate number of starburst failures next to
> >>>>>> the stem, this is with two different rims and a variety of tires and
> >>>>>> tubes. I had originally thought it was from running tubes which are
> >>>>>> too small for the tires but this latest one was with a 27" x 1 1/4"
> >>>>>> tire and a 700c/27" x 32mm tube, the optimal tube for the tire.
> >>>>>> I'm running Velox rim tape on both rims, wide Ritchey 700c 'cross
> >>>>>> rims from about 8 years ago or 27" Sun M13IIs.
> >>>>>> Nothing looks abnormal around the stem hole. What am I missing?
> >>>>> Star-burst holes mean the tube bubbles out spherically and burst. You
> >>>>> must have a hole in the casing that only opens under pressure. If it
> >>>>> is near the stem, you would probably have seen it when inflating the
> >>>>> tire if the wheel was oriented with the stem at the top.
> >>>>>
> >>>>> Take a look.
> >>>> Sorry, I was unclear. They're on either side of the stem on the spoke
> >>>> bed
> >>>> side of the tube and in line with the spoke bed, maybe a 1/4" from the
> >>>> stem.
> >>>> One side will be burst and on the other side one can see where the tube
> >>>> was
> >>>> probably bulging and ready to burst before the other side gave out first.
> >>>> I
> >>>> can get photos later.
> >>>>
> >>>> It seems to me to be roughness around the stem hole but it looks and
> >>>> feels
> >>>> clean to me. And, as mentioned, this happens on two entirely different
> >>>> pairs of rims.
> >>>>
> >>>> Greg
> >>> Dear Greg,
> >>>
> >>> Possibly like this, only with a presta valve?
> >>>
> >>> http://home.comcast.net/~carlfogel/download/tubebump2.jpg
> >>>
> >>> http://home.comcast.net/~carlfogel/download/tubebump.jpg
> >>>
> >> Precisely. Especially like the ones next to the stem.
> >>
> >> What caused the bumps on the one where they're not next to the stem???
> >>
> >> Greg Thomaswho?
> >>

> >
> > When you insert a tube into the tire, are you perhaps using a stem nut?
> > If so, are you tightening it before you get the bead of the tire over the
> > rim? You can trap a bit of the tube under the tire bead this way, leading
> > to a bubble of tube working its way out later and giving you the starburst
> > rupture.

>
> No, I got into the habit of not using a stem nut at all on my mtn bike
> tires. But that brings up the point that in haste I probably am not
> pulling the stem all the way through the rim before I inflate the tube.
> I will be conscious of this now and will probably start using the stem
> nuts on my skinny tired wheels.


Before seating the tire bead around the stem, push the
stem in so that the stem base is inside the wide part
of the casing. Then seat the bead all the way into the
rim. Now pull the stem, seating it against the rim bed.

--
Michael Press
 
Michael Press writes:

>> No, I got into the habit of not using a stem nut at all on my mtn
>> bike tires. But that brings up the point that in haste I probably
>> am not pulling the stem all the way through the rim before I
>> inflate the tube. I will be conscious of this now and will
>> probably start using the stem nuts on my skinny tired wheels.


> Before seating the tire bead around the stem, push the stem in so
> that the stem base is inside the wide part of the casing. Then seat
> the bead all the way into the rim. Now pull the stem, seating it
> against the rim bed.


From the description of the dimples and burst, it seems the tube is
not descending to the bed of the rim, either because its base-pad is
too stiff and wide to fit between the beads of the tire, or because
the stem is too fat for the stem hole in the rim. In any event, it is
not abrasion or sharp edges. These do not cause star burst failures.
Unsupported tube rubber causes star burst failures.

Jobst Brandt