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need to solve ID aneurysm problem

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need to solve ID aneurysm problem

Old 09-12-20, 10:04 AM
  #1  
fred_dot_u
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need to solve ID aneurysm problem

Parameters:
single wall rim
26 x 2.1 tire/tube, schrader valve
all spokes recessed in nipples
no nipple turning done
rim is wonderfully true
original rim strip was rubber
replaced with polyurethane rim strip
second rim strip added later
tire rated to 65 psi, inflated to 60 psi during testing

original puncture located about two o'clock from valve stem
replacement tube punctured about same location
I'll never use slimed tubes again

next replacement tube punctured as shown in photo, adjacent to valve stem
failure appears to be aneurysm style in all cases
"pending" aneurysm on opposite side of valve stem in photo

tire is easy to seat, uniform around the wheel, tube is partially inflated to ensure no overlapped areas, no folds, etc. No tools used to seat tire on rim. Inflation by floor pump, slow but safe, tire checked during inflation for uniform seating.

reading the forum leads to a possibility this is a deep well rim
1125209-tube-keeps-puncturing-near-spoke-hole-2 (can't do url)

I'm not permitted to post the detailed images/photos I've taken until I reach the ten post count.

I've worked on bicycles since I was a kid in the 70s and up to now, used to think I knew what I was doing. The rim is flawless, no nicks, burrs, protrusions, etc.

I'm considering to buy self-adhesive rim tape, the stuff I used in the 80s if it's available and cut segments to fit between the nipple heads, layering it, maybe even using a hole punch, to fill in the radial gap difference, then put the poly rim strip over it.

Suggestions are encouraged and welcomed.
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Old 09-12-20, 10:37 AM
  #2  
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When putting a tire on, do you start opposite the valve and work toward the valve? That position 2 o'clock from the valve stem just sounds suspiciously like the place that the bead on most tires starts to get tight as you put it on. If the tube happened to get caught there, then it'll get pinched and damaged but might hold air long enough for a few rides before failure.

I know this first hand. I've done it a time or two.


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Old 09-12-20, 10:53 AM
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I can eliminate the pinched tube between the tire question. The bulges are the root cause, sort of like the tube slipping out of the bead, but the bulge is inward, toward the hub. When I'm able to drop a photo, you'll see what looks like speed bumps on the exact inside diameter of the tube, running on the line of circumference, not perpendicular. One of the wheels I've built in the past was a double wall rim and it's the kind of bulge you'd expect to see if there wasn't a cap on the hole for the spoke, but these are ovals in the shape of the space between the valve stem and the adjacent spoke nipple. The first failure was also oval and fit in the space between the two nipples, and the blow-out was a longer slit.

https://www.dropbox_dot_com/s/txlg1oq...one.JPG?dl=raw
https://www.dropbox_dot_com/s/xizoxt9...two.JPG?dl=raw
https://www.dropbox_dot_com/s/6mlhncy...ree.JPG?dl=raw
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Old 09-13-20, 07:35 AM
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Moe Zhoost
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I don't see anything odd about your rim that would lead to tube damage; however I have had this mystery situation as well. Have you checked for any sharp spots on the offending nipples? Dragging a microfiber cloth over them would tell you. Still, you would expect the rim strip to take care of most flaws. I have 2 recommendations that worked for me: 1) try a wider rim strip. Sometimes narrow ones move to the point where the nipple head is partially exposed. 2) install a wrap of filament reinforced packing tape tightly around the rim before you add the rim strip.
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Old 09-13-20, 08:50 AM
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Here are your pics.........







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Old 09-13-20, 08:54 AM
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@moe, thanks for the suggestions. The photo shows the recent blow-out and the non-photo blow-outs are the same. The space between the nipples gets distorted in the direction of the hub, distorted to the point where the bubble ruptures into a long slit. The original rim strip (rubber) seated nicely in the rim, and appeared to be slightly embedded in the sides, which made me think the tube was "oozing" to the sides, but the failure is always toward the hub. A single wider polyurethane strip provided the same failure result. Two polyurethane strips moved the failure to the area on both sides of the valve stem, but still the same failure mode, a bulge that eventually blows out.

I had intended to use old-style adhesive rim tape and punch holes to make the tape sit around the nipple heads. I may do that yet, but I noticed that the spoke holes are staggered, making it more challenging to accomplish. I have a 3D printer and may print arched shims of the same concept and use the poly rim strip to hold them in place, perhaps along with some thin double-sided tape.

This sort of patchwork solution makes no sense, though. Why should the tube bulge catastrophically rather than just flow into the gently sloped gaps provided by the rim tape.

In the past, when installing a new tube, I'd powder up the surface to allow it to move without binding to the tire. Maybe I need to apply that concept to the rim strip?
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Old 09-13-20, 08:55 AM
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60 psi for a 26 x 2.1 tire sounds excessive. I would be running that tire at no more than 45 psi and sometimes less
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Old 09-13-20, 08:55 AM
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Now that the photos are expanded into the message (thank you for that), it appears I may be incorrect about the placement. Now it might be that the bulges are atop the nipples, which makes even less sense!
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Old 09-13-20, 08:56 AM
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If the only thing that changed was the rim strip, then I'd have to suspect it. You had decent service with this wheel and the previous rim strip?

To ponder in a different direction, is the tube maybe for a narrower width of tires and is getting stretched thin to fill whatever tire you are using?
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Old 09-13-20, 08:57 AM
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Originally Posted by alcjphil
60 psi for a 26 x 2.1 tire sounds excessive. I would be running that tire at no more than 45 psi and sometimes less
As the sidewall reads max 65 psi, I wanted to push the edge but not exceed it. I'd rather have it pop in the garage than after I've given the bike to its intended recipient.
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Old 09-13-20, 10:16 AM
  #11  
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Originally Posted by fred_dot_u
As the sidewall reads max 65 psi, I wanted to push the edge but not exceed it. I'd rather have it pop in the garage than after I've given the bike to its intended recipient.
Just because your tire is supposed to be able to handle 65 psi doesn't mean that it is necessary or useful to push its boundaries. 60 psi for a tire that wide is too much for normal riding
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Old 09-14-20, 08:07 AM
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As I'm limited to five posts in 24 hours, I'll consolidate my replies in one post.

@Moe Zhoost, the failures appear to be between the spoke nipples, rather than upon them. The heads don't catch on my fingertips (risky, I know) and your suggestion of a cloth also results in no catches.

@Iride01, the first failure after removing the original damaged tube was on a tube that was listed for 2.1 and larger, although I don't recall the max size. The next and more recent failure was on a tube for up to 2.1 which is what is on the sidewall of the tire. As noted, I'm careful to have no twists or folds, by inserting the tube in the tire and applying low pressure, checking for folds, twists, etc.

@alcjphil, I think your advice has great merit. I'm more accustomed to narrow high pressure rubber; this is my first extended exposure to a fat tire on an upright bike. Another aspect I've forgotten (six years since last riding) is that I apply talcum powder to the tire and tube to prevent friction bonding. At the higher pressure, and no talc, the rubber won't move to "fall into" the locations that are getting bulged. Perhaps a bit of talc and more reasonable pressure will come through for me.

I expect delivery of a replacement tube today and can proceed on my journey.
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Old 09-18-20, 08:09 AM
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The delivery of the replacement tube took longer than expected, but it arrived yesterday and was installed forthwith. Of course, I forgot to use talc, but I think that's okay at this point.

https://www.dropbox_dot_com/s/48aqpr5...cer.JPG?dl=raw
replace _dot_ with a period/dot
The image above is of one of the 3D printed spacers I used to reduce the problem, along with reducing the maximum pressure, currently at 40 psi. With the spacers in place and a single rim strip, there are no bumps along the entire rim. It may be overkill, but it works and it's easier to leave it in than to remove it at this stage.
Thanks to everybody who contributed to my quest and my question.

Last edited by fred_dot_u; 09-30-20 at 08:44 AM.
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