DQRider 

Okay, first let me establish my bona fides: I am a quality engineer with 25 years experience, and have been tinkering with bicycles for most of that time. I buy them worn and/or broken, and rebuild them from the frame up during our cold Minnesota winters. (I haven't yet mastered the art of "flipping", and my garage is now full). So I wouldn't bring this to you without first exhausting all my resources on the problem. And this is a really weird problem...

I recently bought two 700c Weinmann LP18 wheelsets for use in a couple of my vintage roadbikes. The sale price was ~$80, so how could I go wrong... right? But as soon as I filled the tires with air preparing them for the next day's ride, something began to go wrong. I would come out in the morning to find at least one of the tires flat.

Of course I checked all the usual things: presta valve shut tight, no bead bulges or breaks, etc. But when I pulled the tube, it looked like this:



I currently have 9 of these in this state. They all fail in different locations, but always on the rim-side of the tube. Now, when I first searched "LP18 flats", I was directed to an older thread that had a similar complaint. But there were no photos, and I never saw where the root cause was identified and a corrective/preventive action determined.

But right away, folks mentioned rim tape. Part of my investigation included a DOE (design of experiments) where I taped one wheel with Velox, one wheel with Schwalbe blue high-pressure tape, and two with a combination of the two: one with a Velox base, the other with Schwalbe.


These are the single-layer wheels; the others are still mounted on a bike, which I left hanging on the wall in disgust.

So I have done my due-diligence in trying to find out what's gone wrong here. My theory is that the little "shoulders" on each side of the center channel are causing stress risers in the rubber of the tubes. But I cannot explain the peculiar linear (as opposed to lateral) pattern of the "snakebite" punctures.



So I need the help of an expert bicycle mechanic that has solved this issue somewhere else. Any takers?

thumpism 

If the two dimples on each tube are the punctures and are the ONLY dimples on each tube, and this happens on every LP 18 you've tried this on, I'd venture to say you have a mystery on your hands. Or is this happening to each tube but only when installed on the same one rim? If only one rim is causing this, that certainly narrows it down but does not explain it.

DQRider 

Every single rim of the 4 does this. Tire size 700c x 28mm, tubes to match (25 - 32), pressures at recommended: 100psi rear, 95 front - max is 105. A mystery indeed...

(edit) Also, different brands of tubes: Michelin A2 Airstop, Kenda, and Bontrager all fail. Even the "thorn-resistant" Bontragers failed in this mode.

sweeks

Have a look at Sheldon Brown's page on flats. It looks like your rim tape may be wider than necessary (scroll down to the image under "re-installing the tire". I doubt that is the problem causing the flats, though. Try a different brand of inner tube.
https://www.sheldonbrown.com/flats.html
Steve
EDIT: Ah... disregard that last suggestion. I'm clueless. It does look as if the tube is unsupported somehow. have you looked for the exact spots on the rims where these herniations occur?

DQRider 

Thanks for taking a swing at it, sweeks. When I said I've "exhausted all my resources", that includes the late lamented Sheldon Brown's excellent writings on the subject, and everything else I could find on the interwebs.

Yes, of course I examined the exact spots on the rims where this occurred. Different locations on each rim, but even more strange - different locations from one flat to another on the same rim!

I was really hoping that someone else had had this happen, and actually solved it.

Spoonrobot 

Who recommended that pressure for 700x28 tires? That's really high unless you're significantly over 200 pounds.

Google shows this has happened to at least two other people. No identification of cause though. If you came into my shop I'd replace both strips with double wrapped Stans tape with a layer of Velox over the top. I think it's a tape issue, especially if the tape does not adhere well to the rim.

https://www.bikeforums.net/bicycle-m...trip-good.html

Completely bamboozled with chronic tube failure - Australian Cycling Forums - Bicycles Network Australia

DQRider 

Thanks Spoonrobot - I've encountered canklecat on the C&V forum, and he's a good guy. First time I've seen photos of the same failure! The Aussie fellow's photos don't show up for me - that damned Pee-Bucket piracy/ransom thing.

So pressure, yeah, I weigh 220 lbs. Sidewall of the Panaracer Paselas says max pressure 105 psi. So I run 100 in the rear because I build my bikes for a more upright riding position. Here is one of the bikes the failure occurred on:



I had a flat rear the morning before I rode, and then the front tube flatted on the way home. Rim tape at that time was Velox on both. I've switched this bike to CR-18 rims and 32mm tires, and no problems for at least 100 miles.

thumpism 

Are you using talc on the tubes when you install them? The powder helps the tube move inside the tire, helps prevent binding, and might help prevent the flats.

The powder makes patching a flat a little more troublesome due to cleanup first, but definitely worth a try.

DQRider 

Yes. Again, while I was experimenting with the variables involved in this issue, I used varying amounts of talcum powder on each iteration. On one install, I used none at all - that's the tube in the far right of the first photo. You can see the residual talc on the rest. But I concluded that none of these tubes lasted long enough for talcum to be a significant factor.

maddog34

try this... inflate tube to a round shape, but still not tense... insert tube into tire.... slip tire onto wheel by HAND ONLY (patience and strong thumbs needed)... inflate tube to only 5-7 lbs.... work your way around the tire twisting it vigorously, side to side... then inflate to 20 lbs., and repeat the twisting side to side... inflate to high pressure.

TGT1

I had the same issue with a Vuelta rim with a very similar internal profile that produced "nipple pimples" with wider tires.

The solution was to put Schwalbe high pressure Mylar tape on with Velox over that.

Cured the problem. Neither one by itself worked.

JanMM

Wow - a genuine mystery! I got nothing.

dabac

I had a batch of Geax tubes that would fail like that. Or more likely, rupture.
An autopsy revealed that the wall thickness of those tubes wasn’t uniform. There was a thin streak coinciding with the deformed spots.
But you’re getting across different brands of tubes.
Can’t think of much else than rim strip then.
Maybe the gauge on your pump is off, causing you to run higher pressures than you think?

cny-bikeman

Wow, first time I've seen so many stumped, with such complete info available. I'll be curious to see what FBinNY has to say, but I'll give it a stab. The fact that the dimples are off-center does point to the rim shoulder or side, but not only is the longitudinal "snakebite" odd, but also the spacing being exactly the same each time. Normally I would lay it off to spoke holes, but I don't see how that could be, given the rim tape.

I was about to ask if tires had been switched, but just saw your last post regarding a wider tire and rim (so far) working better. I just looked up the LP18 specs, and it is listed by Weinman as a 700CX18C/23C rim, which means that there might be a problem running a 28 mm on that rim. Sheldon's rim/tire chart recommends a minimum 15mm inner rim width for a 28 mm tire, and the LP18's are 13.6 mm. The CR18 has an inner width of 17.5 mm, corresponding to an ideal tire width of 28-35 mm.

It seems to me the explanation would be related to an interaction between the tire, rim and road defects. I'm wondering if, when going over an obstacle, the wider tire on the narrow LP18 distorts in such a way that it opens up an area on each side of the deflection from the obstacle, between tire and rim. The tube momentarily expands enough to exceed its plastic limits, or (more likely?) gets pinched between tire and rim side/shoulder, and fails. Also, due to the extra friction, taping over the shoulder could make the problem worse, by preventing the tube from easily returning to the inside of the tire after such distortion occurs. Knowing if others resolved similar issues with a smaller profile tire would help test whether that hypothesis is possibly valid. Of course, given rider weight, upright position and commuting usage a narrower tire is not going to be an option here. I do know that somewhat similar problems can occur around the valve hole with narrow rims and wide tires, as has been discussed previously by FBinNY. If the above is correct then sadly the LP18 (or any narrow rim) is not a good fit with the rider's needs.

p.s. I apologize if someone has been reading this during my numerous edits, necessitated by my discovering info I had missed previously!

chorlton

Might/Will be stating the obvious but have you checked the rim or rim tapes for similar dimples.. From your second picture, the right rim with the blue tape bottom of right Schwalbe logo...

...

Retro Grouch 

Me too.

The question is: "Where is the tube going when it's inflated? Those evenly spaced "bumps" have to be going someplace to get stretched out like that. I would think they would have to correspond to some kind of holes or divots in the rim extrusion but the OP would surely have discovered something like that.

hokiefyd 

I must say that I'm as stumped at others (the longitudinal snake bite is very strange, indeed), but I felt like I just had to post to say how stunning that bike of yours is. It has a great vibe to it!

Okay...carry on...

xenologer

tube over stretch:

narrow channel down center of rim, much narrower than rest of tire/rim
in cross section, your tire/rim pressure containment chamber is a pear-shaped space

but tubes are like soap bubbles, they prefer to expand as smooth round shapes. circular cross sections, not pears
so:
as your tube is inflated, initially it stays round, filling up the larger area of the 'pear' (in tire)
as pressure is increased the rubber is now forced into the narrow area of the rim; however at this point, most of the tube surface is already in contact with the tire and does not want to change position
thus a highly localized area of tube must stretch to fill in that final narrow channel area
it then tears and deflates
you see the result as only a tiny dimple -not a full length impression, because it tore and released pressure before any more tube could stretch and leave deformation marks.

so yes, its a bad rim design, I see similar problems occur on other deep centered rims at work often (LBS mechanic)

Several non-guaranteed fixes:
-talc powder on install, to help tube slide into the narrow area
-oversized tube, carefully installed to avoid pinching, so there's more rubber available to stretch
-build up the center channel with multiple narrow layers of velox rim tape, followed by a more normal width one on top to smooth it out

I prefer the last approach, tho one of the other guys uses the first method
YMMV

True Solution: get wider rims, with a shallower, flatter, inner profile
or get narrower tires
you've got rims with an internal width of around 18mm (even less when the tire beads block it up), and tire casings that are 28? so yeah, pear shaped...

DQRider 

This is why I enjoy the Bike Forums so much. Tons of help there when you need it; the benefit of decades of experience from experts across all cycling disciplines. Even if we don't solve this, it has been a worthwhile experience.

The gage on my pump... hmmm. Trying to think of a way to verify it - maybe put a Schrader adapter on there and check it with my automotive gage (which also doesn't have a calibration sticker). My rule of thumb on tire inflation when I don't have a gauge has always been very little "give" when squeezed between fingers and thumb on the rear, more give on the front. The larger the tire, the more give I allow.

A lot to think about there. One of the things I may not have mentioned is that two of the failures occurred overnight with the bike in the workstand - no weight on the tires. I looked at Sheldon's rim/tire chart when selecting my tires and took the disclaimer at the bottom about erring on the side of caution as sort of permission to push the envelope a bit. I really don't want to go smaller than 28, I really prefer 32s, so maybe the issue is as simple as that? But those consistently spaced dimples in a longitudinal pattern... that's just weird.

Good point. I'll check them with a lighted magnifier when I get a chance. Eyeball and finger-poke examination reveals no such defect, but you spotted this without any problem. Better get my eyes checked, I suppose.

Oh yeah. After the third time this happened, I examined all four rims very closely. No burrs, no irregularities, I'm almost certain the spoke holes have something to do with it, but that spacing is wider than the O.D. of a spoke hole.

Well thank you, hokiefyd! I have discovered that the upper-middle tier of bike boom roadbikes can still be had at bargain prices, and you can build a better all-rounder out of a high-quality chrome moly frame than any of the purpose-built hybrids I've seen. The geometry is livelier, and the lighter weight is always a bonus. Basically I'm building a bunch of Bridgestone XO-1s from different brands and countries.

DQRider 

I think you nailed it, xenologer. I'm using too wide of tires on these rims, causing overstress in the tube at those irregular features around the channel. It doesn't explain the snakebite pattern, but from a practical standpoint, wider rims are the solution.

So I can put these wheels up on CL and explain that they were too narrow for my application, and keep a clean conscience about it... Does that pass the smell test?

cny-bikeman

That does make my scenario less credible, but if the bike was ridden prior to the flats occurring in the stand the tube still could have been weakened previously. Yes, I recognized in my post that it's not practical to go more narrow. Sheldon does seem to allow for exceptions, but your situation seems to prove the rule, indicating that in this case pushing the envelope results in bursting it.

Finally, although xenologer's post is accurate, it does not explain the double dimples, especially the fact that they always occur in exactly one pair, never a single, and never in more than one place on the tube. I stand by my conclusion as the most logical and likely. In any case the solution is the same.

One other thought - is there a particular curb, pavement joint, or similar obstacle close to your home that you almost always pass over on a ride?

DQRider 

Thanks again for the thoughtful response, cny-bikeman. The tubes that went into the bike on the stand were fresh out-of-the-box. And yeah, although we have come up with an acceptable solution (CR18s), those darned double dimples will continue to haunt me. I just don't have the time to pursue it properly. I would love to take it on as a work project, but unfortunately that's just not an option.

(edit) I didn't answer your last question: Not really. I avoid all the potholes, and try to avoid hopping curbs as much as possible. Certainly nothing that could cause a pinch-flat.

bradtx

DQRider, When I was your weight I ran 100 PSI in my 23 mm tires. Try reducing air pressure to 80-85 PSI in your tires.

My daughter is using 28s on her 13 mm (internal) rims. True that she weighs much less and PSI is usually 65-75.

Brad

Iride01 

Several have hit on what might be a good avenue to explore. Maybe they even said it but I missed it.

Might the bead on the wider tires actually be seated, but because of the shoulder angle of the tire on narrow rims, be slightly angled in at the bottom with little gap between both sides and not allowing the tube to evenly inflate and fill the rim cavity?

The tube may be entirely or mostly up in the tire and some sections it gets "extruded" between the tire beads down to the rim but is so thin from the stretching it is compromised and the puckering at the spoke holes is actually a result of the really stretched butyl.

Maybe as you are riding the tube behaves much like one of those long balloons that you squeeze in one place and it pokes out in another, then change your grip some and that bulge goes away and another pokes out. Might be why there are two puckers close together instead of evenly spaced. It's the same hold, just that one got made on an earlier bulge.

It might be interesting to know if the thickness of the tire bead increases on wider tires? I run 25 mm tires on Weinmann A124 rims which are 14 mm internal width. 125 psi on the rear, rider weight is only 168 right now but with winter coming on, I'll be 185 in February. However they are single wall, so there are some differences though the internal profile is much the same with deep center channel and high shoulders.

chorlton

Based on what others have suggested... Are you fitting the tubes to the same rims with the same tyres. If it is not the rims or rim tapes then is it possible that you have in some way nicked the beads on the tyres, perhaps with a tyre lever, in a manner that blah blah blah. Given the 'repeatable' fault is occurring in different positions and the rest is fixed you are left with not putting the tyre back on at the same place every time.