What am I missing, tire-wise?

September 9, 2021 2:17 PM

Why has my back tire flatted twice in nine days?

After a year of riding on my brand new bike with brand new tires (not every day but 3-4 times a week - about 1300 miles), I had not one single flat tire. In the last 8-9 days, though, my back tire has flatted twice.

The tires themselves - Specialized Armadillo Elites - are still in good shape for that much riding (and I'm not looking for recommendations for different tires, I've used Armadillos forever and love them). There's no tears/rips/holes in the tread, it's not delaminating or otherwise falling apart, and neither flat seemed to be caused by a sharp object puncture (I went through the tire inch by inch and found nothing). In both cases, the flatting happened after a ride - the ride itself went without a hitch, and then, hours later, I'd notice that the back tire was completely flat.

I'm stumped as to what else could be causing this - I need to take the tire off and soak the tube to see if maybe this was a pinch flat, but I rode for four days on it between flats, which makes me think it wasn't a pinch?

The only other thing I can think of that is even a little bit strange is that the hole in the wheel (DT Swiss R470-DB, 700cm, if that matters) through which the tube valve goes when mounting the tire is quite a bit more snug than I have experienced on other bikes (not sure if that's due to the rim strip or the diameter of the hole itself), so maybe that is causing some stress on the tube where it joins the valve or something?

As I said, I still need to take the wheel off and look at it again tonight (I noticed the latest flat this morning, after a problem-free 22 mile ride last night). I was just hoping someone could point me in the direction of something I hadn't thought of that might be causing these flats.

posted by pdb to Sports, Hobbies, & Recreation (18 answers total)

Did you change the tube? I'd start with that, even if you can't find the reason on the tire.
posted by bluedaisy at 2:31 PM on September 9, 2021

How old was the replacement tube? Might have just been degraded rubber.

It's always the valve hole/stem.
posted by Dashy at 2:35 PM on September 9, 2021

Response by poster: Not to threadsit, but they were both brand new tubes - I bought them about four months ago. I don't generally mess with patching tubes, any time I get a flat I replace the tube.
posted by pdb at 2:40 PM on September 9, 2021

Best answer: Pinch flats aren't slow leaks. They're immediate. You had a slow leak.

Did the leak happen in the same place both times? To work back where the puncture was on the tire, the trick is to always line up the tire manufacturer's label with the valve hole. This lets you align the tube to the tire to narrow your search.

Sometimes a bit of wire can get embedded in the tire carcass, and is extremely difficult to find. Being able to narrow your search area helps a lot.

This is assuming that the puncture happened on the tire side. It could be a spoke poking into the tube, although that seems unlikely to develop out of the blue.
posted by adamrice at 2:40 PM on September 9, 2021 [4 favorites]

Best answer: What’s your rim strip situation like? Sometimes the spokes or other debris can poke up from the rim and cause a slow flat. I had an epic failure of a morning work commute once due to a busted rim strip.
posted by Maarika at 2:46 PM on September 9, 2021 [1 favorite]

Seconding Dashy, even new tubes often fail in the area where the stem joins the tube.

After you water-test the tube, please come back and let us know what you found.
posted by JimN2TAW at 2:56 PM on September 9, 2021

Yes, you need to see where the previous tube failed. Use the bucket test.
posted by computech_apolloniajames at 3:11 PM on September 9, 2021 [2 favorites]

My Armadillos collected flints and glass over a year of city commuting, then all of a sudden they popped through the kevlar lining several times in one ride.
posted by k3ninho at 3:51 PM on September 9, 2021 [1 favorite]

Best answer: Valve/valve stem issues are not super common, but a real possibility. Finding the hole (in the newest one at minimum) is a good idea. Sometimes tiny bits of debris in the tire or rim tape are only evident under realllly close inspection (or being brushed from one direction), so narrowing down your search radius will save lots of time.

I'd like to add that the mounting of the tire after replacing the tube can (!) cause a flat if your tire is tight and requires a lever. Sometimes a tiny fold of rubber gets pinched in that last moment, and creates either a thin spot or a small hole.

I've SIGNIFICANTLY reduced the frequency of this by just never (well, almost never) using a lever to mount the tire. I'd recommend a quick search of something like "mount tire no levers" to find some guides.

(I've fixed literally thousands of flats, fwiw)
posted by Acari at 3:56 PM on September 9, 2021 [1 favorite]

Best answer: Those overnight leaks are almost always like adamrice explains. Car tires shed tiny wires and they work their way into your tire. They can be practically invisible and having a point of reference between the tire and tube along with finding the hole in the tube is often your only hope. If you haven’t previously lined up the valve stem and the tire label, mark the spot where the valve is on the tire. You can often use a permanent marker, the black even shows on black if you look carefully.
posted by advicepig at 3:59 PM on September 9, 2021

I haven't had a valve-stem flat since swapping out my el-cheapo floor pump for a Lezyne with a screw-on/off pump head. No more yanking the pump head off.
posted by humbug at 4:15 PM on September 9, 2021 [1 favorite]

I get a lot of flats and this sure sounds like a slow leak situation to me. Take the tube out and put in the sink or a bucket of water I bet it will be obvious. Most of the time when this happens to me there is usually something extremely tiny (ie. glass shard, wire) penetrating the tire just barely and it just barely pokes a hole in the tube, leading to a slow leak. Then you change the tube and it happens again, but you won't notice until the next day after it sits all night leaking.

When I get a flat, I always keep track of the orientation of the wheel/tire to the tube when I take it out relative to the valve. Then I make an "OK" symbol with my hands and pass the tube through my fingers near my ear, both feeling for an air leak with my hand and listening/feeling for one with my ear. Then when I find it I can go back and double check that there's nothing stuck in the tire in that general area. If that doesn't work, or it's not obvious what caused the puncture, I (very carefully!!) run my fingertip VERY lightly across the inside of the tire and this uncovers the culprit pretty much every time.

Valve issues are a lot rarer and a lot easier to diagnose.
posted by bradbane at 5:35 PM on September 9, 2021

Best answer: I've fixed so many flats it's absurd. Likely as others say, something very small, teensy shard of glass, wire, thorn embedded in the tire. Try to make notice of the position of the tire, tube and rim to find if this is the case. Inspect the tire inside and out, in sunlight while flexing it to expose any tiny cuts. In normal, relaxed shape, it might not be visible, nor can be felt with the fingers.

It's rare, but I've had tubes fail from manufacturing defect. A seam that was prone to separating or some such thing.

Valve leaks are possible, but I've actually never had one. I've only ever really used schrader valve tubes.

I've occasionally had flats from things like a slipped/rotted rim strip, exposing a spoke/nipple that rubs ever so slightly on the inner part of the tube.

And I've had multiple flats in short sequence from non related causes that are enough to really fuck with your mind. Once in a while, I just gave up, changed out the tire and tube, and all was well again.
posted by 2N2222 at 6:13 PM on September 9, 2021

Response by poster: Yep, I've always done the "line the valve up with the tire label" trick, and this time is no different.

Strangely, though, the bathtub test this time revealed...nothing. I took the tire off, checked the hell out of the rim strip and the inside edges of the wheel and found nothing amiss, checked the tire itself (not under sunlight, but under a powerful light AND a headlamp, both with tire flexed and not), both along the bead and (several times) along the tread, and still found nothing visible or tactile. This took me about 10 minutes, and in that 10 minutes, I had the tube fully inflated and laying on the ground next to my work area, and it lost no pressure at all.

Watching the tube in the tub, for about two minutes, revealed no bubbles.

I remounted the tube in the tire on the wheel and fully inflated it (left it off the bike), so in the morning, either it will still be fully inflated or it will be flat again, at which point I am going to just go to the shop and buy new tires/tubes, because this is making me nuts and I'm on the verge of staring at it too much to be objective about it any more.
posted by pdb at 9:19 PM on September 9, 2021 [1 favorite]

Could you have something in your valve cap that's depressing the seal the valve and letting air out slowly?
posted by Ferreous at 9:47 PM on September 9, 2021 [1 favorite]

"One flat leads to another" is the motto I live by.

Either the same cause - not fixed or not fixed well enough - causes another flat or all the horsing around with taking the wheel, tire, and tube on & off causes something that leads to a flat. This can be anything from a defective new tube straight from the factory to pinching the tube somehow while installing it, debris getting into the tire while it is apart, etc.

Also, almost all devices have a U-shaped service life - the so-called bathtub curve. The idea is that things are far more likely to fail when brand-new and again when quite old and starting to wear out. In between those two points, they tend to just chug along in a pretty reliable way.

So when you replace and old/failed tube with a new one you are connecting the two bad parts of the U curve together - the end of one tube's lifespan and the beginning of another's. End result: Flat tires tend to run in series.

More practically, my thought: Do the tubes have schraeder valves? What I wonder is if the valve stem is a bit loose. This can cause a slow leak in a way that can be quite hard to detect. I've had tubes should up from the factory with loose and very slightly leaking valve stems. A quarter or half turn with a valve stem remover usually fixes the problem.

(It's possible to have a similar problem with presta valves, too, I believe. Thought it's less likely to require tightening and more that the valve is just defective, bent, or broken somehow. Presta valves are fairly delicate.)

Also I have had tubes fail because of the valve stem hole in the wheel being too small/tight/stressing the tube in that spot, and more particularly when there was a sharp edge of the tube and the rim strip shifted a bit and exposed it. So putting a new tube in it would be stressed and pretty hard to get into place, leading to weak spots and sometimes rips, and also abrading the rubber in that area and eventually wearing or cutting through it.

Leaks right around the place where the valve connects to the rest of the tube can be a bit tricky as sometimes they seal up when the stem is in one position and then open up when it is pushed to a different angle or such.

Also, I've had a cut or hole in the side of the valve. That was tricky as (again) it wouldn't really leak, or only slowly, as long as it was under pressure but if you took the tub and out worked the valve back & forth it would eventually find the sweet spot and leak like crazy.
posted by flug at 1:32 AM on September 10, 2021

That sounds super frustrating, pdb. Please let us know how it goes in morning.
posted by computech_apolloniajames at 6:08 AM on September 10, 2021

Response by poster: Either the same cause - not fixed or not fixed well enough - causes another flat

The latter is pretty much my motto when it comes to most things I try, I find...haha. They're presta valves, and I have a suspicion that the valve is causing a problem somehow in the way that flug suggests. Woke up this morning and, sure enough, the tire is flat, so I'm calling it - new tires and tubes today and that should hopefully take care of things.
posted by pdb at 7:01 AM on September 10, 2021 [1 favorite]