It’s a cyclist’s worst nightmare: you’re about to hop on your bike when you look down and notice with horror that your tubeless tire has gone flat! It was totally fine a couple days ago on your last ride, and it wasn’t punctured (that you know of). But now you have a sad saggy tire and no idea why. What do you do? Of course you could pump it up and go ride anyway, and I wouldn’t blame you for trying. But if that doesn’t magically fix it, what should you try next?
I recently experienced this common problem yet again, the day before packing my bike for a flight to a big overseas bikepacking trip. Talk about bad timing! I had to summon all my best tricks to find and fix the problem on a tight timeline. Fortunately the tricks worked, and they’ll work for you too, so keep reading and don’t panic.
Note: This post is about dealing with a tubeless bike tire that’s suddenly not holding air after it’s been successfully installed, maybe even ridden a few times, without obvious signs of a new puncture. If you’re still trying to get the bead seated on the rim so you can pump up the tire for the first time, see Tubeless Tire Installation Tips: Learn From My Mistakes.
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How Tubeless Tires Work
Tubeless tires can sometimes seem like a dark art, but they’re actually a simple system. You have a few different parts: tire, rim, rim tape, valve stem. All those parts need to be airtight and make airtight seals against each other so the tire stays inflated, since there is no tube inside to hold the air.
The job of sealant is to find and fill any small gaps, either between the components or from punctures in the tire. As the liquid sealant contacts air and dries out into a rubbery consistency, it plugs the leaks.
Usually sealant does its job quite well, but when it doesn’t you end up with a tubeless tire that’s not holding air. It’s fairly normal for a tubeless tire to go squishy if left to sit for many months; sealant dries out and very slow leaks take their toll. But if you have to pump up before every ride and it’s flat within a few days, something is definitely not quite right with the system.
Use soapy water to find leaks. Substantial leaks can often be seen (sealant bubbles), heard (hissing sound), or even felt (by holding your face very close to the tire). But smaller ones can be subtle. Spray or pour soapy water on any surface you want to check for leaks – tire tread, valve stem, bead-rim interface, spoke holes – and look for bubbles to help locate the source.
Give it time. Once you think you’ve fixed the problem you’ll need to pump up the tire and wait a bit to see if it’s still losing air. You might even need to do this twice, since air can be lost as the sealant is doing its job. This is why it’s SO important to get your tires sorted out a few days in advance of a big ride!
Get a tubeless tire air tank / inflator. If you fiddle with tubeless tires at home, do yourself a favor and buy an Airshot Inflator. I use the Airshot with my Joe Blow floor pump and it has made seating tubeless tires so much easier. See my detailed review of the Airshot here.
What To Check, Step by Step
Tubeless tires, while not all that complicated, can be kind of a pain. No one really wants to break the bead and get sealant all over the place if they can avoid it. If your tubeless bike tire is not holding air, follow the steps below in order. This will ensure you start with the easiest things to check and fix, progressing to the more complicated steps only as necessary.
Problem: Unsealed Puncture
This is the easiest fix, so let’s start here. Check the tire carefully for signs of a puncture that hasn’t managed to seal itself. Maybe it happened on your last ride and you didn’t notice, but the slow leak has caused your tubeless tire to go flat after sitting for awhile.
Usually you’ll see a little wet spot of sealant on the outside of the tire, and perhaps you can even see the hole or object that caused it. Pump up the tire to a normal pressure and you might hear hissing or see sealant bubbling.
To fix: First, if your tire is low on sealant or it’s been a few months since you topped up, add more sealant (see next section). Once you know there’s plenty of sealant in there, try riding for ten minutes to let the sealant work its magic. If that’s not an option, spin the tire vigorously and/or rotate it so the puncture is downward and leave it for ten minutes. If the hole is too large to seal on its own, time to get out your tubeless plug kit.
Problem: Not Enough Fresh Sealant (In The Right Places)
Even without any punctures, tubeless bike tires need sealant to work well. Without sealant the various parts won’t form an airtight seal, and tires – especially old well-used ones – will slowly leak air.
Sealant dries out over time and is gradually “used up” as it seals punctures and small gaps. Make sure you have the correct amount of relatively fresh sealant in your tires, and top it up every few months. If in doubt you can remove the valve stem and use a “dip stick,” like the one that comes with the Orange Sealant injection system, to see how much is in there.
After you add more sealant and pump up the tire, work the sealant into the necessary places before letting the bike sit. The easiest method is to spin the wheel or go for a quick ride. For more stubborn problems, remove the wheel and get creative about sloshing sealant into every crevice. Techniques to try:
- Bounce the wheel vigorously off the ground to slosh sealant upward into the rim-tape interface or valve stem.
- Hold wheel vertically (as it would be while riding) to let sealant pool in the bottom of the tire, then quickly flip it around a line parallel to the ground to slosh the sealant into the rim tape area. Pay special attention to the valve stem area.
- Hold wheel sideways (axle perpendicular to ground) and shake vigorously to splash sealant onto the bead-rim and rim-tape interfaces.
A video is worth a thousand words here:
Often this method of adding sealant, pumping, shaking and sloshing, and saying a prayer to the bike gods will solve the problem. If it doesn’t, move on to these other ideas.
Problem: Leaky Tire-Rim Interface
I recently encountered this problem for the first time and I don’t think it’s as common as the others, but it’s potentially an easy fix. Ideally the shaking and sloshing techniques above will have fixed it, but if not you can fix it directly.
If you deflate the tire, does any part of the bead pull away from the rim? This part may not be fully sealed when the tire is inflated. Clean off any bits of old sealant from the tire and rim, squirt some new sealant along the tire bead, and reinflate until the bead pops out. If you removed the valve stem, wait an hour or so for the sealant to dry before deflating and reinflating with the valve stem in place.
In my case I have a feeling this problem was caused when the bike wasn’t used for awhile and the tire went flat with the bike’s weight on it.
Problem: Leak at the Valve Stem
When a tubeless bike tire isn’t holding air, a leak at the valve stem is a common and sometimes frustrating reason. Often it’s obvious: with the tire pumped up you’ll hear air and see sealant hissing out from around the stem, especially if you spray it with soapy water.
If you get lucky, you can fix this without taking the tire off. First, check the nut that holds the stem snug against the rim. Is the stem wobbly or can you turn the valve nut with your fingers? Tighten the nut to snug finger-tight, and possibly another partial turn with pliers. You don’t want to overtighten it, but it also shouldn’t be loose.
If tightening the nut doesn’t fix it, make sure there’s plenty of fresh sealant in the tire. With the tire fully inflated, try to slosh sealant into the valve stem area as described above. If this quick fix doesn’t help you’re going to have to remove the tire, at least partially. Roll up your sleeves and get ready for a little mess.
If your tire is still going flat and the valve stem seems to be the culprit, there are two likely possibilities: the valve stem isn’t fully sealing against the rim or there’s a leak in the rim tape (see next section).
To fix a valve stem that isn’t sealing properly, remove it from the rim and inspect the conical rubber part. If it’s cracked or damaged, it’s time to replace the valve stem. You could also try a fix I’ve had luck with in the past, which is to layer a small donut cut from old tube over the rubber. Before (re)installing a valve stem, coat the rubber surface (or tube donut) in sealant. Inflate the tire and see if it now holds air – hopefully it does!
There is also a small chance that a leak near the valve stem is due to the valve core itself. At risk of stating the totally obvious, check to make sure the Presta valve is screwed ALL the way closed! Then make sure the valve core is screwed in tightly using a valve core remover tool. There is a very small possibility your valve core is defective, in which case you can easily replace it.
Tubeless tire still keeps going flat and valve stem seems fine? It’s time to move on to…
Problem: Leaky Rim Tape
This is my least-favorite reason for tubeless tires not holding air because it takes the most work to fix, but don’t despair, you can do it!
If your rim tape isn’t sealing perfectly all around the rim, air will escape. It’s common for this problem to look like a leaky valve stem because the escaping air travels along the rim under the tape to the stem. It can also manifest as leaks at the spoke holes. In either case you’ll probably need to redo your rim tape. A very small leak might have been fixed by adding more sealant and sloshing it around – see above – but if you’re here at this step you presumably already tried that.
When you redo the tape, make sure to clean the rim thoroughly and peel off any dried bits of old sealant. The rim tape should be the correct width for your rim (about 1-4 mm wider than the internal width) and carefully applied. Some people swear by Gorilla Tape if they’ve struggled with other rim tapes in the past.
If All Else Fails…
You’ve tried ALL the steps above, reinstalled the tire, and it’s still going flat within a few hours or a couple days (and you’re sure the rim and tire are both tubeless compatible). You could start from scratch with a different tire, or it might be time to visit your local bike shop for help. I’m always in favor of DIY bike repair and learning about my own bike, but sometimes we need the experts. Good luck!
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