Checking and Adding Tire Sealant

By Jim Langley

Now that the nice riding weather has returned to the northern hemisphere and spring events have sprung, I want to cover a good question for this time of year from a Minnesota roadie, Dale, who asked awhile ago:

“They say that winter may end here in a few months. I switched to tubeless tires on my Trek Domane last season. Do I need to renew the sealant in them before I start riding again? If so, how do I accomplish that?”

Tubeless tires? Sealant? Huh?

To answer, let me backpedal a bit and explain to those who do not know that many road bicycles and wheelsets you might have or can upgrade to, have the option of running what’s known as tubeless tires. As the name suggests, these tires do not have tubes inside.

Why would you care if your tires had tubes inside? Two reasons: the most common flat tire is a pinch flat where you run over a rut, hole or object in the road and pinch your tube and flat. Pinch flats are sometimes called snakebite flats because they show up as two small slices next to each other on the tube – like a snakebite.

Since there’s no tube inside a tubeless tire, pinch flats become a non-issue. The other advantage of tubeless tires is a softer, more supple ride because you can run lower tire pressure since there’s no risk of pinch flatting.

On most bicycles and wheels, in order to run tubeless tires, you need tubeless-compatible rims and tires and a few ounces of sealant. Sealant is a liquid with some type of fibers inside (every manufacturer has their own secret sauce) that when you puncture, almost immediately find the hole and seals it from the inside of the tire so you can keep right on riding.

Better safe than sorry with sealant

So, Dale is asking if the sealant that was installed inside his tubeless tires needs to be renewed or if he can just keep riding with the same stuff in his tires. And, the answer is, Yes, it needs to be renewed. What that really means is that you have to add more sealant inside the tires.

The reason he needs to do this is because sealant dries out, and usually a lot sooner than an entire season. In fact, depending on the type of sealant you use and the conditions where you ride, you might need to add sealant as often as once a month.

The key thing to know is that if you’re not sure how your sealant is holding up, you want to check rather than assume that there’s plenty inside. Because if you assume, that might be the day your sealant fails, and if it’s an important goal ride, the resulting flat tire could be a very bad thing.

Checking sealant

This is a relatively easy job if you can suspend your bicycle or remove and suspend each wheel vertically. With the wheel in this position, any sealant inside will tend to stay inside and not leak out. But, if you care about your flooring, it’s still a good idea to put down newspaper beneath the bike/wheel to catch any that escapes.

Tubeless tires usually lock tightly when inflated, so it can take a little effort to free them from the rim, which you have to do to check the sealant and add more. To do it, let all the air out of the tire and then go around it squeezing the sides of the tire together to push the tire sides and beads (the part tucked down inside the rim) toward the middle of the rim.

You should feel the tire pop and break free. Once you’ve gotten it loose like this, work on it at 12 o’clock on the wheel with tire levers to carefully remove about six inches of only one side of the tire from the rim.

By working on the top of the wheel, any sealant in the tire stays in the bottom of the wheel and won’t spill out. Then, just slowly rotate the section of tire you removed down to the 6 o’clock position and you’ll be able to look inside the tire to gauge how much sealant is still inside.

If the sealant has been in there for months, you’ll probably find some alien-looking matter inside like a science experiment gone wrong – blobs or strings. And you’ll probably only find a little liquid. These things tell you that it’s time to add a fresh dose of sealant to your tires so that you can enjoy flat-free rides again. Before you do this, you can either clean out the debris and old sealant inside, or leave it if you don’t mind the little bit of extra weight and mess – and possible noises.

Adding sealant method 1

Read the instructions on your choice of sealant. It will tell you how much to install based on your tire size (usually 2 to 4 ounces/59 to 118 ml). Pour the correct amount of sealant into the tire. Then, carefully rotate the open part of the tire back to 12 o’clock again. The sealant will now run down inside the tire so it can’t leak out. And you can pop the tire back on at the top.

Now comes the tricky part: installing and seating the tire so that it holds air. Because there’s no tube inside, if the tubeless tire doesn’t seal/seat correctly it will just keep going flat.

As I mentioned, tubeless tires lock on during inflation and it’s this locking that seals them. With luck, because the tire has already been seated on the rim for awhile, you will be able to inflate it and seat it with your home floor pump (these are more powerful than pumps made for taking with you on rides).

A good trick is to go around the tire with a brush wet with soapy warm water to lubricate the beads of the tire to help them pop into place and seal as you inflate the tire.

Tip: If you can’t get the tubeless tire to seal with your floor pump, find a volunteer to pump while you put both hands on the tire and squeeze the tire down onto the rim as they keep filling it with air. Keep trying and move your hands to different positions where you hear air coming out, and in most cases, working together, you can seal the tire with your hands long enough that the tire stops leaking and fills up and seats.

Most tubeless tires make several reassuring pops or snaps when they seat fully, so listen for these. You always want to spin the wheel and look carefully at both sides of the tire, too. If you see any hops or wobbles, the tire isn’t fully seated. It needs to be seated fully or the air will leak out.

Adding sealant method 2

Another way to add sealant is to do it through the valve stem. Most tubeless systems have valve stems with removable cores. Simple turn counterclockwise with a core remover tool, or gently with pliers, to remove.

Once the core is out of the way, you can use your sealant injector of choice (a syringe-like device sold by sealant makers) to pump more into the tire.

Tip: If you have been using tubeless tires for some time and paying attention to how frequently you need to add more sealant, you wouldn’t need to remove the tire to see if you are low on sealant. And instead, you would simply remove the valve core andsquirt in more sealant as needed. Using this technique it’s more likely your tubeless tire will remain seated on the rim for easy inflation and seating.

Consider tooling up

Should you find it a challenge to inflate and seat your tubeless tires, and you already have a home shop or place you work on your bikes, you might consider buying an air compressor. They’ve gotten a lot less expensive over the years and they come in handy for a lot more than making tubeless tire inflation and seating easy.

If you don’t have room for a compressor, you might look into the Bontrager Flash Charger floor pump. This trick inflator has a tank just like an air compressor. You inflate it by pumping and, when full, it provides a powerful blast of air to seat stubborn tubeless tires.

Another handy tool is one you carry for road use. In the event that your sealant has dried up and isn’t working anymore, carry a flat fix like Vittoria’s Pit-Stop (about $15) and you can inflate and inject new sealant into your tire to fix a flat fast.

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Jim Langley is RBR’s Technical Editor. He has been a pro mechanic and cycling writer for more than 40 years. He’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Check out his “cycling aficionado” website at http://www.jimlangley.net, his Q&A blog and updates at Twitter. Jim’s streak of consecutive cycling days has reached more than 8,000. Click to read Jim’s full bio.