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Tubeless tyres have made off-road riding much better, allowing riders to benefit from lower tyre pressures and not suffer the annoyance of thorn-induced punctures. 

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Sealant is a crucial element of the tubeless tyre system, helping the tyre seal and reacting to any pinch flat or tiny puncture, filling it with the reactive sealant chemical reaction, solidifying that hole, and preventing a flat. 

When should I top up or replace my sealant?

For all the mountain and gravel tyre magic tubeless sealant brings, it has a lifecycle. Aged sealant starts to solidify, creating clumps within the tyre casing and ultimately preventing it from blocking holes caused by punctures.

Sealants should be replaced seasonally. A sensible timeline is every six months. Don’t underestimate the influence of CO2 inflation canisters on your sealant health. If you need to do an emergency trailside inflation using a CO2 canister, it will decay the sealant, unlike air. Always replace your tyre sealant after using CO2 emergency inflation to get home. 

However, many sealant manufacturers state service intervals and some may require replacement well before six months. Riding conditions and the environment can also have an effect on how long tyre sealant lasts before solidifying.

Although a number of brands offer dip-stick-like tools, you can tell whether or not you need to replace your sealant by having a look inside. If it's liquid, it's all good. If there's no liquid, it needs topping up. If the liquid is clumpy and clearly drying out, it needs replacing. Additionally, the interior of a tyre can be cleaned of dry sealant to provide a better surface for the sealant to seal against when punctured, and to shed the unnecessary weight of dry sealant.

How much sealant do I need?

That depends on the tyre size. Different tyre sizes require different sealant volumes. And in modern mountain biking, there’s a broad selection of casing sizes, covering everything from narrow cross-country specific tyres to trail-wide enduro and e-bike tyres. 

The most popular mountain bike tyre sizes are 29 x 2.3in and 29 x 2.4in. These are the tyres chosen by most UCI World Cup XCO and downhill racers. Sure, some riders might select 29 x 2.25in tyres for even lower rotational mass and rolling speed, but the 2.3- and 2.4in width casing sizes are what most riders depend on. 

Recommended sealant volumes for a 650b or 27.5-inch tyre are 60-75ml. For 29-inch tyre look at adding about 105-140ml, increasing a touch to 120-140 for downhill use. Of course, sealant has a mass, so the more you add, the more weight you're adding to your bike. For the weight-conscious, it's well worth consideration.

A tyre that's already had sealant in it won't need as much as a brand-new tyre, either.

The tool list

Whether using the syringe method or unseating the tyre and pouring sealant directly into the casing, the required tools for sealant top-ups are simple. 

We recommend a valve core removal tool, which is the best way of tighentin and removing the valve core without inadvertently creating damage. Tyre levers. A pump. And, of course, the sealant, whether it’s in a large container or a smaller bottle with a nozzle. If you’ve bought a large container of sealant, you’ll need a syringe. 

How it’s done

The simple workflow for a sealant top-up is valve core removal, sealant injection, valve core resetting and then adding air. An alternative method is unseating the tyre bead and pouring sealant directly into the casing before reseating and inflating. 

It sounds simple enough, but experienced mountain bikers and gravel riders have tales of woe, having dripped and smeared tyre sealant everywhere it wasn’t supposed to go. Or getting it inside the tyre casing but somehow damaging valves. 

The syringe method

This method will not work with any race-day-type sealants.

1. Remove the valve core

2025 sealant replace core remove.jpg, by Liam Mercer

Attach the valve core removal tool to the valve and rotate counterclockwise to remove it. To safely remove a valve core, we recommend releasing the tyre pressure before removing the valve. You can now access the tyre’s inner casing, allowing sealant to be poured or injected. 

2. Add the sealant

2025 sealant replace inject.jpg, by Liam Mercer

The most efficient, cleanest and least risky way to get the required volume tyre sealant into your tyre after removing the valve core is to use a syringe. Or the smaller sealant bottles or pouches with a valve-sized nozzle. Attach the syringe or nozzle to the valve and slowly pour sealant in. Don’t rush. 

3. Reassemble the valve

Once you’ve added the required volume sealant, gently extract the syringe or detach the bottle nozzle. Be careful not to spill any residue onto the valve structure. Now you’re ready to replace the valve core with the tool, turning it clockwise to fasten. 

4. Inflate and rotate

With the valve core back in place, you can air up your tyres. This is a rare moment in which inflating over your desired pressure can be useful, especially with a brand-new tyre and tubeless setup. Without a proper seal already established, air can escape and having a little extra pressure in the bank can help the sealant seal any holes or gaps.

2025 sealant replace inflate.jpg, by Liam Mercer

To ensure an even distribution of sealant, it’s also worth hand-spinning the tyre for a minute or two after inflating. You can also just pedal down the road for a minute to get the sealant to set. Once you’re done, air down the tyres to your ideal riding pressure, and you will be ready for the trails. 

The direct-pour method 

If you don't have a syringe, you can simply pop a portion of a tyre's bead off of the rim and pour in some sealant from there. This method can be a little messier than the syringe method, and you'll need to re-seat the tyre but it requires no extra tools than what you should already have lying around.

1. Release the pressure and free the tyre bead

2025 sealant replace lever.jpg, by Liam Mercer

To start, release the pressure from the tyre. Once the tyre has deflated, you can unseat or remove it. Often, tyres can be unseated by hand and initially, they will need to be to break the bead from the rim. From there, the bead can be pulled over the rim but if you're riding on tyres with strong sidewalls, a tyre lever will help here.

2. Add the sealant

2025 sealant replace pour.jpg, by Liam Mercer

With the tyre bead folded open, you can now pour some sealant directly into the casing. Or, if you want to avoid riding with a few grams of additional solidified sealant in your tyres, you can remove the entire tyre. Give the inner casing a proper rinse and wipe to remove absolutely all the aged sealant. Once your tyre is clean, refresh with sealant and get ready to reseat it. 

3. Reseat the tyre 

Whether you’ve removed the tyre to clean out and add sealant or just unseated part of the bead to pour in sealant, you’ll need to get those tyre levers handy again to reseat. With the open section of the tyre at the top of the wheel, to stop sealant from falling out, manipulate the bead back onto the rim, pressing with your fingers, and then use the tyre levers for the last inch or two of the bead, which is often the most stubborn, to complete the seal.  

2025 sealant replace gravel infalte.jpg, by Liam Mercer

Pro-tip - If you find that last couple of inches especially difficult to lift onto the rim, go back around the tyre and rim, making sure that both of the tyres' beads are sat in the rim's well, or the deepest part of the rim. This will provide an extra bit of slack that'll make the last bit easier.

Removing the valve core can make reinflation easier, too.

4. Air-up and spin 

Your tyre is now ready to be reinflated, and as with the syringe/nozzle method, you want inflate the tyre until the beads slip into the rim hooks. You'll know this has happened after hearing several loud cracks/pops and the seam that usually runs around the circumference of the tyre is an even distance from the rim.

Once you’ve seated the tyre onto the rim, give it a spin, which helps get that sealant a nice even distribution. After that wheel has finished spinning, readjust to your normal riding tyre pressures and you’re ready to go.

Sealant FAQ

Do valves matter? All mountain bike rim valves aren’t equal. Some are less likely to become clogged with tyre sealant and worth the investment. The traditional Presta valve has a proven design, but it’s had the same configuration and technical specifications for decades. And in that time, rim profiles, tyre casing sizes and the need for sealant have all advanced. 

There are many tubeless valves on the market that aim to improve on the traditional Presta design by reshaping its core, or removing it completely. Doing so makes for a more unrestricted flow of both air and sealant while reducing the chance of becoming clogged with sealant.

Many brands offer such valves with Reserve's Fillmore being prominent, as well as Muc-Off's Big Bore valves, 76 Projects No Clog Hi-Flow valves, and Stan's No Tubes ExoCore, just to name a few. All of these valves also provide improved airflow, making the seating of tubeless tyres easier than with regular Presta valves.

Sealant choice and sustainability

When choosing a sealant, riders must consider what tyre sizes and terrain they ride. If you are a dedicated endurance XC rider, you might only need a sealant that responds effectively to small holes. 

Downhill, Freeride and Enduro riders, descending technical trails with many square edge hits, severe rock gardens and exposed roots, should choose a sealant with molecules and chemistry capable of sealant larger punctures, especially sidewall gashes. 

Mountain bikers and gravel riders, by implication, are environmentally aware. You can’t spend all those hours riding pristine singletrack trails, through wilderness areas and national forests, without being taken by the sense of privilege and responsibility to tread lightly with your chemical legacy. 

Sealant is one of those mountain biking consumables with a legacy reputation for toxicity, either containing latex or ammonia, which isn’t great for the environment if you burp a tyre on trail, and sprat sealant all over a berm. If you ever need to do an emergency sealant top-up on the trail, after unseating a tyre, you want to use a bio-friendly sealant. 

Several brands now offer sealant formulations that are notably less harmful to the environment, without compromising their ability to seal your tubeless tyre and respond as intended to pinch flats and puncture risk. 

Many riders dread the sealant top-up process. It can be wildly messy and frustrating if you rush. But if you’re prepared, using appropriate workflow and tools, replacing your sealant to keep those tubeless tyres performing to their technical potential is quick and easy. 

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