Using Sealant In Your Tires

Tire sealant is a big topic for those trying to understand what can be done to help prevent flats.

5/9/20235 min read

I hear the same story, over and over. A friend encourages another friend to go mountain biking, and the person new to mountain biking discovers the one thing they didn’t think to bring. A tire repair kit! Almost always, the friend who made the invite has one, and gets them back on the trails in nothing flat (pun intended).

Tire sealant is a big topic for those trying to understand what can be done to help prevent flats. Sure, there’s other methods, like solid core tubes, Kevlar reinforced tires, and flat guard inserts, but none of them have both the cool and ick factor at the same time that sealant does.

Sealant comes under many different names. One of the most prominent ones is slime®. Yep, that’s a registered trademark. According to the Wikipedia history of the product, Steve Cegelski began making the product by hand with a power drill and drywall blade in his garage. (I just keep thinking about all the inventions that start in garages! I need to spend more time in mine…) Steve focused on aiding local mountain bikers and his product was often referred to as “that green slimy stuff.” The name slime® stuck. The neon green coloration is readily visible on many shelves at many different locations. In fact, it's so ubiquitous that it’s not uncommon for mountain bikers to call any sealant slime®, but to be correct, referring to all sealants that way is just like referring to tissue as Kleenex, or a copy of something a Xerox (bet that just aged myself). Bottom line is that slime® is just a brand of sealant, not all sealants.

Most sealants operate on the same design principle. Sealants are composed of fibers, binders, and proprietary clogging agents that basically squirt out a newly made hole and rapidly fill it with fiber to clog the hole. It prevents the escape of air, and in doing so, prevents flats from happening as the puncture occurs. It requires the tire to be under pressure, of course!

When purchased in bulk (like we do at Ridgeline Bike & Ski), we can get sealant in such large volumes, that even parceling it out at a marginal profit is cheaper for our customers than they can get a bottle of it, on their own. And as an added bonus, if you’re bike is already in the shop, you don’t have to mess with it. Just ask us and we’ll get ‘er done for a nominal charge.

Tire sealants aren’t perfect though. There’s a bit of lag time between when you start spinning the wheel and when it’s fully distributed through the innertube. Gravity rules, of course, and when the wheel stops, the sealant eventually pools again at the bottom of the tube. In practical terms, this results in a bit of a thump-thump-thump or a wobble when you initially start riding. The weight is not evenly distributed. But also in practical terms, it doesn’t take very many rotations for it to distribute throughout the tube. The amount of sealant required depends on the tire size. This usually amounts to between 4-7 ounces per innertube. For example, a 26” x 2.3-2.4” tube will take about 4-ounces, whereas a 26”x3.0” tube will take about 7-ounces).

The sealant is added through the valve stem, but only AFTER the core is removed. Trying to install sealant though a valve core is a losing battle, and is likely to goop up the valve stem core. Don’t try it. Remember it’s designed to fill small holes! Remove the valve core and push the stuff in while the innertube is unpressurized. This can be done with a bottle and tube (that goes over the valve stem), or with a pump system (like we have at Ridgeline Bike & Ski).

One of my friends, Jerry, has a great story about tire sealant.

Jerry was down in Utah riding the Mill Fork Canyon Trail and returning to their base of operations in Grantsville. His group had finished the mountain trail run and was riding back to town and decided to cut across a large section of open ground to save some time. This was just open land with sparse scrub bushes. He always laughs when talking about the event, because at the other end of the scrub, he noted his tire looked funny. To their horror, he and his biking buddies discovered the scrub area was basically filled with goat heads.

This is a picture of the ominous goat head, otherwise known as the seeds of Acanthospermum hispidum. The image is from the USDA-NRCS PLANTS database. It’s pretty obvious where it gets the common name, “goat head.”

This seed is the bane of all innertubes (and feet) everywhere! Jerry said it looked like his tires had a sweater on. All three of the bikes in the mountain biking party had sealant in their tires, and not one of them had lost a significant amount of pressure, yet. He said they stopped when they got to pavement, and figured they’d have to replace the tubes. While they found that many of the goat heads hadn’t penetrated through his Kevlar tires (another reason to get quality tires), dozens of them had. They would just remove the goat head, and give the wheel a spin. He had to pump it up to keep the pressure high, but he said the tube never needed replacement. In fact, he says the tube lasted another season. Not one member of the party was slowed up, other than the remove, top off the air, and go. He noted he finally changed the tube, it had well over 50 punctures that had been filled.

I should note this is an exceptional experience in my opinion. Not everyone’s experience will be 50+ holes filled! Sometimes, the punctures are too big to fill. Sometimes the puncture is in a location the sealant struggles to fill (like on the sidewall), and sometimes the object just repeatedly keeps nailing the tube (it’s why we remove and check the inside of tires when there’s a flat!) And sometimes… (another pun coming) the poor innertubes just can’t handle the pressure.

The sealant that cost a few bucks probably saved him multiple innertube replacements, many flat-fixes, and kept him riding when he normally wouldn’t have been able to. Overall, Jerry’s story is an excellent example of why so many mountain bikers choose to include sealant as part of their strategies to deal with punctures.

When I told him I was writing this, he suggested I include the fact that even though he had sealant in his tires, he also still carried a full repair/replacement kit on him, because it’s just smart. I agree. In the end, though, all he needed was the portable tire pump to top off the tube.

It’s about the best story I can come up with on why the investment is worth it. If you’ve got sealant in your tires, and you’ve heard the hissss and following FFfffftttt.T.., as the hole seals up, you know the investment was worth the few bucks.

Tire sealant. Sure, it’s a bit messy… but it’s good, and the next goat head you meet is less likely to ruin your day. Visit us online @ or give us a call for anything you may need!