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How Tubeless Tires Work

December 3, 2018


How Tubeless Tires Work

Ready to say goodbye to flats? We’ll look at how tubeless tires work using a combination of tire design, rim features, and liquid sealant.

You might’ve read how a tubeless bike tire setup can help prevent punctures, allow you to run lower pressure, improve comfort and traction, and even reduce weight.

But, exactly how do tubeless tires work to provide all of these benefits? That’s what we’ll briefly explore in this article—starting with the core components.

How Tubeless Bike Tires Work: The 3 Main Parts

When it comes to setting everything up, there are a total of three main components that coordinate with one another:

  1. Rims
  2. Tires
  3. Sealant

Let’s zoom in and take a closer look at each one.

The Difference Between Standard, Tubeless Ready, and UST Bike Rims

When it comes to tubeless setups, rim design is where you’ll encounter the most variety. Still, from a high-level perspective, you’ll only come across three configurations:

Universal Standard Tubeless (UST) Rims

Released way back in 1999, this is the original tubeless clincher system co-designed between high-profile manufacturers like Hutchinson, Mavic, and Michelin.

The internal edges of each sidewall feature a patented hooked design that only seals with tire beads featuring the same shape. In other words, CST tires only work with CST rims, and vice-versa (see image on the right below).

Tubeless Ready/Compatible Rims

Tubeless-ready rims (center image below) implement a different hooked sidewall design than UST models, although it serves that same fundamental purpose—to lock the bead securely into place without relying on a tube.

These sidewalls are also typically higher than a standard rim, with a smooth “ramp” in the center that helps the beads slide up against the sidewalls with added air pressure.

In some instances, manufacturers remove the spoke holes from the interior of their tubeless ready rims. In others, you’ll need to cover them with special rim tape (more soon).

Speaking of which, tubeless ready rims typically feature holes that are large enough to accept aftermarket valves. With standard rims, you might have to pre-drill a wider opening to make everything fit.

We’ll return to both of these topics in a second. First, though, let’s compare these features to a regular rim.

Standard Rims

Taking a look at the standard rim’s cross section (below, left), we can see that its design is very similar to the tubeless ready version.

The biggest differences are that the standard rim’s sidewall is shorter and the flanges are rounder, which won’t create as tight of a seal. The ‘hooked’ design at the top of the sidewall is also less pronounced, and there’s no ramp in the center for easier bead installation.

Taking a look at each cross-section, we can see the design differences between standard (left), tubeless compatible (center), and UST (right) rims.

Tubeless Rim Tape & Rubber Strips

Tubeless ready models also typically feature wider rim tape that fully covers spoke holes, as well as creates an airtight seal between the beads. This isn’t just any tape, though, as it’s constructed of a durable, but pliable, material that’s resistant to the sealant.

When converting a standard rim to tubeless, some manufacturers also offer rubber strips with a pre-attached valve that could better promote an airtight seal; similar to an inner tube sliced in half down the middle.

On the left is traditional tubeless rim tape from DT Swiss, while Stan’s NoTubes (among others) offers butyl rubber strips and valve combinations (right) to help ensure fully sealed spoke holes.

Tubeless Valves vs. Inner Tubes

Valves are attached to inner tubes, which we’re obviously trying to get rid of here.

To address the situation, companies manufacture a variety of valves designed to work with tubeless setups. Typically, this involves a threaded Presta valve with a rubber gasket at one end, and a lock nut on the opposite side to ensure everything remains in place.

These valves also boast removable cores, which allow riders to deflate the tire and top off the sealant (more soon) when the time comes, without having to unseat the bond between the bead and the rim and repeat the process all over again.

Here, we can see DT Swiss’s tubeless rim tape in place, as well as the standard valve attached to the inner tube and the Stan’s NoTubes valve. The most significant distinction is that the latter features a rubber gasket at one end to create an airtight seal.

The Difference Between Standard, Tubeless Ready, & UST Tires

Tubeless or otherwise, bike tires feature one of two bead types: Folding, typically made from flexible Kevlar-based fibers, and non-folding, made from rigid steel wire.

Related: Your Visual Guide to Bike Tires

While mounting rigid beads might require a bit more elbow grease than their folding counterparts, most modern tires and rims can convert to tubeless with the right parts (e.g., rim tape to cover over spoke holes, aftermarket valve w/rubber gasket, and sealant).

How UST Tubeless Tires Work

However, with their patented sidewall and bead shape that’s designed to tightly lock together like puzzle pieces, UST tires take the cake when it comes to reliability. As the Park Tool site explains:

“Rims and tires must meet a certified standard to use the UST label. A UST tire will have a square-shaped bead to match the UST rim. Inside the tire carcass will be a butyl liner, basically inner tube material formed into the inside carcass of the tire body. This extra material does make the tire heavier compared to non-UST tires.”

In fact, this seal is so reliable they point out that riders can use UST tires on UST rims, without requiring any sealant.

How Tubeless ‘Ready/Compatible’ Tires Work

Compared to UST, many manufacturers advertise their tires as ‘tubeless ready’ or ‘tubeless compatible,’ although there are no overarching guidelines or standards for what this actually means. In other words, they’re merely marketing terms.

Related: How Bike Tires Are Made

As such, one manufacturer’s tubeless ready tires might feature a different—and incompatible—design with another’s.

Most manufacturers will indicate whether or not a tire is tubeless ready/compatible on the sidewall, as we can see here with the Panaracer’s popular Gravelking SK.

In general, though, the beads on tubeless compatible tires feature more pronounced edges than regular tires, to help it seat in the sidewall’s flange. They might also boast thicker, heavier casing rubber for added puncture protection.

Pro tip: This doesn’t mean that tubeless tires can’t experience flat tires, though. Instead, sharp objects are more likely to become stuck in the casing and cause it to deflate more slowly, thereby avoiding catastrophic failure. This also allows greater time for the liquid sealant to start plugging the hole.

How Tubeless Tire Sealant Works to Plug Holes

Last, but certainly not least, is the liquid sealant. Orange Seal and Stan’s No Tubes are two of the most popular brands found online and at local bike shops (although there are several others).

‘Micro-Sealing’ Particles

Each manufacturer’s sealant uses their own proprietary formula, although most implement latex as a base ingredient, along with some type of micro-sealing particles. In the instance of Orange Seal, they dub theirs ‘nanites.’

Whatever companies call them, these particles remain suspended in the sealant, quickly accumulate behind a puncture or tear as air escapes, and completely close it off within seconds. After the addition of air from a pump, this allows riders to quickly keep rolling.

Related: 7 Tips For Choosing the Right Bike Pump Model

Eventually, these sealants dry and harden against the inside of the tire, though, which is one way they’re able to prevent punctures in the first place.

This also means you need to re-add sealant to the tire on a regular basis. The removable valve cores mentioned earlier allow riders to accomplish this without unseating the seal between the tire’s bead and the rim.

Tubeless bike tire sealant starts out as a liquid and uses ultra-fine particles to quickly fill large punctures and tears (up to ¼” in the instance of Orange Seal above). Some of the sealant will also dry and form a snakeskin-like texture to further prevent punctures.

The Bottom Line About How Tubeless Tires Work

Now that we’ve looked at how the process works, we can see that setting up tubeless bike tires takes a bit more patience, know-how, and elbow grease than just throwing in a traditional inner tube and heading out the door.

However, the puncture protection it provides, as well as the time saved by not having to repeatedly change tubes on the side of the road or trail—in my opinion—makes the process worthwhile a thousand times over.

And, this is to say nothing of the decreased weight and the improved cushioning and traction enabled by the lower PSIs.

Keep rolling: 5 Essential Tips For Storing Your Bike Tires

Derek has more than two decades of experience as a cyclist, and is the founder of TreadBikely. He currently travels full-time with his family via RV, enjoying the country's best biking destinations. A secular Buddhist, Derek frequently explores the intersection of cycling, mindfulness, and compassion in his writing. #rolloutblissout
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