Tubeless Tire Insert by Fox

In this article, we’ll be discussing a Tubeless Tire Insert by Fox, US publication 20210252918. The publication date is Aug. 19th, 2021 and the filing date is Feb. 11th, 2021. This hasn’t been granted yet.

Brief Summary (tl;dr)

Fox appears to be getting into the tire insert game. This system has an explicit feature, where the insert must be a certain diameter during installation and another diameter after installation. So, there will be a ‘positioning system’ in all the examples, which changes the diameter of the insert. For example, Fox say this insert can be made of a ‘shape memory material’ (among other methods), like a memory foam mattress. I think this one will be the actual product. This would allow easy installation because the insert should be big enough to stretch and slide onto the rim and into the tire. Then, the foam will set/expand and fill the area inside the tire. If it’s anything like a memory foam mattress, it could take like 24 hours. An explicit goal of this type of system would be to help seat the beads, due to the outward pressure from the insert after installation of the tire.


Tire inserts have been around for ages. Here’s one from the 70’s by The General Tire and Rubber Co. I’m not sure if this is the first, but it’s definitely way back. Along with the foam or rubber inserts, there are also pneumatic inserts used in some race cars (NASCAR).

The goal of the vast majority of tire inserts is to prevent flats. But, as we learned from the CushCore article, there are other advantages such as lower tire pressures and improved damping characteristics. After riding on some CushCores for a few months now, I can’t recommend them enough. Yes, the installation process is tough, but that’s part of the novelty and what lends them to be so good at damping.

Other companies such as Huck Norris (left), Tannus (right), Vittoeria, and others are in this market with their own variation of this idea. All of which present new methods for the same idea, aiming to prevent flats and help ride quality.


It seems as though Fox are now entering this market. I was actually really surprised to see this come across my computer since I’ve never seen anything related to a tire in their business structure. They currently own Race Face, Easton, and Marzocchi (source), but this is a business (pretty good one, too), and they see an opportunity. Someone at Fox thought they could make a better tire insert, so they’re going to make it. With their manufacturing power and technical expertise, there’s no reason for them not to try to make some money with it.

Intended Novelty

This isn’t granted, but the intended novelty appears to relate to the ‘mean inner diameter X’ when the tire is being installed on the rim and a ‘mean inner diameter Y’ when the tire is installed on the rim, where X is greater than Y. This is shown to the left.

In other words, the novelty (with all the examples) appears to be a two-step procedure, where the insert has a certain diameter (X) during installation and another diameter (Y) after installation. The diameter is measured from the axle centerline.


Fox don’t like the installation process of currently available inserts.

Fox say:

[Some] inserts can significantly hinder the installation of the tires on the rim. One of the problem a user faces during the installation of the tire on the rim, with a conventional insert, is that when a first tire bead has been inserted in a bead well of the rim, and the insert has been placed on the rim, the insert obstructs the bead well and it becomes incredibly difficult to insert a second tire bead into the bead well and thereby to position the second tire bead onto the rim bed between the sidewalls of the rim.

As a result, the objective is:

The solution revealed herein provides an insert that provides anti-puncture and rim impact protection, allows for installation of the tire on the rim in a more convenient manner, and has sufficient shock absorbing and tire bead retaining characteristics if the rider would need to ride on an otherwise under inflated or flat tire.


First, FIG. 2 shows a very high-level installation process of the insert. The first thing I noticed, and probably you too, is the white thing inside the wheel. After reading it over and over, it looks like this is just a very interesting way to define different diameters or a diameter path. I’m not really sure what’s going on with that. Ignore it.

Anyway, one bead goes into the bead well, and the insert 220 is placed inside the tire. The other bead is placed into the bead well, and you’re good to go. The insert will then change from diameter X to diameter Y, which we’ll talk about next. Fox say this change in diameter is a huge advantage.

As the insert is pressed into the rim bed, it exerts a force on the beads of the tubeless tire. This force causes the beads of the tubeless tire to form a seal with the rim bed.

Next, FIG. 3 shows a few examples as to how the insert will go change from X diameter to Y diameter, which Fox refer to as a ‘positioning system’.

First, I’ll start with what I believe will be the actual product, which doesn’t have any images. Fox say, quite a few times, that this material can be a ‘shape memory’ material. A shape memory material would be commonly known as memory foam, which is a viscoelastic material. These materials have properties of both (you guessed it) viscosity and elasticity. If you’ve ever pulled a memory foam mattress topper out of it’s packaging, you’ll remember that it takes like 24 hours for the foam to reach it’s final shape. They’re soft, and they can expand to many times their packaged shape.

In one embodiment, the insert 220 is a non-inflatable component formed from any of the following materials or combinations thereof: a foam material, a resilient material, a multi-cellular butyl material, a polymer material, a composite material, a multi-layered material, a shape memory material, a multi-layered material having at least one layer comprising a shape memory material, or the like, and/or at least a part of the insert is formed from a shape memory material.

So, here’s how I’m envisioning this thing. You’ll have a circular insert made of memory foam, that can be stretched/shaped to X diameter. This should make it super easy to install. You’ll install it like normal and wait some time. By then, the insert should expand and fill the inner bead area. As a bonus, this should also help seat the beads due to the outward pressure on the bead. I’m fairly certain this is the process shown in FIG. 2, above.  

Alright, let’s talk about the other examples. The figure is a little confusing, so I boxed the corresponding pairs. 350 and 355 are together. 360 and 365 are together. And 370 and 375 are together.

In 350 and 355 (red), the position system 315 is a wire or cable, which is tightened after installation. So it’ll go from X diameter to Y diameter. Note the blue circle; that’s the change in diameter. Fox say the position system includes an adjusting device, which can be:

…a spool or a cord lock, a rotating bolt, or any other suitable device, which allows the user to adjust the positioning system 315 and thereby force the insert 220 to contract and reduce its mean inner diameter… [and] one or more systems, such as handles, stoppers, ratchets, nuts, and others, which facilitate adjusting the positioning system 315 and reducing the mean inner diameter of the insert 220…

In 360 and 365 (green), the position system 320 is a pneumatic system. Fox don’t go into much detail about this one, but it sounds like you’ll take the air out of the enclosed area 320 and the insert will tighten inside the tire. Strange one.

Lastly, examples 370 and 375 (purple) are another strange one that Fox don’t go into too much detail. The little fork-looking thing is attached to the external valve. You pump the tire up, then you deflate this little fork thing and the piston (flat thing) sucks the insert toward the bead.

FIG. 4 shows the final idea. This one is simple. The insert is placed in the tire, the beads are set in the bead well, and while the tire is not inflated, you would push the insert down to lock into the ‘stand off element’ 340. I actually kind of like this one. I’m assuming this thing can be adhered to the rim, but they do say the stand off element can be ‘integrated’ into the rim.

Fox have another example, not shown, where the insert will be placed using temperature or a magnetic field.

The shape memory actuated positioning system is actuated to change the mean inner diameter of the insert 220 by applying external heating or electric resistive heating, or applying a magnetic field to the system.


I have not used anything other than CushCore, so I can’t compare this process to anything else on the market. But, if nothing already exists with the use of viscoelastic foam, I think Fox may be on to something. Remember, it is 100% my assumption that they’ll use this type of foam. It’s entirely possible they’ll go with another type of diameter-changing system.

The only issue I see with using any memory foam material is the fact that it ‘memorizes’ its shape. So, if you were to be slamming through a rock garden and you just happen to hit the same spot twice, the second hit could have a higher chance of damaging the tire, since the foam is will already be deformed. But, that seems highly unlikely. There are a lot of different viscoelastic chemical compositions, so the project is to find a balance of installation/energy absorption/outward pressure/etc.

With the other methods, the foam would probably be something similar to what the other companies are using, so this wouldn’t be a problem.

As far as installation goes, this could be great. Seems pretty straight forward. I can’t speak on how the impact absorption would work for any of the methods, but I’m sure Fox would have it sorted out prior to a public release.

Cool stuff.

8 thoughts

  1. just asking as I know almost nothing about it except that it works in my knee pads, but is there a reason D3O isn’t used as an insert material?

    1. “D3O uses patented and proprietary technologies to create both standard and custom product solutions”

      Sounds expensive. What’s the price per running yard?

  2. no idea on cost, was just referring to the material itself as it’s a common and popular impact material.

  3. They seem to be trying to achieve very broad coverage with the X greater than Y claims, but these would seem to be in conflict with other prior patents in the field,

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