In this article, we’ll be discussing an Insert for a Pneumatic Tire by CushCore, US patent 10,787,043. The publication date is Sept. 29th, 2020 and the filing date is Jan. 11th, 2019. There are two other patents related to this insert, and all three have been granted as novel by the USPTO.
I want to make this clear; this isn’t a review. I do not own CushCore, nor have I ever used it. CushCore asked me to provide a technical article of the explicit legal design to you because they believe in the product and want you to understand the technical aspects of the design. It’s very cool to see a company not rely on marketers to sell a product because they’re confident enough to ask a third party to provide an unfiltered explanation of it. I honestly did not add or remove anything at their request; I just simplified what they’ve already told the USPTO. I know the bike industry maintains a pretty constant level of skepticism of product reporting. I’m hoping this helps.
Brief Summary (tl;dr)
CushCore have developed a tire insert to provide a lower operating pressure, improved damping, and a reduction in pinch flats. The shape of the insert is extremely specific and offers the designers and engineers a high level of tunability. Items such as material, shape, width, lobe size, and indent size can all be adjusted by CushCore for different applications. The important part of their design is the fact that the uninstalled width of the insert is larger than the tire itself. This means there is always an outward pressure being applied to the tire, providing support at lower pressures, affecting damping of the tire, and affecting the prevalence of pinch flats.
A tire insert is a device that goes inside a tire to improve the overall performance of the tire. The insert can affect the ride quality, grip, and rolling resistance – among others. The idea isn’t new. The earliest design that I could find for a tire insert dates back to the 80’s, but I’m certain they existed before that.
Tires have an inherent K-value (spring constant), meaning a tire with only air will act similarly to a spring. Without something to dampen the forces on the tire, there will always be a sinusoidal effect of a tire. The tire itself will inherently absorb some of the effect, but not all of it. Take a look at any huck-to-flat slow-mo video and you’ll see the suspension doesn’t compress linearly — they move in steps. No, it’s not the damper, it’s a function of two different springs with two different spring rates attached to each other. If you’ve ever been on a rigid fat bike, you’ll also know the feeling I’m talking about.
For some background physics, in a car tire damping simulation study by Elsalam et al. from 2016, they concluded that:
…car tire damping coefficient is one of the most effective parameters for the displacement amplitude of the suspension system, having a positive effect on the results, thus always decreasing the amplitude of sprung and un-sprang masses on the suspension system.
With all the money we spend on our suspension, why would we ignore the obvious drawbacks to having two giant springs attached to our bikes? Even more importantly, how the hell do you dampen a tire? Well, CushCore have developed an answer.
I’m typically very suspect of subjective reviews. I’ve spent a lot of time doing research and development in the racecar world, and the number one variable to eliminate is the human. We’re a completely unpredictable species that can be influenced by any number of subconscious factors, which can lead to garbage, subjective results. All in all, we suck for proper testing. That being said, I’d like to quote some lines from a third-party objective study of CushCore’s inserts by Motion Instruments.
The fork up and down movement decreased by 15%… overall vibration was reduced by 10%… in every stroke range, the number of compression strokes were reduced, in some cases by 50%… the top compression speed we noted was also reduced by 15%.
Though Motion Instruments say they retested with more riders on different bikes and got similar results, the proper next step is to have another third-party peer review to confirm the results; but this is a great indication of the actual performance of CushCore.
There are three patents that cover their design. In short, the novelty of all three is the use of a material (foam, rubber, doesn’t matter) that takes up 80%-90% of the volume of a tire and applies an outward biasing force on the inside of the tire. The outward force is extremely explicit to the novelty of these inserts.
FIG. 3 shows some width variables. The WAM value is the preinstalled width of the insert, shown by the dashed lines. The WPT is the interior surface width of the tire. The WAMM value is the installed width of the insert inside the tire. I want a WAM! sticker.
This is obviously exaggerated, but the idea here is that the preinstalled insert WAM width is wider than the tire width WPT. As a result, the insert provides a preloaded lateral force against the interior surface [of the tire]. This is key to the CushCore design and should provide much of the desirable damping characteristics.
In FIG. 1, they show a traditional underinflated tire set up, and have a good explanation of the current drawbacks to this system. This would be analogous to a tubeless setup that most of us probably run. The vertical lines signify the distance-from-center of certain parts of the tire under lateral load.
[As shown in FIG. 1, at lower pressures]… upon introduction of a lateral loading force (arrow 14) to an underinflated tire… the tire may deflect laterally…. The resulting lateral instability of the sidewalls… can reduce torque transmission, accelerate tire wear and fatigue of the tire, result in a rapid depressurization condition or blowout, or worse, reduce steering responsiveness, potentially putting the vehicle operator in a state of peril.
[at higher pressures]… reduced traction at the tread and stiff performance of the tire assembly [may occur]…
So, if you’re tire pressure is too low, you’re going to have issues with acceleration/braking, tire wear, or perilous blowouts. If you’re tire pressure is too high, you’re going to produce lower traction and higher stiffness, leading to sick skids and pumped arms.
CushCore also state a very concise advantage to this system:
A benefit of at least one of the embodiments described herein is the ability to pressurize the inflatable bladder [or tubeless tire] to a lower pressure than typically allowable. Unlike with traditional tire assemblies, [our tire] can operate with lower internal pressures while maintaining sidewall rigidity.
Therefore: To increase traction and soften vibrational harshness, internal pressure within the tire can be reduced, or kept at a relatively low pressure.
FIGs. 2 and 4 show the primary idea of CushCore’s system. Component 106 is the tire insert and component 116 is a tube. As we all know, this system works equally well with a tubeless setup. In fact, they explicitly say this system will work with a tubeless system. Either way, the tire should perform similarly with or without a tube.
The tire assembly may include an inflatable bladder pressing outward against the tread and sidewalls… or operate without the inflatable bladder, rendering it tubeless.
CushCore are opening the possibility to different profiles of the insert down the road. If they can confirm a better performing shape, they’ll probably use it.
…the contact interface 118 between the [insert] and [the tube] can be contoured. More particularly, the contact interface 118 can be ellipsoidal, polygonal, arcuate or concave. Figure 4 shows the concave shape.
They also give another example of a configuration of their insert. They say the insert and the tube can be attached to each other, using something like adhesive, crimps, or ties. I would assume this could be good for racing, to keep everything nice and tight inside the tire.
…the [tube] may be secured to the [insert] at one or more locations along the contact interface 118 by an adhesive… crimped over a portion of the [tube]… or a hook or a line.
FIG. 6 shows a cross-section of the insert. This appears to be similar to the currently offered product. The indent in the middle of the insert (component 136) is very important to the mode of actuation. The indent is what creates the lobes.
CushCore offers a lot of information about the advantages of the lobes; such as the constant outward pressure to the tire:
…the lobes 132a and 134a can deflect as illustrated by dashed lines 132b and 134b. The lobes 132b and 134b may provide an outward biasing force against the interior surface 114 of the tire 104. During operation, the lobes 132b and 134b may flex, or move, relative to each other such that constant, or nearly constant, outward force is applied against the interior surface 114.
Avoidance of pinch flats:
…the lobes 132b and 134b can maintain 40 contact with the interior surface 114 during flexing of the tire sidewalls 108 and 110. This can improve performance of the tire 104 and prevent occurrence of pinch punctures with the rim 102.
…the indent 136 may allow the lobes 132a and 134a to more easily flex inward…or may be triangular, quadrilateral, a combination of straight line segments, a combination of arcuate line segments
The way I’m reading this is CushCore have developed a creative method (among others) to tune the insert by adjusting the indent to allow more or less flexure of the lobes, depending on the application. Are we already seeing this on the current products?
As far as the material goes, they have a shit load of possible options that I have no interest in copying here. In short, they’ll use some kind of elastomer/polymer material that can provide adequate lateral forces on the tire, while also being resilient enough to take a hit and rebound quickly enough for the next hit without packing down.
CushCore have a statement on the hardness of the material. They say it can be between 10 and 100 on the Shore 00 durometer scale. The Shore 00 is used to measure the hardness of soft rubbers and gels. For reference, a gummy bear is about 10 and a tire is about 95 on this scale. This means they can use a large range of hardnesses based on the application of their insert (if needed). I’m not sure what they’re using right now.
The last item is the valve slot. FIG 7 shows a top view of a part of the insert with a slot and FIG. 8 shows the same slot from the side. This is used to assist with inserting the valve during the installation of the insert.
…the use of an opening 702 including a slot 706 extending from a linear passageway 704 may reduce installation time while allowing more favorable angular positioning of the valve stem, thus reducing potential damage to the inflatable bladder and valve stem.
The slot 706 may permit temporary storage of the valve stem during installation, after which the valve stem may be reoriented perpendicular to an external surface of the rim and through the rim opening.
I read a lot about CushCore having a tough installation process. I’ve never installed one so I don’t know. The novelty of the width being greater than the tire width may have something to do with this, but that’s the trade-off. I run DH tires on all my bikes (like an idiot) for security. The obvious trade-off is the terrible installation process and tons of broken levers. It’s hard to develop something with all the benefits and no drawbacks.
In the end, CushCore have designed an insert that has a high degree of tunability. The material, shape, lobe size, indent size, and width allow their insert to have a lot more technical advantages than just a reduction in pinch flats. As far as I can tell, it’s been race proven for a few years now and that’s really all I need to convince me. If it’s raced, it’s probably worth a shit.
Thank you for reading and thank you to CushCore for allowing me to write this for all of you. I hope you learned something today.