Bicycle with Compliant Seat Post Interface by Specialized

In this article, we’ll be discussing a Bicycle with Compliant Seat Post Interface by Specialized, US Patent 10,902,592. The publication date is Feb 16th, 2021 and the filing date is April 6th, 2018.

These images are now copyrighted by me because they have a delicious glass of water in them, which I’m currently enjoying.

June 4th, 2021 Edit: A continuation was released June 3rd, 2021 under the Pub. number 20210163092. If you’d like to steal this article without citing me, you should use that one so I can’t bitch and moan.

Brief Summary (tl;dr)

Specialized are introducing another rigid-bike compliance system. The top of the seat tube is flared, and the flexible seatpost is really long and is clamped closer to the bottom bracket. The seatpost is then attached to a damper located inside the top tube. Since the seat tube is flared, the long seatpost can bend and is damped by the damper in the top tube. The seat post can be replaced with another seatpost with different characteristics for different rider weights.


We’re talking about compliance again. Stiffness is defined as the ability of a solid body to resist deformation by an outside force. The opposite of stiffness is compliance, where a specific amount of flexibility can be designed into a solid body. In a sold body, Finite Element Analysis programs such as FEMAP and NASTRAN allow engineers to design objects of a certain material and apply specific forces in specific directions to synthesize the flexibility properties of a solid object.

Compliance can influence the way a bike feels when ridden over rough or chattery terrain and can preserve your arms and legs from wear. If you’ve been on any long road or gravel ride, you’ll know how tough it can be on the hands, arms, and back. Trek have their IsoSpeed, and Canyon has a compliant stem system, among others, to try to solve this issue. Specialized have a few compliance methods already, such as the Future Shock, which appears to have mixed reviews.

I recently wrote another article about a wild suspended crank and seatpost from Specialized where Specialized are showing an idea for a seatpost that is attached to an eccentric crank, with a tiny shock inside the bottom bracket. When the rider hits a bump, the system compresses and the seatpost-to-crank length is preserved. They’re killin’ it right now. That’s one of my favorites, that I will likely never see.


Specialized are introducing yet another compliant seat post method for their rigid bikes with yet another tiny damper. This time, the seatpost doesn’t move vertically. Rather, the seatpost is clamped really far down the seat tube, providing a larger amount of leverage at the top of the seatpost. As the rider hits bumps, the seat post flexes rearward. There’s a damper inside the top tube to dampen the movement of the seat tube, and the opening of the seat tube is wider than the seatpost to allow for movement.

There’s also some other options where a bumper is placed inside the upper opening of the seat tube to adjust the flexibility of the seatpost. Specialized also state that the seatpost can be changed out for another seat post if the rider is lighter or heavier, to provide a more optimal ride.

Intended novelty

The intended novelty of this one appears to be the fact that they’re using a flexible seat post, an integrated damper in the top tube, where the damper is coupled to the seat post and the seat post clamp is somewhere around 30% to 55% of the total distance of the seat tube, measured from the upper end of the seat tube. Legal claims can be weird, sometimes.


Specialized have a problem statement in this one:

Bicycles designed for paved roads commonly have a rigidly mounted rear wheel, which is light weight and provides rear end stiffness that is desired by most serious road cyclists. In some riding conditions, such as when riding long distances or over rough roads, it would be desirable to reduce the amount of shock or vibration transmitted from the road to the rider. One way to accomplish this is to make the 15 rear end of the bicycle compliant, which facilitates absorbing of the shock and vibration. However, such attempts to make the rear end of a road bike compliant have commonly resulted in an increase in weight or loss of rear end lateral stiffness, both of which are undesired.

Their intent is to reduce fatigue so a rider can remain more alert and fresher throughout long rides when using a rigid framed bike while also trying to preserve a low weight. Anyone that has ridden a road bike on a rough track, or a gravel bike on anything off-road, knows the brutality that the terrain can do to the body. Hands hurt, ass goes numb, feet feel swollen. None of which are ideal for even short rides. They intend to solve this with a new system.


Figure 4 shows an exploded view of this system. Damper 52 is attached to the bike using 2 trunion-style bolts and is attached to the seatpost using clamp 54. This system is covered by a flexible boot to cover the top of the opening of the seat tube so garbage doesn’t get inside.

The boot 54 is made from a suitable elastomeric material, such as silicone. The boot 54… fills the space between the seat post and the upper end of the seat tube 24, thereby prevent intrusion of unwanted substances, such as water or dirt.

Figure 5 shows the system with no weight applied to the seat tube. The tube is clamped down at clamping location 38 and is controlled with the damper.

The illustrated damping member 52 is an oil-filled through shaft damper with a low speed rebound adjuster. It has bushings at each end of the outer tube so it can take side load from the seat post and it has a clevis mounting. Due to the 60 close fit of the end bushings, the damper provides lateral stability to the seat post.

Figure 6 shows the system in full flex. The seat tube is flexible, pulls on the damper, and provides a nice ride.

…the upper end of the seat post 34 can move (e.g., flex) rearwardly and downwardly to facilitate the absorption of shock and vibration travelling from the rear wheel 12 and through the seatstays 28.

Specialized state an alternative design that isn’t shown

It should be appreciated that instead of flexing the seat post could be designed to pivot or hinge relative to the frame. In such an embodiment, a biasing member would need to be used to bias the seat post toward the raised or unstressed position.

Is this cool? I just figured out I can do this. Not lined up perfectly, but shows what it’s doing.

Here’s an interesting line on how the seatpost can be changed for different riders. Specialized will provide different seat tubes with different characteristics.

It is envisioned that different riders might want different stiffnesses for the seat post (e.g., due to rider weight, riding style, or other preference). In this regard, the present invention allows the seat post to be customized to the rider’s preference by changing the material, thickness, shape, or other relevant characteristic to achieve a seat post with the desired dynamic performance.

Additionally, to compensate for different riders, a bushing can be placed in the upper portion of the seat tube, though this idea isn’t shown in the figures.

…in an alternative embodiment, the gap G between the seat post 34 and the flared portion 44 could be filled with a resilient bushing (not shown) to provide extra support to the seat post and resistance to flexing. In this embodiment, in the event that a rider perceives that the seat post 34 is flexing too little or too much, the bushing can be replaced with a softer or stiffer bushing to achieve the desired amount of flexing of the seat post 34.

Figure 7 shows the seat post clamp in detail. This is the part of the novelty where this part is 30% to 45% from the upper part of the seat tube. Attorneys will typically go into this level of detail to get an idea through by “adding claim limitations” to overcome prior art.


Specialized have yet another cool idea for frame compliance. I’m going to go ahead and say this one probably has a better shot at production than the last one. There’s going to be concerns about breaking the seat tube, extra complexity, wearing of the frame from the seatpost, and servicing proprietary stuff. I’m sure Specialized will figured most of that out.  

Whether it gets made or not, its still cool to see where these girl’s and guy’s heads are at. Having been in the research and design for quite some time, I bet it’s great working at this place. It looks like management aren’t afraid to spend the time and money developing out-of-the-box ideas. You want an aero water bottle attached to the frame? Done. You want your crank and seat to move at the same time on a road bike? There it is. How about a hole in your downtube to hold your weed? You got it.

Keep it up Spesh, you make my job easy.

2 thoughts

  1. Nice article! Regarding the seat tube matching with each rider type, in my opinion, going to this level of customization wouldn’t be profitable. They’ll prabably do a customer profile based on rider weight, seat height, fore-aft saddle position, ride profile and chose the case that covers 99%. Bushing can be a viable solution though.


    1. I agree that it would definitely add another level of complexity to production, but I can’t discount the amount of money people are willing to spend on their bikes. Hell, I just spent $80 on a seat that I didn’t need, but it was blue and I wanted it to match…

      Thanks for reading!

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