In this article, we’ll be discussing a Bicycle with Suspended Crank and Saddle by Specialized, US Patent 10,689,048. The publication date is June 23^rd, 2020 and the filing date is Jan 22^nd, 2018.

This is a really cool idea for compliance on a road/gravel bike.

Brief Summary (tl;dr)

Specialized are introducing a suspension system for their rigid bikes. A floating seatpost is attached to the floating crank assembly, which is then attached to an internal shock. When the rider hits a bump, the seatpost and crank compress, and the rider gets a nice comfy ride, while also preserving the seat-to-crank length.

Background

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 (left), and Canyon has a compliant stem system (right), 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.

In the case of this application, Specialized aren’t explicitly leveraging compliance like these other methods, but the goal is the same. They want a nice comfy ride.

There are also some bolt-on methods in the market to reduce fatigue. Cane Creek’s Thudbuster is a seat post that has some linkages and an elastomer/rubber piece to absorb impact. If the Thudbuster is anything like the quality of their suspension, it’s probably a solid piece.

Intro

Specialized are introducing another road bike/hard tail compliance system where the seatpost is connected to an eccentric crank inside the frame. The seatpost and crank are floating bodies which are then attached to a small internal shock located inside the downtube. So, as a rider goes over a bump, both the seatpost and the eccentric crank move to allow for a more supple ride and the seat stays in a relative position to the crank.

Additionally, Specialized have another, simpler, design that solves the same problem with a slightly different variation. This system has a floating seatpost and crank attached to an external shock, and a small link attached to the downtube. This system shows a front derailleur, which may be the reason for this design.

Intended novelty

The intended novelty is pretty simple here. The seatpost is attached to the crank, and the crank is attached to a ‘spring mechanism’ that biases the system in an uncompressed state. So, the seatpost and the crank are all moveable relative to the frame itself. Wild shit right here.

Why

Specialized don’t have an explicit problem statement, but it’s pretty obvious. Their intent is to reduce fatigue so a rider can remain more alert and fresher throughout long rides when using a rigid framed bike. 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 this new system.

What

Figure 2 shows an exploded view of the first example of this idea. We’re focused on seatpost 60, links 64, and the entire eccentric crank assembly 72.

Figures 3 and 4 show the top of the seat tube. The seat tube is larger than the actual seatpost, because the seat tube doesn’t move perfectly up and down; it actually moves down and back during compression. Figure 3 shows the seatpost in an extended state (no bump) and figure 4 shows the seatpost in a compressed state (bump). The seatpost is attached to a simple linkage 64 to keep everything in line.

Figure 5 shows an exploded view of the eccentric crank assembly. Notice the two eccentric plates 76. These openings 80 in eccentric plates 76 are where the crank is located. The bearing housing 84 accepts the crank axle and also provides the connection between the crank assembly and the seatpost. Bearing housing 84 (holding the crank) is housed inside the bottom bracket 62, and they’ll move in sync in an eccentric movement around A1.

Movement of the moving bottom bracket 62 is controlled by an eccentric assembly 72 that guides movement of the moving bottom bracket 62 along an arcuate path.

Now comes the important part. Notice (fig 5) how the eccentric plates 76 have two little holes? Those holes allow the clevis member 92 to mount to the eccentric part of the crank, and the clevis member then attaches to the shock.

…the clevis member 92 provides a connection point between the eccentric assembly 72 and a spring assembly 96 that provides a biasing force on the eccentric assembly 72 in a clockwise direction… This clockwise bias to the eccentric assembly results in an upward bias on the moving bottom bracket 62 and moving seat tube 60.

Figures 6 and 7 show the system in action. Figure 6 shows the seatpost and crank in an extended state, so no compression action. Figure 7 shows the seatpost and crank in a compressed state, so going over bumpy terrain. As the weight of the rider compresses the crank assembly, the whole assembly rotates eccentrically and compresses the shock. Pretty fucking cool.

Specialized also have another example of a simpler system that accomplishes the same goal, without an internal system. In this case, the shock is external and is attached to the seat post and downtube (chainstay?), and the seat post has a bottom bracket on the bottom end. As the rider hits bumps, this system moves via link 126, and the seatpost and bottom bracket move up and down.  

…movement of the moving bottom bracket 124 is not controlled by an eccentric assembly, but rather by a lower link 126 that pivotally connects a frame clevis 128 on the main frame 112 to a crank clevis 130 on the moving bottom bracket 124.

In this example, they have a front derailleur that actually attaches to the moving seat tube to keep the derailleur and crank in place, relative to each other.

Because it is preferred to have the front derailleur 142 stay in position relative to the crank assembly, the front derailleur mount 140 is secured to the moving seat tube 122 using threaded fasteners (not shown) threaded into threaded holes 144 in the moving seat tube 122.

Figures 9 and 10 show the movement during compression.

Conclusion

Obviously, weight is a concern here. The addition of a long-ass seatpost, a complex crank assembly, and an internal shock will definitely add weight, so this invention probably isn’t for the people counting grams. Rather, will be for the weekend riders, maybe older folks that don’t want to break their backs every time they go out. Even more so, this looks like it’d be amazing for the gravel crowd. I’m also interested to see if the first system would work with a front derailleur. Hmm…

I’m also wondering what kind of shock they’ll put in there. If I’m a betting man, and I am, I’d say they’ll put something similar to the tiny shocks they have on their Epic.

I actually think this is awesome and I’d love to see this made. Whether you like specialized or not, they’ve got some of the best designers and thinkers in the biz. And for those of you constantly shitting on Specialized for their legal history; they’ve got every right to protect their employee’s ideas. In the end, Specialized aren’t coming up with these inventions; it’s the engineers, designers, and fabricators. These are normal people, just like you, that spend months and years developing an product, process, or appearance. These big companies want to protect their employee’s ideas, and the employees want their ideas protected. If you had a new invention, wouldn’t you want your company to protect it?