Specialized has been granted a patent
titled "Simplified gas spring setup for a trailing link cycle wheel suspension," which relates to an air spring design for a linkage fork. The inventor is Dave Weagle - the same Dave Weagle behind dw-link suspension (among many other designs) as well as the Trust Shout
linkage forks which we've already reviewed. The design of the fork depicted in the patent is very similar to the two forks Trust developed before the company ceased operations in April 2020
, citing a lack of cash brought on by the coronavirus pandemic. The main thing which makes this patent so interesting is that the applicant is Specialized Bicycle Components.
According to Weagle, when Trust closed their doors an intellectual property portfolio was put together and then sold in order to cover the company's liabilities. That means Specialized now has the patent on the design Weagle created, and can implement it however they'd like, or even put it on hold until the right opportunity comes up.
While Weagle's name is on the patent, he's not involved with Specialized's plans at all, and wasn't able to shed any light as to when (or if) this design might hit the market. Given all of the time and effort that went into creating the original Trust forks, he said, "I'm just happy it didn't get completely mothballed."
The fork described in the patent looks a lot like the Shout and Message forks from Trust Performance.
Specialized have history of developing their own in-house suspension. Who could forget the 2007 Specialized Enduro
with its Specialized-branded shock and 150mm-travel dual-crown fork? Not to mention their Brain inertia-valve technology used in their cross-country bikes. So perhaps "The Big S" is planning on developing an in-house linkage fork based off of Weagle's designs. The Trust Shout and Message both showed potential, but had their faults, not least of which was the hefty price tag. Perhaps with the capital, scale and expertise of Specialized, the full potential of the linkage fork will be unleashed at a more reasonable price point.
As for the patent itself, the fork described shares a lot with both of Trust's forks. It's a trailing link design, meaning the axle sits behind the main body of the fork, and moves in an arc that curves back and then up as the fork compresses. This means that in the middle of the travel the fork offset is shorter than at the start of the travel, which results in greater steering stability (trail) when the fork is compressed. It's a four-bar linkage, which makes it possible to adjust the amount of anti-dive to help it resist compression under braking compared to a telescopic fork.
The fork has a damper in one leg, which sits below an air spring that operates in-line with the damper. A second air spring is housed in the opposite leg. The two springs mean the rider's weight is held up at both sides of the axle, which reduces the twisting force on the axle compared to a single spring. This is important given there's no arch to help keep the two dropouts from moving interdependently of one another, so if there was a spring in only one leg, the wheel would exert a twisting load on the fork chassis .
All the above is shared with the Trust Shout and Message, but the patent underlines that the springs in each leg are not identical. The unit containing a spring and damper is referred to as the shock absorber, and the spring in the other leg as the spring unit. The spring unit has a larger piston area than the shock spring. This is to increase the spring force on the spring-only side, compensating for the damper on the other side, which adds its own force depending on the compression speed. The idea is to make the forces more equal on both sides of the axle, at least at some compression speeds: "the first gas piston area (110) is less than the second gas piston area (111), which allows for a more equal force output between the shock absorber (44) and the spring unit (48 ), which helps to distribute forces more evenly in the linkage and avoid the detrimental results of angular wheel displacement."
Patent documents are written to keep the inventor's options open, but it sounds like the spring-only side will have around 25-30% more piston area, so providing that much more force for a given air pressure. "In some embodiments, the second gas piston area is between 2% and 300% larger than the first gas piston area ... In other embodiments, the second gas piston area is preferably between 15% and 100% larger ... and even more preferably between 25% and 30% larger than the first gas piston area."
Presumably, they could achieve this by increasing the pressure (by around 25-30%) in the spring-only side, but the patent focuses on ease of setup. The different piston areas balance the forces at the same pressure, so the user doesn't have to do any calculations. In fact, the patent suggests the piston areas could be fine-tuned so they offered the recommended spring stiffness when set to the same pressure (in psi) as the rider's weight (in lbs): "The disclosed simplified wheel suspension assemblies are designed to use a first gas piston area and second gas piston area that are sized so that when the suspension assembly is installed on a cycle, the gas pressure inside the shock gas spring 92 (for example when measured in PSI (pounds per square inch)) is equal to a recommended or predetermined pressure that produces an optimum ride for the user's body weight (for example when measured in LBS (pounds))". So for a 160lb rider, just inflate the springs to 160psi and go ride.
The patent goes on to claim that "The disclosed wheel suspension assemblies can be designed to be lighter in weight, lower in friction, more compliant, safer, and perform better than traditional wheel suspension assemblies ... [and] also reduce stiction and increase stability during braking, cornering, and shock absorption, when compared to traditional wheel suspension assemblies." These are similar to the claims made of Trust's forks, although the Message and Shout were a little heavier than their telescopic competitors at the time.
Finally, the patent suggests the fork may be particularly suited to e-bikes, so perhaps that's where the fork will end up, if we ever see it: "E-bikes are heavier and faster than typical mountain bikes. They are usually piloted by less skilled and less fit riders, and require a stronger front suspension to handle normal riding conditions... The beneficial caster effect described above with respect to the disclosed wheel suspension assemblies is an important improvement over traditional wheel suspension assemblies and reduces some of the drawbacks of E-bikes."
DisclaimerI haven't read or heard anything about this other than the patent documents themselves, so I don't know anything about it other than what I can glean from the publicly available patents. I've reached out to Specialized for comment and clarification but so far haven't heard anything back.