One look at the new Specialized Diverge STR may make you scratch your head. The showpiece of the bike is a new rear suspension system that uses an exposed aluminum “string” to connect a flexible frame post to a damper in the top tube.
The design is called Rear Future Shock and is intended to “hang” the driver. It reduces saddle vibration while maintaining the bike’s rigid “Double Diamond” frame and consequently the acceleration and handling you’ve come to expect from many of the best gravel bikes.
Chris D’Aluisio, one of Specialized’s concept engineers and the man behind the brand’s Smartweld technology, began working on the idea over five years ago by hand-prototyping at home.
D’Aluisio’s prototypes show how Future Shock Rear came to be and offer a rare glimpse into the work, breakthroughs and dead ends behind the design of a bike – something you’ll rarely see.
Origins and the first prototype
Chris D’Aluisio first came up with the idea of ”hanging” the rider over the frame of a bike in 2014. As he rode down Eureka Canyon near his home in California, D’Aluisio realized his body provided the suspension he needed; He was able to stay above the bike and the bumps beneath him were no longer a problem.
This realization led to the development of Specialized’s Future Shock, which debuted in 2016 on the Specialized Roubaix, which won Bike of the Year.
The design isolates the cockpit and protects riders from impact at the front end of the bike.
The technology soon found its way into the first-gen Diverge in 2017, with Specialized relying on a compliant seatpost and a dropped seatpost clamp to absorb rear-end bumps.
This design worked for small bumps, but Specialized says it needed more deflection for rougher terrain to keep riders in the saddle and thereby gain more traction and power.
D’Aluisio says the way to get around this problem was to create a design that shifted the rider’s weight in a front-back-down curve, rather than up and down like typical telescopic suspension components in the case is .
That’s the thinking behind the first Diverge STR prototype. To achieve downward and backward movement, the bike has a seat post that attaches to the bottom bracket. A linkage sits at the top of the frame, the damping of which is controlled by a standard air damper.
The bottom bracket is attached to a separate linkage on the underside of the down tube.
“We wanted the bottom bracket to move down and forward to give a bit of chain growth so that when you get out of the saddle and start pedaling, the chain hangs you – [this prevents ] the suspension before compression,” says D’Aluisio.
D’Aluisio says the prototype worked well, but the bottom bracket in its own linkage meant the bike didn’t have the pedaling efficiency of a rigid frame that he desired.
A clean solution
D’Aluisio further developed the concept of the first prototype by introducing a rotating bottom bracket shell and hiding the air shock in the down tube of the frame.
D’Aluisio, who has worked for Specialized for over 20 years and was previously at Cannondale, says this home-made prototype is his favorite bike he’s ever designed because “it did everything I wanted it to do” and that it “so effective”.
Others at Specialized appreciated the cleanliness of this prototype. The brand decided to try the design in sizes larger than D’Aluisio’s 52cm frame, but this revealed limitations.
“The 56 cm [frame] Feedback was good. But with the 58 the feedback wasn’t that good and there were some questions as to what was going on. These riders didn’t feel like they benefited from the saddle,” says D’Aluisio.
Taller riders liked the design when seated, but not when out of the saddle. D’Aluisio says of the larger frames that Specialized had inflated the air shock “so much to try to accommodate the rider’s needs in the saddle that the bottom bracket was out of phase”.
This led to a build-up of stiction—the friction that can prevent static surfaces from moving—and meant the bottom bracket didn’t move on taller riders.
D’Aluisio says this prompted him to push the seat tube idea and abandon the rotating bottom bracket as much as he found the performance on the 52cm frame.
He also says that this design with the air shock was too complex and Specialized could never make it on an industrial scale.
Squint and it looks the same
Abandoning the moving bottom bracket and trying to simplify the design led D’Aluisio to develop this third prototype, which looks remarkably similar to the final Diverge STR design.
“If you squint, it looks the same,” says D’Aluisio.
The prototype has a flex seatmast with a Thomson seat tube attached to a damper in the top tube and a boot that keeps dirt and water out of the system.
The design also introduced adjustability that the old Diverge’s flexible seatpost didn’t have.
D’Aluisio says later versions of this prototype had tendons like those seen on the recent Future Shock Rear.
The bend in the tendon means the shock can be mounted in the top tube rather than requiring a pivot point, ultimately minimizing complexity, play and stiction.
The final design, so to speak
The next step for D’Aluisio and Specialized was to build a test model. Specialized has moved the pivot-free design in Diverge frames from 52cm to 61cm.
The version pictured here is a 2017 Diverge, from when the bike wasn’t even updated the second time around, showing how long this process has been in the works. It has the muffler but not the end string.
At this point, the project was a joint development, with the frames made at Morgan Hill, Specialized’s headquarters in California, and its factories developing the carbon layups for the bike.
Luc Callahan, Specialized’s Road and Engineering Lead, also began testing and developed 352 frame post samples over a three-year period. According to the brand, this is “the longest period of dedicated development for any single road or gravel technology.”
Fast forward to now
Fast forward to now and Specialized says the Future Shock Rear will deliver up to 30mm of travel in the down and back corner, which was essential from the start.
Callahan’s testing resulted in nine different frame posts to suit different frame sizes and rider weights.
The final version of the Specialized Diverge STR visually resembles D’Aluisio’s fourth prototype with its exposed string.
The look of the Future Shock Rear will likely divide opinions, but it may be worth getting used to.
When asked if we can expect to see Future Shock Rear on other bikes, Stewart Thompson, Specialized’s road and gravel guide, said, “It’s an innovation that we really believe in. If we find other uses and possibilities, we would go for it. ”
The design falls into the gravel chassis category for now, but we may see it on the cobbles of Paris-Roubaix in the future.
#Specialized #designed #Diverge #STR
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