How Diverge STR . was designed
One look at what’s new STR . Specialized Variation It can leave you scratching your head. The look of the bike is a new rear suspension that sees a flexible frame shaft connected to a damper in the top tube, via an exposed aluminum “chord.”
The design is called the Rear Future Shock and is said to “suspend” the passenger. It reduces vibrations at the saddle while retaining the bike’s “dual diamond” steel frame and thus the acceleration and handling one would expect from many The best gravel bikes.
Chris D’Alessio, one of the dedicated concept engineers and the man behind the brand’s Smartweld technology, started working on the idea over five years ago, making in-house prototyping.
D’Aluisio’s prototypes reveal how the Future Shock Rear came to be and provide rare insight into the workings, hacks, and dead ends of the bike’s design—something you rarely see.
Asset and first model
Chris D’Aloysio had the idea for a “rider suspension” over a bike frame in 2014. Riding in the Eureka Valley near his California home, D’Aloysio realized that his body provided the suspension he needed; He could stick himself on top of the bike and bumps under him were no longer an issue.
This realization led to the development of the Specialized Future shock, which debuted in 2016 on the award-winning Bike of the Year. Specialized Rubiks.
The design isolates the cockpit, protecting riders from bumps at the front end of the bike.
The technology quickly made its way to the first-generation Diverge in 2017, with Specialized relying on a compatible seat and safety bar clamp for the rear shock absorbers.
This design worked on small bumps, but Specialized says it needs more deflection for rough terrain in order to keep riders in the saddle and gain more traction and power as a result.
D’Aluisio says the way around this problem is to come up with a design that will see the passenger’s weight shift in a forward and backward curve, rather than up and down, as happens with a typical telescopic suspension elements.
That’s the thinking behind the first prototype of the Diverge STR. In order to achieve downward and backward movement, the bike has a seat post attached to the bottom bracket. The linkage is then positioned at the top of the frame, with damping controlled by a standard air shock.
The lower arch Connected to a separate coupling on the underside of the down tube.
“We wanted the bottom bracket to move down and forward to get a little bit of growth in the chain so that, when you get out of the saddle and hit the pedals, the chain gets stuck in you — [this prevents ] Comment from pressure,” says D’Aluisio.
D’Aluisio says the prototype works fine, but the presence of the lower strut in its linkage meant the bike didn’t have the pedaling efficiency of the solid frame it would like.
D’Aluisio developed the concept for the first prototype, introducing a rotating bottom casing and concealing the air shock in the tire’s down tube.
D’Aluisio, who has worked at Specialized for more than 20 years and has been at Cannondale before that, says this prototype, made in-house, is his favorite bike he’s ever built because it “did everything I wanted” and was “so efficient.”
Others at Specialized appreciated the cleanliness of this prototype. The brand decided to experiment with the design in sizes larger than the D’Aluisio’s 52cm frame, but this revealed limitations.
“56 cm [frame] The comments were good. But with 58, the comments weren’t good and there were some questions about what was going on. These riders didn’t feel like they benefited from the saddle,” says D’Aluisio.
Larger riders liked the design when they were seated, but not out of the saddle. D’Aluisio says of the larger tires, the Specialized air shock was “pumping so much to try and meet the rider’s needs in the saddle that the bottom strut was out of phase.”
This created a buildup of friction — friction that can prevent fixed surfaces from moving — and meant the lower strut was not moving for larger passengers.
D’Aluisio says this prompted him to go ahead with the seat tube idea and leave out the swivel bottom strut, yet he found it to perform well on the 52cm tire.
He also says that this design with the air shock was too complex for specialists to make on an industrial scale.
Amblyopia looks the same
Abandoning the movable bottom bracket and attempting to simplify the design led D’Aluisio to develop this third prototype, which looks remarkably like the final Diverge STR design.
“If you shift your eyes, they will look the same,” says D’Aluisio.
The prototype has a flexible seat post with a Thompson seat tube attached to a damper in the top tube and a boot that prevents debris and water from entering the system.
The design also offered adjustability, which the old Diverge’s flex seat didn’t.
D’Aluisio says that later versions of this prototype had strings, like the one seen in Future Shock Rear.
Flexion in the bowstring means the damper can be installed in the top tube, rather than needing a pivot, and ultimately reduces complexity, play and shaping.
The final design, sort of
The next step for D’Aluisio and Specialized was to build a test model. The specialist transferred the axle-free design to tires spaced from 52 cm to 61 cm.
The version pictured here is the 2017 Diverge, from the rear when the bike wasn’t refreshed the second time around, revealing how long this process took. It has the final damper but not the final chord.
At this point, the project was a joint development, with frames being fitted at Morgan Hill, Specialized’s California headquarters, and its factories developing carbon kits for the bike.
Luke Callahan, an engineering and road specialist pioneer, also began testing and developing 352 tire samples over a three-year period. This is the “longest committed development period of any single road or gravel technology,” according to the brand.
Fast forward now
Fast forward so far, Specialized says Future Shock Rear will provide up to 30mm of travel in the bottom and rear bend, which has been essential from the start.
Callahan’s testing created nine different tire shafts, fitting different tire sizes and rider weights.
The latest version of the Specialized Diverge STR is visually similar to D’Aluisio’s fourth prototype with the exposed chord.
The appearance of the Future Shock Rear is likely to divide opinions, but it can be useful to get a feel for it.
When asked if we can expect to see Future Shock Rear on other bikes, road and gravel specialist Stewart Thompson said, “It’s an innovation we really believe in. If we can find other applications and opportunities, I think we will choose it.”
The design is located in gravel suspension The class, for now, but we might see it on the cobbles of Paris-Roubaix in the future.
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