Specialized’s latest published patent documents a “Bicycle Frame with Angled Strut”, wherein a completely new frame tube – an ovalized strut connecting seat & down tubes – appears designed to deliver increased vertical flex compared to a conventional bicycle frame design with a continuous seat tube. This unusual design implies impacts for frame weight, ride comfort, and tire clearance, too, possibly giving us some insights into what a next generation of Specialized’s Spring Classics road racing bike, all-road, or even gravel bike might look like…
Specialized Patent for Bicycle Frame with Angled Strut
The bicycle frame outlined in this European patent from Specialized (EP4122807A1) does away with a continuous seat tube, replacing it with a sort of floating one, if you will, suspended by a portion of ovalized frame tubing that connects it to the downtube around a third of the way up the latter’s length (58). No more traditional frame triangles in this bike… might we refer to the front polygon & rear trapezoid in the future?
The patent claims that these modifications advantageously reduce the vertical stiffness of the bicycle while substantially maintaining or reducing to a lesser extent the horizontal (e.g., lateral or torsional) stiffness of the bicycle, thereby increasing the comfort for the rider while substantially maintaining or only slightly reducing the handling of the bicycle and/or force transfer of the rider to the bicycle.
Use of ovalized tubing such as this is nothing new, of course. Plenty of modern bikes feature flattened tube profiles throughout for engineered vertical flex. Cotic for example has been using an ovalized steel top tube on its mountain bikes and gravel bikes for years, while OneUp’s Carbon Handlebar makes use of an ovalized section between the stem clamp and bar-end regions. In both cases, despite the use of very different materials, the idea is to increase vertical compliance to better isolate the rider from the smaller lumps and bumps on the trail.
Specialized interestingly mention the potential use of steel, aluminum, OR carbon fiber for this bicycle frame. Though, judging by the seamless of curves in the drawings, this is almost definitely intended to materialize in carbon. But that likely suggests that lower-cost versions could employ similar concepts in metal construction, too.
A table within the patent document suggests the angled strut gives the bike frame 172% more deflection in the vertical plane, and 75% more deflection in the horizontal plane – compared to a conventional frame with a regular seat tube that meets the downtube at the bottom bracket. They determined those numbers with a test simulation wherein the conditions were similar to those specified for ISO 4210-6:2015-4.5, or “Fatigue test with vertical force”.
In the Horizontal Stiffness Test simulating ISO 4210-6:2015-4.4 or “Fatigue test with horizontal force”, the Specialized frame with the angled strut is even slightly stiffer in the horizontal plane than the conventional frame.
The patent document reads, “By increasing vertical deflection at a greater rate than the horizontal deflection, ride comfort is increased without substantially increasing the rearward saddle tilt“.
How will this fit into Specialized’s Road & Gravel Bike line-up?
We approached Specialized for comment on this one, successfully securing the expected “No Comment” reply. Alas, we are left to hypothesize.
Let’s not forget that it was only in October of last year that Specialized released the wild-looking Diverge STR. In that design, the actual seat tube is the spring, while a Future Shock housed within the top tube damps a claimed 30mm of travel.
