Bicycle Frame with Angled Strut by Specialized

In this article, we’ll be discussing a Bicycle Frame with Angled Strut by Specialized, US publication 20230034772. The publication date is Feb 2nd, 2023 and the filing date is July 12st, 2021. This is not granted, yet.

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2/16/23 Update: I was sent a video by @gravelbikepolandofficial showing a new Rondo Ruut at an event recently, video here. Looks to be pretty similar, and the timing of this event is interesting.

Brief Summary (tl;dr)

Specialized are working on a new bike frame (gravel or road, not sure) that uses a shorter seat tube (that doesn’t extend to the bottom bracket), and includes a seat stay and strut that extend from the bottom of the seat tube. They say this design allows for a more comfortable ride.


I don’t have an explicit problem here, but I have a solution. Spesh are saying this is a comfort thing, without giving up other important characteristics.

These modifications advantageously reduce the vertical stiffness of the bicycle while substantially maintaining or reducing to a lesser extent the horizontal (e.g., lateral and/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.

The problem is the normal problem of road or gravel bikes; these companies want to address the comfort of a stiff-ass bike without compromising anything else. It’s an important goal that seemingly everyone is trying to solve, and it doesn’t seem easy.


FIG. 1 shows this new funky new bike. All of these components are pretty standard except the seat tube, the seatstay, and the strut. These are the three items we’ll focus on.

From the highest possible level, Spesh define this strut:

A strut member or strut tube 58 extends forward from the lower end of the seat tube 46 to the down tube 42. The strut member 58 intersects the down tube 42 at a mid-section 44 of the down tube 42 between the head tube 38 and the bottom bracket 50.

While this isn’t granted as of yet, it’s interesting to see how they’re actually defining this bike. The difficult part of these documents, and what attorneys get paid for, is explicitly defining an object, process, whatever. I find there are times that it’s very difficult to define a simple structure, like this bike. How do you explain a bunch of sticks in a certain arrangement?

They’re doing this by defining each component as a ratio compared to the down tube, and angles of each component compared to another component. The table below shows the downtube with a relative length of 1, so downtube/downtube would obviously equal 1. The rest of the table shows the length ratios for every other component on this bike. For example, we can see the strut member 58 is 0.36 (36%) of the length of the down tube. For simplicity’s sake, if the downtube is 100 furlongs, the strut member should be 36 furlongs.

The down tube 42 is therefore referred to as having a length of 1.00X with the remaining lengths being a percent age of the length of the down tube 42 (e.g., the headtube 38 extends 26% the length of the down tube 42).

I don’t think there’s anything special about the down tube. It appears as though they just picked it because it’s the longest component, and every other component can be defined as a number less than 1. Seems like a simplicity thing rather than some technical importance. But, I could be wrong here.

FIG. 4B shows relative lengths and angles of the components.

So, what is the actual advantage here? What is the outcome of this design, and why should I buy it? Spesh did some testing on this new bike compared to a conventional bike, and this is what they say:

In comparison to a conventional frame structure having a full seat tube, the main frame 18 of the described embodiment provides reduced vertical stiffness while substantially maintaining or reducing to a lesser extent the horizontal (e.g., lateral and/or torsional) stiffness.

First, some background. The two images below show the two ISO tests they’re basing their tests on. The first is the vertical test (left), where they applied a 1200N static (no cyclical) load are arrow F4. The other test is a horizontal test (right) shown as arrows F2 and F3 with 600N of static load. ISO Test Methods for reference.

The table below shows the results of their ‘simulations’ (sim is likely FEA) of these ISO tests. They compared this new frame to a conventional frame with ‘…a full seat tube, both frames being the same size, designed of the same material with the same wall thickness and same tube shape and diameter.’ So, we can assume this conventional bike is effectively the same in every characteristic other than the orientation of the components.

We can see that this new frame with the strut allows for significantly more vertical deflection (y = 7.9mm) and more horizontal deflection (x=7.2mm) under the vertical load. We can also see less horizontal deflection (x=5.1mm) under the horizontal load. I’m not a huge fan of their csys referencing X and Y here. We’re looking at X and Z in my book.

Here is their explanation of the results.

As reflected in the test results, the main frame 18 produced 172% greater vertical deflection and 75% greater horizontal deflection at the seat during the vertical stiffness test compared to the conventional frame. By increasing the vertical deflection at a greater rate than the horizontal deflection, ride comfort is increased without substantially increasing the rearward saddle tilt. The horizontal stiffness test showed a decrease of 24% in the horizontal deflection for the main frame 18 compared to the conventional frame, which does not substantially impact the ride characteristics (e.g., handling, force transfer, etc.), but it provides evidence that the frame design works well to handle the loads/stresses applied during the horizontal stiffness test, which is believed to correlate to real-world riding.

I understand this ‘rearward saddle tilt’ as a slope, because they want the saddle to go up/down with a reduced fore/aft movement. So, if we do some hella basic math here, we can deduce the conventional bike has a slope of about 1.41 (4.1/2.9), and this new bike has a slope of about 0.91 (7.2/7.9), under exactly 1200N.

This means the conventional bike saddle will tilt backward 1.41mm for every 1mm down, while this new bike will only move backward 0.91mm for every 1mm down based on this exact, specific scenario.

Intended Novelty

I assume most of us are curious about this part because “tHeY cAn’T pAteNt tHaT”. I try not to talk much about novelty with documents that are still in prosecution, but here we are.

They define a bunch of conventional components of a bike (top tube, headtube, etc.), then they say the lower end of the seat tube is ‘spaced from the bottom bracket’, meaning there is space between the bottom of the seat tube and the bottom bracket.

There’s also a seatstay extending from the ‘lower end of the seat tube’.

Then, they say the strut member extends forward from the ‘lower end of the seat tube’ and connects the seat tube to the down tube.

I anticipate them having to narrow their scope a bit, but we’ll see.

This isn’t a legal analysis. Don’t listen to my dumbass. Do your own research if you need to understand what Spesh are claiming.

More Pictures

I just figured out I can do a slideshow. neato.

These are just cross-sections of the strut from FIG. 3.


I know Specialized gets a lot of shit, but I’m a fan of their bikes. We’ve all had a Rockhopper, right? They always seem to be on the cutting edge, and they always seem to be having a good time doing it. They’ve got very creative people, tools to leverage their creativity, and money to take risks. As far as I’m concerned, those are the basic tools needed to be at the forefront. You can’t have every innovation be a winner, so you do your homework, cast a big net, and hope for the best.

Have a great Sunday, folks. Boogity Boogity Boogity.

11 thoughts

  1. I… I really like this. That’s some outside the box thinking. My biggest peeve when using a manipulated seatpost to handle a lot of compliance is that it’s flexing in largely the wrong way. This looks to at least partly correct that. It’s also an aesthetically pleasing, balanced look, and it’s not gadgety or gimmicky like the new Diverge. (The new Diverge also has a significantly rearward bias to its now-damped seatpost compliance.)

  2. If it looks right……..etc. this looks right to my eyes I know from my cfd models that dropped seat stays work (e.g. Felt’s IA and Shiv vs convention double diamond) that said structurally the node that is the BB had lost the brace of the seat tube so their fea probably has some generative optimisation going on hence it “looking right”. That said I’m sure I have seen something similar to this in past in one of the brandless bikes from supermarkets albeit in cold steel.

  3. This is an ebike. Look at the bolts for the speed sensor on the left chaistay. No gravel or road unfortunately.

  4. The diverge just got an update for 2023. This is probably just an updated carbon sirrus/sirrus x.

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