My name is Angelo and I'm from Brazil.
I'm here to share with you my project development during the lockdowns due to the coronavirus. I'm an undergraduate mechanical engineer and addicted to trails and bikes, so I've been searching and designing bikes since 2020 when the pandemic began. I have two prototypes fabricated, one gravel, and one full-suspension MTB.
Without else more chitchat, we'll talk about suspension.
For this project, I thought to develop a trail bike that performs better efficiently pedaling in uphills, without losing the power in the downhill.
In the first step, I developed the geometry using BikeCAD Free, principal dimensions obtaining to the frame. After this, I input these values with the model of suspension and parâmeters of the fork and shock on the software Linkage X3 Personal. Single Pivot is the type of suspension that I used to design this system.
So, why did I choose this kind of suspension?
I think this type is awesome due to its simplicity and performance. I know that a lot of people are going to discord about it, and exists a huge argument to find which system is the better. Let me show you what I developed and the reasons that and we'll see if you agree.
The shock used in this project is an X-Fusion 02 Pro RL, Rx Trail Tune, rebound adjust, lockout 190x42.5mm, and for the fork, RockShox Recon RL 130mm of travel and 29 er wheels. Like this, I got 118/130 mm of suspension travel.
Let's get started talking about the Anti-Rise (AR).
I tried to keep the parameter close to 100%, making the rear wheel suffer less influence on the braking, due to the combination of the influence of the brake force (shock compression) on the suspension and the load transfer (shock extension), allow the system not to compress or extend during braking. Being this pair of forces equalized, the suspension will achieve better performance on obstacles at the same time that braking occurs. Anti-rise is much related to anti-squat, so an equilibrium is always considered.
As I said, I wanted to design a trail bike with better pedaling, what do you think is better to reach this? I think anti-squat will help us to answer this question.
Due to the pedaling of the biker, the suspension is compressed for the biomechanics forces and transfer of mass. Thereby the anti-squat must be more than 100% to try to find the equilibrium of the forces. However, we can't forget too much AS could cause an extension of the suspension, generating an unwished behavior, in opposite direction caused for squat. I believe equilibrate behavior is more useful. On a ride, the biker is always in movement, which causes a lot of forces in different directions, more else when is standing up, being no possible want to control everything with the parameters of the suspension. So, the simplicity of Single Pivot gave us a wished behavior, allowing the rider to feel the bike and set up it easily, without forgetting that a Single Pivot is much less expensive to fabricate and to maintenance when compared with other types.
The SAG that was considered for the bike is 25%, being 29 mm of the rear travel. When pedal sitting the suspension is in the region of the SAG, and pedaling standing up the suspension is more compressed, that is why I designed the AS more than 100%, but close of this value in almost all the travel, allowing to get a better pedaling.
The anti-squat varies according to which cog of the k7 the chain is and as well with compression, this is due to the change in the angle of inclination of the chain to the chainring. Using a 12-speed k7 for this project, the anti-squat presented values between 134.6% (maximum) and 103.1% (minimum), with curves similar to the one shown in the graph, changing a little your inclination, but always close 100%.
Leverage Ratio (LR)
For the leverage ratio curve, as shown in the table, with a difference of -0.21 between the beginning and end of the curve, obtaining a linear behavior, with an average leverage ratio of 2.795. However, the curve has a shape with a slightly regressive characteristic and LR values closer to 3, indicating that the suspension will have softer during travel, characteristic of a Single Pivot.
The shock compression ratio gives another way the system moves and defines, with the LR, the ultimate behavior of the suspension system. Thus, taking into account the type of shock used, which is an air shock, it is identified, according to another table, that the final outcome is slightly progressive.
The construction of each type of shock gives its operating characteristics. Generally speaking, coil shock is linear and air shock is more progressive.
The tables I was talking, are provided by the Youtube Channel, AndreXTR, of playlist: Fundamentals of suspension.
I think the most important parameters are these, and I think this is enough, if the others are discussed, like pedal kickback or others else, it'll be just beat around the bush. Everybody, deep down, knows that mechanisms are simple, what people do is marketing for eye-catching and confuse the people who don't have knowledge in suspension. But, don't get me wrong, other parameters must be considered, just without much fantasy, reach this is just done equilibrium with others.
What about the frame?
Now I'll show some pictures to you to see the CAD model and how was the prototyping, I'm won't talk much about the structural process because the focus is the suspension. I almost forget to say! The material applied to the frame is Chromoly 4130 and your final mass is 3.730 kilograms.
And how do I know the bike has the behavior that was designed?
I did this question for me after the bike is assembled and ready to ride. And how can I know if the manufacture was reliable?
So I put my brain to work and get the conclusion if I had the compression curve I could compare it to the curve in Linkage X3.
For the suspension compression test, it was necessary to fix the bicycle on a table, supporting the bottom bracket so that it did not change its height and interfere with the measurement of the suspension's travel.
Being properly locked, using clubs, each with a thickness of 6 mm, it was possible to compress the suspension by inserting them at the point of contact between the tire and the table. For each club added to the rear wheel, the length of the shock rod had been measured using a caliper, and all measurements were added to a spreadsheet to later generate the compression graph of the shock by the wheel travel. The rear wheel has a stroke of 118 mm and the shock 42.5 mm. For the complete measurement, it was necessary to use clubs with measures equivalent to the union of several clubs with a thickness of 6 mm, allowing measurements to continue to be taken every 6 mm. As can be seen in the graphic, very close curves were obtained, ensuring the suspension behavior as expected and designed. The figures below demonstrate the test.
What about meeting the bike and seeing a little action? YEAH! Take a look at the video that I made.
Therefore, I got a trail bike with better pedaling, ride fast and flow, and downhills fast, and easy control, but due to its 118 mm rear travel, in extremely hard segments of downhill with a lot of obstacles it's struggled a little bit to go through these. But in general, ride fast and fun.
And that's it that I have to share with you. If you'll have questions, make them here or search me on Instagram, I'll answer you. Thank you for your attention, and thanks to my friends and my parents that help me with this project.
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