I've been following the incredibly good-looking and advanced designs coming from Skoa Trucks for a while now, nearly struck in awe by how aesthetically pleasing and forward-thinking their trucks seem. Whether it's the aerodynamic-appearing and self-proclaimed "stronger than others" design of their Stream 7 model, or their "see-an-existing-idea-and-twist-it" take on hanger style with their Vapor model (I'm referencing the double-pointed hanger style popularized by Aera K4 trucks, and many others thereafter), they seem to break the stagnant mold of the precision truck industry every time they release something. Their new Maryhill Spec Stream 7 trucks are the most asymmetrical (stock) trucks currently on the market, and they look infinitely cooler than any other asymmetrical speed trucks I've personally seen.
But earlier today I was looking through Skoa team member Tommy Watson's (@thetomes) Instagram posts and found two which had called out Atlas Truck Co. on their own design claims, trying to explain how a true I-beam is implemented regarding the bend-resistant characteristics of design. And while I admired his get-it-right-or-get-out attitude, I couldn't help but smirk at the situation presented to me, and become slightly perturbed by this naive, ill-informed display of dominance.
How an I-beam works: http://en.wikipedia.org/wiki/I-beam#Design
An I-beam resists bending in the direction perpendicular to its cross-section (along its length), under loads applied parallel to its vertical section (called a "web"). What Skoa is trying to claim is that the sections of their trucks which resemble I-beams resist bending due to loads applied by a rider's weight to the ends of the hanger. Going by how I previously defined an I-beam's intended usage, the Stream 7's "I-beams" do nothing at all when it comes to strength. The cross-sections of the Stream 7's I-beam is parallel to the force applied, meaning the horizontal parts of the "I" shape (called flanges) will be the only thing effectively resisting bending.
Now let's delve into the actual engineering analyses I conducted today to try and prove my claims in the previous paragraph.
It took me all of 15 minutes to design a similar hanger, and also the correct implementation of an I-beam in a separate hanger which had the same design characteristics but with the web of the I-beam rotated 90 degrees to become aligned with the axle axis of the hanger. For reference, these test hangers I designed have no rake and no bushing seat or pivot, because those things don't factor into the testing of the area of the hanger I'm concerned with. All design copyrights or patents Skoa and it's owners hold belong to them. I am not intending on using their designs (or representations/analogs) for any means other than to prove that their claims about their designs are false.
But earlier today I was looking through Skoa team member Tommy Watson's (@thetomes) Instagram posts and found two which had called out Atlas Truck Co. on their own design claims, trying to explain how a true I-beam is implemented regarding the bend-resistant characteristics of design. And while I admired his get-it-right-or-get-out attitude, I couldn't help but smirk at the situation presented to me, and become slightly perturbed by this naive, ill-informed display of dominance.
How an I-beam works: http://en.wikipedia.org/wiki/I-beam#Design
An I-beam resists bending in the direction perpendicular to its cross-section (along its length), under loads applied parallel to its vertical section (called a "web"). What Skoa is trying to claim is that the sections of their trucks which resemble I-beams resist bending due to loads applied by a rider's weight to the ends of the hanger. Going by how I previously defined an I-beam's intended usage, the Stream 7's "I-beams" do nothing at all when it comes to strength. The cross-sections of the Stream 7's I-beam is parallel to the force applied, meaning the horizontal parts of the "I" shape (called flanges) will be the only thing effectively resisting bending.
Now let's delve into the actual engineering analyses I conducted today to try and prove my claims in the previous paragraph.
It took me all of 15 minutes to design a similar hanger, and also the correct implementation of an I-beam in a separate hanger which had the same design characteristics but with the web of the I-beam rotated 90 degrees to become aligned with the axle axis of the hanger. For reference, these test hangers I designed have no rake and no bushing seat or pivot, because those things don't factor into the testing of the area of the hanger I'm concerned with. All design copyrights or patents Skoa and it's owners hold belong to them. I am not intending on using their designs (or representations/analogs) for any means other than to prove that their claims about their designs are false.
Stream 7 Analog1A: A hanger analytically equivalent to that of the Stream 7 hanger 2A: looking directly down the "I-beam" 3A: the area they call an I-beam, highlighted in green for emphasis 4A: Showing the forces applied to the axle holes, and the fixed constraints applied to the bottomside of the hanger and pivot area 5A: Under 800 Newtons of force per axle hole surface (1600N total or about 360lbs) the ends of the hanger would deflect 0.0199mm 6A: The peak stress for this design under these forces sits at 91.2 Newtons per square millimeter | Correct orientation1B: The same hanger as on the left, but with the web rotated correctly 2B: same view orientation as the picture to the left 3B: looking down the axis of the axle, with the I-beam section in green 4B: Showing the forces applied to the axle holes, and the fixed constraints applied to the bottomside of the hanger and pivot area 5B: Under the same forces, the ends of the corrected hanger would deflect only 0.0166mm, which is 17% less than the one on the left 6B: The peak stress for this design is 68.6 N/mm^2, which is 25% lower than the design on the left |
7A: I reset the color scale to go from 0 to 100 N/mm^2, so the two designs could be compared 8A: Here is an orthographic "top" view of the hanger on the same 0-100 scale as 7A&B are | 7B: The stress concentrations are much more spread out, and less intense in this design 8B: look at that, no orange or red whatsoever, and much less stress on the insides of the slots |
Why would Skoa make these claims in the first place? One of the guys that designed this truck has a masters in mechanical engineering, shouldn't he have known better? To answer these valid and necessary questions, I'll quote Skoa's "About - Our Story" page of their website:
"...Uwe Homm and Reinhold Uhrner wanted a precision truck that was reminiscent of 1940s biplane design with a modern, aerodynamic flare." "...the Stream 7 was the first truck to truly incorporate an I-beam into the functionality of the design, adding strength and beauty to the truck in a way that had never been done before. By having these weight reducing holes in the trucks parallel to the ground, Uwe and Reinhold were also able to incorporate aerodynamics into a skateboard truck, another first in the CNC precision truck world."
I've highlighted a few pertinent details here. The words in blue are the true reason I think they designed this truck, then, after realizing it looks a little like an I-beam, they went ahead and added the words in red to the list of reasons this truck is more superior than others.
If you agree/disagree with the hypothesis I have presented here, or have more information to add, please leave a comment below!
Thanks for reading!
"...Uwe Homm and Reinhold Uhrner wanted a precision truck that was reminiscent of 1940s biplane design with a modern, aerodynamic flare." "...the Stream 7 was the first truck to truly incorporate an I-beam into the functionality of the design, adding strength and beauty to the truck in a way that had never been done before. By having these weight reducing holes in the trucks parallel to the ground, Uwe and Reinhold were also able to incorporate aerodynamics into a skateboard truck, another first in the CNC precision truck world."
I've highlighted a few pertinent details here. The words in blue are the true reason I think they designed this truck, then, after realizing it looks a little like an I-beam, they went ahead and added the words in red to the list of reasons this truck is more superior than others.
If you agree/disagree with the hypothesis I have presented here, or have more information to add, please leave a comment below!
Thanks for reading!