- Introduction
- First problem: no bearings between links
- Second problem: wheel contact patch reduced to a point
- Third problem: impossible geometry
- Fourth problem: wheels are always parallel
- Solutions
- Conclusion
Major Arc entered the skateboard market sometime in 2020. The company’s marketing is rather fishy, but I focus on that in another post. Here, I analyze its truck and examine the questionable logic on which it was designed. Specifically, I will look at four problematic aspects that make it geometrically inconsistent, fragile and potentially unsafe1.
First problem: no bearings between links
The first (and admittedly minor) problem has to do with the fact that each truck contains five links or joints that enable its two axles (one for each wheel) to turn when the deck, and baseplate, is tilted. There are two joints per axle and one central joint. As far as I can see, there is no provision for the increased friction this creates. There are no ball-bearings, just five metal-to-metal joints per truck. This makes it energy-inefficient for any skateboard discipline that requires frequent, free and smooth turning.
Second problem: wheel contact patch reduced to a point
The second (and also minor) problem is that, if the deck, on which the trucks are mounted, is flexible, then whenever the skateboard turns, the contact patch of the wheels is reduced from their whole width to just one point. Let me break this down briefly. Notice in pictures 1 and 2 below that the axle plate is meant to be parallel to the ground at all times. What happens when the wheels are turned (that is, whenever the board turns)? Two cases: stiff deck and flexible deck. If the deck is absolutely stiff, the axle plate remains unproblematically parallel to the ground. But if the deck does have some flex, the nose and the tail of the deck face upwards and so do the trucks, due to the weight of the rider plus the centrifugal force bending the deck. Thus, the axle plate of each truck is at an angle with the ground, making the wheels touch the ground only with their edges (remember, the wheels are turned). Consequently, the edges/lips of the wheels will wear out faster. Possibly, cornering is also affected adversely.
Third problem: impossible geometry
The third problem is quite significant. The truck just doesn’t make sense geometrically! It cannot actually turn freely by its own design. To understand this, dear reader, please use your imagination for a moment to see how it works. I’ll do my best to describe this; please bear with me. Look at picture 1 and 2 and consider what happens when the deck is tilted. The part that is towards the outside of the skateboard is on the left side, marked with the points “C” and “D.” This part, when the “Base” is tilted, remains upright, perpendicular to the ground. So, C and D remain on the same vertical line, C on top of D, without moving left or right against each other.
The other end of the truck, marked with points “A” and “B,” is tilted sideways along with the base and remains perpendicular to the deck, not to the ground. This means that the vertical distance between A and B decreases, while they move left and right against each other (see picture 3). But there’s no provision for this to be possible! Both pairs of points: A and C on top and B and D at the bottom, must each remain on the same height by their construction (see picture 4), but at the same time the distance A and B must decrease!
The only way this can happen is with extreme (and unwanted) pressure: 1) on the roadside bushing (which is pressed axially, unlike normal trucks – notice that the boardside bushing is essentially redundant), nut and kingpin, 2) on the deck and the bolts that secure the truck on it, and, 3) most crucially, on the weakest link: the “axle plate” (the gray parts that hold each axle), which will probably be the first part to go; because, something has to give… This mistake shows that the designer’s intention was not to build a functional truck, but something that can be marketed as “cutting edge” to careless consumers.
For more on this, I refer you to the comment section below.
Fourth problem: wheels are always parallel
The fourth and final problem I examine is also major and it has to do with the arcs the wheels follow (pun intended). They are not consistent with logic either. See picture 5: the two “Axle plates,” and therefore also the two wheels on each truck, are always parallel to each other, also when the truck turns. That’s OK only when the truck goes straight. But if the wheels remain parallel when the truck turns, then the wheels on the inside and outside of the turn point at the centers of different turning circles. This happens because “wheels on the inside and outside of a turn […] trace out circles of different radii” (as the wikipedia on Ackermann steering geometry explains the problem), but they are not aligned on the same line, like regular trucks are, nor are they on lines intersecting on the center of concentric circles, like cars are. Basically, they are oriented at different centers, when all four wheels should have been tracing concentric circles. Let me break this down.
Look at picture 6 (click to enlarge), and see that, if for instance it happens that wheel α and wheel δ are dominant, then the skateboard turns around point Δ, marked with an “X”. This means that wheels γ and β are following the dotted circle by sliding sideways. With Major Arc trucks, two wheels are rolling normally and two wheels are sliding sideways at all times, except when the skateboard traces an absolutely straight line, i.e., going perfectly straight. Indeed, there are four possible turning centers and it’s unpredictable on which one of them the setup is running at any moment.
Car makers have, of course, solved this problem with mechanisms like those described in the Wikipedia entry. They needed to solve it, because, again, if the wheels don’t follow the arc that the vehicle follows, they slide sideways the whole time the vehicle turns. “To avoid the need for [wheels] to slip sideways when following the path around a curve,” you need a steering mechanism with which “all wheels have their axles arranged as radii of circles with a common centre point” (again, from the Wikipedia entry). Picture 7, from the wiki entry, hopefully makes this clear.
Skateboards with more traditional trucks (i.e. with one single axle per truck) do not have to deal with this problem at all, because both wheels on each truck are by definition on the same line (see picture 8). The axles are the lines that define the turning circle. Cars do have to deal with this, but since their makers know exactly what the wheelbase of the car is, they can build the steering design that corresponds precisely (or, very approximately) to the Ackermann geometry, with the axle of each wheel pointing at the same turning center. Therefore, even if the Major Arc designers knew or cared about this, they wouldn’t have been able to offer a one-size-fits-all truck. They’d have to make different trucks for different wheelbases. Or, they could only offer the corrected trucks on their own precisely measured, one-wheelbase, completes. Anyway, none of the above is true.
One consequence is that traction diminishes significantly, since static friction is much higher than kinetic friction (Wikipedia). Also significantly diminished should be the life expectancy of the wheels, of course. It can be potentially dangerous too and the skateboard probably feels unpredictable, since the dominant wheels change all the time depending on numerous factors, with each wheel, each truck and the skateboard tracing different circles from moment to moment.
Solutions
To remedy these four issues, the designer would need: 1) ball bearings between every connection; 2) rounded wheels (though a rethink of the design principle is surely due); 3) a fundamentally different design with a mechanism that allows the hanger to rotate freely against the baseplate; 4) a mechanism like the one in picture 7, along with a very precisely calculated wheelbase.
Conclusion
I will close this piece with a question for you, dear reader, and please take one moment to consider the implications. Did Major Arc simply miss all this from conception to production, or were they aware (as this –screenshot– response from a youtuber indicates)? It is tempting to think that, despite it being extremely improbable, they simply missed the problems with the design which render their truck essentially impossible; that, from conception to production, they never considered doing some basic research (that is, a simple online search) and that they didn’t stumble upon “Ackermann” etc; that it never occurred to anyone who saw designs or prototypes that car design might have relevant lessons. Is this scenario plausible, you think?
Or, was it a conscious decision to market something that looks like, but isn’t and never could be, a fancy yet functional truck?
1. This is not a review; it is a geometrical analysis. It is based on analyzing the detailed and revealing illustrations the company publicly shares, in a way that anyone can verify or refute. No part of it requires using these trucks; I have neither used them, nor do I intend to.
Changing Angles 
I’m arriving at some different conclusions regarding the third problem. I do not remotely have the expertise to claim that you’re wrong. I’ve just been thinking through your analysis for the last couple hours trying to figure out where our analyses differ. Here’s the passage where things diverge for me:
“The other end of the truck, marked with points “A” and “B,” is tilted sideways along with the base and remains perpendicular to the deck, not to the ground. [So far so good.] This means that the vertical distance between A and B decreases (while they move left and right against each other).”
That’s where you lose me. When you then write that there’s no provision for this to be possible, I say correct, it’s not possible, because that doesn’t happen. “A” remains on the same plane as “C”. There is a pivot pin on line AC. “B” remains on the same plane as “D”. Looking at Picture 1, when the deck leans “B” moves through the Z axis. The vertical distance between the planes “A” and “B” exist on doesn’t change. What *does* change is the line AB (in three dimensional space), which gets longer, because “B” moves laterally while “A” stays in place.
This movement is perfectly accounted for by the roadside bushing compressing as the kingpin stays on line AB, tilting left/right as viewed from Picture 2. But to reinforce what I was saying, it moves like a pendulum, with point “A” stationary and “B” moving left/right purely horizontally.
When the roadside bushing compresses, it does reduce the loading of the boardside bushing, which is what I think you were referring to when you said the boardside bushing is redundant. However I believe if serves a different purpose.
Imagine if only the front part CD were installed—no “axle plate”, kingpin, etc. If weight were put on the board, I believe (other than the deck flopping to one side or the other), the board would simply sit on the front steering rail that includes point “D”. But when you install the axle plate and wheels (still no kingpin/bushings/etc.) and apply weight, there’d then be leverage trying to lift the inside unsupported end of the axle plate. In essence, because the axles are set to the inside of point “D”, when weight is put on the board there is leverage trying to close the gap between points “A” and “B”. The only thing stopping that from happening is the boardside bushing.
So that’s what I believe to be the purpose of the boardside bushing. It carries a small portion of the total load (since the axle is much closer to “D” than “B”), balancing the torque placed on the axle plate. The boardside bushing is load bearing, and the roadside bushing gets compressed when the baseplate is leaned.
Thoughts?
Thanks for reading and for the comment, Eric! I appreciate it.
To your criticism: I never assumed that the distance (A, B) doesn’t become longer when the board is tilted. That’s indeed the only way it could turn. What I said is that it’s a design mistake.
Let’s assume, for argument’s sake, that the truck does indeed intentionally extend the distance (A,B) when tilting, thus compressing (I repeat: axially) the roadside bushing and the roadside bushing alone. And also let’s assume that intentionally, and only when the truck is at rest (i.e., zero deck tilt), the boardside bushing is there to support the “axle plate” (I admit, I never considered this might have been a design concern; it seems legitimate to me as well, now that you mention it). This is what we have at our hands at the moment anyway, so we might as well assume the best of the designers and take it all as intentional and thoughtfully designed. (I’ve sketched this for the readers)
Aren’t you convinced, however, that compressing bushings axially (i.e., in the direction of the kingpin), instead of squeezing them from the sides (i.e., as bushings are normally used), implies that there is a struggle between the roadside bushing and the joints of the “axle plate” to keep the axle plate flat and parallel to the ground? (Let me note that, according to professionals, PU is deflected but not compressed; if you don’t give PU a place to go, its force must become enormous.) Constantly, except when at rest, the “axle plate” joints are stressed by the rider’s weight and centrifugal force, through the roadside bushing, just to remain parallel to the ground. And where’s the boardside bushing now that we really need it? That’s the first time I see a truck whose bushings are fighting against its own structure. I want to add that, if the “axle plate” were free to follow point B (i.e., if it were not attached to D), then and only then would the bushings get squeezed as they normally are in conventional trucks (i.e., at their edges first, sideways, with room to deflect their volume).
(I’ve sketched this too for the readers)
As for me, I would still guess it is oversight. The stress on the “axle plate” is constant. The boardside bushing does nothing, except support the “axle plate” when at 0 tilt (I grant you this, it makes sense). That’s not how bushings work. Also, I do not know of another truck that creates tension and stress within its own structure by its own design. I think this truck here is exceptional in this sense. So, I’m not convinced it’s intentional. What do you think?
Your observation was extremely pertinent and intelligent and you made a very valid point. I’m not as confident as when I first wrote that part, so I’d appreciate your response!