0.29.2 Weak front suspension levers

Hi all, I have noticed that some vehicles have weak front suspension arms. This can be seen during braking and immediately after stopping. The front wheels shift in the longitudinal axis and then, after stopping, the vehicle rocks back and forth as the suspension arms spring back. But, please note! They don't spring up down, they spring backwards, forwards! Some cars are prone to this problem, but on a catastrophic scale, it's noticeable on the Bruckell Bastion and ETK 800-Series. Gavril Grand Marshal and some other cars are a little less susceptible to this problem. I haven't tested all of them.

Here are some examples of screenshots. You can see the displacement of the wheel in the longitudinal axis. This is the sway immediately after stopping.


Another screenshot for comparison. This is Cherrier in the same situation. As you can see, there is no shift of the front wheel in the longitudinal axis.

 

The vivace has a McPherson strut system which is less prone to this. The Bastion uses a double-wishbone system and so this sort of "sway" is more visible, and is caused (IRL) by the suspension mounts' bushings, not by the arms themselves. This happens IRL as well to a certain degree.

 

Ok, but I don't think the vehicle (IRL) swings after stopping with an amplitude of a few centimeters. There's clearly something wrong here.
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Civetta Scintilla doesn't have anything like that either. And I'm guessing it's not a McPherson suspension.

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I applied a longitudinal load of 550 pounds to the front wheel attachment point on the Civetta Scintilla and did the same for the Bruckell Bastion. You can see that the Bruckell arms are skewed and that the Civetta has almost no deformation.

 

The Scintilla is a Supercar, so its suspension (mainly the bushings) should have a lot less compliance than what's acceptable for cars like the Bastion and the ETK 800. Speaking about the ETK 800, the K-Series has the same problem?

 

Yes, it's the same problem there. But ETK I Series doesn't have this problem and it's not a McPherson suspension either, as far as I understand.

Not a good argument, in my opinion. IRL, even vehicles unprepared for racing, don't sway on springy suspension arms. They're not rubber.
I realize this is a game and I wouldn't pay attention to it if all vehicles had this problem, but only some do.

 

Actually, real life cars, when equipped with multilink suspensions (either front or rear) usually have some compliance on the links bushings that would make the wheels move like that, specially if equipped with upgraded tires and brakes, but stock or old bushings. That's why race builds usually get upgrades bushings to reduce/eliminate those movements.
Although, I agree that the movements are a bit exaggerated in the game and having the option of stiffer bushings would be welcome for those cars. Since the ETK 800, the K-Series and the Bastion are the only cars with those "multilink" front suspensions (since they are inspired by BMW and Mercedes, brands that use layouts like these), it is kind of nice for a game to replicate such behaviour from real life.

 

For all of these cars, there is sport and racing suspension in the game, but it has no effect on the problem.

 

Actually not. They have sport/race struts, but the suspension itself is the same. That would be solved by a real racing suspension, like we have on the new Pessima. If I was a Jbeam expert, I could pin point which beams represent those mounts and make them stiffer for a racing suspension.

 

Suspensions in beamng are already way heavier than irl, and making them stiffer would only make them heavier

 

I think, I got the gist of the problem. Maybe I'm wrong, but it looks like the suspension mechanics were made in error. This applies to all suspensions of this type in the game. It's the same flaw everywhere. The red colored levers where they attach to the wheel have two axles (marked in orange), each lever has its own axle. They should only move up and down, but during the animation of the wheel rotation you can see that these levers also move forward and backward along the longitudinal axis of the car. They have an additional degree of freedom, although even by their design it is clear that this cannot be the case. At the same time, due to a design error in the game, the wheels would not be able to turn at all if the levers did not have this additional (and incorrect) degree of freedom. This is what allows the wheel to move in the longitudinal axis of the car.

 

Maybe the front-back movement is intentional. This is the layout of a F30 BMW's front suspension (a car that the ETK 800 is HEAVILY based on).



As you can see, the two arms have different pivot points, which would make the wheel move front to back when steering. That's why Mercedes have such aggressive camber angles on the front axle, and they use the "Bastion's Layout" since the W211s, maybe earlier. The only limiter to the front-back movement of the suspension, on the real cars, are the bushings

 

Not exactly right. Longitudinal movement of the wheel is hindered by the fact that one of the levers is at a strong angle to the other, so longitudinal movement of the wheel is only possible by turning the steering wheel. If you don't turn the steering wheel, then when you try to move the wheel longitudinally, the tilt arm will work in tension or compression and prevent the wheel from moving back and forth. This will only be possible if the assembly mount has link end play at this point.

In the screenshot from the game, you can see how the arm attachment axes shift if a load is applied. This is not possible irl.

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Makes sense, since the wheel moves only front to back, while the real car would toe in if that movement happened. Probably one of the arms is stretching, or it's mounting nodes/beams are moving

 

That something is wrong here is evidenced by the fact that the ETK I-series suspension is very similar to the ETK 800-series and ETK K-series suspension, but there is no forward and reverse movement of the wheels.