Cars behaving weirdly at high speeds

I've noticed when cars get beyond around 220-230mph they get incredibly floaty and sort of drift back and forth left to right.

I know this could just be because they are creating lift at those speeds but something just feels very unnatural about it, I imagine real life would be a lot less forgiving. Here's an example with the SBR using vanilla parts, no steering input but it wobbles back and forth.



Here's another short video with the ETK800. Engine is a mod I've made but used on the ttSport+ with no other parts changed. The car just seems to float from side to in a way that does not seem realistic... I am prepared to be wrong about this...

 

i'm no expert but i think it's probably the lift the car produces, coupled with the elasticity of rubber tires (and other moving/flexing parts). in real life, i have felt this extreme floatiness and minor swaying at 100+ (mph) in a chevy s10. it's less physical swaying, but you do feel it a lot in the steering wheel. i imagine if i went faster, the car may actually have started to "wobble" like your examples.

different vehicles will be worse than others of course, with different things worsening the effects;

• more tire sidewall
• bad suspension geometry/worn bushings
• softer suspension
• more produced lift at a given speed

all of those things will make it much worse, which is why the effect is at such a high speed in the cars you chose. i would imagine doing these speeds in a hopper or roamer would only amplify the observed effect to a huge degree

 

In my opinion it's almost a little too good... Look at you going down the road in that second video going 250+ without touching the wheel and the car is going dead arrow straight... until you touch the wheel anyways. In my car, I can't go more than about 2000ft without having to make little minute corrections to keep the car between the lines at 50mph, nevermind 5 times that speed.

As stated, the wobble you are experiencing is basically the car moving about on the tires and suspension. If you were to go slap on some higher sidewall tires, this effect would probably be much worse even at lower speeds. Inversely, if you were to pump up the air pressure in the tires, you could probably reduce this as well.

Now it all doesn't come from the tires, as also stated, basically the entire car as a system can move about, bend, twist, and conform to the road surface... all of this added together can help to create this effect.

One last little bit, it appears that you are using a controller, In a real car at highway speeds (70 to 80 plus) depending on the condition and setup of the vehicle, you should actually be able to feel this when coming out of a halfway quick lain change. Your brain has adjusted for this over time to the point that the geometry of the suspension naturally steering out of it and your brain naturally correcting for it that 99% of the time unless you make a very aggressive lane change in a very crappy car, you will never even notice it.

Next time your driving, try stiff arming the wheel... after coming out of a corner, really hold that sucker dead arrow straight... well, keep the car on the road, but try to hold it as straight as possible... you should be able to feel the car settling out on the suspension and tires for a little bit.

The reason it seems so much worse in your two scenarios is because of the extreme speed and forces... this will cause the car to "walk" around as you described quite a bit more... especially seeing as the regular sbr4 is a relatively low downforce car.



On this drive once he start getting up above 200kph (roughly 120mph) you can start to see all the little course corrections he is putting into the wheel. The geometry in the suspension will naturally feed that back to him through the wheel, but he can also feel how the car is moving through the seat and mentally correct for it. Even on dead flat arrow straight roads... you still need to make these corrections to keep the car going straight and true.

The problem here isn't so much the game, but the fact that you appear to be using a controller... you can't feel any of the steering feedback (to have the car help correct itself) nor can you feel any of what the car is doing because... well... it's a game and I am assuming you don't have a sim chair. Since you are using a controller, you get the same effect as if you were stiff arming the wheel (like I mentioned earlier). The car can't help make corrections, and you can't really properly make corrections to the car either. These two effect kind of compound themselves on the flexibility of the rubber tires to basically create a bit of a feedback loop of sorts, which in turn, gives you your wobble.

If you drive in game with a wheel and proper force feedback, I can actually say that 90% of what you are seeing here does actually go away as the car can automatically (because of the suspension geometry) correct the wobble for you through the feedback. The rest you would normally feel through the seat, but again, I don't own a sim chair, so I can't feel that... I can only correct for what my eyes can see. So I can't quite get that last little bit to go away because of that.

That was way more explanation than necessary, but sometimes I can't control myself...

 

Thanks for the reply it was an interesting read.

I do play with game with both controller and wheel, however the G27 doesn't really have good response near the center so a lot of this small correction feeling is lost.

I understand driving at high speed in the real world requires these corrections, but I think this is overlooking that real world roads are never completely flat and smooth, I believe most of the corrections being made are due to these small imperfections. Particularly motor/highways having camber to prevent water collection. Whereas Grid Map is completely flat and smooth.

Even after watching the top speed run of the Bugatti Chiron, many small adjustments are made but they appear to be mostly as a result of bumps (you can see the driver moving in the seat).

Anyway my point wasn't really to say about whether these corrections are required or not, but the way that SBR almost violently moves left and right at 220 mph just seems wrong to me! Maybe it's to do with the front diff feeling some slip and sending the power back and forth to each side.


Maybe the WIP steering centering after damage system (please give it a name!) could help with this. If it allowed for a small amount of "play" in the steering based on controller input and suspension geometry it might allow for this natural correction to occur. As there is no feedback on a controller I can't see this taking much feeling away.

 

Ok ok... I see what your saying... I kinda got off on the wrong bit there then.

One thing to keep in mind though, as you brought up the Chiron... the Chiron is a Megacar designed to do one thing and one thing as elegantly as possible... so that's not really a fair comparison. They will have tons on aerodynamic measures in place to make sure that that car is rock solid at these speeds.

Now while the SBR4 can just about be considered a Supercar... I don't think it falls into the Hypercar, and definitely not the Megacar categories, so it won't have those kind of refinements... I always thought the SBR4 compared rather well with the Porsche Panamera... thus why I linked that video... and while that is a fast and refined car, its nowhere near Bugatti levels of refinement or speed. It's not even on the same planet I would say...

All that being said, I see what your getting at now though. So as a test, go take the SBR4, then chuck the hillclimb wing on it... see if that increases stability some. I say this because the SBR4 does have a rather small wing stock... perhaps that isn't giving it the stability it really needs at these speeds.