Scuderia Ferrari SF90

[MtthsMlw]

[godlameroso]

I love how analytical you guys get.

It's a combination of things. Partly weight transfer(soft compression damping on 3rd spring front, and soft rebound on the 3rd spring rear) would allow the car to pitch like that under braking. Further enhanced by the fact the rear wing flexes downward at speed at the retraction, so raises a few mm as the aero load is removed. Lastly perspective of the car approaching and camber of the turn.

[matteosc]

The first part of this

“The Ferrari more softly sprung to encourage weight transfer”

Is wrong on two counts.

Firstly the “transfer” of tyre load from front to rear is not dependant on the suspension stiffness. They could run no suspension at all and the exact same change would happen. What the stiffness does is affect the amount of movement and how quickly that movement happens. The first is down to the springs and the second the damping elements. So a car with soft suspension moves more in response to the exact same forces experienced by a more stiffly sprung car.

Secondly it’s not “weight” that gets transferred it’s load. Load is the sum of the downward forces acting on the axles. The weight of a car is one of those forces. It is the mass of the car being accelerated downwards by gravity.
...

Did you take into account the wheel radius and possible uphill or downhill movement while braking?

In the simple case of load transfer under braking I don’t think wheel radius or slope has a part to play. The forces involved are either parallel to the road surface or perpendicular to it.

Am I wrong?

You are right and you did a very clear analysis. Wheel radius doesn't matter, plus it is something you cannot modify. Slope would change things a little, but it really doesn't matter in designing a car...
On the weight vs load part you are right in the difference, but while breaking it only the weight to be transfer, so we can use either word.

[henry]

Did you take into account the wheel radius and possible uphill or downhill movement while braking?

In the simple case of load transfer under braking I don’t think wheel radius or slope has a part to play. The forces involved are either parallel to the road surface or perpendicular to it.

Am I wrong?

You are right and you did a very clear analysis. Wheel radius doesn't matter, plus it is something you cannot modify. Slope would change things a little, but it really doesn't matter in designing a car...
On the weight vs load part you are right in the difference, but while breaking it only the weight to be transfer, so we can use either word.

Thanks.

I still disagree about the weight thing . The car weight does not change and nor does its distribution. If the car weighs 800kg and the weight is distributed 54%/46% rear/front before braking it is exactly the same during braking.

[timbo]

I still disagree about the weight thing . The car weight does not change and nor does its distribution. If the car weighs 800kg and the weight is distributed 54%/46% rear/front before braking it is exactly the same during braking.

If you define weight very strictly (i.e. load produced by the gravitational interaction with the Earth) then yeah, it's not shifting (much, there can be miniscule differences due to car's attitude changes, fuel sloshing etc).
The load on the tyres does change and so is the force acting on the springs/dampers.

[jacobianminkowski]

In the simple case of load transfer under braking I don’t think wheel radius or slope has a part to play. The forces involved are either parallel to the road surface or perpendicular to it.

Am I wrong?

You are right and you did a very clear analysis. Wheel radius doesn't matter, plus it is something you cannot modify. Slope would change things a little, but it really doesn't matter in designing a car...
On the weight vs load part you are right in the difference, but while breaking it only the weight to be transfer, so we can use either word.

Thanks.

I still disagree about the weight thing . The car weight does not change and nor does its distribution. If the car weighs 800kg and the weight is distributed 54%/46% rear/front before braking it is exactly the same during braking.

no

[matteosc]

I still disagree about the weight thing . The car weight does not change and nor does its distribution. If the car weighs 800kg and the weight is distributed 54%/46% rear/front before braking it is exactly the same during braking.

If you define weight very strictly (i.e. load produced by the gravitational interaction with the Earth) then yeah, it's not shifting (much, there can be miniscule differences due to car's attitude changes, fuel sloshing etc).
The load on the tyres does change and so is the force acting on the springs/dampers.

Yes, it is just a matter of definitions. What I meant is that the load shift is due to the mass of the car only and not to the aerodynamic load, as it is due to the inertia term.

[LM10]

From the point of view of the SF90 what’s interesting is the amount of movement, suggesting soft springs, and the timing of the movement which suggests the “damping” is responding to something other than just simple movement. People in earlier posts have suggested some possible theories on this.

What exactly do you mean with the timing of the movement? And what would the damping respond to other than simple movement?

By timing I mean how fast or slow the suspension movement is, and in the case of the SF90 how it is displaced in time from the initiating event.

Obviously the damping has to respond to movement, the regulations require it, I was struggling to express the more complex possibilities involved in the time shifting of such events. Maybe I could have found better wording.

Why do you think that the suspension movement is displaced in time from the initiating event? If possible, could you give an example, please?

[roon]

Thank you hollus, this illustrates it the best. And that's also my thought, as I've mentioned it in my last post.

Now, why would this be illegal or banned?

I think it's just normal behavior. Rear end squats when DRS closes. Front end squats as the brakes are applied. Any delay may be due to differences in the endpoint of the DRS zone and the start of the braking zone, or simply a delay in applying the brakes or a progressive increase in braking force by the driver. This was testing, not a race.

https://media.giphy.com/media/1yTgcCeZM ... source.gif

I also think it's normal behavior. But going a bit more into detail. These are the regulations:

10.1.2 Any suspension system fitted to the front wheels must be so arranged that its response results only from changes in load applied to the front wheels.
10.1.3 Any suspension system fitted to the rear wheels must be so arranged that its response results only from changes in load applied to the rear wheels.

So, the rear end squats when DRS closes, meaning that load is applied to the rear wheels. But what about the visible lift of the front wing at this moment? Can it just be seen as a consequence of the rear diving? Of course, it would make sense that the front needs to lift when the rear dives as both are interacting with each other. But then it means the regulations above are open for funny interpretations. I mean, when DRS closes, load is applied to the rear wheels through RW, but is as per regulation also load applied to the front wheels?

The rules are a bit impossibly worded. Consider that the rear wing is behind the rear axle. An increase in rear wing downforce should cause the car to pivot over the rear axle, causing the front axle to experience a reduced load, translating to a slight increase in front ride height. If this reduces front wing performance at the same time, the effect could be exaggerated.

[timbo]

The rules are a bit impossibly worded. Consider that the rear wing is behind the rear axle. An increase in rear wing downforce should cause the car to pivot over the rear axle, causing the front axle to experience a reduced load, translating to a slight increase in front ride height. If this reduces front wing performance at the same time, the effect could be exaggerated.

Not only that but the RW is a freaking barn door and has a ton of drag, and the point where this drag acts is clearly above CofG, so this drag itself creates a momentum which should raise the front somewhat.

[roon]

The rules are a bit impossibly worded. Consider that the rear wing is behind the rear axle. An increase in rear wing downforce should cause the car to pivot over the rear axle, causing the front axle to experience a reduced load, translating to a slight increase in front ride height. If this reduces front wing performance at the same time, the effect could be exaggerated.

Not only that but the RW is a freaking barn door and has a ton of drag, and the point where this drag acts is clearly above CofG, so this drag itself creates a momentum which should raise the front somewhat.

Good point. Roughly speaking you might say the wing is about 4x farther above the rear axle centerline than it is behind it. If the rear wing has something like a 4:1 L/D ratio, the drag force may be contributing a similar amount of lift to the front axle.

[matteosc]

The rules are a bit impossibly worded. Consider that the rear wing is behind the rear axle. An increase in rear wing downforce should cause the car to pivot over the rear axle, causing the front axle to experience a reduced load, translating to a slight increase in front ride height. If this reduces front wing performance at the same time, the effect could be exaggerated.

Not only that but the RW is a freaking barn door and has a ton of drag, and the point where this drag acts is clearly above CofG, so this drag itself creates a momentum which should raise the front somewhat.

I don't think they are impossibly worded. The change in load on the wheel can be caused by whatever external cause. The rule says that you cannot have a spring or a damper on the back axis which is working based on anything else than what happen on the back axis, whatever is the cause. This was done for avoiding linking through a pipe the front and the back axes, influencing directly the suspension behavior of one axis with what was happening on the other axis.

[roon]

The rules are a bit impossibly worded. Consider that the rear wing is behind the rear axle. An increase in rear wing downforce should cause the car to pivot over the rear axle, causing the front axle to experience a reduced load, translating to a slight increase in front ride height. If this reduces front wing performance at the same time, the effect could be exaggerated.

Not only that but the RW is a freaking barn door and has a ton of drag, and the point where this drag acts is clearly above CofG, so this drag itself creates a momentum which should raise the front somewhat.

I don't think they are impossibly worded. The change in load on the wheel can be caused by whatever external cause. The rule says that you cannot have a spring or a damper on the back axis which is working based on anything else than what happen on the back axis, whatever is the cause. This was done for avoiding linking through a pipe the front and the back axes, influencing directly the suspension behavior of one axis with what was happening on the other axis.

Good point. So one has to figure out an indirect form of influence to regain the effect.

[wuzak]

In that gif of the Ferrari braking, the car loses about half of its speed. So the rear wing will be giving about 25% of the downforce. Which explains why it rises. Also, the braking shifts the load to the front wheels.


I also expect that the spring damper system controlling that movement is a rising rate system, where the initial part is soft, while it gets very stiff near the end of the travel. This could explain the initial "jump" as the load comes off the rear.

[matteosc]

In that gif of the Ferrari braking, the car loses about half of its speed. So the rear wing will be giving about 25% of the downforce. Which explains why it rises. Also, the braking shifts the load to the front wheels.


I also expect that the spring damper system controlling that movement is a rising rate system, where the initial part is soft, while it gets very stiff near the end of the travel. This could explain the initial "jump" as the load comes off the rear.

Downforce is reducing on the front wing also, don't forget that. That said, the comparison with Red Bull shows that Ferrari is moving way more and way more "abruptly". Very nonlinear response from the back suspension.