Gr.1 speed glitch

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Pururut

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Greece
Greece
Gr. 1 cars tends to have better top speeds if you adjust their suspension with some non sensetical setup. Maximize their front hight and frequency, minimize their back hight and frenquency. With some proper tuning they nearly gain 40 kmh more top speed.

I dont know if anyone witness this but i dont think any suspension setting should increase the top speed of a car that much.
 
Pururut
Gr. 1 cars tends to have better top speeds if you adjust their suspension with some non sensetical setup. Maximize their front hight and frequency, minimize their back hight and frenquency. With some proper tuning they nearly gain 40 kmh more top speed.

I dont know if anyone witness this but i dont think any suspension setting should increase the top speed of a car that much.
Click to expand...

It's not a glitch, just a consequence of physics called "rake angle".

A negative rake angle is where the rear is lower than the front of the car.
With this, as the load at the rear wing builds with speed, the rear of the car is forced toward the ground, and at a certain speed the airflow over the rear wing stalls, reducing drag and downforce. This in turn causes the front to lift, reducing the effectiveness of the front wing.

This is what the Mercedes-Benz team tried with the CLR back in 1999 to improve speeds on the Mulsanne straight.
However, M-B got too greedy with the rake angle, and we all knew what happened because of that...
CLRflip1.jpg
 
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Makes at least some physical sense:
Reduced down-force will result in more "forward" force, thus more speed
Front up, rear down should result in airplane like behavior, though ... but i don't think they have implemented that in their physics engine;)

(****, too late, did a race before clicking "post")

TheChosenOne: "and at a certain speed the airflow over the rear wing stalls, both reducing downforce and drag"
That, however is complete BS. Stall => more drag.
Possibly, M-B was after the "reduce downforce" part, which might be good enough, since the drag of a small (compared to car) wing is not that important...

If they (Polyphony) correctly take the rear wing angle into account it will also be slightly lower than standard thus reducing downforce, too. The main downforce comes from the ground effect, though...

After all: the reason for the "nonsensical" setup seems to be the fact that the wing is not adjustable
 
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The Chosen One
It's not a glitch, just a consequence of physics called "rake angle".

A negative rake angle is where the rear is lower than the front of the car.
With this, as the load at the rear wing builds with speed, the rear of the car is forced toward the ground, and at a certain speed the airflow over the rear wing stalls, both reducing downforce and drag, and as a result the potential top speed increases. This in turn causes the front to lift, reducing the effectiveness of the front wing.

This is what the Mercedes-Benz team tried with the CLR back in 1999 to improve speeds on the Mulsanne straight.
However, M-B got too greedy with the rake angle, and we all knew what happened because of that...
CLRflip1.jpg
Click to expand...

Then this explains the top speed increas. Then adjusting any car that that has front downforce like this will increas its top speed. Correct?
 
The Chosen One
It's not a glitch, just a consequence of physics called "rake angle".

A negative rake angle is where the rear is lower than the front of the car.
With this, as the load at the rear wing builds with speed, the rear of the car is forced toward the ground, and at a certain speed the airflow over the rear wing stalls, both reducing downforce and drag, and as a result the potential top speed increases. This in turn causes the front to lift, reducing the effectiveness of the front wing.

This is what the Mercedes-Benz team tried with the CLR back in 1999 to improve speeds on the Mulsanne straight.
However, M-B got too greedy with the rake angle, and we all knew what happened because of that...
CLRflip1.jpg
Click to expand...
The cars flipped multiple times in practice and qualifying before flipping again during the race. If it was just negative rake, why didn’t they just adjust the suspension?
 
Sander 001
The cars flipped multiple times in practice and qualifying before flipping again during the race. If it was just negative rake, why didn’t they just adjust the suspension?
Click to expand...
That's not a question for me to answer, but I will say that adjusting the suspension might have helped. However M-B decided to increase front downforce to combat this effect.
In (at least) two of the incidents, the flip occurred after the CLR was trailing another car over a crest.

Among the main flaws of of the CLR were its huge overhang on the front and rear along with a relatively short wheelbase, which was almost 200mm shorter than the Toyota GT-ONE. Because of these factors, the entire car is more sensitive to changes in pitch angle.

As the CLR went faster, the rear wing generated even more at downforce, firmly planting the rear wheels and providing a pivot point for the car to pitch. As the nose lifts at the front, the rear of the car gets closer to the track and the rear wing in turn generates even more downforce. Then, as the front of the car lifts, air pushes the underside of the car, causing the car to flip.

4307-8.jpg


For comparison, modern LMP1 machines have shorter overhang.

audi_motorsport-140325-1026__large.jpg
 
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nuu1212
That, however is complete BS. Stall => more drag.
Click to expand...

Doesn’t that only apply for wings that produce lift? I’m sure it’s the opposite for wings producing downforce.
 
The Chosen One
That's not a question for me to answer, but I will say that adjusting the suspension might have helped. However M-B decided to increase front downforce to combat this effect.
In (at least) two of the incidents, the flip occurred after the CLR was trailing another car over a crest.

Among the main flaws of of the CLR were its huge overhang on the front and rear along with a relatively short wheelbase, which was almost 200mm shorter than the Toyota GT-ONE. Because of these factors, the entire car is more sensitive to changes in pitch angle.

As the CLR went faster, the rear wing generated even more at downforce, firmly planting the rear wheels and providing a pivot point for the car to pitch. As the nose lifts at the front, the rear of the car gets closer to the track and the rear wing in turn generates even more downforce. Then, as the front of the car lifts, air pushes the underside of the car, causing the car to flip.

4307-8.jpg


For comparison, modern LMP1 machines have shorter overhang.

audi_motorsport-140325-1026__large.jpg
Click to expand...
Google tells me they did an investigation and concluded it were the overhangs and changed the regulations. Did they change the regulations for rake?
 
Sander 001
Google tells me they did an investigation and concluded it were the overhangs and changed the regulations. Did they change the regulations for rake?
Click to expand...
I can't point to a specific rule change or regulation that explicitly describes the rake angle, but I am sure there are some rules dictating maximum pitch angle from X Newtons of force applied to the wings on the cars, or that there are certain "aerodynamic stability" requirements.

The CLR was incredibly sensitive to pitch changes, as it only took 2 degrees of pitch to send the car flying end-over-end.
 
Pururut
Then this explains the top speed increas. Then adjusting any car that that has front downforce like this will increas its top speed. Correct?
Click to expand...
It should be fairly similar on all cars, with added downforce or not, the principles are the same. But the effects will be far more noticeable with race cars and some of the more modern super/hypercars.

If you are going to use negative rake for this purpose, be sure to make this the first thing you tune on the car.
Any change in rake will have an effect on the caster angles of both front and rear suspension (causing a a few changes in the suspension's dynamic range) and will alter the car's weight distribution, as well as the aerodynamic effects already explained in this thread so far (Great info guys :bowdown: :gtpflag:).

The more dramatic the change in rake, the more implications it has on other parts of a set-up. Braking, steering and turning performances will also be greatly effected by drastic changes in rake angle.

:cheers:
 
nuu1212
Front up, rear down should result in airplane like behavior, though ... but i don't think they have implemented that in their physics engine;)
Click to expand...
It may seem like so, but remember that the CLR flip was a result of a combination of factors that no longer exist in modern LMP racing at Le Mans:

  • High negative rake
  • Huge elevation changes on Mulsanne and the run up to Indianapolis
  • Huge front and rear overhang
  • More focus on top speed performance, compromising aerodynamic stability
  • Low downforce cars
 
nuu1212
Back to the original question:
I don't think that this setup should account for 40km/h
and I think the car should become pretty undrivable.

the ground effect downforce is pretty complicated, though, how could PD ever get this realistic...
e.g. see https://eprints.soton.ac.uk/42969/1/GetPDFServlet.pdf
Click to expand...
There are a lot of video at youtube about it. without suspension setting Alpine VGT can reach 445-450 kmh with suspension setting it can reach 490 kmh.

 
nuu1212
Back to the original question:
I don't think that this setup should account for 40km/h
and I think the car should become pretty undrivable.

the ground effect downforce is pretty complicated, though, how could PD ever get this realistic...
e.g. see https://eprints.soton.ac.uk/42969/1/GetPDFServlet.pdf
Click to expand...
Firstly, thanks for the link :cheers:.

And to answer your questions, best I can anyway :dopey:. 40km/h isn't really all that much if you're already going 320km/h and over, especially in a high downforce racecar. if the car only weighs 800kg and produces 1600kg of downforce, you car is doing that speed and weighing 2400kgs. If you can use rake to drop the effects of the aero part it has the same effect as lightening the car. And a lighter car will go faster, the engine has less work to do. If the gearing allows it of course.

And yes, it can cause some cars to become hard-damn near impossible to drive
But I find it can be a good technique to use in some of the more front heavy FF and 4WD/AWD cars to help limit the dive under braking and allow the weight to get rearwards quicker to help rotate the car :).
 

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