Best weight distribution front/rear

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Best weight distribution front/rear

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I have some questions about weight distribution on F1 cars...

What is the best/optimum weight distribution front to rear in F1 cars ? What is the current weight distribution of F1 cars? Is it 45%/55% front to rear ?

What are the chassis, suspension and aero designers/engineers trying to achieve with understeer vs oversteer with weight distribution?

Has the hybrid era with KERS, MGU-H/K and batteries forced F1 teams to sacrifice the optimum weight distribution to a more unfavorable distribution weight compared to the 1990's and early 2000's F1 cars ?

In 2004, I remember reading that the Renault had a little less weight on the front with around a 40%/60% or 42%/58% front to rear as to why they were so quick off the line and gave them an advantage in mid corner and accelerating out of the corners sooner than the Williams...

In the Chinese GP that year (2004) Ralf Schumacher complained that he couldn't keep up with the Renaults as they exit the corners so much sooner than he could in the Williams. Was that due to the Renault chassis or did the Renault engine have better low end torque/HP than the BMW ?


In road cars for years it seemed that the best weight distribution for mid/rear engine cars was 42%/58% front to rear.

42% front, 58% rear is used in these road cars below...

1990 Acura/Honda NSX
1992-1998 McLaren F1 road car.
1995 Ferrari F50
2019 McLaren GT - (42.5/57.5)

Gordan Murray who designed the McLaren F1 road car talked about how he got the inspiration for the McLaren road car from owning a 1990 Acura/Honda NSX.

Greg Locock
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Re: Best weight distribution front/rear

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Weight distribution by itself is a fairly meaningless parameter IN ISOLATION if you don't know much about the tires and especially if they are different front to rear. I ran a lap simulation for a car with identical tires all round and varied the weight distribution from 40:60 right through to 60:40 and the differences weren't huge.

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Re: Best weight distribution front/rear

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Greg Locock wrote: โ†‘
Tue Oct 18, 2022 10:10 pm
Weight distribution by itself is a fairly meaningless parameter IN ISOLATION if you don't know much about the tires and especially if they are different front to rear. I ran a lap simulation for a car with identical tires all round and varied the weight distribution from 40:60 right through to 60:40 and the differences weren't huge.
But, there's got to be a good reason why F1 and Indy car designers design cars that have wider rear tires?

What about cars that are mid/rear engine and the rear tires are wider than the front tires with a 40/60 or 60/40 weight distribution? Does it cause understeer or oversteer ?

Below is a quote from another forum, just to add some thought to this topic...

"Let's not forget about polar moment too. A car with most of the mass concentrated near the center of mass (like a mid-engine car) will have a lower polar moment and will tend to change direction more quickly. Unfortunately this means it is less stable and will rotate faster (harder for most people to catch) when it loses grip when compared to a car with a high polar moment. The 944/968 mentioned previously as well as the C5/C6 Corvettes have very nearly 50:50 weight distribution, but also have a larger polar moment because although the center of mass is near the centerline of the wheelbase, the mass is spread out because the engine is up front and the transaxle is in the rear. This means that they are inherently more stable and change directions more slowly than a car with a lower polar moment."

Rodak
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Re: Best weight distribution front/rear

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I have some questions about weight distribution on F1 cars...

What is the best/optimum weight distribution front to rear in F1 cars ? What is the current weight distribution of F1 cars? Is it 45%/55% front to rear ?
You don't really have much choice in F1. From the 2022 Technical Regulations:
4.2 Mass distribution
With the car resting on a horizontal plane the mass measured at the front and rear axles must
not be less than the mass specified in Article 4.1 factored by 0.440 and 0.540 respectively at
all times during the qualifying practice session. Rounding will be to nearest 0.5kg.
If, when required for checking, a car is not already fitted with dry-weather tyres, its mass will
be determined using a set of dry-weather tyres selected by the FIA technical delegate.

Greg Locock
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Re: Best weight distribution front/rear

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Bear in mind that static weight distribution matters even less with aero. 40/60 at zero speed becomes whatever you like at top speed. F1 has big driven axle tires for acceleration, then you adjust everything else around that.

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Zynerji
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Re: Best weight distribution front/rear

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Greg Locock wrote: โ†‘
Wed Oct 19, 2022 9:20 pm
Bear in mind that static weight distribution matters even less with aero. 40/60 at zero speed becomes whatever you like at top speed. F1 has big driven axle tires for acceleration, then you adjust everything else around that.

Can you elaborate as to how the rear-bias of weight effects the turning polar moment? Maybe get into how a shifting aero-load "weight" balance would then become a dynamic moment as speed decreases into a corner?๐Ÿค”

Rodak
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Re: Best weight distribution front/rear

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Zynerji wrote: โ†‘
Wed Oct 19, 2022 11:37 pm
Greg Locock wrote: โ†‘
Wed Oct 19, 2022 9:20 pm
Bear in mind that static weight distribution matters even less with aero. 40/60 at zero speed becomes whatever you like at top speed. F1 has big driven axle tires for acceleration, then you adjust everything else around that.

Can you elaborate as to how the rear-bias of weight effects the turning polar moment? Maybe get into how a shifting aero-load "weight" balance would then become a dynamic moment as speed decreases into a corner?๐Ÿค”
As I posted above, the c.g. is essentially defined by the FIA by front/rear weight distribution. The polar moment is determined by where the front and rear weight is located. The closer the front/rear mass c.g. is to the car's c.g. the less the polar moment (basically leverage) effect is and the more responsive the car will be to turning forces.

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Zynerji
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Re: Best weight distribution front/rear

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Rodak wrote: โ†‘
Thu Oct 20, 2022 1:40 am
Zynerji wrote: โ†‘
Wed Oct 19, 2022 11:37 pm
Greg Locock wrote: โ†‘
Wed Oct 19, 2022 9:20 pm
Bear in mind that static weight distribution matters even less with aero. 40/60 at zero speed becomes whatever you like at top speed. F1 has big driven axle tires for acceleration, then you adjust everything else around that.

Can you elaborate as to how the rear-bias of weight effects the turning polar moment? Maybe get into how a shifting aero-load "weight" balance would then become a dynamic moment as speed decreases into a corner?๐Ÿค”
As I posted above, the c.g. is essentially defined by the FIA by front/rear weight distribution. The polar moment is determined by where the front and rear weight is located. The closer the front/rear mass c.g. is to the car's c.g. the less the polar moment (basically leverage) effect is and the more responsive the car will be to turning forces.
I understand that, but does the polar moment shift while decelerating/aero unloading, or is it an instant moment?

Greg Locock
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Re: Best weight distribution front/rear

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The second polar moment of inertia, intergal dm*r^2, doesn't change with speed.

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Re: Best weight distribution front/rear

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Rodak wrote: โ†‘
Thu Oct 20, 2022 1:40 am
... the c.g. is essentially defined by the FIA by front/rear weight distribution.
.. The closer the front/rear mass c.g. is to the car's c.g. .... the more responsive the car will be to turning forces.
turning forces ?

to turn from a road going north to a road going east the car does 2 jobs ....
1. change where it's going from north to east - this is a big job
2. change where it's pointing from north to east - this a small job
PMI is only involved in job 2

if the car 'loses grip' it eg can do job 2 without doing job 1
it will rotate about the point of minimum rotational inertia - this won't be the cg
rear-engined cars have less inertia about this point than do comparable mid-engined cars


low-PMI (in yaw) is also low-PMI in pitch - such road cars have inferior ride
as cars did pre-WW2 - until independent front suspension came along so enabling increased PMI

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Zynerji
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Re: Best weight distribution front/rear

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Greg Locock wrote: โ†‘
Thu Oct 20, 2022 7:38 am
The second polar moment of inertia, intergal dm*r^2, doesn't change with speed.
Regardless of shifting aero load? Like, how does it work in Pouhon? Entry then second apex. Are they identical though at different speeds?

I would almost think that there is a tensor in there linked to static weight distribution + aero "weight" distribution(derived by speed/aero map), and suspension response (load shifting under yaw).

I'm not an engineer, so please take this as a plea for help!๐Ÿ˜‚

Greg Locock
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No. The yaw response is always governed by the wheel forces, wheel base, and PMoI. Aero affects the wheel forces.

Claude's got it more or less right here

http://downloads.optimumg.com/Technical_Papers/RCE2.pdf

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Re: Best weight distribution front/rear

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Greg Locock wrote: โ†‘
Thu Oct 20, 2022 9:58 pm
No. The yaw response is always governed by the wheel forces, wheel base, and PMoI. Aero affects the wheel forces.

Claude's got it more or less right here

http://downloads.optimumg.com/Technical_Papers/RCE2.pdf
There are side forces coming from the drag of the aero package when the car is in yaw so the trajectory is not only governed by wheel forces and the downforce augmented wheel forces.

A rocket as an example. In yaw, a rocket can be classified as stable when the CofP is behind the Cg because it means that drag forces will always act to return the rocket to 0 yaw angle if you draw a force/moment diagram. If CoP is in front of the CG the opposite is the case and the rocket is unstable because small yaw angles will cause a side force which, due its position ahead of the CG, will cause the rocket to continue to rotate away from the 0 yaw angle.

Image


Unfortunately I can't put a number on it, so it's possible that the aero forces are not significant compared with the force acting at the tires when the car is in yaw, however in a physics model, the aero forces would need to be included because they are not zero. It really depends on the speed. Naturally, at higher speeds the aero effects become greater and especially at high speeds in yaw, the drag force will contribute to the stability (or instability) in yaw if the CofP is in the wrong place.

Greg Locock
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yes, good point. but the yaw angle at high speed is tiny, less than 3 degrees.

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Re: Best weight distribution front/rear

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Which engine placement location in the car would be the best/optimal place for best handling or has the least negative drawbacks? A front engine car, mid/rear engine car or rear engine car?

Why did designers choose the 42/58 front to rear weight distribution for...

1990 Acura/Honda NSX
1993-1998 McLaren F1 road car
1995 Ferrari F50
2019 McLaren GT

?

Honda used the CRAY supercomputer to aid in the design of the NSX's frame to find where to stiffen it.