Weight distribution and inertia

Question

Real cars like mine I try to reproduce usually have a bit more weight on the front and are also designed to have more understeer as this is meant to be safer.

I define the Z-Axis of center of mass so that the "Load N" values of the wheels in the telemetry window on a flat surface resemble the targeted weight distribution. Is this the way to go?

But what about inertia, when I set it ti positive like suggested for a front-engine the car is extremely sensible for oversteer. I only seem to get plausible results if I:

1. Set inertia to negative 1
2. Set positive inertia but with a weight distribution of the inverse as it should be.

The question is if in this case, the inertia should be positive and the handling should be adjusted otherwise, although I see limited possibilities there.

Does inertia define center of gravity (!= center of mass)?
What does an inertia bias value of 1 or 5 mean?

Answer 1

I define the Z-Axis of center of mass so that the "Load N" values of the wheels in the telemetry window on a flat surface resemble the targeted weight distribution. Is this the way to go?

Yes, exactly.

Does inertia define center of gravity (!= center of mass)?

As for what I understand, center of gravity and center of mass are the same for practical purposes in VPP. Inertia and center of mass are independent from each other.

What does an inertia bias value of 1 or 5 mean?

It's the rotation of the inertia tensor along the X axis in degrees. In practice, positive values favour oversteer and negative values favour understeer.

Inertia Bias should be set up in the last place after configuring mass, center of mass and suspension:

• If the resulting car oversteers too much but it should oversteer less or even understeer, then reduce Inertia Bias or move it to negative values.
• If the car understeers too much but it should understeer less or even oversteer, then increase Inertia Bias.

Note that the inertia effects at high speeds may be superseded by the aerodynamic setup. Example: if aerodynamic components provide more downforce at the front axle than at the rear axle then the car will tend to oversteer at high speeds regardless the inertia setup.

Comments

OK good, what I wanted to clarify was if negative inertia bias could be cheating in this case, but maybe it's not. It is hard to get real world data and if you have them they are too complicated for me yet to process :P Like this: http://www.car-engineer.com/vehicle-inertia-calculation-tool/

My issues were especially at slow speed corners (below 80 km/h) so aero is not the issue, also power-oversteer wasn't it. I might also have to play more with the Y Axis of CoM and Inertia parameters.

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I don't think it's cheating, just behavior matching. If the real car behave in some way, then there's an inertia value that matches that behavior, no matter it's positive or negative.