Wheel size discussion

[MCoach]

AG, MCoach,

Look at what yaw inertia will do for a given step or ramp steer on Lateral Acceleration Response Time (LART), Yaw Velocity Damping (YVD), Lateral Acceleration, Cg slip angle, and Yaw velocity Overshoot, Lateral Acceleration, Cg slip angle, and Yaw velocity settling time and look at a Bode Diagram with amplitude and phase shift for different yaw inertia (and by the way different tire - 10 and 13 " relaxation lengths) and you will tell me if yaw inertia is important or not.

If you are non convinced by the simulation and/or as a useful addition to your simulation, put a ballast at the CG (let's say 10 to 12 kgs), probably close to the driver's butt to keep the same a and b (same weight distribution - that is very important because 0.25 % weight distribution variation makes a significant handling difference - the ratio yaw moment derivative vs the yaw velocity derivative is a^2 and b^2 sensitive - if you don't you will change too many parameters at the time) and the same CG height.
Ask your driver to make a few laps and/or, even better, a simple slalom with 6 to 10 cones.

Then split your ballast in the same proportion as your weight distribution in 2 parts as far away as possible, keeping the same weight distribution and CG height (a part your ballast somewhere in the nose, the other part near the differential)
Ask your driver to drive the same course and ask him if he feels the difference. Look at your gyro signal and the derivative of your gyro signal vs your steering input.
Compare the change of yaw inertia due to your centered or split ballast with the yaw inertia of let's say 10 kg and 12 kg of non suspended mass per corner.

I have. Differentials such as near locked diffs and spools seem more important. Sideforce from hella big end plates and elements seem more important.

UNC Charlotte ballast tested about 15-20lbs of ballast added to the very nose of the car and then removed. Some of the drivers at least felt a difference, nearly identical lap times.