Hello, friend !
I have just been pointed to your work and it looks so promising ! I made my own similar work for GTA IV, with the materials.dat and such. I see the release date is imminent, how is it going ?
Did you manage to fix the motorcycles also? "Realistic Bike Physics and Power" mod did make great inroads there, imo. I replicated and modified those values across all my bikes, I'd suggest to take some inspiration from there if you haven't started on bikes yet