Ok, what is the reason for handling problem then? is it flex of frame or something undefined? If it is something undefined, one tricky aspect can be collision triangles, sometimes node can collide to axle collision triangles, causing your suspension setup not to work as it is kinda steel against steel situation.
Not %100 sure the car will launch and will lift up in a odd way on the right side but thats expected with the diff it has... so i add a wheelie bar and then it launches and the rear wheels just lift up off the ground... i can show you im messing with it rn on stream
If there is enough mass and velocity, that could happen. wheelie bars might need some cushioning, like spring/damper setup or flex to structure to kill that energy that rotates vehicle's nose up, so that it is not so sudden stop, if it is sudden stop, then energy has nowhere to go but up. Also make sure your bumpstops use lot higher damping than official ones, because those will launch car to air like a pogo stick. I'm sure more clever guys can figure out exact problem if you post it to here or mod support.
maybe add an option to add turn to the rear wheels, or do what fufsgfen said and make the bar flex and dampers. also there is a tire and wheel mod out there you might want to use for testing and just recommend it when the mod is finally released. and, its just me, but pro mods dont ever look right without giant tires. the 15x14s on this would look tiny, so if you could add some fatties i'd pay money for this mod
