A lot actually. Every part can affect physics - e.g. you can add 500kg block to your left headlight. First, check chassis with things that are necessary to run (steering wheel, two seats - for symmetry, engine and suspension). If it still turns to one direction, check chassis' _main .cfg, look for
body 0.000 -0.068 0.419 0.000 0.000 0.000 114.778 cars\racers\Fiat_500_data\meshes\_phys_chassis_cockpit.scx ;0x0000003F
lines, and play with them, until you get decent result.
