I always make sure to check the limits tho... anyway...
tried something else, made a new one with bigger wheels, 7L V12 Petrol, 520 torque, transaxial medium 4 speed, should be able to take 550, but when I get over 70km/h it feels like it's slipping all over, however.. when it finally gets to 99km/h it does the same kinda jerk and slows to 96km/h... and once it decided to flip on me too.
But I'll test it out further tomorrow.
Wheels could be loosing adhesion to the ground at high RPM. Toy with physprop_jalopytire and makesphere