Max velocity is total_power * 80.
Safe velocity is (assuming one engine):
power * type_constant * k_mass * k_dynamics * 80
type_constant is 0.6 for gas, 0.65 for diesel, 0.9 for electric
k_mass is currently rather forgiving, because vehicle components are quite light. A car weights 750 kg - compare to real life car that is closer to 3000 kg.
k_dynamics is k_aerodynamics * k_friction
k_friction is usually rather high (as in, doesn’t impair much). Exceptions are vehicles with huge wheel area, like rollers.
k_aerodynamics is also really forgiving: you need a vehicle with 7 tile width to get it down below 0.5