stock SetVehicleSpeed(vehicleid, Float:Speed)   
{   
        new   
            Float:X,   
            Float:Y,   
            Float:Z,   
            Float:Angle;   

        GetVehicleZAngle(vehicleid, Angle);   
        Speed = Speed/200;   
        X = Speed * floatsin(-Angle, degrees);   
        Y = Speed * floatcos(-Angle, degrees);   
        SetVehicleVelocity(vehicleid, X, Y, Z);   
}  

SetVehicleSpeed(id машины, 20.0 (скорость));