Создать класс колесо, имеющий радиус

#include<iostream>
#include<vector>
#include<string>
 
class Wheel  // класс колесо
{
 
private:
    unsigned rad;
 
public:
    Wheel()
        : rad(0)
    {}
    Wheel(unsigned radius)
        : rad(radius)
    {}
    void set_rad(unsigned radius)
    {
        this->rad = radius;
    }
    unsigned get_rad() const
    {
        return this->rad;
    }
};
 
 
class Car
{
 
private:
    std::vector<Wheel> car_wheel;
    std::string firma_name;
 
public:
    Car()
        : firma_name("unknow_firma")
    {}
    Car(unsigned kol_wheel, unsigned rad_wheel, std::string firma_name)
        : firma_name(firma_name)
    {
        for (int i = 0; i < kol_wheel; ++i)
            car_wheel.push_back(Wheel(rad_wheel));
    }
    void set_firma(std::string name)
    {
        this->firma_name = name;
    }
    std::string get_firma_name() const
    {
        return this->firma_name;
    }
    std::vector<Wheel> get_wheel() const
    {
        return this->car_wheel;
    }
};
 
class HeavyCar : public Car
{
 
private:
    unsigned capacity;
 
public:
    HeavyCar(unsigned kol_wheel, unsigned rad_wheel, std::string firma_name, unsigned car_capacity)
        : Car(kol_wheel, rad_wheel, firma_name)
        , capacity(car_capacity)
    {}
    void set_capacity(unsigned car_capacity)
    {
        this->capacity = car_capacity;
    }
    unsigned get_capacity() const
    {
        return this->capacity;
    }
};
 
 
int main()
{
    Wheel wheel_1(5);
    std::cout << "radius kolesa = " << wheel_1.get_rad() << std::endl;
    wheel_1.set_rad(10);
    std::cout << "meniaem radius" << wheel_1.get_rad() << std::endl;
 
    std::cout << std::endl;
 
    Car vaz_2109(4,13,"TAZ");
    std::cout << "firma " <<  vaz_2109.get_firma_name() << std::endl;
    std::cout << "rad_kolesa = " << vaz_2109.get_wheel()[0].get_rad() << std::endl;
 
    std::cout << std::endl;
 
    HeavyCar kamaz(10, 20, "TAZ", 20);
    std::cout << "firma " <<  kamaz.get_firma_name() << std::endl;
    std::cout << "rad_kolesa = " << kamaz.get_wheel()[0].get_rad() << std::endl;
    std::cout << "capacity =  " <<  kamaz.get_capacity() << std::endl;
 
    std::system("pause");
    return 0;
}