So you would rather have tires as an entire slab of metal? Interesting. I wonder if the idea inspired by the initial wooden wheels. Because even they realized they shouldn’t use the entire wooden slab as the wheel, no matter how heavy the cart it needed to pull.
The transition shown above was made considering the fact that slab-wheels, as I would like to call them, increases the weight while the whole purpose of the spike-centered wheels, also what I like to call them, is to evenly distribute the weight of the cart along with reducing the weight of the wheel itself.
Why? You may ask. The holes in the tires are there to reduce weight, Moreover, The Suspension system of the entire vehicle that the tire is supporting will function efficiently if the mass of the tire at resting position is kept to the minimum. It is important to notice that creating lightweight tires will make the car run more smoothly too!
We compared the moment of inertia from a rotating object to the moment of inertia of a resting object. Given that the moment of inertia is dependent on the mass of the rotating object and the radius of the rotating object.
Inertia usually for a solid disk becomes for a hoop, a thinner structure. Hence, the resistance of gravity has been reduced to half resulting in a significant smoothness in the rotation of the tires.
Another minor factor here is angular momentum. The lesser the weight of the rotating object, the lesser the inertia of the tires which will reduce the angular momentum. When the car is turning, the conservation of angular momentum will cause the body of the car to move away from the turning direction. The weight reduction will help lower that angular moment to avoid any incidents of body roll when turning the corner. Hence, making the lighter tires allows weight reduction and is cost effective.
Another utility of these holes is that they help with ventilation. They exist to allow proper airflow to cool the brakes.