I wanted to add that there are a bunch of factors at play in this optimization problem that might not be obvious. For example, there are diminishing returns in

I wanted to add that there are a bunch of factors at play in this optimization problem that might not be obvious. For example, there are diminishing returns in reduced wear from distributing load over more tires at some point. More tires & rolling parts also tend to increase rolling resistance, even ignoring extra weight that tends to come with a more complex design. Another potential advantage of having more axles is to reduce the frontal area of the vehicle by arranging tires in the direction of travel instead of putting them side by side on the same axle. Frontal area is a big component of the drag on a vehicle, along with speed and drag coefficient.