More wheel surface area probably reduces this somewhat. I suspect that it’s the fourth power of the pressure, with the number of axles being used as a proxy for this.
It’s probably still well over four orders of magnitude, mind you.
The empirical finding that yields the fourth-power law is based on vehicle weight, not pressure.
I’m sure somebody has done far more detailed modeling, but that’d entail consideration not only of weight distribution, but the properties of different road surfaces and their relative frequencies of occurrence relative to road usage patterns. Modeling all that can get messy fast. Hence the populatiry of the fourth-power rule of thumb, which isn’t a bad gross approximation.
Car 1 is a Honda Civic. Perfectly ordinary, just like you find all over today.
Car 2 is the same model of Civic, but modified so that it has eight half-sized tires, four per axle. It has the same contact area with the ground and the same mass. It’s pretty intuitive that this would not significantly change the amount of road wear.
Car 3 has been modified relative to car 2 so that it has four axles with two wheels per axle instead of two axles with four wheels each. Same mass, same contact area, just distributed a bit differently. Can I prove that car 3 doesn’t cause 1/16 the damage of car 2? No, but I’d be very surprised if it did.
Yes, axle weight is a reasonable proxy, I don’t disagree. However, when making broad statements, it’s good to be as precise as possible.
More wheel surface area probably reduces this somewhat. I suspect that it’s the fourth power of the pressure, with the number of axles being used as a proxy for this.
It’s probably still well over four orders of magnitude, mind you.
The empirical finding that yields the fourth-power law is based on vehicle weight, not pressure.
I’m sure somebody has done far more detailed modeling, but that’d entail consideration not only of weight distribution, but the properties of different road surfaces and their relative frequencies of occurrence relative to road usage patterns. Modeling all that can get messy fast. Hence the populatiry of the fourth-power rule of thumb, which isn’t a bad gross approximation.
Imagine three cars:
Yes, axle weight is a reasonable proxy, I don’t disagree. However, when making broad statements, it’s good to be as precise as possible.