> I think as a starting point, I would expect that tire wear should remain roughly in proportion to road wear

IMO this would be a suspect assumption to make w/o data to back it up. You've got two dissimilar materials interacting (in very different modes). E.g. rolling a metal ball bearing on a wood surface would obviously cause the wood to degrade far more than the ball bearing, (and even a wooden ball rolling on a wood surface would wear substantially less due to the mode difference).

(If I had to guess the road has a higher wear as the surface has a tensile stress around the contact patch of the tyre, causing most of the damage, but this is just armchair engineering at this stage).

You quoted me out of context by cutting off a very important qualification to my statement:

given the same tires on each vehicle

I don’t endorse the broader statement which would imply the same wear regardless of tire material. That claim is clearly false.

The point I was after to make is that you can't assume that road wear scales the same way as tyre wear (I was assuming same material fwiw, just different loads). They are being worn under very different modes/scenarios.

Given that roads and tires experience the same forces under driving conditions (Newton’s Third Law guarantees this) I think it’s a reasonable prior assumption to start from. There are of course other environmental factors that accelerate road wear (rain and water erosion, freeze thaw expansion) but those conditions were not included in the study that produced the Fourth Power Law.

This assumes that road wear and tyre wear are caused by the same mechanism, but tyre wear is presumably caused predominantly by friction, whereas road wear is at least in part (and perhaps predominantly) caused by compression, creating pot holes by causing the earth underneath to move.

It's quite noticeable (to me at least) that the areas with highest wear are usually places that have heavy vehicles (buses and lorries) braking and accelerating. Traffic lights and bus stops will often have bumps/dips that seem to demonstrate a shearing force between the road surface layers.

I have always assumed it was just due to the uneven distribution of weight by vehicles often being stationary in the same spot, so those points are subject to more compression forces than the surrounding road surface.

If it were acceleration and deceleration I’d have expected the effect to be less localised, as breaking and accelerating happens over a much longer distance.

But, I have no actual idea. It’s just probably not friction…