[kwhitefoot]

Larger displacement engines are almost invariably in larger, heavier, vehicles. Axle weight determines road wear. I agree that using the axle weight would be better but displacement taxes were also a luxury tax.

Some of my cars over the years:

Mini: 600 kg, 850 cc

Rover 75: 1 700 kg, 2 500 cc

Chevy Van: 2500 kg, 5 000 cc

[AnthonyMouse]

> Larger displacement engines are almost invariably in larger, heavier, vehicles.

This isn't even a good approximation because turbochargers (which nearly all heavy, diesel vehicles have) significantly increase power at the same displacement. The 5 liter Mustang weighs less than 4000 pounds. Here's a >10,000 pound bus with a 3.2L diesel engine:

https://www.tescobus.com/bus-for-sale/collins/school/