It doesn’t help that much. Each tire of a fully loaded 18 wheeler carries 4.4x the weight of a typical car tire. 4.4 ^ 4 = 378x the damage per tire but there are also 4.5x the tires so your at 1,700x the damage.

That’s an oversimplification, but it doesn’t really matter if it’s 99.9% or 95% of the damage ware is still absolutely dominated by heavy vehicles.

And how many more SUVs go through that road? If there's a few hundred SUVs for every 18 wheeler, it's no longer negligible: it's 10 or 30% of the damage.

And it could be a lot more negligible, if that mostly drive alone, drove a car with half the weight.

Most SUV’s aren’t that heavy.

I used 4,000lb for the car, a 2024 Chevrolet Suburban which is huge only clocks in at a 5,824 lbs. Load another 1,000lb for passengers etc and (6,824/4000) ^ 4 = 8.5x a car or 0.5% what I calculated for a full 18 wheeler.

Sure there’s more cars than 18 wheelers but 7,000lb is a rather extreme outlier in terms of SUV weight.

Well, my 7 seater has a kerb weight of 2780 lbs (and it's a hybrid, the petrol is lighter); fully loaded it's under 4400 lbs.

And it's probably heavier than most cars around here, because most cars are not 7 seaters, but 4/5 seat hatches.

US SUVs and pickup trucks wouldn't fit most parking lots around here (to tall, to wide to even get in), but somehow the problem is never the size/weight of cars people got used to drive.

That statement is only true in aggregate. If you you're taxing individual vehicle owners SUVs will still get taxed way less than trucks.