> You have started out with the assumption that these higher efficiency tires are worse gripping.
Generally speaking, with tires you are trading off wear, grip, efficiency, and cost, among other things (like off-road durability which is irrelevant here). When you make a tire roll more efficiently, it tends to make it perform worse at gripping the road in all sorts of conditions, especially adverse conditions like rain and snow. I am speaking in generalities because there are thousands of tires from dozens of manufacturers and this is not a law of physics, but it is generally true in practice. Tires today are worlds better than tires of 50 years ago but this is still true to a first approximation.
So yes, I am making that assumption.
> So either the manufacturer-supplied originals are more dangerous than replacement tires, or your argument is missing something.
The tires that come on your car from the factory are optimized for one thing and one thing only: for the OEM to sell you the car.
OEM tires are famously (infamously?) often worse in terms of wear and grip than the equivalent tire available aftermarket because they are cheaper to produce (bringing down sticker price), roll more efficiently (helping them hit EPA fuel economy numbers), and quieter on test drives. Having a cheaper tire that is quieter on test drives and hits EPA numbers that are competitive with comparable models helps sell the car.
Higher treadwear doesn't help the OEM sell the car because your test drive isn't long enough to drive the car for 60,000 miles let alone 600. Higher grip doesn't either, as average buyers won't notice tire grip on a 15 minute drive on dry pavement and enthusiasts will replace the tires anyway. With the exception of certain enthusiast vehicles, if running a cheaper tire from the factory gets the price of the car from $40,000 to $39,950, the OEM will do it, even if the buyer has to replace the tire 20,000 miles sooner and it doesn't grip as well on dry pavement or in rain or snow.
> The rest of your quasi-questions all would need to be evaluated to see if they are true or not... and one would hope that at least some of them were evaluated when creating the policy. You seem to be assuming they were not, without any real evidence one way or the other.
I'm not sure what makes my questions "quasi", I'm just having a friendly conversation about tires on the internet.
There's almost nothing in human history with a worse record of causing unintended consequences than government regulation, even well-intentioned (cookie banners?), so I think I say charitably with some basis in historical fact that governments have a spotty record when it comes to understanding and predicting the second-order effects of the regulations they make. I ask my questions with that understanding. And I say all this as someone who is broadly sympathetic to and often in favor of many government regulations that reduce CO2 emissions and make cars more efficient. I enjoy clean air as much as the next person.