Performance in snow/ice with OEM tires?

I was repeatedly warned by the dealer not to alter the tires as a small percentage difference in rotational distance can mess with the computers. Another guy who bought his at the same time put on a nice set of 19s off (I think) his F-Pace which looked sharp. Here is the thing—the dealer made him sign off that he was warned about installing unapproved wheels and tires. I think that will protect them against a warranty claim in the future maybe.

From the way they describe it, the car is constantly measuring and adjusting the motors from front to rear and left to right and if you start messing with the size of the wheel you can cause problems. Specifically what problems, I am not sure. It would be nice if you could access the computer and type in what size wheel/tire combo you have so it can make the adjustments.

The other theory could be that they just wanted me to buy their snow tire package on those horrific 18” wheels. No thank-you.

Trivia - Racing tires are not uniform in diameter. They mark the circumference on them with grease pencil so you pick a matching pair for the rear.
I would estimate there are differences in street tires too. The temperature of the mold and the injected rubber cause this. The hotter the injected 'rubber' is, the smaller the tire it produces. It shrinks when it cools. So workshift changes and unheated/cooled factories produce inconsistencies.

If a tire loses 1/8" of tread, the circumference drops about 1%. But hot/cold weather and pressure can change that even more.

And the Weird Factor. Tread squirm and centripetal expansion. The faster the tire spins the larger the dia. BUT, the more torque that is applied, the smaller the effective diameter.
Rubber stretches. When torque is applied, the area behind the contact patch is stretched, and the area in front is compressed. Some folk think this is 'slip' but it's not. It happens even when you have slicks glued to the track with VHT.

So small differences in circumference on tires is expected.

22” Winter Tires

It’s my experience and practise to have separate winter tires/rims; all season tires are a compromise in performance -they’re better than having summer tires on the winter but not the greatest to have them in the summer. I live in Chicago where they do a good job plowing but having winter tires sure gives me the secure footing necessary to drive through smaller streets. So in my case I chose winter tires because: 1 - it mitigates the dilemma of having the limited selections and increased cost to find 22” winter tires. 2 - it eliminates the necessity to get the winter tires swapped out from the summer tires, which has a cost to them; aside from the cost to have them swapped out your also paying for a probable rebalance, every time. 3 - optimal winter driving is achieved by using smaller diameter and narrower wheels, so in my case I settled with a set of 20” winter tires and rims from Tire Rack - they tried to talk me into 18” but they wouldn’t looki as cool with the 20’s on my new iPace. The local Jag dealer also told me that by going with the 20” it would NOT hinder nor affect nor require any type of adjustment on the motors......no ill effect at all.

All I need is a one time balance and I simply have the tires “marked” so when the winter season arrives I know where they were mounted last season so they are rotated to optimize wear. If your lucky ask the tire store if they store tires - I get mine stored for $175 USD per year ( 2 swaps) - may sound pricy but it eliminates me having to carry them in my garage attic and it also allows my wife to have the tires mounted if I’m out of town.

..........Just a thought to consider