There are also all season tires (marked M+S I think) that work through all the year but not particularly well in any season. The problem with changing tires is winter tires life span which is typically 5 years. Thus if you don't drive much, you end up disposing not much used ones every 5 years resulting in ecological and financial problems.

Yes even in places where there's no legal requirement because it is better to do that and because insurer can fuck you up if you don't have correct tyres

Do people just randomly have 4 extra tires in their homes to change when the time comes?

Yes. Either that or the spare set of tires is stored where they get their tires changed (and checked) twice a year.

PS: It's a set of wheels including tires (often the cheaper steal rims as that's not the stuff you drive fast with anyway...) for those having them at home of course. I would not actually change tires myself...

PPS: And as it's completely normal, it's not unusual to get a used car with a second set of wheels.

If you're in a country where there's is snow or just cold temperatures, you don't "randomly" have 4 extra tires. You literally need them for at least a few months. Typically you'd swap over in late October, then back in March/April depending on how it's going. Swapping them yourself is trivial enough, but it's also incredibly cheap to get them swapped at a shop.

Note that at least last I checked, the proper transition temperature isn't "freezing" or "there is snow", but about 7-8°C. That's when winter tires will have better grip, and summer tires grip steeply diminishes below this. Once there is actual snow, your just actually up shit creek with no paddle on summer tires. But if you have to emergency brake at like 3°C for example, it makes a significant difference what kind you got on your vehicle.

Pretty much yes! In the Nordics and the Alps most families own two sets, usually each on its own wheels (then you can change them by ourself, slo many times theres somekind of storage or you can use storaging and changing as a service), so the swap takes half an hour at home or a few minutes at a tyre shop. Many don't keep them at home at all: tyre shops run "tyre hotels" that store your off-season set and swap it for you twice a year.

The other route is all-season tyres with the snowflake-on-a-mountain mark (3PMSF): in most countries with a winter rule, Germany included, they count as winter tyres, so one set does the whole year. Where winters are mild that's the usual choice.

summer tires harden in cold temperatures, making them less grippy even without ice or snow. and winter tires get too soft in warmer air, meaning they stretch more, which can lead to overheating and blowout. so you do need both. there are some tires that are allowed year-round, but they're less efficient.

also it's usually not just extra tires, but complete wheel sets. that way you can change them yourself.

Yes. Either that or a workshops holds them for you (🤑).

I don't have to change my tires but I do. They are stored in my shed, but people who don't have space at home may pay for them to be stored at the mechanic's facilities.

On days with fresh snow I often see several cars in ditches on my drive to work. I live in a rural area and have also had to dodge out-of-control cars and trucks so I want to make sure I can depend on the grip.

Eta: I once skidded right through an intersection on a red light because I was in a rental on summer tires. Never again lol!

These days there exist four-season tyres, which to my knowledge meet the requirements of countries that require winter tyres in winter or wintery conditions.