Question: Tires

Hello fellow tuners,
I have been tinkering around in the cars and a lot of stuff is self-explanatory and for others I found videos, but not for this.

I found no explanation for which wheels to use in what situations.
The game tells me that wheel-type X has more grip. But on which conditions?

Are racing tires always better? Even offroad?

I accidentally did drive with my racing tires in the snow yesterday instead of selecting a car with snow tires,
and it didn’t really change much.

Currently got 2 Vipers for the S1 class, one with Racing and the other one with Offroad/Snow Tires.

Also, shouldn’t smaller tires be better on ice and snow? Does the engine calculate that in?

In the meantime I found, that having Offroad-Tires is pretty much mandatory for snow-tracks.

Noone?