Lord Parkin
aka emperor
You probably want to read this article.Can someone explain to me exactly how cultural border clash works?
Do they make a check every turn, because I have noticed that some tiles will come under my dominion even though the cities borders haven't expanded anymore.
Anyone now in numbers how this works?

Basically - every tile that you own, you put a bit of culture into each turn (more for tiles closer to the city, less for tiles far from the city). If your city is generating a large amount of culture per turn relative to nearby cities, then after a time those tiles will probably become yours.