Solved

New league, beginning in pro tier. Why?

I just created my own league to play together with some friends. After creating, I immediately entered the pro tier without noticing.. My friend is in the rookie tier and I want to race against him. Why does the game instantly promote me to pro tier after joining? Is it because I was in pro tier in the league I just left? If this is a bug, can any admin relegate me to rookie in some way perhaps?

What tier you are in is independent of what league you're in, meaning, if you are ever promoted or relegated, that is always the tier you'll be in.
Since you'd like to race with your friend, I've relegated you to Rookie. A warning though, he'll be heavily outperformed by you and won't be likely to win any races, so I'm not sure if this will be exciting for him.

Okay. I will keep that in mind. Thanks a lot!