Thanks for your patience
Before (but I’m talking when I was young 
) I was riding a road bike but years ago so I’m probably not used anymore… but I’ll check parts you mentioned just to be sure, thanks.
I’m pretty sure I just need a while to get used. I choosed the 18" for a slight increase of speed but I probably made a mistake… will see.
About the rack indeed I tried to tight the bolt but doesnt go more than that.
It goes down in the correct position, if I press it attach to the frame correctly but does not stay up like in the picture. Just this. I’ll ask the vendor as I have no idea on why this happens.
Thanks anyway I will post some picture soon 