I am making a beer mug cake, using four 4" round cakes. Do I need to add support between the layers, or can I just sit each layer on each other? The cakes aren't very heavy or very big, so I'm just asking...

Thanks!

better to be safe than sorry..... I would

Yeah I would - thats like stacking a 2 tier. Like the poster above said - better safe than sorry.

They say anything over 4inchs needs support. I just did a 4 layer honey pot and definitly supported and center doweled. The pot was sitting on top of another layer.
In hindsite I wish I had of filled, then put it back in a fridge to chill, then iced. I had to center dowel cause it kept sliding around where the board was in the center.