Do you have to use dowel support on a 2 tier cake?

Yes....My first try years ago doing a stacked cake, I did not use dowel rods and the filling oozed out of the bottom tier because of the weight of the top tier!!!!

Duplicate post, please also see:

http://www.cakecentral.com/cake-decorating-ftopict-644567-.html

HTH

It is a rule to add supports whenever you stack tiers.

If the top tier is super small, I still suggest you minimal support.