It depends on how much "larger" your larger suitcase is. I used to travel with a 24 inch bag, and if it didn't fit over the seat, it would fit in the rack at the end of the car, or in the space between the seats. But a 30 inch bag could be hard to fit on some trains.
Even more important than size is weight. Since you have to heft your own stuff - there are no porters, separate luggage compartments, checked luggage, etc. - make sure it's not too heavy.
The Man in Seat 61, referenced in several replies above, is a great resource, but be careful - you can spend days reading it, as there's so much there. Start with his great answer to your question - how is luggage handled on European trains? http://seat61.com/luggage-on-european-trains.htm
And yes, Eurail is a pass, but there is no such thing as "the Euro Rail." There are national rail companies (Renfe for Spain, Trenitalia for Italy, etc); there are competitors on some routes in some countries (like Italo in Italy); there are private lines on routes where the national rail company doesn't go (like FEVE in Spain or Trenord or Circumvesuviana in Italy), and there are multinational corsortia that run trains through several countries (like Eurostar from England to France and Belgium, or Thalys from Belgium to France, Netherlands, or Germany).
To find train schedules for almost all of Europe in one easy-to-use place, use the Bahn (German Rail) website http://reiseauskunft.bahn.de/bin/query.exe/en, following Rick's tutorial: http://www.ricksteves.com/travel-tips/transportation/trains/online-schedules