Luggage

Hello there,

It's my first time going to Japan and it's quite overwhelming to put all the info together.
That said, i hope someone can help me with a question that i've came across, and it's about luggage. I'm planning to travel with a hand bag that doesn't need any reservation, but i'll also carry a bigger bag which i've seen i need to make a reservation (Bag size A+B+C = 160~240cm)
Do you guys know If the same rule applies to all rail transportation on Japan? I can book it for free anytime i'll use a train?

Thank you very much,
Best regards,

Rodrigo.