Thank you! The JR guys I asked WANTED to speak English to me. He misspoke! Hahaha — I ended up speaking on JP at the end but he gave a good effort. Yes, the definition they use for oversized is important. I’ll probably be back to talk about this in more detail.
ONLY in JAPAN
2022-11-20 07:24:44 +0000 UTC
Going by the JR Central Website, it's any luggage between 160cm total dimensions and 250cm total dimensions need a reservation.
As a guideline, a Medium Samsonite OC2Lite 68cm case's advertised total dimensions are 150cm.
Anything over 250cm is probably not even allowed on board.