Pre-C19, I regularly took my Moulton and my S&S Frezoni on Eurostar. Max dimension 85cm and bagged = no problems. London checked dimensions once or twice. Only one London X-ray machine was big enough to let them fit through.
Try to get on as early as possible or the luggage racks suitable for big bags get filled up with little bags.
Pre-C19, I regularly took my Moulton and my S&S Frezoni on Eurostar. Max dimension 85cm and bagged = no problems. London checked dimensions once or twice. Only one London X-ray machine was big enough to let them fit through.
Try to get on as early as possible or the luggage racks suitable for big bags get filled up with little bags.