But when it comes to train travel, there's little if any advantage, usually you can either get a bike on, or you can't, the exceptions to this are the size of a Brompton.
Agree. Most of the time I can get a full-size bike on French trains. The TGV trains require removal of wheels and bagging, which is a faff. AFAIK the only possibility on Eurostar is a bagged folder. My Brompton was OK on this.
The advantage of something that packs as small as a Brompton is when the transport is crowded and it isn't possible to squeeze a full-size bike on, some examples of this :
- for commuting when the first train was cancelled and everyone took the second one. All the full size bikes were left behind.
- TGV in peak holiday season, where I removed the saddle and the QR left pedal to squeeze the Brompton into the space between a seat and the central partition.
- a ferry replacement when they had to use a smaller boat to replace the usual one that had mechanical problems. All bikes were banned, but I managed to take our two bagged Bromptons.
Before Covid I regularly took the Brompton on urban buses, always in a bag to avoid any awkward questions. I now also always use a bag for hotels, as I was once told off by the owner when I took an uncovered Brompton into a hotel room. But there has always been a solution in the hotels I have used when touring with a full size bike.