Going on holiday to France with your bike is pretty straight forward, but as with a lot of things, its better to book in advance.
The Eurostar allows you to take your bike in 1 of 3 ways into Europe.
1) Reserve a place for your bike on the train in advance - For peace of mind, you can reserve a place for your bike on the train you’re travelling on for £30 one way, subject to availability.
2) Fold it up - If your bike is placed in a suitable bike bag no longer than 85cm, you can carry it on board as part of your baggage allowance.
3) Use the registered baggage service on the day of departure - For fully assembled bikes or bike bags over 120cm at their longest, you can use their registered baggage service for only €29 one way from Paris, €25 from Brussels and £25 from London. They will do everything they can to ensure your bike travels on the same train as you. But if it can’t, they guarantee that you will be able to collect it at your Eurostar destination station within 24 hours of your departure. If you can fold or dismantle your bike and place it in a bike bag between 85cm and 120cm at its longest, then you can use their turn-up-and-go registered luggage service for just €15 from Paris or Brussels and £10 from London. Your bike will generally travel on the same train as you unless there is not enough space. If this is the case, they will send it on the next available train.
On trains running from London to Avignon, Provence and the French Alps, bike bags measuring between 85 and 120cm can be carried on board as part of a passenger’s baggage allowance.
Once you're in France getting around with your bike can be straight forward, but again planning ahead and getting to the station early are highly recommended.
Domestic or regional trains (TER) and Tourist trains quite often allow you to transport your bike for free, although you may have to put it in a bike compartment, or hang it from a hook to save space, or fold it up and take it on as hand luggage. Spaces are limited and you cannot reserve in advance, and in some regions bikes aren't permitted Monday-Friday during working hours as the trains are too busy with pedestrians.
Regional trains in Ile-de-France, the region surrounding Paris, are called Transilien. These are the country’s busiest commuter trains. They operate into all of Paris’ stations and run on lines with a letter associated (line K, line P, etc.). They also include the RER trains, which run on lines A to E. You can take your bike on board a Transilien Monday to Friday, before 6.30am, between 9.30am and 4.30pm, then after 7.30pm; At any time on weekends and bank holidays and at any time if it is folded or placed in a bike bag and does not cause fellow passengers any inconvenience.
On Intercity trains it's best if you can dismantle your bike and carry it on in a bag no more than 120x90cm. Some of these trains require a seat reservation, whereas others do not. Consequently, according to the type of train, it may or may not be necessary to book, or pay for, a place for your bike.