Thanks for the excellent information. Arriving at CDG terminal 1 in April with a bicycle. Considering two options for getting to Paris:
- RER B. Are there lifts/elevators to access the different levels (ie from ticket purchase level at Roissypole/T3 to platform level) or will I need to navigate the escalators/stairs?
2. Roissy bus. Can I take a bicycle on this bus either boxed or unboxed?
Do you have any views on the better option?
Yes there are elevators at CDG Terminal 1 train station (inside Roissypole building) from the ticket purchase level to the train platform level; you won't need to navigate stairs/escalators. You can check the current elevator status on this webpage showing elevator status across the entire Paris public transit system. See this Paris transportation wheelchair accessibility article (scroll down a bit) for more details on using that elevator status page.
Also, in this photo, on the CDG Terminal 1 train station article, if you enlarge the photo, you can see blue sign reading "Access aux trains". The top left corner points to the location of the elevators for the CDG Terminal 1 / Terminal 3 train station after passing through fare gates. One of the fare gates will be double wide allowing passage of wheelchairs / bikes.
I'd suggest using either the lead or tail train car for your bike and yourself as there are usually empty sections (no seats) where you can stay with your bike. Some train cars are designated with bicycle areas, but it's not consistent across all trains (you can check by looking for a bicycle decal on the train car door). Note that you're not supposed to bring your bike aboard trains during rush hours: from 06:30-09:00 and 16:30 - 19:00. See this Transilien page for more information (in French. Transilien is the group responsible for RER lines in the Paris outer metro area).
I would suggest avoiding Roissybus with a bicycle. It's not officially allowed to bring bicycles aboard Paris buses, Metro, trams (with an exception for Metro 1 on Sundays).
Have a good trip!