Hi, you cannot pre book bikes on, it is 1st come basis max 2 bikes per bus. Not doing it this yr.
http://www.oxfordtube.com/londontube.php
12. Can I take my bike?
We have a large storage area on each coach where bikes can be placed during the journey. If the coach/storage area is full then all customers, including those with a bike, must wait for the next coach. Up to two cycles may be carried at any one time, subject to available space.