The proposed HS2 rolling stock tender specification does not preclude a bidder offering a tilting train solution. Once bids are received they will be assessed for meeting the tender specification, which is designed to get the best technical and value for money rolling stock solution.
Trains which can tilt are more expensive to buy and maintain, because of the tilt equipment needed on board. HS2 Ltd assumes that a tilting train would have a maximum operating speed of 300km/h on the high speed network, where they will primarily operate, whereas a non-tilting train would have a maximum operating speed of 360km/h, so the use of tilt trains would significantly decrease the benefits from reduced journey times. HS2 Ltd also assumes that a tilting train would have a lower seating capacity than a non-tilting train. This would significantly reduce the benefits gained from seating capacity.