The Class 221 are similar to the Class 220 Voyager units .
The Class 221 were built with a tilting mechanism enabling up to six degrees of tilt to allow higher speeds on curved tracks , most have five coaches , and they have a different bogie design .
The Class 221 are similar to the Class 220 Voyager units , but were built with a tilting mechanism enabling up to six degrees of tilt to allow higher speeds on curved tracks , most have five coaches , and they have a different bogie design .