Attack bikes carry two crew and usually mount a heavy weapon on a side car or similar arrangement. Attack bikes function in almost the same way as bikes but can fire two weapons in the shooting phase and have an improved save to account for their two crew. In close combat an attack bike is treated as a single trooper with two attacks.
Attack Bikes
Source: Core Rulebook 3E, p. 94
Attack bikes carry two crew and a heavy weapon, can fire two weapons in the shooting phase, and fight in close combat as a single trooper with two attacks.