Even though I have no HDD mounted in my car. I worked as a reliability engineer for the disk drive industry. The reason that a lot of people have not had problems with vibration issues is that the industry has greatly made advancements in the error correction built into the hard drives. The older ones could fail by just touching the side of a PC case. this also has to do with improvments to the servo and the speed of the drives today (air bearings and others). As far as shock goes the real factor is the duration of the shock pulse the drive sees (under 2ms) unless it is a huge shock. The thing to rember when fixturing the HDD is that there are materials that will dampen shock however amplify vibration and vise versa there are shock isolaters that will do the job. My job was not to buy the isolaters just did OEM testing for PC makers and their chassis. One factor that really matters is rotational shock and vibration these 2 will effect the HDD more that linear. the worst shock axis is the Z axis this is the HDD in its normal postion (flat).