Hard disks that are designed for laptops are designed for these types of circumstances. Obviously when they're in use, the read/write heads are just micrometers above the spinning platters and any light bump will cause the heads to contact the platters. Which means instant ruin.
Some high-end laptops and/or hard disks have G-sensors that will sense a sudden change in G-forces. Regardless of what the hard disk is doing at that time, they will force the heads to move to the "park" position instantaneously if the thresholds are exceeded. This will save your heads and platters in case of, for instance, a fall.
However, when the hard disk is spun down the heads are "parked" in a safe location away from the platters. In this position, they can easily survive the biggest jolts - even jolts that would destroy the laptop itself, such as dropping the whole laptop on a concrete surface. Which is a lot more than what your laptop is going to endure on the motorcycle thanks to suspension and a padded case/bag.
Hard disks are routinely spun down. In fact laptop hard disks are designed with many tens of thousands of spin down/spin up cycles in mind. If you have not messed around with your power saver settings, a spin down will typically happen:
- When you shutdown, hibernate or sleep your laptop.
- When you close the lid even if this doesn't cause a hibernate or sleep
- When the laptop is not in use for more than 5 or 10 minutes and running on battery power
- When the laptop is not in use for more than 30 minutes and running on AC power.
To be sure, check your Power Saver settings and adjust if required.
Obviously if you have a laptop with SSD you have even less to worry about. SSD is now standard in high-end laptops. Low-end or older laptops can typically be upgraded to SSD and I highly recommend you do so. Your laptop will boot up a lot faster and in general will feel much more responsive especially for disk-intensive operations.