The optical-image stabilisation and closed-loop autofocus systems - mechanisms that helps capture clear, sharp images by counteracting movement - can be harmed by engine vibrations.
The phones should therefore not be attached to powerful bikes, for purposes like navigation, the support page on Apple's website said.
Owners of scooters and mopeds should use "vibration-dampening mounts", it added.
The notice said: "The advanced camera systems in some iPhone models include technology like optical image stabilization and closed-loop autofocus to help you capture great photos even in difficult conditions.
"These systems work to automatically counteract movement, vibrations, and the effects of gravity to let you focus on taking a great shot."
Apple continues to say that "long-term direct exposure to high-amplitude vibrations within certain frequency ranges" can degrade these systems' performance, reducing the image quality.
"It is recommended to avoid exposing your iPhone to extended high-amplitude vibrations," the notice added.
"Attaching your iPhone to vehicles with small-volume or electric engines, such as mopeds and scooters, may lead to comparatively lower-amplitude vibrations, but if you do so a vibration dampening mount is recommended to lessen the risk of damage to your iPhone."