Normal road-bike vibration is unlikely to damage a DSLR by itself, especially if the camera is in a bag. A padded camera bag or added foam will reduce high-frequency vibration further. The bigger risk is sharp impacts: crashes, the bike falling over, or the bag swinging into something.

Several cyclists report carrying DSLRs for long distances, including on gravel and cobblestones, without problems. So for typical road riding, this is generally not something to worry about.

To reduce risk:

• use a padded camera insert or bag
• keep the camera from moving around inside the bag
• protect it from hard knocks and falls
• consider a smaller mirrorless camera if you want less weight and more room for padding
• if you ride in very rough, wet, or muddy conditions, a rugged/tough compact camera may be a better choice

In short: for road cycling on tarmac, a DSLR should usually be fine if it’s carried securely and cushioned against impacts.