How do you secure bikes overnight on a multi-day ride when you are sleeping in a public campground?

The mental shift that helps: at a campground you are not defending against a professional with tools, you are defending against opportunism. Someone walking past at 2am who sees a bike they could ride away in four seconds.

That changes what works. You do not need a lock that resists an angle grinder; you need one that makes the bike not worth the ten seconds and the noise.

What that means in practice:

• Lock the bikes to each other. Several bikes cabled together cannot be ridden off and are awkward to carry. With three or four bikes this is most of your security and costs one lightweight cable between the group.
• Add a fixed object if there is one. A tree, a picnic table, a post.
• Keep them close and visible from the tent. Right outside, not around the corner.
• Remove the obvious escape. A quick-release front wheel through the rear triangle, or simply taking a wheel into the tent, means nobody rides away.

Two lightweight additions that punch above their weight.

A cable through everything, including into the tent. Run the far end of the cable inside and lie on it, or clip it to something inside. Nobody is quietly extracting a bike attached to a sleeping person. This is a genuinely old trick among tourers and it works because the failure mode of theft is that it must be quiet.

A small alarm. There are tiny motion alarms meant for luggage that weigh almost nothing and are painfully loud. In a campground full of people, noise is the thing an opportunist most wants to avoid, and it also wakes you.

Between the two, you have made the bike loud to move and impossible to move silently, at a cost of a couple of hundred grams.

One more that is worth asking about rather than assuming: many campgrounds have somewhere better than your pitch.

A locked equipment store, a reception area, a shower block that locks at night. Staff at places used to cyclists often have a routine for this and will offer it if asked. It is the single highest-value thing you can do and it takes one conversation at check-in.

The practical detail people forget: strip the bike overnight.

Bags, computer, lights, pump, tools: all of it comes off and comes inside anyway for weather reasons. A stripped bike is less attractive than a loaded one, and more importantly, if the worst does happen you have lost a bike rather than a bike plus everything needed to continue.

Also take a photo of each bike with the frame number visible before you leave home, and keep it on your phone. It costs a minute and it is the difference between a report the police can act on and a description of a black gravel bike.