Wikipedia states that a trailer is an unpowered vehicle towed by a powered vehicle.

I've been away from LFS and the forums when the mods were released, so I'm not sure if this topic was discussed (I searched, but didn't come across anything?).

Currently is there any possibility of coupling car with a trailer, providing that the necessary parts are designed on both the car and the trailer? Similarly, can a truck couple with a semi-trailer?

As per my understanding, with "fixed" parts this would not work. However, I see that some vehicles have movable parts (pop-up headlights, movable dump box, street sweeper attachments etc.). Along the same lines, if the tow ball attachment can be deployed and retracted, would that be able to attach to a suitably designed trailer coupler? Similarly, if the coupling on the semi-trailer truck can be deployed and retracted, would it be able to couple with a semi-trailer?

Would this work if the truck and the trailer were suitably designed in the LFS editor? Or would Scawen need to make some changes (to the collision model?) for it work? Or is this impossible?

Since this is in the suggestion section, I agree with this, because it makes the game more interesting for the cruise players.

But since the post looks more like a question:
Currently, this is not possible. Only fixed trailers are available, no separate parts. The rotation method you mentioned doesn't work with the anti-collision, because LOD2 and LOD3 (which are responsible for the long-distance view and anti-collision) are bound only to the main object, which can't have rotation. Even if rotation worked, people would fly away with the current anti-collision system.

In theory, objects should have a different anti-collision system, but they don't. Even if objects had a different anti-collision, that would mean that one player would be the driver and another player would be the trailer. I don't think people will enjoy being trailed.

So I agree with the suggestion to have separate trailers attached to mods.

Interesting. Thanks a lot for the detailed input. And yes, I meant the trailer as an object that can be interacted with (not as an unpowered 'vehicle' for another player). i.e. trailers as objects that can be coupled/decoupled at as necessary.

Does this collision model apply for the tyres as well? For example, can a smaller car stay on a recovery truck, or would the contact between the truck's bed and the car's tyres cause issues?

Quote from Silverracer :

Interesting. Thanks a lot for the detailed input. And yes, I meant the trailer as an object that can be interacted with (not as an unpowered 'vehicle' for another player). i.e. trailers as objects that can be coupled/decoupled at as necessary.

Does this collision model apply for the tyres as well? For example, can a smaller car stay on a recovery truck, or would the contact between the truck's bed and the car's tyres cause issues?

Since I have already tested this, the tires won't cause any issues. Actually, there are a few tow trucks in the game already and you can try them with another player. But with the current physics - the towed vehicle must drive together with the towing truck or it will fall. The game doesn't know if you are on top of a truck, and it keeps your car in one position, so when the tow truck moves, the towed vehicle falls.
Example of a working tow truck: https://www.lfs.net/files/vehmods/8D7133 (by Androphp)

EDIT: I was actually thinking about this in this post - https://www.lfs.net/forum/post/2084414#post2084414

https://www.lfs.net/forum/thread/105972 This is as close as "trailer" we can get in LFS right now, i think it would be hard to implement by Scawen but if it just takes a couple of months to code it in then all the semi truck mods will be happy

Quote from r3zp3k7 :

The game doesn't know if you are on top of a truck, and it keeps your car in one position...

Ah, so its not due to a collisions-related issue. Thanks for the info!

Quote from dh7938726 :

This is as close as "trailer" we can get in LFS right now

Thanks!