With a Model 3 from Tesla, you can currently only order the trailer hitch. Obviously, it cannot be retrofitted or integrated. In general, one may notice that purely electric cars have problems with the issue trailers. Only as an SUV are they suitable for significant trailer operation, the absolute front runner is the Model X from Tesla with 2,250 kg.

Why is this so? Actually, a purely electric car should be predestined for such a task with its high weight and a lot of torque from the low speed range. We cannot answer the question exactly at this point, but we suspect a problem in the extended area of the brakes.

In the past, the attachment of a trailer hitch was not an issue for the vehicle brake at all. After all, an unbraked trailer was and is limited to 750kg and the brake seemed to be able to have that easily in reserve. If not, as is the case with small cars, for example, then the registration in the vehicle documents were adjusted accordingly.

So you only had to screw and possibly drill properly and the mechanical stability was guaranteed. In addition, there was a socket that provided for the transmission of all light signals to the rear. The highlight was then the switching off of the rear fog light by a switch in the plug connection.

That has changed fundamentally. With the advent of bus systems, the rear lights were no longer controlled directly, but by a control unit that implements the commands from the front. At the same time, a very short check and a warning in the event of defects are possible before the start of the journey. So you couldn't just switch on an additional light or brake unit.

Well, you might think that with an additional small control unit or a corresponding ability of the existing one, this would be taken into account and done, right? This has changed fundamentally with the advent of assistance systems, for example. Various control units in the vehicle need to know that trailer operation is possible and that one is being towed along. The former was ruled out by teaching the system after installing the trailer coupling.

Why? As the simplest example, the rear-view camera would constantly report that you are close to a wall or that someone is too close. Incidentally, the effort is inconceivable if one day the task of this camera is taken over by a camera on the trailer, e.g. indispensable for some systems in autonomous driving.

It is questionable whether this will also be necessary for systems that warn of a rear-end collision and initiate appropriate safety measures. In any case, the view to the rear has been permanently disturbed up to now, at most it makes sense to take a look at the drawbar and trailer hitch when coupling. The voltage sensors at the rear can also be switched off because a warning of cross traffic would come too late when reversing.

Back to the beginning. A (new) trailer coupling must therefore usually be reported to the system in the vehicle. The system can find out whether coupling is in progress by querying the socket. There is generally no separate connection in hydraulics, as is the case with the compressed air brake, for trailers with overrun brakes. Of course, the driver does not notice this, at most if a stagger control for trailer operation has been ordered in addition to the new purchase.

Anyone who has hopefully only got into a slight side motion when towing a trailer will know that other measures must be taken here than are necessary when oversteering the solo vehicle. We know from trucks that you have to make sure that a truck trailer must be held by the parking brake even if all the compressed air has escaped. Nowadays this can be the part of the electronic parking brake for hydraulic brakes.

A trailer wouldn't make autonomous driving any easier either. Already the possible warning when leaving the lane may no longer work because the sensors may not be able to look past the trailer to the rear. Everything that goes in the direction of self-driving must at least be adapted. Just think of the cruise control with distance control, which now has to take a longer possible braking distance into account.

Of course, the entire navigation must also know from the trailer, actually, how wide, tall and heavy it is, too. That brings us back to the electric car, the range of which is of course shrinking, which must be taken into account when planning charging stations. This planning must probably also know whether 80 or 100 km/h is allowed for the trailer, or it gets this information from previous experience with trailer driving.

As you can see, you can take the topic of connectivity almost as far as you want when driving with a trailer, e.g. e.g. highlighting certain traffic signs that are particularly interesting for this vehicle. We have not mentioned the drive, which presumably requires more changes in management such as engine temperature and gear selection in case of the combustion engine. The electric car would then perhaps be slightly less affected, but because of the above reasons, one probably refrains from the adaptation of heavier trailers at the moment.