What's up with Mercedes? F1 struggles and Bahrain worries explained

There's no getting away from the fact that Mercedes had a somewhat troubled Bahrain test last week. Such has been the team's historical dominance that there is a widespread disbelief that they are actually behind the pacesetters - but in the tests at least, it very much was.

The W13's performance was being compromised by aerodynamic 'porpoising' - to an extent greater than most other cars and certainly more than the Red Bull and Ferrari.

Preventing the car from generating that violent bouncing motion on its suspension is not difficult in itself, but the trick is not losing a lot of performance by doing so.

Running the car a little higher on its suspension will prevent the phenomenon from being triggered, but will surrender a lot of downforce in the process.

Each team needs to find its own car's sweet spot for each given track between good downforce and a lack of the bouncing motion which as well as being very uncomfortable and possibly physically damaging for the driver if sustained for a full race distance, also presents reliability concerns.

Red Bull, Ferrari and McLaren appear to have found that sweet spot. Mercedes, by the end of the test, had not.

Its new narrow sidepod inlet car created a stir when it appeared on the first day of the Bahrain tests and in the team's simulations this version of the car was significantly faster than the wider-inlet car which ran at Barcelona.

Around the Spanish track, which did not induce the porpoising anything like as much as in Sakhir, the Mercedes was quite possibly the fastest car. But in Bahrain, the theoretically faster version of that car was around 0.7s off the pace set by Max Verstappen's Red Bull (which itself had been significantly modified).

It is clear we have not yet