THE first week of preseason testing ahead of the 2018 Formula 1 season has been one of the most difficult to read anything into, the main reason being the cold, even snowy, weather for much of the first week of testing at the Circuit de Catalunya in Spain. Nevertheless, even though the fuel loads, engine mappings and run plans are unknown to outside observers, there is always something to learn from cars on track. MercedesIt is easy enough to assume that Mercedes has built a good car for the 2018 season. With the exception of a suspected oil or fuel pressure issue early in the week, there didn’t appear to be significant issues with the reliability of the W09. Though they hit the track relatively slowly, as the week progressed the car too began to come into its own. What was evident was that both drivers, Lewis Hamilton and Valtteri Bottas, seemed to struggle with oversteer while heating the tyres. Naturally, it’s still a work in progress, but Mercedes would be pleased with their work thus far.FerrariIn contrast, Ferrari seemed to start the week on the front foot with a car that appeared to be an impressive step forward. The SF71H looked stable and showed no reliability issues whatsoever. As the test progressed, however, Ferrari seemed to stagnate slightly in its performance. There was no real improvement from the car that rolled out of the pitlane on day one. This could very well have been Ferrari’s run plan, which will make their performance in the second test all the most interesting. It is quite clear, however, that Ferrari and Mercedes maintain an advantage in engine performance. Red BullIt was a rather muddled few days for Red Bull. While the first day likely went according to plan, much of the rest of the test session was spent fidgeting with aero parts. Similarly, Max Verstappen’s time in the cockpit was affected by fuel leaks and ending up in the kitty litter. The good news is that when it’s on track and running smoothly, the Red Bull looks a good car. It may be early days yet, but it is quite evident that the Renault engine is still somewhat adrift of the performance of the Mercedes and Ferrari engine. Renault and McLarenThe Renault works team look to be the leaders of the midfield after the first few days of testing. The car looks settled in the hands of both Nico Hulkenberg and Carlos Sainz Jr and appears to be a good platform to build from for 2018. While Renault may be topping the midfield it’s likely only by a slight margin over McLaren. Fernando Alonso and Stoffel Vandoorne’s new orange-and-blue liveried car looks quite solid and, most important, reliable with the Renault power unit now in the back of the car. Toro RossoThe announcement that Toro Rosso was partnering with Honda was a surprise given the Japanese manufacturer’s dire runs with McLaren. However, in stark contrast to 2017 the Honda engine ran with notable reliably. While the Toro Rosso didn’t set any headline grabbing laptimes it seems that the team and Honda are willing to work together which will be vital for their season prospects. The second preseason test takes place this week, ahead of the opening round of the season in Australia on March 25.