It's the engine, stupid!

Even though Mercedes were dominating the 2014 season, there was some hope that the other teams would catch up in 2015. Williams, for example, were very strong at the end of 2014 and Red Bull were likely to perform better in 2015 with an upgraded Renault engine, so the future looked promising. In the end these predictions did not materialize and Mercedes were dominating again in the 2015 season, which was a big disappointment. Where did it all go wrong and why did Ferrari suddenly become Mercedes's closest rivals?

In 2014 Mercedes had by far the best car-engine combination. Williams had more or less the same engine, but a relatively poor chassis, while Red Bull had possibly the best chassis, but a much weaker engine. Apparently, neither Williams, nor Renault managed to make much progress over the winter, which left a much improved Ferrari as the only real threat for Mercedes, even though they still lacked a considerable amount of single-lap pace.

Although Ferrari had improved on all areas, only the improvements on the powerunit really stood out. In fact, the Ferrari chassis was even worse compared to Mercedes's in 2015, as an analysis on pure relative pace (based on the fastest lap by every team) shows.

Data (from F1 Fanatic):

• Outright pace in 2014 and 2015
• Track characteristics

I've used the relative pace of the teams (except Caterham, which was not included in the dataset and Manor for various reasons) for all races in the past two seasons. As the pace is relative to the fastest time, I think it makes sense to compare the pace to the mean pace-deficit of the field. In this way the relative performance of the frontrunners can be estimated. I've removed the outliers in the data and then I've correlated these relative performances to track characteristics.

Track characteristics:

• Number of corners per kilometer to test the performance of the car's chassis
• Percentage full throttle to test the performance of the engine

I've estimated the relative performance of each chassis and each engine for both seasons. These were the results:

Chassis performance in 2014 (red) and 2015 (green).

Engine performance in 2014 (red) and 2015 (green).

The chassis performance indicates how much the relative performance of a car improves with the number of corners per kilometer (which ranges from 1.9 in Monza to 5.7 in Monaco). As expected, Mercedes and Red Bull have the highest chassis performance (around 0.3% per corner per kilometer), followed by Ferrari. The chassis performances did not change too much between 2014 and 2015. The weaker teams did not really catch up. Only McLaren (different design philosophy), Force India and Toro Rosso managed to slightly improve their chassis compared to Mercedes. Mercedes's closest contenders actually all dropped back.

Interestingly, the Mercedes engine had on average the same edge over its rivals in 2015 as in 2014, as the engine performance shows. Their relative advantage was about 0.01% per percentage full throttle per lap (which is between 34 and 76%). Ferrari, however, made huge gains (which probably explains why Sauber did much better in 2015, as their chassis performance was still quite bad), while Renault was even less competitive than in 2014.

The combined effect of chassis and engine performance meant that Williams and Red Bull dropped away compared to Mercedes, as their loss of chassis performance was not compensated by a gain in engine performance. Ferrari, however, were the only of the three teams to gain a lot of horsepower, which meant that the prancing horse was the only top team to gain on Mercedes. This is clearly visible when the estimated average relative performances of 2014 and 2015 are plotted against each other:

The team average performance-level in 2014 and 2015.

On an average circuit Mercedes were 1.5% faster than the average car in both seasons, while Ferrari improved from 0.4 to 0.9%. Williams dropped from nearly 0.6% to nearly 0.4%, while Red Bull went from 0.6% to 0.2%. The other teams were quite consistent, and their relative performances did not change more than 0.2% from one year to another. Lotus and McLaren were, however, the exceptions. That was no coincidence, as they were the only teams to switch engine supplier. Lotus switched from Renault to Mercedes and benefited, while McLaren switched from Mercedes to Honda and instantly became a backmarker. With the aerodynamic development going relatively slowly, a good powerunit is more important than ever.