It seems this year is once again very much evolving around tire performance. Both Ferrari and Mercedes seem to be very closely matched,but many of the car characteristics have evolved from last year. This year with arguably close to engine performance parity and tires becoming even softer for the benefit of the show, arguably, optimizing tire performance will be crucial.
We've already seen this year how this can affect the outcome of a race. Melbourne, Mercedes was the dominant team to beat. On pole by a big margin, strong throughout the race and only lost it due to a miscalculation and an untimely safety car. Then Bahrain, China and Baku showed Ferrari ahead in qualifying with Mercedes struggling on the softest compounds, but stronger relatively on the harder compounds they used during the race. Barcelona, again, Mercedes on top. How can this all be explained?
Some random thoughts: (feel free to correct or add to it)
I think the tire situation is very complex. Some of the confusion perhaps comes that people are taking some of the past characteristics (perhaps from 2014-2016) and applying it to this year too. That obviously doesn't work, for one, because the car changed significantly and also has different characteristics, but secondly, because the banning of FRIC and their suspension trickery meant that the car has a different effect on tires. I also firmly believe that with the significant engine advantage Mercedes had over a couple of seasons, that they could run higher downforce levels (relative to other teams) and that also had an influence on how much energy went into the tires. Back then, and I think this was quite evident during wet and rainy conditions, the Mercedes was always very strong in retaining heat in their tires and have a lot of downforce.
Anyway, that was back then, so lets move on.
I'm going to assume that the W09 is very similar to the W08 in regards to its sensitivity in extracting its maximum potential (aka, a narrow operating window). Get it wrong, the car is outside the working range, sometimes with all for wheels, sometimes only at the front or at the rear. This is where the name 'Diva' comes from. Ferrari (and RedBull) seem to have cars that have a wider operating window, meaning that they are less suspect to set-up changes or can get the tires operating in the correct temperature windows more easily. This doesn't necessarily mean that the Mercedes has bad tire degradation (quite to the contrary), but obviously being able to get the tires into the correct working range is crucial in order to get the best performance out of the car.
Grip is everything. Temperature is linked to tire pressure and tire pressure has a bearing on tire-contact-patch. An over-inflated tire will offer less contact-patch and therefore less grip. Tire surface temperature is important too - if it gets too hot, the rubber could become greasy, hence less grip. Track layout is obviously very much linked to the tires/cars performance too.
A long straight could have the effect that the tire cools down, long high g-force corners means lots of load and energy going through the tire, heating it up. Therefore, a track like Baku is very different to say Barcelona. Baku has lots of low-speed 90° bends and long straights, Barcelona lots of high-speed corners and a chicane in S3 that requires lots of mechanical grip. Then you also have track surface and track temperature to take into consideration. A race track will usually have a lots of grip (high abrasion), a street circuit doesn't. A rubbered in track will also have an influence too (track evolution throughout the weekend). Then we have some anomalies like Barcelona, France and Silverstone where the tarmac is new, very dark (less reflective to the sunlight). From what I understand, new tarmac is less grippy too, hence why this year, we had less tire wear that made 1-stops possible (compared to last where pretty much everyone was on a 2-stop).
There is also one more influence, one that I already mentioned above: The importance of getting all tires into the correct temperature/working range, from fronts to rears. I believe some of it is down to if the track is front or rear limited. Front limited means the front tires start sliding before the rear tires. The speed you can carry through the corner is then limited by the maximum grip the front tires can generate, regardless of how much rear grip you have. Obviously this also has an influence of tire temperatures too and how much energy can be put into the tire.
So how to put all this data together? Is there a trend in all of this?
Here are the different Pirelli tire compounds for this year:
In Bahrain, China and Baku (to some extent), there was a clear trend that Mercedes favors the harder compounds. This was also largely the case last year too. According to the above chart, the harder the compound, the higher the operating temperature range of the tire. This would suggest that the Mercedes is indeed quite 'aggressive' on its tire - in other words, they can put a lot of energy into the tire that would mean that perhaps they are on the higher side of the temperature range. In Bahrain they clearly struggled on the softest compounds (the US), so I think the Mercedes was overheating the tire. While the SS tire has the same temperature working range, obviously being of harder compound means that you would require more energy to put the same heat/energy into the tire.
It will be interesting to see how things shape up once the team arrive at Monaco and the hyper-softs will be used. Going forward, it will be of upmost importance for Mercedes to maximize their potential on the 'quickest' tire. They might get around to using harder compounds during the race, but qualifying will be dictated by pace on the softest tire available. Get it wrong and they may be on the back foot going into most races.