When the track temperature comes up and its surface becomes oilier, the mechanism of grip changes; the tyre is gripping less against the track surface and more against itself as there is a temperature mismatch between the tyre’s tread and its core. At a front-limited circuit like Shanghai – front-limited mainly because of the super-long duration of turns 1-2-3 and 12-13 – this means that a tyre like the Pirelli soft, with a high working temperature range, will tend to grain more readily on a hot circuit when fitted to a Ferrari than it will on a Mercedes, which grinds the tyre harder into the track and thereby achieves a more equitable balance between tyre surface and tyre core temperature. Conversely, at lower, grippier track temperatures, the medium Pirelli – a tyre with a low working temperature range – on the Ferrari will be less susceptible to graining its front left than the Mercedes. In these conditions, it will treat both tyres better than the Mercedes – other than over a single qualifying lap when it might struggle to reach temperature by the start of the lap.
When the long runs were completed during Friday afternoon practice, track temperature was close to its optimum for grip at around 36deg C. So the Ferrari could run the soft tyre for longer than the Mercedes and at a comparable lap time – to such an extent that on the Ferrari the soft looked a faster race tyre than the medium, whereas the Mercedes couldn’t make the soft as quick as the medium.
The slower Ferrari, in other words, could access the greater performance of the faster tyre better than the Mercedes – just as at Malaysia, though not to the extent that it could make one stop less. But it did mean that it could potentially do the optimum two stop strategy on two sets of softs and one of mediums. The Mercedes, by contrast, looked consigned to stints of one soft/two mediums. It was a potentially close match, despite the Merc’s much superior qualifying pace.
But Sunday was sunny, the Shanghai sky unusually clear – and the track temperature had soared to 46-47deg C by the 2.00pm start. The picture was now potentially very different. With lower track surface grip, suddenly the Mercedes could work the soft tyre properly. Mercedes began to think about switching to the soft/soft/medium strategy that it suspected Ferrari was going to favour. But it couldn’t be sure; it was just their theory at this stage.
