Track rubber is not grip you can count on

A circuit that gained two seconds across a weekend can hand most of it back after one shower or one support race.

Everybody understands that a track rubbers in and gets faster. Fewer people think carefully about what that layer actually is, and the sloppy version of the idea leads teams into strategy decisions that look reasonable on Saturday and fall apart on Sunday afternoon.

The rubber laid down by running cars fills the surface texture and gives the tyre a compatible material to grip against. That is real and it is worth serious lap time. But the layer is thin, it is compound specific, and it is fragile. Run a support series on very different rubber and the new layer does not simply add to the old one. It can sit on top like a mismatched coat of paint and produce a surface that is slower than either would be alone. Rain washes it away almost entirely. Heat can make it greasy rather than grippy.

That last point deserves more attention than it gets. Rubber on the racing line does not behave the same at every temperature. On a hot afternoon a heavily rubbered surface can start to release, and the drivers who were fastest on the line in the morning find grip has moved a metre wide of it. Off-line becomes the place to be, and every model built on Friday assumed otherwise.

My position is that teams over-trust track evolution as a strategic input. You will hear that a late run in qualifying is worth a tenth because the track is coming to you. Sometimes it is. Sometimes the wind has picked up, the surface has cooled or a support race has left a different compound smeared across the second sector, and the late runner throws away a lap for a benefit that had already peaked twenty minutes earlier.

The measurable version of this is boring and better. Track temperature, air temperature, wind direction and the actual lap time of cars going out at intervals. Watch what the track is doing rather than what it usually does.

There is one more thing. Track evolution helps everyone, so it changes nothing about relative position unless it changes it unevenly, and it does change it unevenly. A car that needs more grip to reach its tyre working range gains more from evolution than a car already in the window.

The last hour of practice is a different circuit from the first. Plan for two circuits.