The temperatures at Spa this weekend have been much higher than anticipated, and that means the tyres are being punished more than expected.

Friday's running confirmed that tyre wear would be excessive, and means that teams will have to prepare for a tough strategy call in deciding which tyres to run in qualifying and the race.

Williams Valtteri Bottas said: "It's really tricky with these temperatures. The supersoft tyre on this kind of track, where you put so much energy into the tyre, is good for sector one, maybe sector two, then it's finished.

"And even with the soft, during the long runs, the amount you need to manage the tyres is incredible. Especially with these tyre pressures you have to run, it's tricky."

Daniel Ricciardo said: "It is definitely very tricky the supersoft. It is difficult to make it last the whole lap...it lasts but you don't really gain much of a performance from it towards the end of the lap.

"It will be tricky with high fuel, I did a few laps on it but it was sliding a lot. We expected that with this heat but it will make the strategy and everything for Sunday more interesting."

Pirelli estimates that the laptime difference between the supersoft and the soft is 1.2 seconds, with the medium likely to be around 1.5 seconds slower again.

That leaves open the possibility that teams may try to get through Q2 on the soft so they can start the race without needing to use the supersoft.

Pirelli's F1 racing manager Mario Isola said: "The best strategy could be medium/soft and could be two or three stops if the supersoft lasts five or six laps at the start.

"They could even use the medium. We know it is slower but if degradation is much lower it becomes a possible compound for the race.

"It will be interesting to see if anyone is qualifying in Q2 on the soft tyre, starting the race with the soft. And this is a good point to see for tomorrow.

"If somebody has to use the supersoft, it means a short stint in the beginning, because with a full tank when they try to do a long run the degradation was very high. There is quite a big difference between a full tank and a qualifying situation."

Pirelli also said that its latest weather forecast was for cooler conditions from tomorrow, which could help ease the levels of degradation.