Lotus worried about car's weather-sensitive pace

The E20 has proved it is good enough to win races this season, but Kimi Raikkonen and Romain Grosjean have struggled with pace on occasions when the temperatures drop.

Boullier said its poor speed at times of the cooler Monaco race, compared to how strong it was when it was warmer, was further evidence of the situation Lotus is facing.

"It was worrying seeing in the race our pace getting worse, so it is very related to the weather conditions," Boullier told AUTOSPORT.

"When you know the tyres will degrade, what you want to do is design a car that will not degrade the tyres. But what we were not expecting is that because of this, which is a strength in one hand, it also became a weakness when the temperatures come down."

The influence of temperature on Lotus's form has been evident at several races this year.

Raikkonen and Grosjean had been favourites for victory in Spain on the back of strong race form in hot free practice sessions, but when conditions cooled on race day they no longer had the speed to match Pastor Maldonado in the Williams and Fernando Alonso in the Ferrari.

In Bahrain, Raikkonen and Grosjean appeared to have the fastest car in the race when temperatures got hotter on the Sunday, having not been pole position threats in qualifying.