Carlos Sainz believes a lack of confidence prevented him from getting the most out of the team's STR12 in last Sunday's Australian Grand Prix.
The Spanish driver put in a consistent which brought an eighth-place finish and points to kick off his 2017 campaign, but inside the cockpit it wasn't all that easy.
"I lacked a bit of confidence so I couldn't really extract everything but it's a balance situation that hopefully we'll sort out for China," Sainz explained.
"Honestly speaking, it hasn't been my case for the whole weekend, only on Friday was I at 100 percent feeling with the car."
The Red Bull charger was also forced to make way for Daniil Kvyat at one point on Sunday, with the Russian on an alternative strategy. But Sainz complied with the team order without any fuss.
- Sainz relieved with P8 after earlier struggles
"I had to let my teammate through because my team asked me to, although he had to stop again, so we missed out on seventh place by a bit."
It'll be a battle royal in the mid-field, if Melbourne was any indication, but for Sainz it still isn't clear where Toro Rosso will be in the hierarchy.
"Williams showed that especially in race pace they're one step ahead," he said.
"The Haas, I don't know how they would've done with the soft, and the ultra-softs they were maybe a tenth faster a lap.
"Then it's us, I do believe we are faster than Force India, but they were that tiny bit cleverer than us with an [attempted] undercut."