The mystery behind Isack Hadjar's radio messages with Red Bull race engineer Richard Wood during the United States Grand Prix has now been clarified.

An exasperated Hadjar exchanged several messages with his engineer following his first pit stop, where he questioned why he had been put on the hard tyres for his second and final stint.

The Frenchman's communication issues have been put down to problems with his radio that also affected Max Verstappen - but it turns out there was an additional car issue on top of that which cost Hadjar valuable time at the Circuit of the Americas.

Isack Hadjar's US GP radio messages explained

As per Motorsport.com, Hadjar's radio issues meant he was communicating with his race engineer about the hard tyre choice as he was driving out of the pit lane.

However, the Frenchman forgot to alter the throttle map setting on his steering wheel, which had been set before his pit stop. It is reported that, instead, he had to apply around 40 per cent of power to the throttle pedal for it to react normally.

In turn, that had an impact on his second stint. Throttle application is particularly important when it comes to managing tyre wear, to avoid what is described as 'slip' when exiting corners.

Despite that, Hadjar still managed to finish in sixth place, 34 seconds behind race winner Kimi Antonelli. He could not, though, hold off a charging Lewis Hamilton, who comfortably overtook the Frenchman shortly after he had pitted for the second time on lap 38.

Hamilton could potentially have challenged Hadjar's team-mate Verstappen for third place in the closing laps on fresher tyres, but a virtual safety car (VSC) deployed following Valtteri Bottas' engine failure on lap 52 ultimately scuppered his chances.

Isack Hadjar reveals Red Bull radio issue

Speaking in his post-race media interviews, Hadjar explained that he couldn't hear his engineer's messages in the pit lane - which contributed to his throttle map issue.

"I have poor radio coverage," he said. "I can't hear what's happening in the pits. Then I leave the pits with the wrong map, and then I'm losing a second a lap, every lap, on that hard tyre."

Referencing Red Bull's clutch issues at the beginning of races, which is affecting the race starts off the line for both Verstappen and Hadjar, he explained: "At the moment, it's the little things we can't do. I have a poor radio, I don't even know what's happening. I dropped the clutch. It's going into a nightmare.

"We fix these two, we might be on the podium. The hardest things it seems like we can do, and the silly things we can't."

Team principal Laurent Mekies said: "If we were understanding it we would have solved it [the radio], so we don't fully understand why we are being hit by these issues. We can obviously hear everyone's radio, and we have been struggling more than what we would have liked to."