On Sunday evening after the Russian Grand Prix, Mercedes and Lewis Hamilton were left with no definitive answer for the three-time champion's lack of pace over the weekend.
It was one of those rare race weekends in which Hamilton was well off the pace, qualifying half a second off pole in fourth and finishing the race in the same position, 36 seconds off the lead. In stark contrast, teammate Valtteri Bottas was able to qualify within 0.1s of pole position and went on to win the race following a strong start from third on the grid.
Throughout Friday practice, Hamilton struggled to get his tyre temperatures in their optimum working range and as a result failed to hook up a single flying lap with three best sector times. In individual sectors he looked quick, but in the 90-degree corners that make up the majority of the lap, the grip from his rear tyres would sporadically elude him.
After qualifying fourth, he claimed a series of setup changes had managed to get the tyres in their working range but that the underlying balance of the car had left him struggling for grip in the final sector. He confirmed Bottas, who was nearly half a second quicker in qualifying, was using the same setup and was simply able to extract more lap time from it. Mercedes discovered a slightly damaged floor on Hamilton's car in Q3, but it was fixed before the race and the team doubts it was the reason for the big gap to Bottas.
Following the race, team boss Toto Wolff said there was no obvious reason for the difference in performance between Bottas and Hamilton.
"Why it didn't go on Lewis' car we just need to find out, I don't want to speculate," he said. "My opinion is that he knows his way around here, he has won two races here so he has an extreme record in winning races in Sochi. So it's something between the car, tyres and driver that didn't work and we need to find out what it is.
"I think there was more wrong that just one topic. In his debrief he felt that he couldn't make the car and the tyres function. We know it is very difficult to keep the tyres in the right window and it's something we need to work on because the Ferrari seems to struggle less -- the window is probably larger. He [Lewis] was never in that window. Whether it was a tyre specific issue or setup we need to find out. But if one thing is for sure, if there's someone who knows his way around Sochi it is Lewis."
Hamilton has an inkling of what was going wrong, but was not willing to divulge details after the race.
"I can't explain right now but we'll do some work over this week to fully understand it," he said. "I have some feelings about how it felt in the race and qualifying, I have some ideas but as I said lots of work over the week to figure out where we are."
To add to the handling issues, Hamilton was told to back off the pace early in the race to keep his engine temperature under control. He said the situation was unusual and ultimately meant he could not take the fight to Kimi Raikkonen in third.
"No I have not had that [in the past], I don't remember the last time we had that. It just meant I was out of the race from the get go.
"I think I could kind of match the times of the guys in front maybe, but the tyres wouldn't have lasted as long. It was probably not a good set up that I had, then with the backing off with the temperatures I was losing 0.7s per lap."
Hamilton was losing time to Bottas in the low- and medium-speed corners, which he put down to his teammate's ability to find a better compromise with the car's differential. He said his task now is to find out why Bottas could live with the balance of the car in Russia while he struggled.
"I don't really know the details, I have to ask my engineers for some of it, but yeah... The direction he was able to go, I wasn't able to go basically and I need to understand fully why. "Our driving styles are quite similar so just setup, and I'm not quite sure what else on the car was stopping me going in that direction."
Much like Bottas' struggles in the final two stints in Bahrain, Hamilton's lack of pace in Russia appears to centre around an understanding of how to get the best from the tyres. Not only does that cast a new light on Bottas' race two weeks ago, it backs up the theory that the Mercedes has a narrower operating window on Pirelli's new tyres than the Ferrari.
"I think everything we do is very marginal with the compounds and their interaction with the surface of the track," Wolff explained. "The ambient temperature, the track temperature, the surface bulk, carcass temperature -- there is so much you have to get right in order to be in that [performance] window. One thing is for sure, we have a very fast race car and a very fast qualifying car and we just need to tune it. This is an exciting exercise. "