MONTMELO, Spain -- Ferrari's Sebastian Vettel finished the second day of pre-season testing at the top of the timesheets after beating the Mercedes of Valtteri Bottas to the fastest time by 0.303s.
After Daniel Ricciardo set the pace for Red Bull on day one, Vettel used Pirelli's soft compound tyre to lower the benchmark time by 0.5s to a 1:19.673 on Tuesday. Bottas also dipped into the 1:19s in the afternoon session but was on the slower medium tyre when he set his time.
However, attempting to make comparisons at this stage is unwise, especially as the bitterly cold conditions means the teams have yet to make a start on performance testing.
"It's cold. It's very cold," Vettel said. "So I think the most important thing if you look at the table we did nearly 100 laps. Considering that it was snowing also at the end of the day it's OK.
"It's very difficult to get the tyres to work and I think everybody is having the same issues. It's only three or four degrees and the asphalt is 10 degrees so it's very, very cold. Not the conditions that we normally run. I think the car is working, we didn't have any problems reliability-wise.
"Have we made a step forward in terms of performance? I don't know yet but in terms of general operation it's been very smooth so it's good to come here, switch on the car and be able to run. The limiting factor was the weather."
A bitterly cold start to the session resulted in just a handful of installation laps during the first hour. With Pirelli's tyres struggling to operate if they are not warmed to 90C, air temperatures below zero and a track temperature of 2.2C meant there was little point in risking an accident in taking to the circuit.
The sun came out in the hour before the lunch break, and as the temperature nudged 5C a decision was taken to scrap the usual one-hour lunch break and allow the drivers to make the most of the conditions by continuing to run between 1pm and 2pm. The majority of teams did just that and Mercedes -- keen to maximise running in the dry and slightly warmer temperatures -- made a call to scrap its planned driver swap at lunch and keep Valtteri Bottas in the car for the entire day. As a result, reigning world champion Lewis Hamilton did not take to the track and has only completed 25 laps in two days.
After topping the timesheets on Monday, Red Bull completed just three laps in the morning due to a fuel leak on Max Verstappen's car. The issue was fixed by the afternoon and he went on to complete a further 62 laps by the end of the day and set the fourth fastest time.
"We had a fuel leak and checked everything in the car because the track was in a very bad state anyway, so we didn't really lose track time," Vestappen explained. "And then afterwards we completed quite a bit of what we wanted to do. We tested a few things on the car and I was happy so it was a positive day."
Running was also limited for McLaren, which completed just 37 laps over the course of the day. The car spent most of the afternoon in the garage after the engine cover showed tell-tale signs of overheating around the exhaust. It later emerged that a clip holding the exhaust in place had come loose resulting in parts of the wiring loom becoming damaged. It follows a wheelnut failure for Fernando Alonso on Monday and means the team's lap count is just 19 laps higher than the same time last year when it was struggling with Honda reliability issues. For the record, Stoffel Vandoorne finished Tuesday's session third fastest after setting a 1:20.325 on Pirelli's new hyper-soft tyre -- the softest and fastest compound in its range.
Haas also completed limited mileage, with just 36 laps on the board at the end of the session due to the bad weather and some unfortunately timed mechanical issues. Kevin Magnussen took a trip through the gravel at Turn 4, just missing a collision with the barrier, but said the conditions were nearly impossible until modifications had been made to the car.
"I was going 22 seconds slower than the fastest car at that point, and we weren't setting the car up for those conditions, so you need to allow heat from the brakes into the rims to have a chance of getting heat into the tyres in these conditions and we didn't do that," Magnussen said. "So we were expecting to survive without cutting in the brake drums, but eventually we realised there was no chance, we needed to modify it to get some heat, and then it was fine. But that run was worse than being in the wet on slicks, it was worse than that! It was on an out lap and I couldn't stay on track, so not ideal."
Magnussen made it back out for four laps at the end of the session after damage from his excursion had been repaired.
There were two red flags during the session; one when Charles Leclerc beached his Sauber at Turn 4 in the early afternoon and another when the track had to be cleaned of gravel dragged onto the circuit by Vettel going off at Turn 2. Leclerc had another trip through the gravel at Turn 4 later in the session but managed to rallycross his way back to the track. Leclerc finished the day with 81 laps and the 10th fastest time.
Elsewhere, Carlos Sainz was fifth fastest in the Renault after completing 65 laps. Nico Hulkenberg had been due in the car in the afternoon, but like Mercedes the French team opted to stay with just one driver throughout.
Toro Rosso and its new engine supplier Honda had another positive day with a total of 80 laps and the sixth fastest time. Reliability had been a concern ahead of the start of testing following McLaren's woes with Honda over the past three years, but so far the new STR13 has avoided any major dramas.
Williams also completed a solid day of testing split between race driver Sergey Sirotkin and reserve driver Robert Kubica. It was Kubica's first time at the wheel of the new FW41 and he completed 47 laps with the seventh fastest time, 0.327s faster than Sirotkin in eighth.
Esteban Ocon added 79 laps to Force India's total for the week and set the ninth fastest time.
With conditions expected to worsen on Wednesday and rain forecast for Thursday, it may not be until the second week of testing that the teams get stuck in to serious performance testing.
Times at close:
1. Vettel, Ferrari, 1:19.673, 98 laps (Soft)
2. Bottas, Mercedes, 1:19.976, 94 laps (Medium)
3. Vandoorne, McLaren, 1:20.325, 37 laps (Hyper-soft)
4. Verstappen, Red Bull, 1:21.236, 67 laps (Medium)
5. Sainz, Renault, 1:21.212, 65 laps (Soft)
6. Gasly, Toro Rosso, 1:21.318, 82 laps (Soft)
7. Kubica, Williams, 1:21.495, 48 laps (Soft)
8. Sirotkin, Williams, 1:21.822, 52 laps (Soft)
9. Ocon, Force India, 1:21.841, 79 laps (Soft)
10. Leclerc, Sauber, 1:22.721, 81 laps (Soft)
11. Magnussen, Haas, 1.22.727, 36 laps (Soft)