Formula One's faster and more powerful cars for 2017 were put through their paces for the first time in Barcelona this week.
Here, AFP Sports looks at five things we learned from the first four days of pre-season testing:
- Mercedes still in front
The more things change, the more they stay the same. After three years of total dominance, even a drastic overhaul of the sport's rules hasn't stopped Mercedes from setting the pace.
Valtteri Bottas showed he can prove an able replacement to retired world champion Nico Rosberg by posting the best time of the week and since 2009 at the Circuit de Catalunya in 1min 19.705sec.
Bottas and Lewis Hamilton were also carrying out race simulations whilst some at the back of the paddock were struggling to get out of the garage on the first two days.
- Ferrari pace encouraging
However, those hoping for more of a contest at the front of the grid this season will have been encouraged by the early signs from Ferrari's SF70H.
Kimi Raikkonen was fastest on Tuesday and Thursday, whilst Sebastian Vettel outpaced Bottas when both were on the same soft tyre compound on Wednesday.
- McLaren woes continue
If Mercedes' dominance has become predictable, then so have the woes of a former championship contender in McLaren.
Two years on from joining forces with engine supplier Honda, McLaren look further off the pace than ever.
More unreliability problems meant McLaren were second last when it came to laps completed and only Toro Rosso were slower once they did get on the track.
- Faster cars pose physical toil
Hamilton admitted on Tuesday to having "bruises and bumps where I've never really had them before" as a result of the increased physical toil in dragging bigger and heavier cars at much greater speed.
Rosberg claimed the "monstrous" new machines would make the drivers "proper gladiators" and warned races could be decided on who is the fittest and strongest driver.
"We might even see drivers losing race wins because of just being game over physically and that's what we need," said the German.
- Barcelona not the place for rain
The need for tyre manufacturer Pirelli to try out their new wet and intermediate tyres on Friday led to the unusual situation of water spraying up behind cars bathed in the Barcelona sunshine.
With no help from the elements, and no sprinkler system on hand, huge trucks dumping gallons of water were needed to create the artificial wet surface both overnight and again in the lunch break between morning and afternoon sessions.