If the W04 has problems with, tyres,heat, exhaust or balance (lack of downforce). Then it means the team havent learned form there past mistakes. So if you see burning bodywork, or hear reports of high tyre deg, see the old FW at testing, then you will know that they have made the same design mistakes again. You can only be positive if there laptimes are consistent, that the only point i will be looking at this winter test. Not how quick but how consistent. In the 2012, Mclaren,Red Bull,Williams and Lotus had really consistent laptimes and those cars were quick in the beginnen of the season in the race. Red Bull had problems with Qualy but there pace was good not the best. Mercedes struggleda alot the lap delta could showed really high fluctuations lap 1 could be 1.20.2 and lap 2 was 1.20.5 lap 3 1.21.0 lap 4 1.21.3. If thats the trend again then Lewis and Rosberg are in for a hard and cruel season. I hope for their sake that, that doenst happen. The most important are consistent high fuel run laptimes, if can do a run of 15 laps with 1 sec delta. Then the care is good. Last year Mercs lap delta for 15 laps was as high as 2-3 secs.
So compare laptime delta and not actual laptimes because those dont tell the real story! Every team can do a quali run and set the fastest time....And if the intial lapdelta are bad, dont buy the bs about care setup, or there argument that a lot will change before the first race or that they are tyre testing. Because the Lotus E20 was quick from the start and only when faster. The setup cant make a bad car a good car.