Looks to me like Josh was concentrating more on testing side to make the car better while David was working on the win and benefiting from the testing Josh could do for him without costing him slower runs. Since you only get 6 or so packs on the track, it is not easy to dial in a new car especially when there are only two drivers doing the testing (no matter if you are/or are not a world champion level driver). I might be incorrect, this is just my internet observation. Either way, the car is a winner
