To anyone that's thinking of downloading this game for the first time, I sincerely suggest not to. The developers are so out of touch with their playerbase that we get constant updates that damage the playerbase one way or another.
To grind the vehicles of a tech tree in a reasonable amount of time you are forced to pay for a premium account and on top of that a premium vehicle. Without a premium account or a premium vehicle you'll probably take a year or more to do so. And let's not get started on the repair costs that are unimaginably high that some vehicle are just unplayable. Please consider playing something else, and this is coming from someone with 2300+ hours on the game.