Are all vehicles same? When i drive some of them i can handle better, some vehicles seems not good at handling. Is it just me or happening to you too ?
Reason for overlevelling crystals, when you put low level gems for experience, they need low amount of xp. For example 1 level ruby gem needs 1000 xp to be level 2. At that point when you leave game for a long time, when you are afk, needed xp to level up dont change, dont go up. The time you stay afk, its all same xp to level up. 1 level ruby gem and 100 level ruby gem needs same amount xp when you close the game. After they are upgraded, needed xp to level up stays same while afk.