I am 17 and i paid 7k on my truck and my parents paid the other 8k on it it is a 2007 ford Ranger. But i want to trade it in on a speed bike but my mom flipped out on me telling me absolutely not and that if i want one that i will have to get over it. And then she told my girlfriend who is not living with us because she is pregnant. And then they both ganged up on me. I feel like this is my choice i did pay for half of my truck and everything. How can i convince them to let me get a speed bike?