How to convince my parents into letting me have a dirt bike?

[Daniel]

I am a 13 year old boy and my parents will not let me have a dirt bike. My friend has a ssr 110 pit bike (dirt bike) and they usually let me ride it and i have become quite good at it, i always were a helmet but no suit or anything because we are only riding in my neighborhood (my parents know). My uncle loves dirt biking and his kids (17 and 20) both go with him. My cousin who is 17 has a yamaha ttr 125, and my cousin who is 20 has a ttr XXX (i don't know what he has but he is in college and barely rides it so my 17 year old cousin rides it which leaves the ttr 125 for me to ride) They invited me to go to there house for about 2 weeks and they want to take me real dirt biking my parents approved and told me to be careful and i said "yes of course." Now the problem is that they will not let me own one, they let me ride them and everything but not to own one!! They think its too dangerous. My dad use to ride motorcycles. I really really LOVE riding dirt bikes and i have a passion for it. Money is not a factor. My dad is one of those dad`s that instead of saying it calmly he gets kinda mad and puts everyone in a bad mood so i don`t know how to talk to him because every time i bring it up he gets mad PLEASE PLEASE HELP!!!!