I'm guessing that you would probably need a co-signer. If your parents have good credit, you can take advantage of that and build some credit for yourself. Also, the amount you can borrow will be limited depending on how old the bike is. My bank will loan 80% of the list price of a new bike, and the interest rates are very good (less than 8%/year). Shop around for the best rates. If you can't get financed, perhaps your parents will take out the loan and let you pay them. It's a commitment, though. If you let your payments lapse, you will have a very hard time getting credit in the near future. Think about whether or not you are ready for the responsibility and make your decision from there.
Good luck. :)