Justin Bieber is back at his charitable ways. This time around, the 17-year-old is auctioning off the custom motorcycle skate pro Rob Dyrdek gave him on the August season premiere of 'Rob Dyrdek's Fantasy Factory.'

The purple Campagna T-Rex features two seats, three wheels and Bieber's initials painted on the hood. The singer "won" the one-of-a-kind ride after Dyrdek challenged him to "fight that fear" on his show and drive a go kart into a foam pit.

The Canadian star and avid skateboarder became fast friends with the MTV star over the summer when he got to ride with Dyrdek and Street League's Terry Kennedy and Greg Lutzka. "Skateboarding today with Legends!!!" Bieber tweeted. "Got these dudes rockin to the MY WORLD 2.0 album!! Awesome day!!!"

There are nine days left on the CharityBuzz auction, which closes on Oct. 27, and the high bid is currently at $16,555. Proceeds will benefit The Rob Dyrdek foundation, which promotes healthy communities by developing local skate parks and encouraging the sport of skateboarding.

Bieber is also involved in another auction with the online organization in which Beliebers can win two tickets and a meet-and-greet with the pop star at an upcoming headlining show in New York City. The auction, which will benefit KaBoom, ends at 12:18PM ET today.