Papa BRAD PITT's in hot water with ANGELINA JOLIE after he gave their son MADDOX a new dirt bike for his birthday.

Angelina thinks the young­ster, who turned 11 on Aug. 5, is going to break his neck stunt riding around on the Suzuki DR-Z125, which can reach speeds of 50 miles an hour, and she’s letting Brad know she’s not happy.

Brad, 48, had purchased the bike back in June but didn’t let Angelina in on his surprise for Maddox, the oldest of their six children.

Now, Brad’s telling Angelina that he’ll make sure Maddox learns how to handle the bike safely and always wear a helmet. But she’s still livid.

A source told The ENQUIRER that Angelina “took Brad aside and pointed out that all the safety gear in the world probably wasn’t going to help him much if he goes flying over the handlebars and lands on his neck!” They bought Maddox a motorbike back in 2006, however, she has since had concerns about his riding ability.

Brad insisted that he would never put their son in danger, but a furious Angelina just stormed off in a huff, says the source.

For now, Brad, a longtime motorcycle enthusiast, continues to oversee the building of an off-road track at the family’s French estate that he and Maddox can use.

“The track is not going to be too challenging at first,” maintained the source. “Brad wants Maddox to get used to riding the new bike – and then he’ll have bigger hills built as time goes on.

“He thinks getting the bike will make for a great father and son bonding experience.”

But Brad will still have to convince Angelina of THAT.