BALTIMORE, Maryland (AFP) - Michael Phelps, the US swim star who set records with 22 Olympic medals and 18 Olympic titles, has signed a golf equipment deal with PING, the club manufacturer announced on Wednesday.

Phelps says he is "getting serious" about golf, which he began playing five years ago, and the 27-year-old American said the deal to play a full set of the company's clubs announced on the firm's website has already started to pay off.

"I know how difficult the game of golf is but I'm really serious about getting better," Phelps said.

"The experts at PING have already helped me a lot. They looked at my swing on the range and dialed me into clubs that perfectly fit my stance and swing."

The lanky form that helped Phelps dominate in Olympic pools at Athens, Beijing and London presented special problems when it came to finding clubs and maximising his potential.

"Considering how tall I am and the length of my arms, they showed me how important and beneficial it is that I play with custom-fit clubs," Phelps said.

"Once I had clubs that were built specifically for me, my ball flight improved right away."

Phelps began his endorsement deal Wednesday at the US PGA Phoenix Open, where he was paired with reigning Masters champion Bubba Watson.

Hank Haney, the former coach of Tiger Woods among other top golfers, will devote the next edition of his reality television series to helping Phelps improve his game. Telecasts featuring Phelps begin in February.