(動名詞/現在分詞) 騎四輪沙灘車 (all-terrain vehicle)。
quad (動詞):騎四輪沙灘車
quadder (名詞):沙灘車騎士。

沙灘車的英文叫做 all-terrain vehicle (ATV), quad 或 quad bike。

"Debris gets piled up on their engines or exhaust systems and it heats up then falls off and causes wild fires.

"We're asking individuals, as they're quadding, to check their vehicles and keep them clean and clear of debris."
—Dave Dormer, "Officials try to head off ATV tragedies," Calgary Sun, May 13, 2011

Despite Mother Nature's cruel joke with the weather so far this spring, summer really is just around the corner. That means Albertans will soon be swimming, mountain biking, horseback riding, quadding, boating, hiking and participating in a myriad of other outdoor activities they've had to put off for what seems like forever.
—Delon Shurtz, "STARS encouraging safe summer," Lethbridge Herald, May 24, 2011