Bolder, 26, turned down a loan move to his former club Hull in order to join the Rs.
And he told the club website: "I don't doubt the squad's ability, I just think we need a bit of confidence.
"Hopefully that's where I come in, and I'm looking forward to the hard work beginning."
Meanwhile, teenage defender Jon Munday has become the latest player to leave Loftus Road after having his contract terminated.