The San Diego Chargers are trying to retain running back Mike Tolbert, Kevin Acee of the San Diego Union-Tribune reports.

Acee adds that the Chargers have not made an offer, but that the teams sides have engaged in preliminary talks about keeping the 5-9, 243-pound Tolbert in the team's backfield.

After an off-season where the Chargers a.) used the "First- and Third-Round" restricted free agent tender, at a cost of $7.283 million, to keep Darren Sproles for the 2010 season, and b.) packaged picks and inside linebacker Tim Dobbins to move up to select running back Ryan Mathews with the 12th overall pick in the 2010 NFL Draft, which came with a five-year, $25.65 million contract, it's Tolbert who has been "The Man" in the Chargers' backfield.

Signed in 2008 as an undrafted free agent out of Coastal Carolina, Tolbert moved to running back in the off-season and now leads the Chargers in carries (178), yards (737) and touchdowns (11) this season, which he's playing under the one-year, "Exclusive Rights Free Agent" tender worth $470,000.

San Diego spent $11.5 million this season on Mathews and Sproles, who have combined for 163 carries, 719 yards, and 3 touchdowns on the ground.

Sproles does return kicks, has returned punts, and is second on the team with 49 receptions.Mathews has battled injuries, but has run well of late and will likely play a larger role in the offense in 2011 and beyond.

Chargers head coach Norv Turner understands that the game has changed to where teams need two running backs.

"I think you do (need two backs)," Turner said. "I’ve never been that guy, but this game has become so physical. You see so many eight-man fronts, and you want to run the ball. A week ago when they both had 16 carries and (17 apiece on Thursday), it works out. It saves them for a season and for a career."