After a challenging rookie season in which he started eight games but failed to establish himself as the Bears’ center for the next decade, Hroniss Grasu is bigger and stronger — but more importantly, smarter.

The 2015 third-round draft pick from Oregon is on a mission to gradually gain “good” weight — he’s up to 310 pounds at 6-3 after playing last year mostly at 297. But the biggest reason Grasu expects to be a much better player in 2016 than he was last year is his increased knowledge of the playbook that will allow him to play at the same speed as everyone else — reacting instead of thinking.

“It’s night-and-day with my knowledge of the playbook, from last season to now,” the affable Grasu said this week during the Bears’ organized team activities workouts at Halas Hall. “I expect to be playing faster and with more confidence and [then the added] strength and speed will show up.

“There’s still plenty of room for work, but that’s one thing I feel the most confident about is knowing the whole playbook and knowing where guys got to be. I don’t have to think that much. Give me a play call, give me a certain defensive front, I can call it out right away and play fast.”

Learning the playbook at the NFL level turned out to be a bit of an eye-opener for Grasu, who played for the first time in Week 5 against the Chiefs after veteran Will Montgomery suffered a broken arm the previous week. The Bears averaged 3.8 rushing yards per carry in Grasu’s eight starts. They averaged 4.2 yards per carry with Montgomery and Matt Slauson at center.

“In college, I knew the playbook right away and I was playing fast,” he said. “Here — I don’t want to make excuses, but I had to learn the playbook and that’s on me. I thought I knew a lot about the playbook but once I got through this offseason, I realized, ‘Wow, it’s crazy how much better you can be [from] Year 1 to Year 2.’”

The Bears used the draft and free agency to attempt to upgrade their offensive line this offseason — drafting guard Cody Whitehair in the second round and signing Ted Larsen and Manny Ramirez. But player development could provide the biggest upgrade if an athletic player such as Grasu makes the jump from Year 1 to Year 2.

“If you think about the college season as a mile, and then all of a sudden you have to change your race to a two-mile, you have to train and prepare differently,” Bears coach John Fox said. “They don’t have that opportunity as rookies. That’s why you see a big jump from these guys from that first year to second year. They can actually train for the two-mile now.”

Ramirez started at center for the Broncos in 2013 when they went to the Super Bowl. Larsen started nine games at center for the Buccaneers in 2011-12. And Bears general manager Ryan Pace said the rookie Whitehair has potential at center. But the job is Grasu’s to lose. “[Competition] is the nature of the business,” Bears offensive line coach Dave Magazu said. “You gotta put it on tape. And he’s gotta play.”

Grasu welcomes the competition.

“I love it,” Grasu said. “I’m all for whatever it takes to make the Chicago Bears a better team. The more guys we get in this room, that’s great. Manny has been helping me out every day to be the best player I can be. I’m going to do the same for other guys.

“I’m very confident in myself and very confident, very confident in the guys around me and confident in the coaches helping me get better. I’m confident in the whole offense, the whole team. That’s what it’s about. When you’re confident, you’re going to p lay faster and be more physical. I’m getting a lot better at that.”