CORTLAND — That was quite a roller coaster the Jets forced Jeff Cumberland to ride this offseason.

The former undrafted free agent thought he had been handed the starting job at tight end when the team allowed Dustin Keller to leave in free agency, but the good feelings for Cumberland only lasted until Kellen Winslow Jr. was signed in June.

Cumberland was listed as the starter on the first depth chart the Jets released this week, but he said yesterday the Winslow move did exactly what new general manager John Idzik no doubt wanted.

“It let me know that these guys [Idzik and Rex Ryan] weren’t playing around, and that I needed to get going and work harder and never let myself think I could ever take a day off on the field or in workouts,” Cumberland said after a training-camp practice at SUNY Cortland.

Suitably motivated (he even changed his jersey number to 87 from 86 to signify a fresh start), Cumberland dropped 10 pounds, threw himself into learning new coordinator Marty Mornhinweg’s West Coast offense and reported to camp in what he describes as the best football shape of his life.

The 6-foot-4, 260-pound Cumberland’s goal is not only to stave off Winslow and four other contenders for the job at tight end, but to keep all of them on the bench.

“I know in my heart that I’m capable of staying on the field,” the soft-spoken Cumberland said. “I can be the guy to go out there and make plays as well as block and be a three-down tight end instead of just a receiving tight end.”

Competition wasn’t the only thing that changed Cumberland’s approach. He tore his Achilles’ tendon in September 2011, an injury that the former Illinois standout admits put a crimp in the 4.4-second speed that had attracted the Jets to him in the first place.

It was during the rehab from that injury Cumberland realized that being a one-trick pony — a vertical receiving threat — wasn’t going to keep him on the field.

That point was driven home last season, when Cumberland took advantage of Keller’s injury woes by catching 29 passes for 359 yards (a solid 12.4-yard average) and three touchdowns yet still couldn’t seem to earn Ryan’s full confidence.

As a result, Cumberland attacked this offseason with what he described as a strong sense of determination — a drive that wasn’t impacted at all by the former first-rounder Winslow’s late signing.

“I can honestly say I’ve worked harder this offseason than I have any offseason before,” Cumberland said.

Ryan said last week Cumberland’s work is paying off so far.

“I see Cumberland kind of gaining his speed back,” the Jets’ coach said. “I told him, I said, ‘You look faster in [jersey No.] 87.’ I don’t know if that’s true or not, but he looked faster to me. I like the way he’s catching the football, too.”

Cumberland said he knows he has skeptics but is convinced the best is still ahead.

“I do feel like I can surprise a lot of people,” he said. “Some people know who I am, but a lot of people don’t and a lot of people have their doubts. I plan on going out there and changing their minds.”