For the first time in years, Crabtree is healthy in body and healthy in spirit, done with what he thought was a lot of negativity on his old team.

“A lot of people don’t know that the Niners offered me a contract, I just didn’t take it,” Crabtree said. “I wanted a fresh start. It was more money too — the Niners offered me more money than anybody did — but business is business and I wanted to come to a team that really wanted and needed me.”

He is excited about how the Raiders have come together the last few months.

“I like the guys around me and I would do anything for them, on or off the field,” Crabtree said. “We’re going to have fun.”

Crabtree might have been misunderstood with the 49ers, at times labeled a diva or a malcontent. And he can be hard to read at times, as Rodney Baker, the executive director of Crabtree’s charitable foundation, will attest.

“If you know him, he is going to show you love,” Baker said. “But if he doesn’t know you, he doesn’t know you. As Mike likes to say, he is an authentic guy. He is not going to pretend, or try to pretend.”

With the Raiders, Crabtree immediately hit it off with quarterback Derek Carr. Crabtree knew Derek’s brother, David, when they were teammates in San Francisco, and immediately liked Derek’s competitive nature.

“Little brother has a chip on his shoulder,” Crabtree said, laughing.

Crabtree and Carr always seem to be in the other’s ear on the practice field.

“He’s awesome, one of the coolest people I’ve ever been around,” Carr said. “He makes catching look really boring and easy. It’s like catching the ball is something he has to do so he can have it. I can’t say enough good things about him.”

Crabtree doesn’t want to take shots at any of his former teammates but sometimes he can’t help it.

“I needed new scenery. It wasn’t for me,” Crabtree said. “I needed a quarterback that can deliver the ball, and that was hungry like I was.”

Niners quarterback Colin Kaepernick actually is one of the few players still standing after a tumultuous offseason down in Santa Clara.

“With all the stuff going on on the other side, it just feels so good to be on this side,” Crabtree said. “Just play ball and don’t worry about too much. Just play ball.”

Crabtree insists he doesn’t pay much attention to all of the 49ers’ defections, retirements and arrests. He is not very convincing.

“All I can do is just focus on me, I don’t really get into all that stuff,” he said. “They said all types of stuff about me that was false. They said I was this type of guy or that type of guy. I’m the same dude, man. I don’t bother nobody. … I play ball, that’s what I do.”

And Crabtree is playing well again, the team’s most impressive player at training camp. He finally is all the way back from a nagging foot injury and a torn Achilles tendon from a couple of years ago.

“With an Achilles injury, you might feel like you’re healthy but the burst is not there,” said Crabtree, who turns 28 on Monday. “I came back in six months, usually it takes a year, but I came back really fast to do what I could to help the team make the playoffs.

“Now, I look forward to see what I can contribute to this team. Injuries slow you down, man. You aren’t the same person.”

Carr echoes former 49ers coach Jim Harbaugh’s sentiment that Crabtree has the best hands he’s ever seen. And he makes up for a lack of elite speed with know-how.

“He knows coverage,” Carr said. “He knows how to set up his routes so that he can win. He plays that chess match with the corner throughout the game. If there’s a certain coverage and he knows the read’s not coming to him, he’ll make it look like something to set something else up down the line.”

Crabtree also has been a mentor to first-round pick Amari Cooper, giving him tips and urging Carr to throw more passes to the rookie in the preseason.

“Coop is nice,” Crabtree said. “He’s like my little brother, and watching him do work is going to be exciting. It’s important to get a feel for the game in the preseason.”

Crabtree has a lot of little brothers and sisters, thanks to his Crab5 Foundation back in his hometown Dallas area. The foundation has annual free football camps as well as opportunities for inner city kids to explore and develop their interests in the arts, music, other sports and academics.

“We’ll send the whole band to the Grambling-Prairie View game, fashion kids to New York, actors to Los Angeles,” Crabtree said. “They get that exposure. I was really big on that because I never had that. Open the doors a little bit for these guys.”

Crabtree never went to a football camp as a kid. But he found a way to get the swag that he now gives out to kids at his camps.

His mom, Bessie Turner, sold concessions at Texas Stadium, and Crabtree would help to raise money for his little league team. After the games, he would run down to the field to get gloves and towels from players that he would wear in his games.

Crabtree grew up in the same Oak Cliff area of Dallas that former Raiders great Tim Brown did.

“He was from my neighborhood,” Crabtree said. “He made it possible. ‘I can make it, man.’ … I used to sneak in and watch him work out. He didn’t know that.

“He used to work out at a middle school and I would sneak in, and watch him run all the different routes. Then, I finally met him about eight years ago. That’s my dude.”

Which made it even cooler when Crabtree decided to sign a one-year, incentive-heavy deal with the Raiders.

Not that anybody back home could figure out why he would sign with a team that was 11-37 the last three years.

“If everybody goes left, Mike is going to go right,” Baker said. “People were like, ‘Why would you go to the Raiders?’ But he had a real connection with Derek Carr and he just knew that was going to be his home.”

Home, 40 miles north, is where the heart is for Crabtree.

Vic Tafur is a San Francisco Chronicle staff writer. E-mail: vtafur@sfchronicle.com Twitter: @VicTafur