Nothing against Sammy Hagar, but he’s no David Lee Roth.

Diamond Dave’s flash and sex appeal and arena-size vocals helped define the Van Halen sound, just as much as the group’s namesake/guitar wiz, Eddie Van Halen.

Roth’s replacement, Hagar, didn’t have quite the flair. Hagar’s successor, former Extreme lead singer Gary Cherone, isn’t likely to turn any heads either.

Sorry, Ed, there’s only one Diamond Dave.

“Their whole band has swung around in a different direction,” Roth said in a recent interview. “The old Van Halen made you wanna dance and screw, and the new Van Halen encourages us to drink Pepsi and milk and drive a Nissan.”

That’s all fine and dandy, but it’s not Roth’s cup of tea. He cares to remember “what made classic Van Halen tick”: the massive egos, a healthy dose of conflict, the insatiable urge to break rules. He says as much and more in his just-released, no-holds-barred autobiography, “Crazy From the Heat” (Hyperion).

Talking with Roth is akin to reading his book. It’s one steady stream of consciousness, as if you’re sharing a cocktail with him in a tiki hut bar on Borneo and he’s shooting the breeze. No subject is taboo, and no one escapes his wickedly funny barbs.

“There’s no ghost writing, nobody pointing me in a direction. Some people say it tends to ramble on, and I’m like, ‘Naw, really?’ ” he said, sarcastically. “I don’t care if it rains, I’m waterproof, nothing drowns me out.”

If anything, his version of the truth, undoubtedly different from anyone else in Van Halen, is entertaining.

“The content I think is not what you traditionally read in a book,” he said. “I haven’t been through 18 months of therapy and I want to apologize as part of my 40 stages or whatever.

“There’s been people who’ve pissed me off to some degree, so there’s a little name-calling, and there’s a hurt feeling or two, but no family members were kidnapped, no household pets have disappeared. I think everybody got off pretty easy here.”

One of the most telling moments is when Roth recounts Van Halen’s flirtations with a possible reunion, fueled by an appearance on the MTV Awards last year. “So what’s so difficult about a reunion with these guys? I don’t have to love them. I don’t have to love you to make great music with you,” he writes in his book. He recorded two new songs for Van Halen’s “Greatest Hits” album; the next thing he hears, Van Halen is auditioning for Hagar’s replacement.

“Any first week in a screen-writing class at a university,” Roth said in last week’s interview, “the professor will say to you, ‘Where does conflict belong in a screenplay?’ Answer: Everywhere! Why should this band be any different? The fireworks, the anxiety, sure it’s worth 20 bucks (to see them perform).”

Any thoughts of a reunion went out the window after that fiasco. Roth didn’t slink away; he finished his book and also helped Rhino Records piece together a career retrospective, titled “The Best” (out Oct. 28).

From “Yankee Rose” to the album’s new recording, “Don’t Piss Me Off,” Roth is proud of his post-Van Halen achievements.

“Over the summers past,” he said, “there was an effort level there, you can hear it. Slow song, fast song, in-between song, you hear the desire, you hear the energy. And I think you can hear that it’s legit.”

BWF (before we forget): David Lee Roth’s solo album discography – “Crazy From the Heat” EP (Warner, 1985); “Eat ‘Em and Smile” (1986); “Skyscraper” (1988); “A Little Ain’t Enough” (1991); “Your Filthy Little Mouth” (1994); “The Best” (Rhino, 1997); “DLR Band” (Wawazat!!, 1998); “Diamond Dave” (Magna Carta, 2003).