So many road trip comedies and only one lifetime to get through them all.

It’s a conundrum, a dilemma for anybody who cherishes the genre as much as I do.

On a sliding scale, “The Long Dumb Road” is closer to “The Guilt Trip” or “We’re the Millers” than “Midnight Run,” “Nebraska,” “Sideways” or any of the acknowledged recent classics of the genre.

It’s a scruffy road comedy that isn’t quite scruffy enough, even though it co-stars eternally shambolic Jason Mantzoukas, currently not-shaving and appearing on “Brooklyn-Nine-Nine” and “I’m Sorry.”

But a little chemistry always makes the trip bearable, and pairing him with Tony Revolori (“The Grand Budapest Hotel”) pays dividends in this affable amble across the American Southwest.

Affluent suburban Texas teen Nathan (Revolori) is off to art school, vintage Pentax 35mm camera in hand, minivan loaded for life in LA. It being an old minivan, it doesn’t make it out of Texas.

Luckily for the kid, there’s a garage close by. And Richard (Mantzoukas) is just in the process of melting down (LOUDLY) and quitting. The best way to pay him when he gets the van running again is to give him a lift…”just 45 minutes up to road, place called Alpine.”

If you know your road comedies, you’ll know that “45 minutes” is an illusion, that “just drop me off anywhere” will not hold.

And if you know the genre, you’ll know to expect the “Planes, Trains and Automobiles” mismatch.

Nathan is sheltered, uptight and flush with his parents’ cash for the trek. Richard, he of the greasy t-shirt beneath the stained hoodie, a riot of hair, wild eyes and manic patter? He’s the opposite.

He leaps from “Wanna a road brew?” (he keeps a beer bottle in his shirt pocket) to “So what’s your story? You party?” to “Wanna share this pretty rad jazz cigarette?” (coolest name for a joint) to “You’re an artist? So what’s your philosophy? What have you got to say?”

The two make a mid-winter (no snow) journey from Texas in the general direction of LA, with inter-titles signifying stops along the way — Marfa, Texas, Las Cruces, Truth or Consequences, Albuquerque, Gila, Silver City…

And with the stops come mild misadventures straight from the road comedy screenwriting app — bar fight, robbery, tracking down an old love, new romance, car troubles and the kindness of strangers.

When the formula is this tried and true a movie has to get by on chemistry and its banter.

Favorite movie? It’s “The Graduate” vs. “Fast and the Furious: Tokyo Drift.”

Richard somehow doesn’t realize there were MORE “Fast and Furious” movies, that series co-star Paul Walker died.

“Dude, you’re blowing my mind!”

Nathan? He’s never been to Richard’s impromptu choice of next destination — Vegas.

“Dude, all the best hookers are in strip clubs.”

Music? Nathan has this iPod his ex-girlfriend gave him.

“There’s like three Indigo Girls records on here. Is that why you dumped her? ‘Cause I totally get it.”

The meet-up with the long lost flame goes so very wrong that it gets “Long Dumb” off on the right foot. An ill-fated meeting with one of Richard’s old running mates (Ron Livingston, amusingly cast against type) is an unexpected laugh.

Mantzoukas makes Richard a mercurial mess, disarmingly charming one second, self-sabotaging (and Nathan sabotaging) the next. He poses for Nathan’s camera — “This is America at its purest, dude.” His philosophy? “Friends, shelter and a little bit of food in my belly.”

Richard is going to put Nathan’s declared eschewing of his “pretty sheltered life,” planned from SATs to college to marriage to its severest test.

Nathan will be like “my little brother. I’m gonna teach you everything…rip the condom off’a your mind.”

Richard’s lived 35 years just rolling with the punches, adrift, a guy with “We GOT this” answers for everything.

“You need to be more zen about how things happen,” he preaches. But remember, he’s an idiot.

“This is so stupid.”

“I know, right? Let’s do it.”

Director and Hannah Fidell and her co-writer Carson Mell remade their short film “The Road,” and had just promise in that script to get Livingston, Taissa Farmiga, Grace Gummer and Pamela Reed on board.

But it’s hard to see anything at all to this without Mantzoukas. He’s the beating heart of the comedy and the soundtrack to the film, rarely shutting up long enough to take a breath, collect his thoughts or plan ahead.

Whatever everybody else is doing, he sounds like he’s improvising, making this up as he goes along. He’s just the sort of guy you’d pick up hitchhiking — probably harmless, entirely too chatty and just edgy enough to make you plan your next rest stop where you can hopefully ditch him.

Provided the car starts when you’re making your break.

MPAA Rating:R for pervasive language, sexual content and some drug use

Cast: Tony Revolori, Jason Mantzoukas, Grace Gummer, Taissa Farmiga and Pamela Reed

Credits:Directed by Hannah Fidell, script by Hannah Fidell and Carson Mell A Universal release.

Running time: 1:30