TAMMY (Rated R)

As far as can be recalled, the last time Susan Sarandon had a starring role in a road-trip movie it was definitely not a comedy.

“Thelma & Louise” involved travels in a vintage Ford Thunderbird that ended very badly for its titular characters.

This time around, Sarandon is oddly teamed up with comedic sensation Melissa McCarthy for a road trip full of misadventures, but one that is supposed to be a comedy.

Sad to say, even with the considerable presence of McCarthy, “Tammy” does not hit on all comedic cylinders.

Before even the unspooling of the first frame, “Tammy” offers hope and promise of funny things to come.

That’s because Melissa McCarthy, following hit comedies like “Bridesmaids,” “Identity Thief” and “The Heat,” knows how to deliver the laughs.

Expectations rise even higher, knowing that McCarthy, in collaboration with her real-life husband Ben Falcone (also the film’s director), wrote the screenplay for “Tammy.” At this point, it seems like almost a sure thing as California Chrome to win the Triple Crown.

As the titular character, McCarthy’s Tammy is a walking disaster. On her way to work at a crummy fast food joint, Tammy has the misfortune of hitting a deer, causing her rusted Corolla to be totaled and eventually consumed by engine fire.

Naturally, arriving late to work, Tammy is summarily fired from her job. She throws a tantrum, tossing packets of ketchup at the obnoxious manager and manhandling food items so as to make then inedible, all the while making snide remarks about Topper Jack’s.

The trifecta of bad news comes when she arrives home early to find her spouse (Nat Faxon) entertaining the next-door neighbor (Toni Collette) with a romantic dinner. She complains that her louse of a husband never cooked nice meals for her.

Deciding to pack and leave her Illinois hometown, Tammy first visits her mother Deb (Allison Janney), who lives only two doors away.

A practitioner of tough-love, Deb refuses to loan a vehicle to Tammy, even her absent father’s old pickup truck.

With no money or wheels, Tammy’s only way out of her miserable small town experience is to hook up with her alcoholic and diabetic grandmother Pearl (Susan Sarandon), who just happens to have a roll of cash and a Buick sedan perfect for road travel.

The catch, of course, is that Tammy is now stuck with Grandma Pearl, a randy character who hasn’t quite left behind a past of indulging in sex, drugs and rock ‘n roll adventures.

Pearl claims to have slept with the wrong member of the Allman Brothers and to have once made a pass at Tammy’s father (Dan Aykroyd).

Seeing McCarthy and Sarandon together as members of a family two generations apart, it’s hard to see past an age difference not that wide, even though Sarandon’s Pearl wears a frizzy wig and has ankles inflamed to the size of tree trunks.

Thoughts of Johnny Knoxville’s “Bad Grandpa” sweep into the mind, as Grandma Pearl does her best to be outrageous, though she doesn’t have any body parts stuck in a vending machine.

However, she lets herself get seduced in the back of the sedan by an equally randy and drunk Earl (Gary Cole) that she meets at honky-tonk bar.

Meanwhile, as if it to bring a tender, softer touch to the proceedings, Tammy is introduced to Earl’s responsible, mature son Bobby (Mark Duplass), who appears shy and reserved, quite the opposite of his freewheeling, boozy father.

Plenty of wacky things happen in this movie. Tammy wrecks an expensive rented jet ski by slamming into to a dock. Grandma Pearl ends up in jail on a drug charge, and Tammy unwisely holds up a Topper Jack’s to get bail money.

Later on, the duo attempts to destroy all incriminating evidence with the help of Pearl’s savvy cousin Lenore (Kathy Bates), who happens to be very wealthy and lives in a lakeside mansion with her partner Susanne (Sandra Oh).

Then there’s Lenore’s lesbian Fourth of July barbecue bash to which the only non-females to show up are Bobby and Earl.

The movie’s full of detours, and there’s a stint where Tammy ends up in prison for the hold-up and other assorted crimes.

With the help of friends, Tammy and Pearl finally make it to Niagara Falls, where the film’s saving grace is that, contrary to some idle chatter, nobody decides to make a jump to the bottom.

“Tammy” is the kind of film that requires a leap of faith in its creative and acting team to have come up with something truly hilarious.

Regrettably, it doesn’t happen, though there are humorous scenes, which are practically inevitable when you have Melissa McCarthy involved.

Tim Riley writes film and television reviews for Lake County News.