It’s Time To Evaluate The Car Testimony From ‘My Cousin Vinny’ To See If Its Critics Have A Point

If you had to pick a scene from a movie that almost every piston-happy gearhead likes, but stipulated, for your own perverse motives, that the scene must not include a car, then I suspect that there would only be one scene that would actually qualify: the courtroom scenes from My Cousin Vinny. For a scene that has zero actual cars in it, there is some genuinely hardcore car-ificating happening here. There’s a lot of fairly technical and geeky automotive discussion going on, and while it’s surprisingly accurate for a mainstream, mass-market comedy movie, there have been some out there who have noted some oversights. I want to look at the most common of these complaints, and actually try and figure out how much that matters.

Who’s with me? Fantastic. First, in case you’re unaware of the movie, here’s a quick rundown: it was a 1992 comedy that had a surprisingly high-stakes plot for a comedy: two college kids from New York driving to Los Angeles end up accused of a crime that could end in their, holy crap, executions. They’re too broke for an actual lawyer, so one of them calls their cousin, who is a new, inexperienced lawyer, the titular (giggle) Vinny.

Part of the case crucially hinges on evidence involving some skidmarks and tire treads. Vinny’s (Joe Pesci) fiancée, Mona Lisa, played delightfully by Marisa Tomei, happens to be an expert on cars, having grown up in a family of mechanics. Vinny needs her as an expert witness, and she’s greeted with skepticism by the court, which is, of course, pretty well steeped in the old marinade of chauvinism and a disbelief that women know jack about cars. The opposing lawyer tests her, of course:

Lisa passes that test with the confident aplomb of an astronaut. Her automotive knowledge is established here, especially for mid-century American cars. Later, we get to the crux of why Vinny wanted her there in the first place, as she is able to effectively destroy the primary piece of evidence via her evaluation of the tire marks and her knowledge of cars of the era:

It’s also worth noting that the woman-who-knows-a-lot-about-cars trope has been used in movies plenty before and since then, but I think My Cousin Vinny handles it with a lot more grace and charm than the usual inane, ham-fisted way it’s handled, which is where they get a woman to look at a car and then recite a whole paragraph of specs while all the dudes around nod in disbelief.

The 2014 Need for Speed movie did this especially eye-rollingly, with the hilariously-named Imogen Poots:

Oy. Terrible.

Anyway, let’s get back to Vinny; to prove Vinny’s cousin’s innocence, he needed to show that the car that was allegedly spotted and left the tire marks was not the 1964 Buick Skylark that his cousin drove. Lisa’s assessment of the tire tracks notes three important points: the Skylark did not have a limited-slip differential (the tire/skid marks left were of equal length, suggesting that both wheels received equal traction); the Skylark has a solid rear axle, and the tire marks, one of which was on a curb and the other not, could only be made by a car with independent rear suspension, as both are full tire tracks and not showing a partial/sidewall mark that a non-independent axle would have made; and finally, that the Skylark is about the same dimensions as a Pontiac Tempest, which had independent rear suspension and a limited-slip diff.

Oh, and they both could be had in the same GM minty green color.

Here’s a transcript of the scene, if we need to refer to it:

Mona Lisa Vito

The car that made these two, equal-length tire marks had positraction. You can’t make those marks without positraction, which was not available on the ’64 Buick Skylark!

Vinny Gambini

And why not? What is positraction?

Mona Lisa Vito

It’s a limited slip differential which distributes power equally to both the right and left tires. The ’64 Skylark had a regular differential, which, anyone who’s been stuck in the mud in Alabama knows, you step on the gas, one tire spins, the other tire does nothing.

Vinny Gambini

Is that it?

Mona Lisa Vito

No, there’s more! You see? When the left tire mark goes up on the curb and the right tire mark stays flat and even? Well, the ’64 Skylark had a solid rear axle, so when the left tire would go up on the curb, the right tire would tilt out and ride along its edge. But that didn’t happen here. The tire mark stayed flat and even. This car had an independent rear suspension. Now, in the ’60’s, there were only two other cars made in America that had positraction, and independent rear suspension, and enough power to make these marks. One was the Corvette, which could never be confused with the Buick Skylark. The other had the same body length, height, width, weight, wheel base, and wheel track as the ’64 Skylark, and that was the 1963 Pontiac Tempest.

Vinny Gambini

And because both cars were made by GM, were both cars available in metallic mint green paint?

Mona Lisa Vito

They were!

Vinny Gambini

Thank you, Ms. Vito. No more questions. Thank you very, very much.

Now, one of the biggest criticisms of her testimony is that it wouldn’t just have been the Corvette and Pontiac Tempest that could have had independent rear suspension and a limited-slip differential. There’s another car that could have had these traits: the Chevrolet Corvair.

The screenwriter of the movie, Dale Launer, seems to have known this, but didn’t think it’d matter. He told the website The Wrap in an interview:

“I thought, ‘Well, no one’s really going to know that. I can think of one person I personally know who would know that. Oddly enough, I had not seen him since high school, and I saw him at the premiere. He said [laughs], ‘You know, there were actually three cars with independent rear suspension.’”

Yes, the Positraction limited-slip diff (that name was just used for Chevys; other GM brands called it Positive Traction) was available on the Corvair, but I’m not so sure the rear-engined Corvair’s presence would have changed Lisa’s point, really. Well, depending on what year Corvair, I suppose. That’s because even though Corvairs always had independent rear suspension, early Corvairs used a swing axle design, which would have changed the tire marks of the raised tire:

So, a ’65 and up Corvair with the Positraction diff could be a suspect, but likely not the early ones. Which brings us to the Tempest.

The Tempest, while not rear-engined, did have a rear transaxle, and was also a swing-axle design; it was independent rear suspension, sure, but it would have left the same type of tire marks as the early Corvair if one tire was higher or lower: that tire would have only left a partial mark, unlike what was shown.

Also, the Tempest did not have an option for a limited-slip differential! This article on Curbside Classic, also evaluating this very same scene, noted that back in 2023. All of this means that the Tempest really wasn’t a viable option to have left those tire marks after all.

The issues about the slightly different wheelbases and sizes of the Tempest vs. the Skylark I don’t think really matter; they’re within inches of one another, and are both fairly conventional-looking three-box sedans (or convertibles, in this case). Witnesses weren’t rushing over with tape measures or anything.

While these errors may sound devastating to Lisa’s testimony, I don’t actually think they were. Her fundamental assessment still stands and is still just as accurate as ever: the car that left those marks must have had an independent rear suspension and a limited-slip differential. Her evaluation of that was spot-on.

From there, all that really needs to happen is that the ’64 Skylark of the accused kids needs to be shown to not have those features. It definitely has a solid axle, so there goes the independent suspension part, and the Positive Traction differential was an option (and I don’t really think all that common, either), so as long as the court can be shown that the Skylark has neither of those things, they should be off the hook!

So, let’s recap here. While the main critiques of Mona Lisa Vito’s expert witness testimony are valid – the Pontiac Tempest was really not a viable suspect, while a later Corvair with the later double-jointed rear suspension and Positraction differential was – they really don’t change the most important point of the testimony, which is that the 1964 Skylark could not have left those tracks.

Even with these caveats, the scene remains one of the more technically accurate bits of automotive exposition in a movie, especially a non-car-focused movie. It’s not 100% accurate, but it’s still a great scene.