Where is the rim of the wheel?

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One of the most important parts of any car, truck, or SUV also happens to be one of the most commonly mislabeled. Whether you call them wheels, rims, or "those round things at each corner," everything from the comfort of your car's suspension to the feel of your steering to your fuel economy can be impacted by those four circular pieces of metal.

But when someone talks about a vehicle's wheels, are they also talking about the rims? The answer is both yes and no. The two terms, wheels and rims, are often used interchangeably, even by automotive experts, but wheels and rims aren't really the same thing. Here's a look at the differences, along with a quick history lesson on a long-running quirk in our relationship with car wheels and rims.

Wheels and Rims: What's the Difference?

The simplest way to think of it is that a rim is part of the wheel, even though the word "rim" is commonly used as slang for an entire wheel. Got it? No? We'll explain.

Let's say you're checking out a new SUV and you have a choice of wheels that are either 18 or 19 inches in diameter. Each set is encircled by a corresponding tire and secured to the brake and suspension assemblies by a series of lug nuts in the center of the wheel (or hub). The rim itself is the outer edge of the wheel, where the metal meets the rubber of the tire—and it's the diameter of the rim that's measured to determine wheel size.

What's the job of a rim?

It's up to the wheel's rim to give the entire wheel strength and support—and, of course, to maintain an airtight seal with the tire. When a wheel has a nasty encounter with a jagged pothole or unforgiving curb, the part that usually bears the brunt of the impact is the rim.

Now that you know your wheels from your rims, here's one more term for those who really want to impress their friends: The inner part of the wheel—the section between the outboard rim and the inside rim—is called the barrel.

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Why Do We Kick Tires?

We've likely all done it when considering a car or truck, especially if the vehicle is used. You walk around the car, take a look at the bodywork, and peek into the interior. And then, thump! You give one or more of the tires a light kick. What's going on here? Why is tire kicking something so many of us do?

There are a few versions of the backstory, but they all come back to the dawn of the automotive era, when tire quality was notoriously dubious. In the early 1900s, most roads were little more than narrow, bumpy lanes. Combined with the similarly narrow and fragile tires of the time, it was the perfect recipe for flats and broken wheels—the earliest of which were made of wooden spokes like those on a horse-drawn carriage. Car shoppers back then often kicked a tire to make sure the wheel and tire wouldn't fall to pieces or burst apart.

While modern wheels, rims, and tires are highly unlikely to succumb to such a blow, this quirky car-buying habit remains.

“Hey, check out my new rims!” quips your car enthusiast friend. But what part of the vehicle are they referring to? If your mind jumps to car wheels, you’re not alone. When it comes to the question of rims vs. wheels, the terms are often used interchangeably. However, the rim is just one part of the wheel — and an important one at that.

What are wheels?

To understand the difference between wheels and rims, it helps to know how automobile wheels work. Let’s start with the basics. While sometimes people think of tires when they talk about wheels, technically your wheels and tires are separate entities that ultimately combine to form the tire-wheel assembly.

Rims play an important role in this setup. As the outer edges of the wheel, your rims secure the tire on to the wheel by forming an airtight seal. But rims are only one part of the wheel equation. In addition to rims, wheels are comprised of other important features:

• Wheel bearing: This is the part of the wheel assembly that connects the wheel to the axle.
• Lug nuts: Located around a wheel’s center, these nuts secure the wheel to the vehicle. 
• Center cap: These caps help keep dirt and grime away from the wheel bearings and lug nuts. They often sport a manufacturer’s logo.
• Hubcap: Larger than center caps, these disks are hammered or clipped on the hub of the wheel, covering the lug nuts. Hubcaps used to be more common, helping protect steel wheels from the corrosive effects of winter weather, road salt and other harsh chemicals. Nowadays, wheels are increasingly made of aluminum or metal alloys, which tend to better protect against corrosion, making hubcaps less of a fixture.
• Spokes: These are the metal arms that connect a wheel’s center to its outer reaches, such as the rim and the barrel.
• Barrel: While your rims are the outward-facing edge, the curved portion of the wheel outside of the spokes is known as the barrel.
• Wheel cover: A wheel cover helps protect the entire surface of the wheel. Wheel covers are often designed to make the wheel look more appealing and may also be used as a cosmetic fix for minor scratches.

What are rims?

As we mentioned, the main difference between wheels and rims is not technically a difference at all: rims are simply one important part of the wheel. Of course, in popular culture the phrase “Nice rims!” has long been used as shorthand for complimenting someone’s wheels, particularly in reference to a sharply designed or intricate wheel cover. But what we’re talking about here is what rims actually are: the two outer edges of each side of your wheel.

What do rims do?

As the edge points of contact between the tire and the wheel, rims help hold tires properly in place. As stated, they also help maintain an airtight seal between the tire and the wheel.

For these reasons, your rims play a crucial role in supporting the entire wheel assembly and its place in your car’s suspension system. If you drive over a bump or pothole, the rim is the part of the wheel that receives the initial impact after it passes through the tire.

You may think of your tires and rims as the front line of defense against the rigors of the road. If your rims get banged or dented, it may affect the performance of your vehicle, from flat tires and reduced handling to distracting vibrations inside the cabin.

What do rims look like?

If you look at a wheel from the top without a tire on it, you’ll see that it dips down in a “U” shape, which continues along its circumference. The rims are the upturned stems of this U-shaped design. The outermost edges of the tire, known as “tire beads,” press against the rim when inflated to form the tight seal.

What are rims made of?

Your rims are made from the same alloy or metal as the rest of your wheel. They’re also often specially treated with a protective coating during the manufacturing process to help extend their longevity.

How to know what size rims you have?

Knowing how to determine rim size can be helpful, because wheel size and tire size depend in part on the diameter of the rim.

Your rim size can be found in several places. Firstly, you can check the sidewall of the tires that came with the wheel. If you no longer have those tires, the information may also be found in various places such as the inside frame of the driver’s door, on the gas tank hatch, on the glove box door or stamped on the back of the wheel itself. When in doubt, checking your owner's manual is always a good idea.

If you spot a numeric sequence like “16x6 5-110,” the initial two dimensions give you the diameter of the rims and the width between them (16 inches and six inches in this case). The other two dimensions refer to the number of bolt holes and their diameter (five lug nuts in a circular formation measuring 110 millimeters at its widest point in this case).

Do rims come with new tires?

Generally, when you replace your tires you don’t also need to buy new rims, unless you’re investing in a wheel-tire combo, possibly due to damage to your rims.

How do rims become damaged?

Rims can become dented by curbs or potholes and corroded by road salt. Similar to tires, they also tend to wear with age. Signs of a damaged rim may include sudden changes to handling, vibration when steering, problems with your wheel alignment and tires that repeatedly deflate. It’s generally best not to leave any concerns with your car’s suspension to chance. Consider asking a trusted mechanic for advice.

The difference between wheels and rims

Let’s return to where we started: the difference between wheels and rims. As explained above, it comes down to a matter of detail. The wheel is the metal unit that attaches the wheel hub to an automobile via an axle, while rims are the outermost part of the wheel assembly. Perhaps think of it this way: “rim” means “edge,” and rims are located on the edges of your wheels.

In the more colloquial sense, “rims” may refer to the wheel covers you might sometimes see on a car, typically added for aesthetic reasons. Though somewhat of a misnomer, this correlation might possibly have come about because the rim size does dictate the size of wheel cover required.

In summary

The difference between wheels and rims is more than simply semantic. If it weren’t for your rims, your tires wouldn’t be properly secured to your wheels, leading to a ride that is shaky and potentially dangerous. Understanding rims vs. wheels may also make it easier to explain any issues with your wheel assembly to your mechanic. Although actual rims may not have the decorative flair of modern-day wheel covers, this crucial wheel component still deserves its chance to shine.