Tire rims hold the rubber tire in place so that the vehicle can function. With so many sizes and styles available, you may wonder what the difference is, how rims work, and if the differences matter.
Rims are also known as wheels and are necessary for all automobiles, from passenger cars to commercial vehicles. Wheels provide two uses: they reduce friction and they provide leverage. The rim is an important part of the wheel because it rotates around rods that are called axles. Some friction is necessary to turn the wheels, and that is provided by the tire contacting the pavement. This helps the vehicle move along. The rim magnifies the amount of force applied, which provides the leverage. The amount of leverage depends on how large the wheel or rim is. This impacts performance for your vehicle.
Why Rims Matter
Many people focus on rims because of their aesthetic appearance. Change out the style or size of rims and you can create a new look. Bigger rims may make a vehicle appear more muscular or sportier while smaller rims create a low profile look.
Rims do more than just make your vehicle look good. A good set of car rims enhance your vehicle’s performance and provide a smoother ride. Changing the size of the rims on your vehicle impacts the alignment, handling, braking, and acceleration as well as the calibration of the speedometer.
Considerations before installing an aftermarket rim:
Make sure it fits in the wheel-well
Consider the correct backspacing, which is the width of the wheel and the location of the mounting plate
Ensure it matches the vehicle’s bolt pattern
Determine if there is an adequate selection of tires to fit
Make sure the wheels don’t rub anything on the vehicle
Working with professionals to choose new rims helps ensure that you select a design that is suitable for your vehicle.
Components of the Rim
Outboard face – this is the part of the rim that you see on your vehicle, while people often select it for the design, it also provides the structure for the rim.
Center bore – the empty hole in the middle of the rim that is often covered by a cap when the rim is on the car.
Plate – the section around the center bore that contains the bolt holes for the lugs. It connects to the axle seat and the rotor while everything else on the wheel connects to the plate.
Spokes – the long, thin structures that connect from the plate to the edge of the rim. They come in four-spoke, five-spoke and other patterns. They also provide part of the design element of the wheel.
Dish – the part of the wheel that connects to the spokes, the exterior of the wheel
Bolt circle – the circle that is created by the centers of the bolts
Valve stem – provides a hole to fill the tire with air, may be made of rubber or metal
Important Measurements of the Rim
When fitting a rim to a vehicle, there are two important measurements to consider. The first is the center bore, which is the hole in the middle of the rim. This fits the axle that is attached to the hub of the vehicle. It holds the wheel in place and is measured in millimeters.
The second measurement is a combination of the bolt pattern and the bore circle diameter. The bolt pattern is how many holes are in the rims that bolts or lugs attach to. Four- and five-lug patterns are common in most vehicles.
The bore circle diameter is the diameter of the circle measured in millimeters or in inches. For four-lug rims, you measure the two opposing holes. With the five-lug rims, you look for the two holes that are directly opposite from each other.
What Rims are Made Of
Car rims can be designed from a variety of materials. The choice not only affects the look of the rims but the performance through its strength, weight and durability.
Steel rims – these rims are often the most affordable and may come with hubcaps
Aluminum alloy rims – one of the most popular choices to bridge the importance of affordability and durability, also very stylish
Carbon fiber rims – newer than other materials, offers lightweight design while providing durability
Wheels made of aluminum alloy may feature several different finishes, including polished, painted, machined and chromed. Each finish has a unique look and requires specific maintenance to keep it looking good.
Construction of Aluminum Wheels
When choosing aluminum wheels for your vehicle, you also must decide what kind of construction you want. Forged aluminum is the most durable method because it takes a solid piece of aluminum and puts a massive amount of pressure and heat against it to crush it into shape. The resulting rim is lightweight and strong.
Low pressure casting forces the molten aluminum into the mold to pack it tightly and increase its strength. Counter pressure casting uses the opposite idea with a vacuum that sucks the metal into the mold. The process is different, but the results are the same as with low pressure casting.
Gravity casting is the simplest process and involves pouring the metal into a mold. More metal must be used to provide the necessary strength and creates a heavier rim.
Flow forming is another process where the aluminum is stretched using high-pressure rollers and heat. Many older racing wheels used this process.
Problems with Rims
The rim must fit the vehicle and all of the other component that make up the performance of the automobile. If the rim doesn’t fit the vehicle, it can lessen performance and stability, causing a higher risk of a collision.
Another issue is that the rim must be durable enough for the type of driving you do. Lightweight rims are more susceptible to dents and cracks. A truck that hauls heavy equipment or an SUV that goes off-roading will need different rims than a passenger car that travels in the city or on the highway.
This article originally appeared on YourMechanic.com as How Rims Work and Why They Matter and was authored by Joyce Morse.