Car Wheel Parts and Their Functions

Educational

Sep 27th, 2021

Car Wheel Parts and Their Functions

Over the years, cars have taken various body types, designs, and shapes. Some auto parts are now obsolete and eliminated or replaced with new versions. Among the parts that have remained in use since the invention of automobiles are the car wheels.

These circular structures produce rotary motion and are responsible for moving the car from one point to another. Wheels are indispensable to cars and since their invention in 3500 BC, these circular blocks have taken various designs, structures, and styles. Nonetheless, their function has remained the same.

The wheel has many parts, each performing different functions, but not everyone who drives a car knows all car wheel parts. Do you? I hope you do, but in case you’ll want to refresh yourself about all these car parts and understand their structure, functions, and adaptations, then this article is for you.

What Are the Different Car Wheel Parts Names & Their Functions?

1. Tyre – the car wheel part that touches the ground

The tyre is, of course, the prominent component of any car wheel. After all, it's the outermost part and the first thing that you notice when you look at a car wheel. The tyre is the ring-shaped outer covering and the part of the car that touches the ground. 

Most of the car tyres are inflated with compressed air, thus called pneumatic. They are made from rubber (synthetic or natural), carbon black, and some chemical compounds.

Tyres cover and prevent the wheel rim from rubbing or touching the ground. It also cushions and acts as a shock absorber when you drive on bumpy terrains. The main parts of the tyre are the treads and its body.

The tread or track is the outermost rubberised part of a tyre. It is in direct contact with the ground and wears out over time. The tread has grooves and notches, called the tread pattern. This pattern has two important roles - to increase friction between the ground surface and the tyre and to direct water and debris away from the wheel.

The body, on the other hand, acts as a housing for a specified quantity of compressed air. Tyres come in various sizes to fit different cars. You can find the size and other specs of your car's tyre stamped on its sidewall. You may also find it etched or printed on the glovebox door, on your door jamb (driver's side), or within the fuel tank hatch.

The specifications found on the tyre's sidewall include the following:

  • Width of the tyre
  • The ratio of height to width of the tyre
  • The diameter of the wheel
  • Treadwear, traction, and temperature grades
  • Tyre ply composition and materials used
  • Load index and speed symbol
  • Inflation and load limit

How much is a wheel rim?

If you think your tyres need replacing, prepare to spend from $100 to $700 for each tyre. Why is the price range so wide? Find your answers and learn more about the factors that affect the cost of replacing tyres.  

2. Rim – the cylinder that holds the tyre

The rim is the skeletal outer edge that holds the tyre. It is cylindrical, allowing it to hold and seal the ring-shaped casing to the wheel. For tubeless tyres, proper fitting between the tyre and the rim is crucial to seal the air inside. Old-generation cars had inner tubes housed between the rim and the tyre.

Wheel rims are made from sturdy metal such as steel to withstand the force and load of the car. The width and diameter of the rim determine the size of the car tyre. You can get customised rims as aftermarket car spare parts. These customised rims are coloured and styled to your liking, but they come with additional cost.

The barrel of the rim creates a surface for mounting of the tyre. The inner diameter of the barrel is the drop centre, which determines the mount wheel type. For front-mounted wheels, the drop centre is near the wheel's front face. On the other hand, rear-mount wheels have drop centres near the wheel’s back face.

The barrel edges are shaped to form flanges, which ensure that the tyre doesn't slip off when the car is in motion. Inside them are flat sections referred to as beads. These flat sections provide a surface upon which the edge of the tyre rests.

Is it called wheel or rim?

Confusion usually arises between the car wheel rim (or rim) and the car wheel (or wheel). People sometimes refer to the wheel as the rim and vice versa. Let's differentiate between the two - the rim is only a part of the wheel, while the wheel comprises of the rim, tyre, and other components. 

So, if you’re referring to the cylindrical metallic part to which the tyre attaches, then that’s the rim. If you mean the whole rotating part that enables the car to move, then it’s the wheel.

3. Hub – the car wheel part that attaches the wheel to the car 

The wheel hub is the centremost part and has studs onto which the wheel attaches. It has a central bore which is the port for fitting the wheel on the axle. The brake rotors rest against the wheel hub to ensure the car brakes when the driver presses on the brake pedal.

A removable centre cap on the outer side of the wheel covers the central bore. The hub and rim are usually linked by a wheel disc which is either detachable or permanently conjoined with the rim. In other car wheels, spokes are used to connect the rim and the hub. The spokes additionally give the wheel its structural integrity. Today, most wheels have stylised spokes for added appeal.

When buying an aftermarket car wheel, make sure that the central bore is equal to the size of the OEM or OE wheel. Using wheels with a larger central bore will cost you more since you will need hub centric rings to fill the gap.

For spoked car wheels, just outside the centre cap is the centre disc. The depth of this disc relative to the centreline determines the wheel offset.

Lug holes are usually machined to create bolt circles on the centre disc. Lug holes are the holes into which the lug nuts are fastened. The lug holes create bolt circles with a diameter called the bolt circle diameter (BCD). It is this diameter, as well as the number of holes that define the bolt pattern.

What does a wheel hub do?

The hub assembly connects the wheel to the car and allows the wheel to turn. It holds the wheel speed sensor and is crucial in the steering, braking, and traction functions of your car.

4. Valve System - the car wheel part that helps manage tyre pressure 

Car tyres get inflated or deflated through their valve system. Car wheels have a valve mechanism integrated with the tyre pressure monitoring system to help the driver know the pressure condition at all times. For more information about tyre pressure sensor, tyre maintenance, and other matters pertaining your car, please visit our blog at Carpart Australia.


By Sam O.