Every car, from Ferrari to Ford Pinto, relies on the simplest machine: the wheel. There is no bypassing (pun intended) right next to the fire, the wheel could be the greatest discovery man has ever made. Without wheels and tires, cars and trucks would be little more than expensive lawn ornaments.
From car to car, wheels and tires perform the same function. The only difference is in size, style, and structure. In order to expand your knowledge base about cars, trucks, and how they work, the basic parts of a car wheel and tire are explained below. When you know more about your vehicle, you can look after it better and keep it running for many years.
What are Wheels?
Wheels are those primitive circular blocks that rotate in order for the car to move. They are placed vertically under the vehicle which doesn’t only allow movements but also provides the support of the vehicle and heavy loads.
Parts of a Car Wheel
The wheel includes the hub, spokes, and rim. The point of contact for the axle seat, the lug bolts, and the lateral surface of the rotor.
1. The Tire
The tire is, of course, the outstanding component of every car wheel. After all, it’s the outermost part and the first thing you notice when you look at a car wheel. The tire is a ring-shaped outer shell. Most car tires are inflated using compressed air, which is known as pneumatic. They are made of rubber (synthetic or natural), carbon black, and some chemical compounds.
Tyres cover and prevent the rim from rubbing or touching the ground. It cushions and also acts as a shock absorber when you’re driving on bumpy terrain. The main parts of the tire are the treads and its body.
The tread or track is the outermost rubberized part of a tire. It is in direct contact with the ground and wears out over time. The tread has grooves and notches called a tread pattern. This pattern has two important functions to increase the friction between the ground surface and the tire and to draw water and dirt away from the wheel.
The body, on the other hand, acts as a housing for a specified quantity of compressed air. Tires come in various sizes to fit different cars. You can find the size and other specs of your car’s tire 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
2. The Rim
Confusion usually arises between the rim and the wheel. People sometimes refer to the wheel as a rim and vice versa. Let’s distinguish between the two the rim is only part of the wheel, while the wheel is made up of the rim, tire and other components.
The rim is the outer edge of the skeleton that holds the tire in place. It is cylindrical and allows the annular housing to be held and sealed on the wheel. With tubeless tires, proper assembly between the tire and the rim is crucial to seal the air inside. Old generation cars had tubes between the rim and the tire.
The rims are made of sturdy metal such as steel to withstand the force and load of the vehicle. The width and diameter of the rim determine the size of the car tire. You can get custom rims as aftermarket auto parts. These bespoke rims are colored and styled to your liking but come at an additional cost.
The barrel of the rim creates a surface for the tire to be mounted on. The inside diameter of the cylinder is the center of fall, which determines the type of wheel mounted. For front-mounted wheels, the drop center is near the front of the wheel. On the other hand, rear-mounted wheels have fall centers near the back of the wheel.
The barrel edges are shaped to form flanges that ensure the tire does not slip while driving. Inside them are flat sections referred to as beads. These flat sections form a surface on which the edge of the tire rests.
3. The Hub
The hub is the most central part and has studs to which the wheel is attached. It has a central hole that is the opening for mounting the wheel on the axle. The brake discs lie against the wheel hub to ensure that the car brakes when the driver steps on the brake pedal.
A removable center cap on the outside of the wheel covers the central hole. The hub and the rim are usually connected by a wheel disc which is either detachable or permanently attached to the rim. Other automobile wheels use spokes to connect the rim and hub. The spokes also give the wheel its structural integrity. Most of the wheels these days have stylized spokes for added appeal.
When purchasing an aftermarket car wheel, make sure that the central hole is the same size as the OEM or OE wheel. Using wheels with a larger central bore will cost you more as you will need hub-centered rings to fill in the gap.
In the case of spoked car wheels, the center disk is located directly outside the center cap. The depth of this disc relative to the centerline determines the wheel offset.
Lug holes are typically machined to create bolt circles on the center disc. Lug holes are the holes where the wheel nuts are attached. The Lug holes create bolt circles with a diameter called the bolt circle diameter (BCD). This diameter and the number of holes define the bolt pattern.
4. Valve System
Car tires are inflated or deflated through their valve system. Car wheels have a valve mechanism that is integrated into the tire pressure monitoring system so that the driver knows the pressure status at all times.
How to Read Tire Sizes?
When you look for new tires, you’ll come across size names such as 235/75R15 or P215/65R15. These labels can be confusing if you’re not sure how to read them, but once you learn the language of tires, they become clearer.
On the left side of the slash symbol, you’ll find three numbers and sometimes letters. The numbers represent how wide the tires are, in millimeters, from sidewall to sidewall. The bigger this number is, the more road the tire touches.
If you see a letter on the left side, it refers to the tire type. Letters you might see are:
- “P,” for passenger vehicle tire. This letter also lets you know that the tire is made to meet standards in the United States. When there is no letter, it means it’s made to meet European standards. The two types have different load capacities.
- “LT,” for light truck. Tire sizes that start with these letters are intended to be used for light trucks. They’ll have higher psi recommendations to better take on trailers and heavy loads.
- “ST,” for special trailer. Tires sizes with these letters are for trailer wheels only.
Using a P215/65R15-size tire as an example, we can tell that the tire is for a passenger vehicle and has a 215-millimeter width.
On the right side of the slash symbol, you’ll find two numbers, a letter, and two more numbers. The first set of numbers represents the aspect ratio of the tire’s height to its width. In our P215/65R15 example, those numbers are 65, which means the tire’s sidewall height is 65% as large as the tire’s width.
The middle letter on the right side of the slash tells you about the tire’s construction method and will most commonly be “R,” or radial. This means the layers of the tire run radially across it.
The last number is important, as it tells you what size wheel the tire fits. In our example, this number is 15, which means the tire fits a wheel with a 15-inch diameter.