The difference between wheels and rims is that wheels comprise an entire unit made up of several pieces, whereas rims are just one of the components of a wheel. Many people use the terms “wheel” and “rim” interchangeably, most commonly using the term “rims” for a set of aftermarket wheels that usually offer a noticeably fancier or upscale appearance from stock parts.
Parts of a Wheel
Since the wheel is made of several different parts, it is important to know what those parts are and what they are for, and since rims are just one part of the wheel, we will address them first.
Read More: Tire Size Explained
The rim is the outer edge of a wheel. In other words, it would be the part of the wheel that would contact the road surface should the tire be removed or popped.
Sometimes, the rim is also referred to as the barrel, but this is usually more associated with the parts of the rim that are generally unseen as they are covered by a vehicle’s tire.
There are several different parts that make up the rim just as there are several parts that make up the wheel.
The center bore is the large hole in the center of the wheel. It fits into the hub assembly or axle of the vehicle, and its job is to align the wheel properly on its assembly to reduce vibration and wheel failure.
Sometimes, the center bore is covered to provide a more aesthetically-pleasing look to the vehicle. Not all vehicles have a hub-centric wheel setup. Vehicles with steel wheels in particular are actually lug-centric and do not use a center bore to align the wheel.
Lug holes are the holes in which the lug nuts or bolts are designed to be screwed into place in order to keep the wheel mounted on the vehicle.
Depending on the vehicle, there may be different numbers of lug holes, all of which together form the bolt pattern.
Many vehicles have a five-bolt pattern – wheels containing five lug holes for five lug nuts or bolts – but many aftermarket wheels can have up to seven or eight. This is important to know if a wheel upgrade is anticipated.
The bolt circle is the diameter of the circle formed by the lug holes of the wheel. Essentially, a bolt circle is created by playing connect-the-dots with each lug hole.
The wheel disc is the part of the wheel in which the center bore and lug nuts or bolts are drilled. It is also the part of the wheel that supports the spokes.
In short, it is the part of the wheel that obscures your line of sight to the brakes and other components behind the wheel itself. Depending on the type of vehicle and wheel, some vehicles have a larger wheel disc than others. Vehicles designed to be sporty or stylish often have a small wheel disc to accentuate the spokes. Luxury vehicles and heavy-duty trucks often have a large center disc.
Spokes are the focus-point of any wheel. They are what connect the center disc to the rim of the wheel, and they are generally what gives a wheel its style.
Recently, wheel size on new vehicles has grown, and with that, spokes have become even more of a focal point than they have been in the past. Even luxury cars with a large center disc can have ornate spokes.
Sporty vehicles often have straight, simple, and thin spokes, while trucks and luxury vehicles can have thicker, more robust spokes.
The valve stem itself is more part of the tire and mounting process than it is a part of the wheel, but each wheel is equipped with a hole in which the valve stem fits.
The valve stem is a small metal tube that is put through the valve stem hole through which tire pressure is monitored and through which air is added or removed.
A damaged valve stem is a common reason for slow leaks, allowing air to gradually be released from the tire.
Other Parts of a Rim
Not only is a vehicle’s wheel made up of several different parts, but the rim itself is also made of several different sections. Some are visible and some are not unless the tire is completely removed.
The rim lip is the visible part of the rim that extends the width of the wheel and travels its circumference underneath the tire. Usually, the part of the lip that is most easily visible from the side of the wheel where the spokes meet the rim and outward is called the outer lip.
If any part of the wheel is damaged, the lip is most likely going to get damaged first, and it is also the recipient of a very common type of damage called curb rash.
Curb rash is the damage that results in chipping, rubbing, or grinding down of the rim lip closest to the tire. This is caused by things like potholes, aggressive driving, and general wear and tear. If curb rash becomes or lip damage becomes bad enough, tire mounting can become impossible and replacement wheels may become necessary.
The flange is the very first part of the rim that turns in to face the tire where the lip ends. It is the first line of defense for keeping the tire mounted to the wheel, and mounting a tire requires careful placement of the tire over the extended flange.
Flanges can also be easily damaged since the flange is essentially the opposite side of the edge of the rim lip. Like the lip, if the flange is damaged enough, it could prevent a mounted tire from holding air or being properly and safely mounted.
Each tire has a bead, a thick circular loop that travels the length of the inside of a tire on each side. The bead rests, or bead seats as some call them, are the next part of the rim just inside the flange.
As the inside of the rim flattens from the vertical flange there are two grooves that form a shallow valley in which the tire beads sit and are sealed. It is here that the actual wheel and tire connection is made.
Mounting humps follow the bead rests on the inside of the rim as a means of keeping the tire mounted opposite the rim flange. They perform basically the same function as the flange, but they keep the wheel from slipping toward the center of the rim rather than slipping off the rim on the outside.
The drop center, or tire well, aids in the mounting of the tire and is a deep well within the rim that travels the circumference of the wheel. It allows the tire to be slid over the barrel – the width of the rim – without damaging the tire bead or other parts of the tire.
After the tire is placed within the drop center, it can be properly slid into place within the bead rests by unfolding from the drop center.
Contrary to popular opinion, wheels and rims are two different things. Wheels are the parts of a vehicle that hold the tire, provide the physical connection to the vehicle itself, and provide some style as well. The rim is just one of the many parts of a wheel. It is outside of the wheel – the part that actually holds the tire – and is made of many different parts itself, most of which ensure that the tire does not fall off the vehicle.