A new set of wheels can update the look or even improve a vehicle’s performance. CARiD has a big selection of wheels, for all kinds of vehicles, and in various finishes: chrome, black, matte, custom-painted colors, and more. If there’s a design rolling down the street, it’s for sale here.
This article covers some basic terms a person might come across during the ordering process for a new set of wheels wheel. The guide includes definitions of terms customers might not be familiar with – such as offset, center bore, backspacing, bolt pattern, and more. These, and others below, are all measurements for different wheel dimensions, and each one affects whether a wheel properly fits a vehicle.
Wheel Diameter
What Is Wheel Diameter And How Is It Measured?
Diameter is the most familiar wheel dimension: When someone says a vehicle has “20-inch rims,” the person is referring to the wheel diameter.
The diameter is the distance between the bead-seating areas (where the tire seals to the rim) across the center of the wheel. The diameter determines how large the wheel appears when a person looks at a car or truck on the road.
It wasn’t so long ago that 14- and 15-inch wheels were common sizes for most cars. Today, 16- and 17-inch diameters are widely available, with 19-, 20-inch, and even larger sizes available on some vehicles. In the aftermarket, the sky’s the limit with diameters up to 30 inches and beyond.
What Is Plus-Sizing?
Plus-sizing is when someone fits wheels with a larger diameter than the stock pieces. A “plus one” (or +1) upgrade means increasing the wheels’ diameter by an inch, and a “plus two” reflects a 2-inch increase in diameter – and so on.
As the wheel diameter increases, the tire’s sidewall height needs to be smaller so that the total diameter of the wheel-and-tire combination remains approximately the same. This approach also minimizes changes to the speedometer’s accuracy.
For example, take a vehicle that wears a 205-millimeter wide tire with a 55 sidewall aspect ratio on a 16-inch wheel, which would be size 205/55R16. An owner can replace that tire with a 215/45R17 as a plus one or a 225/40R18 tire as a plus two. Note how the aspect ratio decreases in these examples, from 55 to start to 45 and 40 for the larger diameters.
What Are The Benefits Of Plus-Sizing?
Plus-sizing shows off more of the wheel and less of the tire sidewall, which some folks find more aesthetically attractive. Larger-diameter wheels are also usually wider, allowing them to fit broader tires, so there’s more rubber on the road for increased traction and improved handling. Plus, a shorter sidewall doesn’t flex as much when cornering for a crisp response when turning the steering wheel.
What Are The Disadvantages Of Plus-Sizing?
Lower-profile tires have some disadvantages. The shorter sidewalls provide less cushioning, leading to a stiffer ride. That reduction in ride quality is more noticeable on bad, broken, or gravel roads than on smooth paving.
Low-profile tires are also more at risk of damage over potholes. After a hard hit, a blister bubble may form in the sidewall, or the tire may blow out completely. Reduced cushioning from the tires can also damage the wheels. The rim’s edge can bend as it slams into deep potholes, creating an out-of-round condition requiring the wheel’s repair. In worst-case scenarios, the wheel may even crack.
Larger wheels also tend to weigh more, which has several disadvantages. Since they’re heavier, it takes more horsepower to accelerate, so fuel economy can suffer.
Likewise, more braking power is required to slow a heavier wheel. The additional weight also creates more inertia in the springs and shock absorbers, reducing responsiveness. Plus, the steering may feel more sluggish.
What About Wheels and Tires For Lifted Trucks?
One of the many advantages of a lift kit for trucks and SUVs, whether two inches, six inches, or more, is the ability to fit humongous tires in the wheel wells. However, off-road tires use a different measuring system. For example, 35x12.5/17 refers to a 35-inch exterior diameter, 12.5-inch width, and a 17-inch interior diameter – indicating the wheel diameter that this tire fits. Read our related article Understanding Off-Road Tire Size Measurements for a much deeper explanation.
Can Incorrect Speedometer Readings Caused By Larger Tires Be Corrected?
Increasing the wheel-and-tire’s total diameter can lead to inaccurate speedometer and odometer readings. To rectify this, CARiD sells portable controllers that plug into a vehicle. After entering the original and replacement tire sizes, this device tells the car’s computer what the new calibrations should be. To see some specific controllers, check out our speedometer calibrator pages.
Wheel Width
What Is Wheel Width And How Is It Measured?
The wheel width is the distance between the bead seating areas across the rim. The most important consideration is that this dimension is the proper size for the tires.
Every tire manufacturer specifies a range of widths for each tire size. Once mounted, the tire’s actual width can increase by almost an inch in some cases when going from the narrowest to the broadest wheel allowed. This situation may not sound like much, but it can be critical when selecting a tire and wheel package. A tire on a narrower wheel within the range may fit on the vehicle, but the same tire on a wider wheel might not.
What Are The Pros and Cons Of Installing Wider Wheels?
When properly matched, wider wheels with broader tires mean there’s more rubber on the road which allows for increased increased traction. Hugely powerful drag-racing cars use super-wide racing slicks so there’s enough grip to make use of all of that horsepower. Wider tires perform also allow cars to perform better on racetracks and skidpads, because they allow for higher cornering g-forces than skinny tires. Plus, wider tires’ grip aids in braking; scrubning off speed faster to reduce stopping distances.
A wider wheel and tire package also has some disadvantages. Wider tires are more susceptible to following ruts in the road – pulling the vehicle from one side to another if the driver isn’t paying attention. Wider tires also don’t cut a path in wet or snowy conditions as well as narrower options, and they are more likely to aquaplane and lose grip in heavy rain conditions. They have a higher rolling resistance, which means the engine must work harder to move more rubber over the road, causing fuel economy to suffer.
What Is Staggered Wheel Fitment?
Staggered wheel fitment means a vehicle’s rear wheels and tires are bigger and/or broader than the ones on the front. It’s a common modification for folks looking to upgrade rear-wheel-drive performance vehicles. The layout provides more grip for the back tires to get better traction when putting the power down or when accelerating out of a corner.
For these reasons, many high-performance vehicles come with staggered wheel fitment from the factory. It’s also why hot-rodders have installedl supersized rear tires since the day after the dawn of the automobile.
CARiD has a tire-shopping tool readers can use to enter their vehicle’s year, make, and model to shop for recommended replacement sizes, even if you’re running a staggered setup.
Wheel Offset
What Is Offset?
Offset is the distance between the wheel’s mounting surface, which is where the it bolts to the vehicle, and the wheel’s true centerline. For example, a wheel with zero offset has a mounting point on the wheel centerline. Positive offset is when the mounting surface is closer to the outside of the wheel, and negative offset places the mounting surface farther inside the wheel.
How Does Changing Wheel Offset Affect A Vehicle?
Putting an aftermarket wheel with more negative offset than the original layout causes the wheels and tires to stick out farther from the vehicle than the stock setup. Potentially, there could be clearance problems between the tire and the fender.
Conversely, a new wheel with a positive offset sits farther inside the wheel well. There can also be clearance issues from the tire or wheel contacting brake or suspension components.
Wider aftermarket wheels can increase the amount of negative offset, so it’s essential to select a design with an offset that’s the same as or very close to the vehicle’s stock set.
Fitting wheels with a negative offset widens a vehicle’s footprint because the tire contact patches are further apart. While this reduces side-to-side load weight transfer and increases grip, it can make steering response sluggish in some models.
“Rolling” the fenders is one way to create more clearance if a tire is rubbing. This alteration requires a tool that bolts to the wheel hub. As it moves back and forth, a roller applies pressure along the fender lip to gradually push the sheet metal outward. If that approach doesn’t create enough space, cutting the metal and installing fender flares may be necessary. Both of these modifications are permanent and may negatively affect a vehicle’s resale value. (They also often create a custom vehicle that looks totally bitchn’.)
Backspacing And Center Bore
What Is Backspacing?
While offset measures the distance from the hub mounting surface to the wheel’s centerline, backspace is the distance between the mounting surface and the inner edge of the wheel rim. The offset and backspace must be correct on a replacement wheel to ensure it fits properly inside the well without contacting the fender, frame, or other components.
What Is Center Bore?
The center bore is the machined hole in the center of the wheel that fits over the flange that extends from the wheel hub. It centers the wheel on the hub while tightening the lug nuts and prevents wheel runout, which can cause vibration.
What Are Centering Rings And Why Might I Need Them?
To make a wheel fit as many different vehicles as possible, aftermarket manufacturers usually machine the center bore to a larger size and then use centering rings to create a tight fit.
The centering ring fills any space between the wheel hub and the center bore. It centers the wheel on the hub so that no wobbling or vibrations occur at speed. A properly sized centering ring is crucial to vehicle safety, handling, and ride comfort.
Hub-Centric Vs. Lug-Centric Wheels
Lug-centric wheels center as the lug bolts become tighter with no support from the hub itself. To reduce the risk of runout and vibration, never tighten lug-centric wheels with the vehicle’s weight on them. Hub-centric wheels are supported by the hub and by the lugs.
Hug-centric wheels aren’t really a thing, but we think the world might be a nicer place if they were – wheel manufacturers, we’re looking at you to lead the way here.
Bolt Pattern
Wheels attach to the hub with lug nuts that fasten to studs or with lug bolts that thread into holes. Cars and light trucks can have four to eight studs/holes. The distance between adjacent fastening points can also vary, which is why a five-hole wheel doesn’t fit every vehicle with five studs.
What Is A Bolt Pattern?
Manufacturers note a wheel’s bolt pattern as the number of fastening points and the distance between two of them. For example, the bolt pattern 4 x 4.5 means there four studs/holes with 4.5 inches between them. The bolt pattern can also be in metric notation, with 4 x 100 mm signifying four studs/holes with 100 millimeters between them.
What Is Pitch Circle Diameter?
Pitch circle diameter (PCD) is the diameter of an imaginary circle that passes through the center of all wheel mounting points. This number comes from measuring the distance between any two lug holes. Then, divide by .7071 for a 4-stud wheel, by .5878 for a 5-stud wheel, or by .5 for a 6-stud wheel to arrive at the PCD.
Wheel Spacers And Adapters
What Are Spacers, And Why Might I Use Them?
Wheel spacers are round metal plates that mount to the wheel hub assembly to create a negative offset. They also create the look of wider wheels and tires without the expense and effort of purchasing and fitting new parts. Wheel spacers are also helpful for creating extra clearance for big brake kits, springs, or other suspension upgrades.
Spacers are available in a variety of diameters and bolt patterns. Enter a vehicle’s make, model, and year to let CARiD determine the right match.
What Are Adapters, And How Are They Different From Spacers?
Wheel adapters go a step further than spacers. Both devices mount on the wheel hub assembly to create a more negative offset, but adapters change a vehicle’s bolt pattern. For example, they can convert a model to have a five-bolt setup instead of the factory four-bolt layout. This method allows for fitting a wheel with a different pitch circle diameter.
Adapters allow greater freedom of choice when selecting aftermarket wheels because the new pieces don’t have to match the OEM bolt pattern. Typically, longer bolts or studs will be part of the kit to ensure the wheel fastens securely to the hub.
What Are The Disadvantages of Wheel Spacers and Adapters?
Wheel adapters with an excessive amount of thickness can have several drawbacks. For example, positioning the wheels significantly farther out can negatively affect the vehicle’s suspension geometry.
When a wheel is on the hub, as designers intended, the vehicle’s load rests squarely and evenly on the bearings. When a wheel sits farther out, the angle of the load on the wheel bearings changes and becomes uneven, which can cause premature bearing failure. Alignment specs can be affected to the point of causing premature tire wear and greater steering difficulty.
TPMS Sensors With New Wheels and Tires
By law, vehicles in the United States from the 2008 model year or newer must have a tire pressure monitoring system (TPMS). This system consists of an onboard computer that reads radio signals from sensors inside the tire.
When changing tires, a technician needs to transfer these sensors or install new ones in the fresh rubber. Without readings from all four tires, there would be a constant warning message about low pressure or an error in the system.
Rather than paying to have the old tires dismounted to retrieve the sensors, consider purchasing a new set of TPMS sensors when mounting new wheels. Old ones only last until their batteries wear out. Essentially, TPMS sensors are wear items that require replacement sooner or later anyway.
Buying New Wheels And Tires
CARiD has a Shop by Service Type tool that lets customers search for the type of work a vehicle needs and select the make, model, and year. The site shows exactly the parts needed for a job. There’s also a similar method for finding aftermarket wheels where buyers can shop by vehicle, style, and brand.
When purchasing wheels and tires together from CARiD in the same order, we’ll mount and balance them at no extra cost before shipping them. And since there’s no extra labor to install new TPMS sensors during this process, we’ll also perform their installation for free. For this reason, tire pressure sensors are an option within our wheel and tire drop-down menu. We’ve set up our website so that if your vehicle requires TPMS sensors, they’ll be pre-selected on the order automatically (a buyer can unselect them if that’s what the customer prefers).
By understanding wheel specifications like diameter, width, backspacing, and more, ordering the right wheels and tires for a vehicle becomes much easier. This knowledge lets folks focus on the most important detail for a new set of wheels – style!
