With big wheels becoming more and more popular, a logical question to ask is if bigger wheels are necessarily better wheels. Like many automotive questions, there is no simple answer to be found. A lot of it depends on what you want from your wheels.
A simple answer to this question is that wheels should be sized in proportion to a vehicle and to the loads they carry. Rims on an 18-wheeler are big because they’re designed to carry extremely heavy loads. The wheels on a Smart Car are small, because there’s no room or need for big wheels. But that’s not why you’re reading this article.
In the end, if you want big custom wheels because they look appealing to you - just go for it. We understand this, because we agree a well-designed wheel is better to look at when it fills space previously taken up by a boring, black tire wall. Wheels are a passion to us at CARiD – and staying on top of changes is why we have a dedicated Wheel & Tire department staff.
However, to avoid disappointment once they’re on your vehicle, it’s important to realize that bigger wheels can be significantly heavier. If the wheels are for cruising and show, this isn’t such a big deal. If they are meant for a commuter vehicle you’ll have to live with, you’ll pay a price in lost fuel economy and ride comfort. And if you’re looking to boost road-handling, extra weight can actually make a vehicle more difficult to control and less enjoyable to drive.
In this article, we’ll discuss key things you need to know when shopping for custom wheels, and we’ll look at how they can affect acceleration, cornering, and even fuel economy.
Lightweight Wheels Perform Better
When all other factors are equal, wheels that weigh less will always outperform heavier ones in every category. The reason is fairly simple: A rotating wheel acts like a flywheel and wants to keep going at the same speed and in the same direction it is already going. If you were to examine flywheels or gyroscopes, they are designed with a very light center and a thick and heavy outer perimeter to make them rotate at a stable speed in a stable direction no matter what happens. This is not desirable in a road wheel.
The big problem with big wheels is that the outer perimeter area (known as the “barrel”) gets heavier and heavier as wheel diameter increases. Braking can suffer, and steering will feel sluggish and less responsive.
Tires Must Stay Flat And On The Road
On that note, enter real-world potholes, surface irregularities, and expansion gaps in the road which cause wheels to hop up and down.
Good road-holding is achieved by keeping the contact surface of the tires in constant contact with the road surface. If the wheels bounce or if the tires don't stay flat against the pavement, the vehicle loses its grip. Keeping the rubber flat against the road becomes a daunting task when speeds increase, turns get sharper, and road surfaces are uneven.
The more weight that springs and shock absorbers have to deal with, the harder they must work to prevent wheels from bouncing. This is why racers and manufacturers of performance cars make reducing unsprung weight a huge priority when they seek road-holding improvements.
In other words: It’s harder to push a bigger, heavier wheel flat against the ground again after it bounces up. And because of the weight, it takes a little bit longer to happen as well. So in the end, the hugest wheels can end up being a drawback on real-world pavement situations.
Very Big Wheels Require Extra Weight Reduction Measures
Some rules of thumb apply when it comes to wheel sizes. Beyond 16” in diameter, steel wheels get too heavy for practical use. For everyday drivers, cast lightweight alloy wheels are a good choice up to 20 inches. For performance cars which will be driven with spirit, lightweight forged wheels are superior and even necessary when wheels reach the 18" diameter point.
Forged wheels can be made lighter than cast wheels. This is because the forging process changes the molecular structure of metal, providing more tensile strength and more resistance to cracking and bending forces. As a result, a forged wheel can be made with thinner metal profiles and still meet high strength requirements.
A big part of any wheel is the barrel, which is the section in between the outer and inner wheel faces. Because this section essentially forms the outer edge of the wheel, its outboard location means the force of any weight that exists there will be magnified the most during rotation.
Because forging of wheels is a very expensive process, wheel manufacturers have come up with ways to combine cast centers with forged barrels to save weight in that strategic location. This is done by joining multiple pieces together, or by "spinning" the barrel of a cast wheel – which provides most (but not all) of the advantages of forged wheels at a lower cost.
Forging of wheel barrels is done in rotary forging machines, where the cast "blank" is heated, rotated at high speed and pressed against a template by rollers. This process produces a very strong barrel with almost negligible runout.
Low Profile Tires Perform Better – Up To A Point
The performance reason for using bigger rims is that they make it possible to fit tires with lower and stiffer sidewalls without affecting overall wheel/tire diameter and running into wheel well clearance issues. Low and stiff tire sidewalls found on low profile tires effectively keep the tire's tread flatter on the road than high and flexing tire walls can.
In our related article Custom Wheels 101, we detail how, in order to maintain the same approximate tire diameter, sidewall height must become shorter as wheel diameter increases. Moving to a bigger wheel and shorter-sidewall tire is known as "Plus-Sizing". A plus one upgrade means the rim increases one inch in diameter, while a plus two reflects a rim diameter increase of two inches. (We also recommend reading that article if you’re interested in learning more about offset, back spacing, bolt patterns, speedometer corrections, and more.)
Low profile tires are also wider than higher profile tires, because the air cushion volume inside the tire must stay sufficient enough to carry the load of the vehicle. Thus, a low profile tire has a bigger contact patch staying flat against the road. Up to a point, the improvement in road-holding from low profile tires more than compensates the drawbacks of a bigger and heavier wheel.
Today's cars engineered for high-performance typically feature 18"- 20" factory wheel sizes and tire profiles as low as 30 (this means the tire sidewall height is only 30% of the tread width). Larger wheels such as these usually feature forged construction to keep them as light as possible. Wheels larger than 20 inches are more for show than for go, because they really end up weighing too much to be a performance asset.
It’s also important to note that you’ll get maximum handling benefits from bigger wheels and lower profile tires if your vehicle has a suspension capable of handling performance driving. Adding bigger and bigger rims to a standard car built for ride comfort will result in diminishing returns sooner instead of later.
A Scientific Test
Seeking to answer how plus-sizing affects performance in a scientific fashion, Car & Driver Magazine performed a rim-and-tire comparison test on a stock Volkswagen Golf base model - swapping on similar alloy wheels ranging from 15 inches to 19 inches along with applicably-sized tires from Goodyear of a comparable design. They measured a 10 percent drop in fuel economy and a 4 percent loss in 0-to-60 mph acceleration from the 15s to the 19s.
When it came to skidpad performance on a perfectly smooth test track, grip predictably improved as wheels got larger. However, the 19-inch wheel package (with wider wheels and tires than the others) actually lost out to the 18-inch wheel combination which had the best results of all.
Goodyear commented on those results, saying that the extra width of the 19-inch tire could have given the outside wheel more biting grip on the pavement. This, in turn, could increase body roll and give the inside tire less grip as weight lifted off that side – resulting in less total grip overall. Also, the factory suspension of this particular base model was not designed for maximum roadholding, nor was it upgraded.
The lesson here is without suspension enhancements, you may not get to enjoy much of the handling benefits of going up numerous plus-sizes. But you can bank on experiencing the disadvantages.
Summing It Up
To sum it up: The most important parameter for vehicle performance is the weight of the wheel. Replacing a standard size steel wheel with the same size of cast light alloy wheel will improve acceleration, fuel economy, and road-holding considerably without any reduction in comfort. Plus-sized wheels and tires will boost road-holding even more, but only up to a point – which can vary based on a number of factors specific to your vehicle’s capability and driving environment. Additionally, ride comfort generally drops as you plus-size up. And if you want wheels that are bigger than 18", look for forged wheels or wheels with forged (spun) barrels.
We’ve got lots of great-looking wheels to choose from, and we know making a final selection may not be easy. If you need some additional guidance in your search, we’ll be happy to answer any questions you have – just give us a call seven days a week!