Are Bigger Wheels Better Wheels?
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
This diagram shows the various parts of a typical wheel. Since the barrel is closest to the wheel’s edge, keeping this section as light as possible pays dividends.
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.