Types of Wheels Explained (Cast vs. Flow Formed vs. Forged)

While new wheels aren’t a choice made as often as say new tires or preventative maintenance, various factors go into making the right wheel choice for you and your vehicle when it’s finally time to replace/upgrade your vehicle’s old shoes. 

Wheels or Rims: Which is Correct?

Before we start diving into the various materials and manufacturing techniques, we should probably get the name down correctly.

While many people use the terms rim and wheel interchangeably, each word has its own distinct meaning in a technical sense. Rims are simply one of the components that make up a wheel, rather than the entire thing itself. 

A wheel consists of a few major structural components, including a barrel, rim, and spokes. Rims make up only the outermost part of the wheel assembly, hence the name. 

We’re not going to tell you which term to use (because, honestly, it doesn’t make a difference.), however, we will continue to refer to it as a wheel for the rest of the article for simplicity’s sake. 

Material Type: Alloy vs. Steel

The biggest differentiator between wheels on the market is their material makeup. Steel wheels have been a tried and true option for manufacturers looking to make a cheap, durable, no-frills product. While not renowned for their looks or performance, there’s no denying that steel wheels will put up with the most use and abuse of any material on the market. 

Orange BMW with alloy wheels

Steel falls flat in the weight department, which is no surprise. The weight of a wheel has a large effect on the handling, fuel efficiency, and performance of your vehicle. This is due to wheels contributing to the vehicle’s “unsprung weight” and raising the rotational mass the engine has to fight. Unsprung weight is any weight on the vehicle that is not supported by the suspension system (wheels, axles, brakes, tires, etc.), and it has a much larger effect on the driving dynamics of the vehicle compared to sprung weight. 

Additionally, any weight connected to the engine can dramatically impact the power your vehicle puts to the ground. This concept is known as “rotational mass”. In much the same way that a sports car owner may put a lighter flywheel in their transmission to improve engine response and power output, upgrading to lower-weight wheels can help improve the performance of your vehicle by reducing power-sapping rotational mass. 

All of this means that the traditional hefty steelie won’t hold up with modern options in any of those departments.

Alloy, on the other hand, flips that script almost entirely. Alloy wheels tend to be the more expensive option between the two, as their construction allows for less unsprung weight and rotational mass. This means that alloy provides significant benefits in fuel economy, handling, acceleration, and braking. 

These reasons are why they’re the most common material used on modern vehicles, as the tradeoff between weight and durability is one that most are willing to make. 

Manufacturing Process (Alloy Wheels)

While material plays a large role in the characteristics of the wheel, another defining factor is the way that the wheel was manufactured, specifically in alloy wheels. Different ways of forming the alloy result in different structural makeups which affect the strength of the wheel. The most common methods for manufacturing alloy wheels include:

Cast

Casting is the most common manufacturing method for alloy wheels, making up 90% of OEM wheels equipped on new cars. This is due in part to the low manufacturing cost compared to flow-formed and forged, as casting is the simplest way to produce wheels.

Cast wheels are exactly what they sound like, with molten metal being cast directly into the desired shape within a mold. There are two main methods of casting used to accomplish this: gravity casting and low-pressure casting. 

Gravity casting is the lowest cost and lowest quality method of production, making use of gravity to push the molten alloy into all the crevices. While cheap, this will produce a less dense casting, which will have more defects and air bubbles. To make up for these, gravity-cast wheels are often designed with extra material to strengthen them, which increases weight.

Low-pressure casting solves this density issue by injecting the alloy into the mold with pressure, rather than letting it just flow in. Low-pressure cast wheels carry a slight premium over gravity cast, but are also lighter and stronger. 

Forged

Forged wheels have developed a reputation as the premium option for aftermarket wheels, and for good reason. 

Forged wheels are produced in a completely different way than their cast counterparts. It starts with a large cylinder of high-quality aluminum alloy that gets heated to a malleable state. It’s then hydraulically compressed under over 8,000 tons of pressure into a smaller and denser block. These blocks are then milled with a CNC machine into the final shape with all appropriate details and finishing touches. 

Part of what makes forged wheels so good is their structure on a microscopic scale. As the metal is heated and formed from its natural state rather than completely melted, the alloy retains the uniformity of its grain (as pictured below), which allows forged wheels to have superior weight-to-strength ratios.

Cast vs forged alloy grain flow

This impressive strength means that wheel manufacturers can decrease the amount of material needed to keep the wheel adequately strong, in turn decreasing the weight of the wheel. That’s where forged wheels shine, as their extremely strong and light construction allows for the performance benefits of light alloy wheels while still being stronger than cast alloy options. Forged wheels are around 3x stronger than cast while being 25% lighter.

So, there’s got to be a catch, right? Unfortunately, due to their complex manufacturing process and expensive raw materials, forged wheels demand a hefty price tag (like… really hefty). Despite their numerous benefits, aftermarket forged wheels usually only make sense for a select group of quality or performance-focused buyers.

Flow Formed (Rotary Forged)

Known by a variety of names depending on the manufacturer, the flow-forming process strikes a balance between cast and forged wheels for those looking for a quality option without the exorbitant premium. 

Flow-formed wheels start with casting a wheel with the low-pressure process we covered earlier, except it’s cast at a narrower width than the final product will be. Using heat and outward pressure on a rotary machine, the narrow wheel is stretched and compressed out to its final width and shape. This technique has a similar effect on the alloy’s internal grain structure as the forging process, which gives the wheel higher tensile strength.

Flow-formed options provide a great mix of weight, strength, and price that neither cast nor forged wheels can. While the spokes still have the normal cast alloy characteristics, the increased strength and decreased weight of the barrel give the wheels much of the benefit that makes forged wheels so sought after. 

What Wheel Type is Right For Me?

The question of what wheel is right for you and your vehicle comes down to a variety of factors, but we’ll try to break it down into what situations might make sense for that type of wheel.

Steel wheels, while not the prettiest or flashy choice, still have a place on many vehicles. Their undeniable durability and low cost mean that they’re a great choice in situations where the wheel will see some wear and tear. They make great budget options for off-roading or a winter tire package you won’t have to worry about too much.

Alloy makes more sense in the majority of cases, and you’ll have a wide range of options at various price points to choose from. Now you just have to decide what type of alloy wheels you want.

Cast wheels are a cost-effective way to get the look and feel of alloys without paying a premium. There’s a reason they’re equipped on the vast majority of new vehicles sold. On the aftermarket side, you’ll be spoiled for choice with various styles and finishes to decide from to find the perfect look for your car. 

Forged wheels are the pinnacle of wheel manufacturing at the moment. There’s just not a true match for the strength-to-weight ratio and handling benefits that the process brings to the table. They’re simply the best option for performance-focused vehicles that see a lot of track time. However, if you’re not chasing lap times or looking for the absolute highest quality available, the truth is you probably don’t need them. While 3x lighter than cast alloy, look to pay at least 3x more to have your vehicle fitted with these bad boys. 

That’s where flow-formed (AKA rotary forged, spun forged, or flow forged depending on the manufacturer) wheels come into play. Flow-formed options fall much closer to the price of cast wheels than forged, but maintain much of the benefit of their pricey counterparts. This is why flow-formed wheels often see use in spec racing series like the Honda Challenge, as their weight benefits can’t be beaten for the price. It’s important to understand, however, that flow-formed wheels are not forged wheels and need to be treated with that understanding (despite what the names some manufacturers might try to imply). While their barrels have strength somewhat similar to forged, the spokes are untouched during the process and remain only as strong as the original alloy casting. 

Wheel Replacement and Upgrades at Scott’s U-Save

If you’re looking for new wheels or advice for finding the right ones, the experts at Scott’s U-Save have you covered. Our team is made up of enthusiasts committed to helping you make the right decision for you and your vehicle. Call or schedule with our wheel experts today at our locations in Steger, New Lenox, and Schererville!

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