Wheel Construction Types
By: Tony Whatley
An educated customer is the best customer.
I get a lot of emails from custom wheel shoppers, asking what the differences are between cast aluminum wheels, flow-formed wheels, 1-piece forged wheels, 2-piece forged wheels, and 3-piece forged wheels. I always take my time to explain the differences in construction methods, as I prefer to educate my customers in order to allow them to select the wheels that best fit their needs.
There are predominantly 6 different methods for construction of wheels. Each one varies in quality, weight, strength, and price. There are pros and cons for each type. Hopefully after reading this thread, you gain a better understanding of each.
a. Cast aluminum
b. Flow-formed / Rotary forged / Spun forged
c. Forged 1-piece monoblock
d. Forged 2-piece welded construction
e. Forged 2-piece bolted construction
f. Forged 3-piece bolted construction
Cast Aluminum Wheels
These are the lowest priced wheels, and are typically what are found on production vehicles. If you are shopping for wheels that cost under a grand for the entire set, those are certainly going to be cast wheels. Cast aluminum wheels are created by pouring molten aluminum into a mold that is shaped like a wheel. This produces a wheel casting. Some final machining work is then done to clean up the rough surface, and paint/finishing is applied.
Pros: Lowest price, easiest to mass-produce.
Cons: More brittle than forged wheels. Spoke details and edges aren’t as sharp as a machined forged wheel. Heaviest weight of all wheel construction types. Lowest quality. Limited offsets, width increments, diameter selection available. Nearly impossible to repair when cracked or severely bent – safely, that is. A damaged cast wheel usually needs to be replaced.
Flow-Formed / Rotary Forged / Spun Forged
Flow-Formed wheels start out identical to cast poured wheels, but with an excess of material left remaining on the outer edge of the spoke section. The casting process above is used to create the spoke pattern only. Then the wheel casting is put into a flow-forming machine to form the barrel section. This is done using high heat and high pressure rollers, which “flow-form” the barrel by extruding the outer excess material across a barrel-shaped mandrel.
This results in a stronger outer barrel, with aligned aluminum grain structure. Since this barrel section is forged, it can be a much thinner cross-section of material than a cast wheel barrel, which results in the wheel being much lighter than a cast wheel. The resulting wheel is a cast spoke wheel with a barrel that has the mechanical properties of a forged wheel. These rotary forged wheels are stronger and lighter than cast wheels.
Pros: Low Price, lightweight, higher strength than cast wheels.
Cons: Cast face still lacks the sharp edges and details of a CNC machined forged wheel. Limited width increments and diameters available. Hard to repair when severely bent or cracked, due to thin barrel thickness.
Forged 1-Piece Monoblock Wheels
The term “Monoblock” is used throughout the industry to describe the 1-piece forged wheels. “Mono” meaning one, and “Block” meaning it was created from one block of forged aluminum. The block in this case is actually a round bar stock of high quality, aerospace-quality 6061-T6 Aluminum Alloy. The round bar is pressed in a huge forging machine, to stamp out a wheel shaped blank. Forging is a hot working process, and helps to align the grain structure of the alloy. This results in a very strong, very lightweight wheel construction material. The wheel blank is then flow-formed to create the barrel shape. Following that process, the wheel blank is loaded into a CNC milling machine and there the spoke pattern is milled out.
Pros: Typically the lightest of the forged wheel construction methods.
Cons: Priced about the same as expensive 3-piece construction. Difficult to repair when bent or severely damaged. Limited diameters/widths and offset ranges available, due to shape of raw material.
Forged 2-Piece Welded Construction Wheels
These are considered the entry level forged wheels, as they are priced slightly lower than 3-piece forged wheels. The centers start out as a blank of forged 6061-T6 Aluminum alloy, and the spoke patterns are CNC machined with a milling machine. The wheel hoop is also a spun forged aluminum material. On a 2-piece wheel, the center is simply welded to the hoop on the backside of the wheel. Some manufacturers also offer cast aluminum centers, to reduce cost. Quality and weight of the cast centers is not as good as forged centers, however.
Pros: Lowest Price of the Forged wheels. Same weight, appearance, quality as 3-piece wheels. Great range of offsets / backspacing available.
Cons: Limited diameter / width increments available, due to barrel sizes being set. Cannot easily chrome plate or paint the lip, since it has to be welded on. More difficult to repair a bent lip compared to a 3-piece wheel, as the center has to be cut out and a new hoop welded on.
Forged 2-Piece Bolted Construction Wheels
These are built very similar to the 2-piece welded construction wheels above, but use a hoop that has a bolting ring already in place. Instead of welding the center to the hoop, it is simply bolted on. This is the least common method of forged wheel construction, as the hoops tend to cost more than simple welded hoops. Some manufacturers also offer cast aluminum centers, to reduce cost. Quality, strength, and weight of the cast center is not as good as forged/machined center, however.
Pros: Lips can be easily chrome plated or painted, since no welding required. Easier to replace a hoop when it gets bent.
Cons: Limited diameter / width increments available. Few wheel brands offer this type of construction. Cost is nearly the same as a 3-piece wheel.
Forged 3-Piece Wheels
Three piece forged wheels are usually the most expensive wheel construction, mostly due to the assembly labor and components used. The wheels consist of three main pieces; the center, the outer lip hoop, and the inner barrel hoop. These three parts are held together with a series of perimeter bolts. High-temp silicone RTV is used to seal between the two hoops. Some manufacturers also offer cast aluminum centers, to reduce cost. Quality, strength, and weight of the cast center is not as good as forged/machined center, however. Pricing differences usually indicate whether cast or machined centers are used.
Pros: Most width increments available, truly perfect fitments available. Easiest of all wheels to repair if lip gets bent or damaged, as hoops are easy to replace. Easy to paint
or chrome plate lip, since no welding is required. Can have different color rear hoop and outer hoop, since they are two different pieces. Highest resale value for used wheels.
Cons: Most expensive forged wheel construction. RTV silicone seal can be damaged by inexperience tire installers, resulting in leaks.
Thanks for reading. Hopefully this helps educate you about the differences, while you are shopping and comparing wheel brands and prices. Feel free to ask any questions regarding wheel construction, I'll be glad to help.