We get this question all the time, and figured this would be a good opportunity to shed some light on what goes into making an aftermarket wheel. Most tend to think a wheel falls into 2 categories – forged and cast. While this is generally true, there are variations that make a very big impact in the finished product.
At the bottom of the pyramid you have Gravity Cast wheels. This is a fairly simple production technique whereby molten aluminum is literally poured into a mold. Because of the simple process, the mold can be quite complex and intricate. This affords the manufacturer a wider range of styles to play with, and offers the greatest flexibility of design. The downside of course is the technique itself. Since you’re relying on plain old gravity to fill the mold, it’s not perfect. The net result is a wheel that has more empty space between the molecules vs. more involved manufacturing processes. They also tend to be on the heavier side of things, as the goal is style in design vs all out strength. The upside is the price for these wheels can be downright cheap. But so can the quality. Often times, the wheels are made in plants of dubious quality, and attention to detail is sometimes shoddy. You can tell the el cheapo stuff by casting flash on the backside of the spokes and hub.
Next up you’ve got Pressure Cast Wheels. As the name implies, this technique relies on external pressure to fill the mold. As you can probably guess, the result is a wheel where there is far less empty space between the molecules. This method is a bit more limiting in overall style, but the strength to weight ratio is much higher compared to plain gravity cast wheels. This is the most common method used by the larger OEM manufacturers, because it affords them a good compromise between design and strength. Within the Pressure Cast family you have both higher pressure and low pressure. Differences are as stated – the amount of pressure exerted on the aluminun in the mold.
The next technique is relatively new compared to the above, and is employed by several manufacturers such as SSR, Enkei, etc. It’s called Flow Forming, or Spun Form, Hybrid Forged, etc. This process employs a pressure cast technique at first, to achieve a general shape. Rollers are then used to literally pull, or press, the material to shape the final design. Many high end OEM manufacturers use this technique on their wheels. While it’s still technically a casting technique, the process allows a wheel to be incredibly strong (since the molecules are very densely packed), and light weight at the same time. While the production costs are the highest among the cast methods, it still allows the wheel to be about 50% less costly than a forged variant. SSR Type F, Type C RS, several designs from Weds and BBS and several in Enkei’s Racing series employ this technique. Enkei has licensed the process to several other traditional cast manufacturers such as Konig and AME over the years as well.
The pinnacle of the wheel production pyramid is of course forging. In this process, a single, billet hunk of aluminum is literally stamped into a design using very high pressure applied to a die. Because of the costs involved from the raw materials, to the production equipment, these are far and away the most expensive types of wheels. However, they also tend to have the best weight to strength ratio. The designs are often quite limited because of the cost to produces the dies. These tend to be simpler overall designs (aka Volk TE37, BBS LM and LMR, etc.).
From there you get into a variety of materials. Aluminum and Magnesium are the most often used metals. In recent years, we’ve also seen hybrids employing both carbon and aluminum bonded together. The cost of these more exotic materials is high, but it’s done in the pursuit of the lightest weight, and highest level of strength.
When you begin to examine the above in greater detail, you also begin to see that the process is only part of the equation. There are bad quality cast wheels and good quality cast wheels. There are wheels who’s designs are based on a forging model, that are replicated in cast models. There are wheels who’s design is based upon a low or high pressure, or spun technique, and some company turns around and does a low pressure cast version. From the outside, it all looks the same. The price is certainly more attractive. Sometimes it works well, sometimes it doesn’t. This is why the better cast manufacturers don’t replicate every wheel under the sun – because they know it’s an accident waiting to happen. Another important consideration is who is making the wheel in the first place. Some firms own their own factories, some simply come up with a design and broker manufacturing out to the lowest bidder. The problem is the consumer never sees this side of the market, they only see the finished product. When it arrives to you new in the box, it can look all shiny and pretty. Turn the wheel over and examine the spokes, and you can begin to see the origins, and the quality of the wheel. The better quality wheels tend to be finished in very great detail even on the backside, and no casting flaws can be seen, and no extra flashing. The cheap stuff looks…well, cheap.
Hopefully that helps shed some light on what some differences are between the various wheel manufacturing techniques.