HRE Performance Wheels

Often we talk about quality when we talk about forged wheels but what exactly are we talking about? Well, it turns out that quality encompasses just about everything from start to finish and since wheels are functional as well as stylistic, a lack of quality can adversely affect the performance of your car or even worse… cause a safety concern.

So there is a lot that goes into making a high quality wheel: raw materials, design, engineering, fitment, production accuracy, finish quality, etc. Let’s just start at the beginning for now and discuss the raw materials and specifically castings vs. forgings.

Back in the old days (2000!!) there were only a small handful of companies making forged wheels. At the time, the major discussion was always about cast wheels vs. forged wheels. Things have changed recently but in case you haven’t kept up I’ll give a quick and rather simplistic summary.

Casting
Basically castings are made from molten aluminum that is poured into a mold. Lot’s of fire and heat. After it is cast and cooled, there is usually some final machining and finishing work to get it to fit the right application and to have a nice finish. Some cast wheels are heat-treated as well. This is how most wheels are made and a high quality pressure cast product that is well engineered can indeed result in a very nice quality wheel. What did I just say??!!! Think about it… if all cast wheels were terrible, we wouldn’t all have them on our cars from the factory. However, some poor quality aftermarket cast wheels that aren’t made to OE standards can definitely be of inferior quality. The major advantage to cast wheels is that they are relatively cheap and really easy to make in high volumes. The major disadvantage is that they tend to be heavier than forged wheels due to their relatively low material strength properties.

Forging
Forged wheels are different in that they start out as aluminum billet, typically 6-7 inch diameter bar stock. These are then cut into the right length (the volume needed), heated, and pressed into shape (using very accurate dies and successive steps) under about 6-12000 tons of pressure. The forging process imparts a lot of energy into the metal and changes the internal grain structure of the aluminum (metals have a crystalline structure) and this change in the grain structure is what gives a forging additional strength in comparison to the original billet rod. They are then heat treated to a T6 condition in the case of 6061-T6 to get the right mix of strength and ductility. A forged aluminum wheel has a higher specific strength as well as higher toughness (engineering term for its ability to absorb energy) in comparison to a casting. This allows an engineer to design a wheel that is lighter, stiffer and less susceptible to cracking under impact and with better fatigue properties than a casting.

So now that you know a forged wheel can be lighter and stronger than a casting, why does it matter? That’ll be part of my next post where I’ll discuss unsprung mass and rotational inertia.

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