Correlation between weight of wheels, and the strength of the wheels. Why its important to not go TOO light!

We came across a post someone made on Facebook and it was pretty interesting. It discussed wheel weights, and strength of the wheels. It mentioned how with lighter wheels they can flex more under hard cornering, affecting your cornering and handling. Pretty fascinating.

“One thing I often end up telling friends to their surprise, is that a lighter wheel is not always better. A lighter wheel has advantages, but also disadvantages. Advantage: reduced rotational mass and lower unsprung weight.

Disadvantage: sometimes it comes at the cost of lower stiffness and strength. You can increase strength by forging, but you won’t increase stiffness. A forged wheel has superior yield and tensile strength, more resistance to bending and breaking, but it is not stiffer. Young’s modulus for both forged and cast aluminum is the same, about 70 GPa.

Wheels flex under stress. Cast or forged doesn’t matter. Under heavy G’s there will be some deformation. The larger the diameter, the more susceptible. How much flex? I’ve read around 1 degree of flex per 1g of load. So imagine you run 3 degrees of negative camber, and due to the flex in your wheel that gets cut in half to 1.5 degrees while cornering. That’s a significant amount. It makes the car feel less stable in a corner due to this sudden change in alignment. It becomes the same as deflection in a suspension bushing or chassis flex.

What reduces flex is increased stiffness, and that’s based not on forged/cast, but mainly on the cross sectional area of the spokes. The thicker the spoke, the less “flex”. Of course thickness then adds weight, but for that you gain less flex. I’m making some general statements here, but you definitely can give up things shaving too much weight off. Low weight sells wheels. There’s incentive for a manufacturer…. especially for lesser known brands that don’t have the technology to properly design and produce a strong wheel. They aren’t going to tell you about the increased tendency to fail nor about deflection, since you won’t ask. Just something to keep in mind.”