Wheels are a great upgrade to make when you're trying to improve a car's appearance and performance. Reducing the unsprung weight (weight that isn't supported by the suspension) can help a car's tires stay in contact with the road when going over bumps. having one's tires in contact with the road is definitely a good thing. 

That's why BMW is finally making wheels out of the coolest and lightest material we make cars out of: carbon fiber. There were two prototypes that BMW showed to the public at the Innovation Days event in Munich: an all carbon fiber wheel, and a hybrid wheel consisting of a carbon fiber rim and alloy spokes. The former is 35% lighter than a high performance alloy wheel, and the latter is 25% lighter.

They'll be hitting the market in the next year or two.

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[via BMW