F1 cars use carbon brake discs and pads that operate between 200 degrees and 1,000 degrees (Celcius). 

To ensure the brake system does not overheat and cook itself, cooling is provided through ducts that direct the fast-flowing ambient air onto the brake system. 

This is why you see wheels smoking at the startline and the pit crew place cooling fans on the brake ducts when the car is stopped. 

Andrew Burden

The author Kiwi F1 Fan