# Dimensions - Disc Brake Surface Area

Dimensions -- Disc Brake Surface Area

During frequent braking under race conditions the disk brake rotors on the car described above reach a temperature of 500C. These disk brakes rely on forced convection to cool them. The dimensions of each disk rotor are: outer radius 130mm; inner radius 50mm; thickness 10mm. (Assume the disk is a simple donut shape ).

i) What is the surface area of the disk rotor (in m2)? (Include both sides and the edges)

ii) Given the heat transfer of the disk rotor is 120 W/m2/K, how much heat energy is radiatred from each of the disk rotors when the ambient air temperature is 30 C

Help with solutions and working out would be greatly appreciated.

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brewnog
Gold Member

Have a go yourself here first.

Ranger Mike
Gold Member

welcome and you are close ...heat on rotoes is in excess of 650 C..over 1200 degrees F
the rotor is NOT a flat disc and has cooling grooves amchined into the sufaces ( on each side) to dispate build of of gases under braking conditions. The disc is not soldu but in fact, is machined to provide more cooling area...have you seen a disc rotor used in this application?

The brake fluid itself may be cylced through a cooler to reduce tmeperatures.

forced air to cool..some classes permit the use of electric fans to cool the caliper rotor which means the frontal area of the car would have less open area for air inlet thus reducing aero drag ..i.e faster car

simple calcualtions not taking int o account the above will not be correct

Last edited:
Mech_Engineer