If you are fitting new pads as well, you will also need to look here.

Disc And Pad Thickness

On the smart car, the brakes discs are 9mm thick when new. The maximum wear they can have before being replaced is only 1mm. You can measure them with a caliper gauge, if they are anywhere near 8mm or below you should change them ASAP.

Fitting The Discs

You will need the following tools:
Jack,
Axle stand,
15mm socket to remove wheel,
13mm ring or open end spanner,
17mm open end spanner,
E18 socket,
T30 screwdriver,
Clamp to push piston back.

First of all loosen front wheel nuts, jack up the car and place the axle stand securely.
Lower onto the stand. Check for security of car on stand - you're going to be working on it!



With the wheel removed it will look like this.