Brake discs/rotors wear down as they are used; how fast or slow depends on a great number of variables like riding style and brake pad material.

How thick your rotors need to be will depend on whether you have a single-disc model or dual-disc model. For a single-disc brake setup:
- 6.8-7.2mm
- LIMIT: 6.0mm
For the dual-disc models:
- 4.8-5.2mm
- LIMIT: 4.0mm
Below the limit? Insufficient heat dissipation due to less material can cause brake fade sooner, and depending on where you live and how unlucky you are with your mechanic of choice you may face registration issues. You can source new ones from Metalgear in Australia as at August 2014 – they’re around $139AU each.