Brake Discs

Bike brake discs (also known as rotors) are metal discs that bolt onto the hub (called 6-bolt which is very common) or slide onto the hub and use a lock-ring to secure brake disc (Shimano's Center-Lock design).

Brakes discs come in various sizes; from 140mm (seen on road bikes) to 220mm (for heavy-duty EMTBs).

If you're going up a size, you must use a suitable adapter.