EXPERT
What you need to know
Words : Mel Falconer
The disc is an integral part of any hydraulic brake system from the late Sixties onwards – worn or warped discs can adversely affect overall braking quality . We take a look at our least understood bit of bike metal .
What about OE discs ? Most standard discs are made from a fairly low-grade stainless steel , and are pressed plate . Discs of this type are typically made from a big , rolled out metal coil ( can be 10-12ft in diameter ). This gets heated up in order to flatten it out , then laser cut , and then pressed out before it is heat treated again . Where the discs came from in the original coil makes a difference . If a disc was made from the outside of the coil , it won ’ t bend too much , but if made from nearer the middle , it ’ ll bend more when it gets overheated in use ( stainless steel tries to revert back to its original shape when hot ). Disc thickness is also important here : an OE disc is normally around 5mm thick , but if disc material ( mass ) is reduced further ( e . g . to reduce gyroscopic effect ), it decreases the disc ’ s heat absorbing capability , and warping can then become an issue .
What materials are used to make road discs ? Stainless Steel : This is the most common type of disc found today . The amount of chromium in stainless steel determines the corrosion ( rust ) prevention and makes it look shiny ; it works by a chromium oxide film forming on the surface of the disc , preventing corrosion spreading inside to the internal structure . If stainless steel gets damaged , it can ‘ self-repair ’ due to the chromium reacting with oxygen and moisture in the environment to reform the oxide layer . Most aftermarket stainless steel discs contain
68 KIWI RIDER