APRILIA RS 125 : Aprilia RS 125 Brake disc wear limits and how to measure

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Discs must be kept clean without rust , oil , grease or any other dirt etc. It should be free of any deep scratches that may affect performance

FRONT BRAKE Semi Floating 320mm Disc Wear limit is 3.5mm

REAR BRAKE Disc Brake, 220mm Wear limit is 3.5mm

Front Brake discs are semi floating , consist of 2 parts one part attached to wheel and the breaking band ( some models have fully floating .)

for more on Floating brake discs see below

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Fixed and Floating Brake Discs

There are three principal types of motorcycle brake discs: fixed, fully floating & semi floating.

A fixed brake disc is a one piece brake disc. That is, its brake pad contact face and wheel mounting face are all part of the same piece of metal. They are relatively cheap to produce and they perform perfectly well within certain parameters, but if they are subjected to serious heat then they are unable to dilate or expand because they are not floating.

Both fully floating brake discs and semi-floating brake discs are constructed in two parts. An aluminium centre part which is fixed to the motorcycle wheel and a stainless rotor part which the brake pads push on.

When the rotor is subjected to serious heat it expands. By allowing it to float separately from the mounting face it is free to expand and shrink again at will without being constrained by its mounting. When this expansion takes place is does so in all directions at once and it will not be constrained. If you prevent this from happening in one direction (by fixing it on its mounting face) it has no choice but to warp, so floating discs and semi-floating discs are made in two parts to allow the discs to expand and prevent them from warping. This is mainly a high performance type brake disc.

Bikes of more moderate performance can use fixed brake discs perfectly happily and you will also see that most rear brake discs are fixed. This is because they don’t get used as hard and therefore subjected to as much heat. Even so, most rear brake discs are thicker than front brake discs and this is a compromise because the cooling is not as good as the front discs. They don’t get as hot but don’t cool as well either, so the thicker material helps prevent them from warping.