Disc brake pads together with a bike rotor, deliver great braking power. In this article you will learn about why there are many different shapes and sizes of disc rotors and how to replace them.
When the pads hit the bike rotor heat is generated from the braking action and it has to be dispersed.
Bike rotor – Different types, sizes and shapes
There are different types, sizes, and shapes of discs to tackle this side effect of braking.
Standard – This is a one piece, stainless steel design. They are the cheapest and lightest option. Some of these are not hardened and designed only for resin pads.
2 piece – They have a carrier core attached to a braking surface. Two piece rotors are stiffer and less likely to warp. The carrier is a stiffer structure than the simple plate and it provides better support to the business end of the rotor. They are also better at shedding heat. The aluminium carrier core is a better heat sink than steel plate.
Finned – This 2 piece type of disc rotor is designed to prevent heating and fading in extreme conditions by dissipating large amounts of heat through extra fins. Ideal for long down hill rides.
Another way of dealing with the heat is by increasing the size of the braking surface.
This is the reason why disc rotors comes in different diameters. The bigger the rotor the more time there is for heat to disperse before it hits the pads again.
The final feature of a disc rotor are the holes and patterns on the braking surface.
Apart from being aesthetically pleasing they have two other functions. Firstly, the cut-outs shed water and dirt that would otherwise build up when riding.
Secondly the position of the cut-outs allows them to lightly score the pads and stop them being polished by the rotor and subsequently glazing.
Checking the wear of a disc rotor
As the brake pads wear then so does the rotor and this needs to be investigated.
First check the minimum thickness recommended by the rotor manufacturer. Some of the rotors will have this information edged on them.
Use Vernier calipers to measure the thickness. If it is below or near the minimum recommended thickness then replace the rotor. You can also check the wear by touching it. If you feel a step where the braking surface and the spider arm meet then it’s a sign of wear and for safety reasons it would be a good time to replace it.
There are two type of bike rotor mounts: 6 bolt and centre lock.
Replacing a 6 bolt bike rotor
Removing 6 bolt bike rotor
To remove a 6 bolt rotor release the bolts in a cross pattern.
By crossing the axle each time the pressure on the rotor is slackened evenly. Release one of the bolts a quarter of a turn. All the bolts will be quite stiff so make sure not to ruin the head of the bolt. Now release the others using the cross pattern. Loose and remove the bolts. Grasp the rotor in the centre and lift it clear of the wheel. Don’t to touch the braking surface as it will get contaminated.
Installing 6 bolt bike rotor
Before you fit or replace a rotor check if it’s the correct way around. The rotor arms need to point left and the writing on the rotor surface needs to be visible.
If you fit the rotor wrong way around the arms could collapse during braking.
Grasp the rotor in the centre and place it on the hub. Fit the bolts and lock washers, if they are included. Don’t tighten them yet. Once the bolt heads are close to the rotor tighten them using the cross pattern.
Replacing a centre lock bike rotor
To remove and replace a centre lock rotors you will need either a cassette removal tool and a wrench
or Hollowtech II bottom bracket removal tool.
Removing centre lock bike rotor
Stand behind the wheel and support it between your feet.
Find which tool you need and place it in or over the lock ring pointing up towards your right arm.
Push the lever down anticlockwise.
Once loose remove the lockring.
Grasp the rotor in the centre and lift it clear of the wheel.
Installing centre lock bike rotor
Hold the rotor in the centre and place it on the hub.
Fit the lockring and tighten by hand.
Now use the tool for final tightening. Make sure it’s secure.
Once you have replaced your rotor it’s time to replace the brake pads. You can find a step by step guide in our article here.
– By increasing the size of the braking surface. The bigger the rotor the more time there is for heat to disperse before it hits the pads again.
– By adding aluminium core and fins. The aluminium carrier core is a better heat sink than steel plate. Extra fins prevent rotor overheating and fading in extreme conditions by dissipating larger amounts of heat