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Adapting a disc brake


Whether you're going for a full assembly or have decided to upgrade to a larger diameter, fitting a disc brake is always a headache!

Apart from the length of the hoses, attention should be paid to the standard of mounting of the discs and calipers.


Required tools

1/ Required tools

- 5" BTR spanner

- Bottom bracket remover hollowtech or 25" torx key

discs

2/ Discs

There are 2 standards on the market:

- the "centerlock" developed by shimano:
the disc is fixed in its centre by a single nut which is screwed around the hub axle.
This type of disc is mounted and dismounted using a Hollowtech case remover.

- the international standard, more commonly known as "6 holes":
the disc is fixed to the hub with 6 torx screws. You will need a 25mm torx spanner to mount and dismount this type of disc.

Calliper bracket (IS)

3.1/ Calliper bracket (IS)

The international standard, also called "IS": the fixing screws are located in the direction of the wheel axis. The centering of the caliper on the disc is a bit tedious and is done by means of washers of different thicknesses to be inserted between the caliper and the bracket. In direct mounting (without adapter), the front diameter is 140mm and the rear 160mm

Caliper bracket (PM)

3.2/ Caliper bracket (PM)

The Post Mount standard, also called "PM": the fixing screws are in the direction of travel and the adjustment is done simply thanks to the oblong holes (oval) of the caliper. In direct mounting (without adapter), the front and rear disc diameters are 140mm.

Although the Post Mount standard is tending to supplant the International Standard on the new market, the IS is still very much in evidence on the used market. But don't panic, all mounts are possible with adapters!

We have taken for example a NS bike frame with IS standard, we want to mount a PM caliper with a 180 disc. We therefore need an IS to PM adapter with a 40mm extension.

replace the disk

4/ Remove the wheel and replace the disc

Be sure to observe the direction of rotation of the wheel indicated by arrows.

frame adapter

5/ Replace the frame adapter

Please note that the direction of installation is usually indicated by an arrow

new calliper

6/ Installing the new caliper

Install the new caliper without tightening it completely, then reassemble the wheel, taking care not to force the new disc.

caliper on the disc

7/ Centre the caliper on the disc

Operate the brake lever, by squeezing the disc, the caliper will move slightly towards the ideal operating position. With the brake applied, slightly tighten the caliper fixing screws to hold the caliper in place.

Final settings

8/ Final settings

The oblong shape of the caliper screw holes allows the caliper to be correctly centred on the disc Release the brake, turn the wheel, if the caliper is not well centred on the disc, you can "slide" it slightly from right to left to fine-tune the adjustment.

Once you are satisfied, tighten the caliper screws firmly.

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