Specialized Aethos: Front Brake Caliper Adapter and Disc Rotors

The Specialized Aethos uses mostly standard components and specifications. For example, it uses a standard threaded bottom bracket and round seat post on the frame. There is no internal routing around the head tube and steerer tube of the fork as well.

However, there is one non-standard design on the fork, which is the disc brake mounting area. Although it uses a flat mount brake design, the distance between the holes are not the flat mount standard.

According to Specialized, the holes are closer than the usual flat mount standard, so that they can make the end section of the fork leg hollow, in order to save some weight. Not sure if it is worth it to make this non-standard design, when most other areas are standard.

Flat mount holes on the front fork, where the hole to hole distance is closer than usual.

Special flat mount adapter (top) supplied with the Aethos frameset, and it means only a 160 mm front rotor can be used.

Adapter and hole distance (between slots at both ends) is shorter than the standard design (below).

Aethos front brake adapter is lighter as well since it is shorter, at just 9 grams.

Standard Shimano front flat mount adapter is 12 grams.

Aethos front brake adapter mounted on the Dura-Ace R9270 brake caliper. 

140 mm rotor cannot be used, only 160 mm is possible.

As for the brake rotor, I have a collection to choose from. 

From left to right: RT800, RT900, MT800, MT900.

As already tried on the Focus Paralane, I will be using a 160 mm rotor on the front and a 140 mm rotor at the rear. It has sufficient brake power while also saving some weight. The same 160/140 mm rotor setup is used on the Fnhon DB12.

140 mm rotor vs 160 mm rotor, both are XTR MT900 rotors. Note the difference between a new rotor (left) and a used rotor (right).

140 mm rotor without lock ring is only 88 grams.

160 mm rotor is heavier at 106 grams.

As mentioned in the Focus Paralane post, using a 140 mm rotor instead of 160 mm at the rear saves about 35 grams. On the Specialized Aethos where I am building a lightweight bike, every gram counts.