Specialized Aethos: Headset, Spacers and Expander Plug

Joining the Aethos frame to the Aethos fork is the headset and other small parts around the headset. As mentioned earlier in the posts, the Specialized S-Works Aethos uses an integrated headset design, with the bearing races already molded directly into the head tube of the frame, and steerer tube of the fork. This eliminates any extra headset bearing races that needs to be pressed into the frame, such as on the Fnhon Gust or Fnhon Tornado frames.

Headset bearing races already molded into the head tube, at the top and bottom.

The frameset includes the headset bearings, and here are some pictures of it. Good reference for the future when a new replacement bearing needs to be sourced.

Headset top bearing, with 1 1/8" inner diameter and a 45 degree chamfer.

Headset bottom bearing, with a 49.5 mm outer diameter, 40.5 mm inner diameter, and 6.5 mm height.

Together with the compression ring, the headset bearings weighs 39 grams.

Here are all the carbon stem spacers that are included with the Aethos frameset. 3x 10 mm, 1x 5 mm and another 5 mm spacer on the right.

The spacers are scalloped, with more material removed from the inside, such that only 3 points are touching the steerer tube. All in the name of reducing weight!

Each 10 mm scalloped spacer weighs just 3 grams, but this is similar to other lightweight carbon spacers (about 4 grams), so not much savings here.

For reference, here are the other types of stem spacers. From left to right: Thin carbon spacer, standard carbon spacer, aluminium spacer. All are 10 mm tall.

Thin carbon spacer weighs 3 grams, same as the special scalloped ones on the Aethos.

Standard carbon spacer with thicker walls is 4 grams for 10 mm height.

Aluminium spacers are double the weight at 8 grams for 10 mm height.

Carbon headset cover is also lightweight at just 5 grams.

Next, let's take a look at the expander plug, or otherwise called compression plug. This part goes into the inside of the steerer tube, and expands to secure itself inside. It acts as an anchor point for the top cap to compress downwards on the stem, applying pre-load on the headset bearings.

The Aethos frameset comes with its own expander plug. At the same time, I also ordered the S-Works SL Stem, as the stem is not included with the frameset. The stem actually comes with its own expander plug as well, but of a different design. Check out the comparison below.

Expander plug that is included with the S-Works SL stem. Different from the one included with the Aethos frameset.

Side by side comparison. Expander plug from the stem on the left, while the right side expander plug is from the Aethos frameset. I think the bolt material is different as well.

The shaft of the expander plug on the right side has material removed, in order to shave off even more weight from the Aethos frameset. Both have thin and slotted flanges for reduced weight.

Expander plug from the stem, weighs 27 grams. About the same as the one found on the Cervelo Aspero.

The Aethos version is even lighter, at just 17 grams!

For maximum weight savings, use the Aethos expander plug (17 grams), together with the top cap and screw from the S-Works SL stem (4 grams).

For comparison, the Cervelo Aspero expander plug is 28 grams, while the top cap and screw is 15 grams, giving a total of 43 grams. This makes the Aethos version less than half the weight. Every little bit counts when you are building a weight weenie bike!