Rotor Offset Adapter: 6 Bolt Ashima Rotor on 6 Bolt Hub

Previously I wrote about the special adapter which is used to install a 6 bolt rotor on a Birdy-spec Centerlock hub. The adapter was 5 mm taller to account for the rotor position offset.

Now, what if you want to use a Birdy-spec 6 bolt hub on a standard front fork with standard rotor position? Since the Birdy front hub has the rotor position offset 5 mm inwards, it will not be compatible to standard front forks.

With the adapter shown below, when installed on a Birdy front hub, it pushes the rotor outwards by 5 mm, which will put it at the standard position for standard bikes.

6 bolt adapter used to offset the rotor by 5 mm outwards

Note that the adapter set also comes with 2x 5 mm spacers, with an internal diameter of 12 mm. This is because this adapter set is actually meant for MTB thru axle front wheels, to modify older 100 mm OLD front wheels to be compatible with newer Boost front forks with 110 mm OLD.

6 bolt adapter is about 5 mm thick as required.

Weight is just 5 grams as it is made of aluminium

A longer rotor bolt is needed, since there is now an additional 5 mm thickness from the adapter. I got a few different longer bolts to try out to see which is more suitable.

Standard Shimano rotor bolt on the left, longer rotor bolt on the right came with the adapter set.

Shimano steel rotor bolts weigh 12 grams for a set of 6.

Longer rotor bolts weigh 18 grams. Made of steel as well.

Titanium longer bolt on the left, compared to the standard Shimano rotor bolt.

I didn't realize that the titanium bolt head diameter was larger, it may not fit on the rotor.

Set of 6 longer titanium rotor bolts weigh just 11 grams

The reason I got this 6 bolt rotor adapter set is because I want to install the Birdy-spec Ascent Cirrus Elite carbon wheelset onto the Fnhon Ultegra Di2 12 speed folding bike. I had previously modified the Birdy AXS 12 speed to use the awesome looking Suncord 4 spoke carbon wheelset, and the Ascent wheelset is now available to be used on another bike.

Since the Ascent Cirrus Elite carbon wheelset has a 6 bolt hub, that will mean that I need 6 bolt rotors as well. I could reuse the Shimano RT66 6 bolt rotors, but I decided to try something new and lighter. That is how I ended up buying a new set of Ashima Ai2 lightweight rotors.

Pair of Shimano Ai2 super lightweight rotors! The smaller 140 mm rotor is for the rear of the Fnhon Ultegra Di2.

The Ashima rotors come with its own set of rotor bolts as well, of the standard short variety.

Both the 160 mm and 140 mm rotors side by side. There is more empty space than rotor!

160 mm rotor with narrow spider arms. It is important to install the rotor in the correct direction to ensure that it is loaded in the stronger orientation.

160 mm rotor weighs only 74 grams, as compared to 112 grams for the Shimano RT66.

140 mm rotor shown here. The cutouts at the brake pad contact area are so big that I'm not sure if the braking will be effective, or it will end up shredding the brake pads.

140 mm rotor weighs just 65 grams! The Dura-Ace CL900 140 mm rotor weighs 95 grams without lock ring.

6 bolt rotor adapter to be used with the Ashima 6 bolt rotor.

Adapter to be used under the rotor, to push it outwards by 5 mm.

4 different rotor bolts. Left is the longer titanium bolt with large bolt head; middle 2 are the stock Shimano (black) and Ashima (silver) bolts; right side is the longer bolt that came with the adapter set.

Here is how the 4 different bolts look on the rotor. Seems that the bigger bolt head on the titanium rotor bolt is still compatible.

In the blog posts for the Fnhon Ultegra Di2 12 speed bike, I will show in more detail the installation of the rotor and the adapter.

Rotor Offset Adapter: 6 Bolt Rotor on Centerlock Hub

The wheelset on the Birdy AXS 12 Speed has been upgraded to the awesome looking Suncord 4 Spoke carbon wheelset! The wheelset came with a Centerlock hub that is compatible to Centerlock disc rotors. However, the rotor position is not the standard spacing. Rather, it is offset 5 mm inwards, as first explained on the Ascent Cirrus Elite carbon wheelset post.

I found this very interesting, as it meant that the wheelset is only compatible to Birdy bikes in stock condition. One problem with supplying bikes for Birdy wheelset is the special front hub that is needed, with the inward offset rotor position and clearance needed around the hub flanges to accommodate the folding.

I realized that Suncord has done a clever thing with the design of their hubs. Instead of having dedicated front hubs with different rotor spacings for Birdy and other bikes, they decided to base all the front hub designs on the smaller Birdy rotor spacing. Then, to make it compatible to other bikes, just a 5 mm offset adapter is needed to push out the rotor position to the usual spacing.

That is what I am going to show you today, an interesting adapter which I have not seen before.

Most brake adapters convert Centerlock hubs to make it compatible to 6 bolt rotors. This is a standard conversion which converts a standard Centerlock rotor position to a standard 6 bolt rotor position. Both rotors have the same distance from the hub centreline.

However, the adapter below not only converts a Centerlock hub to fit a 6 bolt rotor, it also moves the rotor position outwards by 5 mm! That is how a Birdy Centerlock hub can be made to fit standard bikes, while using a 6 bolt rotor.

Centerlock spline position on the Suncord wheelset, which is offset 5 mm inwards for Birdy bikes.

Although the special adapter is not included with the Suncord wheelset, it can be purchased from the same seller for a small cost.

At first glance, this looks like a standard Centerlock-to-6 bolt adapter.

However, the adapter is thicker (+5 mm), while the threaded lockring also has longer threads.

Special +5 mm adapter set on top, normal adapter set below that is 5 mm thinner.

Special lockring with longer threads on the left, compared to the standard Centerlock lockring on the right.

If you noticed the wording on the lockrings above, you will see that the special longer lockring states "100 to 110 for 9/12/15 Thru Axle only". That refers to the front hub OLD used on MTB, which used to be 100 mm. However, MTB started having wider front hubs for increased strength, and the OLD was increased to 110 mm, and this standard is called Boost.

In a way, this is the same concept being reused, where older 100 mm MTB front hubs were boosted to 110 mm to be compatible to new Boost MTB suspension forks. The additional 10 mm was added equally to both sides, 5 mm on the left and 5 mm on the right of the hub. This is why the lockring is 5 mm longer, and is exactly what is needed for this special adapter set.

Centerlock to 6 bolt adapters, with the special adapter on the left being 5 mm taller. Specially designed for Birdy front hubs, to make it compatible to standard (non-Birdy) forks.

Standard adapter plus lockring is 29 grams

Special adapter set weighs 40 grams due to more material. However it is just a 11 gram increase which is a small price to pay for universal compatibility.

Here is how a 6 bolt rotor fits onto the special adapter for Centerlock hubs. The lockring will then clamp down on top and secure everything.

When fitted properly, the 6 holes on the rotor should fit fully over the 6 steel pins on the adapter. This  special adapter moves the rotor position 5 mm outwards.

With this special adapter, you can buy a Birdy wheelset, and still be able to retrofit it to a standard bike later on, if you decide to move the wheelset to a different bike.