Birdy AXS: Assembly Part 1

In the previous posts, the stock drivetrain and suspension setup of the Birdy City was studied, followed by disassembly of the frameset and the suspension fork.

The Ascent Cirrus Elite carbon wheelset is new, as the Birdy requires a special front hub design. Otherwise, most of the other components will come from the Fnhon DB12 folding bike, as the Birdy will replace the Fnhon as my main folding bike. That said, the Fnhon frameset will not be abandoned, as it will be used for another project. 

I got a new set of hydraulic brake calipers for the Birdy, as the existing XTR brake calipers on the Fnhon will continue to be used for the new Fnhon build. The Birdy still uses the conventional Post Mount brake mounting, both at the front and the rear, which does not allow me to use the newer Flat Mount brake calipers. As I prefer a direct hose connection to the brake caliper instead of having a banjo bolt connection, this means that I will choose the XTR M9100 brake caliper that I have used previously. Alternatives are the non-series BR-R785 and the Deore BR-M6100.

XTR M9100 hydraulic brake calipers! However, the version that is currently in stock comes with metal brake pads, and not resin brake pads.

Metal brake pads with no fins and titanium backing. Click here to see how the model naming works!

As I prefer resin brake pads, I just need to buy them separately. These are resin brake pads without fins and with titanium backing.

Weight of each XTR brake caliper set is 99 grams, with all the parts shown here.

The XTR BL-M9120 brake levers will be disconnected and transferred over to the Birdy. Since the brake hose length will be different anyway, this is not an issue. The Ergon GP1 grips will be carried over as well, as they are still in good condition. I have been using the same pair of Ergon grips since it was first installed on the Dahon MuEX.

Other new components are shown below.

New Toseek carbon handlebar with 31.8 mm clamp diameter and 580 mm width. I could not reuse the previous Toseek handlebar as the clamp diameter is smaller at 25.4 mm and I did not want to use an adapter.

Decided to get a good smooth rolling bottom bracket from Ascent Bikes, as the Shimano ones are not smooth from what I experienced on the Specialized Aethos build.

Lightweight titanium rear QR axle

Lightweight titanium front QR axle

I also got a kickstand for the Birdy, as it is just more practical to have one. There are many types available in the market, with all types of prices and design. I saw that this Mr. TiParts version looks pretty OK and not too expensive, so decided to give it a try.

Birdy kickstand, with the longer 20 inch version chosen as I will be changing the wheel size from 18" to 20".

This is the thickness of the metal plate that will be clamped under the QR axle. Theoretically this means that the QR axle needs to be at least this much longer to ensure sufficient thread engagement.

This lightweight kickstand weighs just 93 grams due to the carbon shaft.

New XTR brake calipers and kickstand installed!

Front brake caliper installed. Still experimenting with the hydraulic hose routing to find the best setup.

During assembly, I found that I needed to adjust two of the plastic stoppers that come into effect during folding.

Stopper 1: Controls the position of the rear triangle relative to the main frame when folded. Stopper will contact the bottom of the main frame bottom bracket shell.

Stopper 2: Small clearance with the seat post when the bike is folded and the seat post lowered. Stopper rests against the seat post when the folded bike is lifted, to prevent the rear triangle from unfolding itself. Same concept as on the Brompton.

Both of these stoppers are located on the rear triangle as shown below.

Stopper 1 on the left of the picture, while stopper 2 is shown on the right.

Stopper 1 is supposed to rest against the bottom bracket shell, to limit the movement of the rear triangle when folded. This is the stock setting before adjustment.

As seen above, Stopper 1 is not contacting the bottom bracket shell, as the left crank arm actually touches first. This is because the Shimano crank arm has a squarish clamp area around the bottom bracket spindle, instead of the stock Birdy crankset which has a rounded area around the square taper spindle. On the stock setup with the 18" wheels and Birdy crankset, Stopper 1 will touch the frame.

The squarish clamp area on the Ultegra 6800 crank arm will interfere with the rear triangle.

Another picture showing the interference. Hope the frame designers can refine the frame design next time to provide a bit more clearance.

Nevertheless, it is not a big problem as the stopper can be adjusted to extend a bit further. This will allow the stopper to touch the frame first, before the crank arm touches the rear triangle.

Stopper 2 is affected by the setting of Stopper 1. When Stopper 1 is extended to avoid crank arm interference, it causes Stopper 2 to get closer to the seat post. In fact, Stopper 2 actually sticks out so much that it blocks the seat post from going all the way down during folding.

Unfortunately, there is a limit to how far I can screw in Stopper 2 to avoid the seat post. Even when tightened all the way in, Stopper 2 still sticks out a bit too much and blocks the seat post.

Therefore, I had to reduce the thickness of Stopper 2 so that I can screw it further in. An alternative way is to remove Stopper 2 completely, but it also means that the bare frame will touch the seat post.

Flat surface beside the thread of plastic Stopper 2 has been grinded away to reduce the thickness.

After modifying Stopper 2, it is able to be screwed further in to avoid the seat post. Only a very small gap is present with the seat post as shown here.

Before installing the SRAM Force AXS rear derailleur, the hanger alignment is checked with a special tool to ensure optimal shifting performance.

More details to come in Part 2 of the Birdy re-assembly!