Birdy AXS: Assembly Part 2

Even before I got the Birdy City, I already planned to make major modifications on it. In fact, the modification ideas have already been floating around in my head for quite some time, just that I didn't proceed with it.

For full bike modification projects, I think it is a good idea to test out the bike in its stock condition first, so that you know the baseline performance. Afterwards, when the modifications are complete, the performance can be compared so that you can appreciate the upgrades and improvements.

As planned, many of the drivetrain and components will be moved over from the Fnhon DB12, as the Birdy will be replacing the Fnhon as my go-to folding bike. As such, I won't be sharing the details of the existing components, as the information can be found over at the Fnhon DB12 blog page.

For those components that are new, the details have already been shared in the earlier posts, or you can find the links at the relevant picture captions below.

Let's start with a picture of the completed bike, before zooming into each component for more detailed pictures.

Birdy upgrade complete! The new model is now Birdy AXS 12 Speed.

Unique front suspension design on the Birdy makes it very distinctive.

Side view of the Birdy front suspension fork, and the uncommon fixed height, non-telescopic handlepost.

Another view of the fixed height handlepost, which I presume is lighter and stiffer than the telescopic type.

Super clean handlebar area with only 2 brake hoses!

XTR BL-M9120 brake levers, a luxurious and lightweight choice.

SRAM GX AXS wireless shifter, with the comfortable and durable Ergon GP1 grips.

With the Ascent Cirrus Elite high profile 406 carbon rims, it pairs well with the Shimano RT66 6-bolt rotors.

Direct hose connection on the lightweight XTR BR-M9100 hydraulic brake calipers.

Internal cable routing on the Birdy main frame, where the rear brake hose enters the frame just behind the headset.

Rear brake hose exits the main frame above the bottom bracket, and enters the non-drive side of the rear triangle. This arrangement follows the stock cable routing method.

Rear wheel with the kickstand installed

XTR rear brake caliper as well. Both brake rotors have a diameter of 160 mm.

Here is the 12 speed drivetrain 100% ported over from the Fnhon DB12.

Wolf Tooth 44T chain ring for SRAM 12 speed Flat Top chains. See what is unique about the Flat Top chains and chain rings here.

Trusty Ultegra 6800 crankset that has been with me since the Dahon MuEX folding bike.

Ingenious little chain tensioner that takes up the chain slack when the Birdy is folded. 

This needs to be adjusted depending on the chain ring size and chain length.

With the chain in the middle of the Force AXS 10-36T 12 speed cassette.

At the lowest gear (largest 36T sprocket), the rear derailleur cage looks over-extended. This is due to the Birdy chain stay being longer than the Fnhon chain stay, while the chain length is the same.

Lots of cage clearance with the ground, which is why the SRAM Force AXS rear derailleur is a good choice for small wheeled bikes.

At the top gear (smallest 10T sprocket).

Still quite a distance before the cage touches the stopper, so I can easily extend the chain to relieve the chain tension when using the low gear.

Full bike view from the other side. I like how the black components allow the Sky Blue frameset to really stand out.

Here is how it looks with the Mr TiParts kickstand deployed. The length is just right for a 20" 406 wheel setup.

When the kickstand is used, the front wheel tends to flop and roll towards the non-drive side. Something to take note if parked on a slight gradient.

With this, the Birdy modification is complete! The bike has been completely transformed from the stock condition.

Stock Birdy City Specifications:

18" 355 aluminium wheelset

9 speed drivetrain with mechanical shifting

Mechanical disc brakes

Square taper crankset and bottom bracket

10.8 kg without pedals

New Birdy AXS Specifications:

20" 406 carbon wheelset

12 speed drivetrain with electronic wireless shifting

Hydraulic disc brakes

Hollowtech crankset and bottom bracket

9.2 kg without pedals

Full upgraded specifications and detailed weight breakdown shown in the table.

As you can see, I wildly underestimated the weight of the frameset (main frame, rear triangle and front suspension fork). This is why the actual weight turned out to be 1 kg more than my initial estimate before I got the bike.

Compared to the Fnhon DB12 (8.9 kg without pedals), the Birdy AXS weighs about 300 grams more, at 9.2 kg without pedals. Although it is heavier, it is probably worth the extra suspension feature that the Birdy has. You could also add comfort to the bike by using wider tires at lower air pressure, but this would also make the bike more sluggish.

At this point, it would be challenging and expensive to reduce the bike weight any more, as you would need to use boutique carbon components such as THM crankset, lightweight saddle and seat post, as well as minimalist pedals.