Birdy AXS: Ascent Cirrus Elite Carbon Wheelset (20" 406)

Finally, after thoroughly studying the Birdy City in its stock configuration, and disassembling the frameset to study the individual frame parts, I can now move on to share about the new components!

Prior to getting the Birdy City, I already had a rough idea of what I wanted to modify on the Birdy. Most of the components are decent, and would be good enough for casual riding. However, since I wanted to use the Birdy to replace my existing Fnhon DB12 folding bike, I plan to transfer most the compatible components such as the SRAM AXS drivetrain over to the Birdy.

The main major component that cannot be transferred over would be the custom 451 wheelset on the Fnhon DB12. For a start, the 451 wheel size is too big to fit on the Birdy, as it can only accept a maximum wheel size of 406, and that is with slim tires.

Next, the Birdy requires a special front hub, with inward offset hub flanges and rotor mounting. Therefore, a new wheelset is needed for the Birdy, due to the special hub design.

Whenever I want to get a new wheelset, I will always consider getting one from Ascent Bikes. I have actually gotten quite a few wheelsets from them, with some of them custom built.

1) Extra strong 20" 406 wheels custom built for the Bike Friday Haul-A-Day cargo bike.

2) Low profile lightweight 20" 451 wheels custom built for the Fnhon DB12 folding bike.

3) Zenith Elite 700C road wheelset with a quiet rear hub for the Cervelo Aspero, and later the Focus Paralane.

Therefore, I decided to get a high end carbon wheelset from Ascent Bikes for the Birdy. The model is Cirrus Elite, which comes in either 406 or 451 rim sizes, and various other hubs. In this case mine is a pretty standard configuration for Birdy bikes.

Birdy Wheelset Specifications:

Birdy compatible Hubsmith front hub and rear hub.

Quick release axles.

100 mm front OLD, 135 mm rear OLD.

Shimano HG spline on the rear hub.

Disc brake mounting (only 6 bolt is available, not Centerlock).

50 mm tall 406 carbon rims with black bladed spokes and spoke nipples.

3M reflective decals (Darklight).

The wheelset is actually hand built in Singapore, with some of the components flown in from overseas. So you could actually customize it if you wanted to, subject to part compatibility and availability. I did not have to wait long for the wheelset, it took just slightly over a week.

New wheelset fresh from Ascent Bikes!

Birdy AXS: Birdy Front Suspension Fork

I will be dedicating a whole post to write about the front suspension fork of the Birdy folding bike, as it is unique and very interesting. Also, I managed to disassemble the entire suspension fork, so there are lots of parts for me to study.

As shown in the earlier introduction post, the hook of the front latch needs to engage the coil of the front suspension spring. The spring coil needs to be rotated to a specific angle to match the hook shape of the latch.

Birdy AXS: Birdy Bike Frame and Handlepost

In the previous few posts, I have studied the stock setup of the Birdy City, followed by comparing the geometry and size, and finally dismantling the frameset. Now, I will study these individual frameset parts in more detail, by checking out the design and the weight.

Frameset parts laid out in an exploded view.

Birdy AXS: Dismantling the Birdy Bike Frame

In order to study the Birdy frameset, all the stock components need to be disassembled. Most of them are not a problem, except for the square taper crankset and bottom bracket. I have a slight phobia of square taper cranksets, due to having stripped the crank arm threads when extracting one a long time ago. Same for the bottom bracket with multiple small splines that are hard to engage properly.

For removing the square taper crankset, I make sure that the square taper extractor tool is well greased on the threads, so as to maximise the thread engagement to avoid damage. As for removing the square taper bottom bracket, I made a simple tool modification to make sure the bottom bracket tool does not slip off during usage.

As shown below, I used an actual crank arm bolt plus a few large washers to keep the tool on the bottom bracket spindle, when applying torque on the tool. This virtually eliminates tool slippage and spline damage. Just take note that as you loosen the bottom bracket cups, you will need to release the crank arm fixing bolt slightly to enable the bottom bracket to back out.

Using a spare crank arm fixing bolt and a few washers to keep the tool in place. The crank arm fixing bolt is screwed into the thread of the bottom bracket spindle.

Birdy AXS: Stock Birdy Bike Ride Before Modifications

Now that I have studied the stock Birdy City in more detail, it is time to go for some test rides, to see how the stock setup performs. This will give a baseline feel before I disassemble and modify the Birdy folding bike.

During the test rides, the main areas that I will pay attention to would be the shifting performance, braking performance, rolling resistance, and suspension feel. Later on, after the bike has been upgraded, I will compare and see how much or little these areas have changed.

Before even riding, I have to adjust the saddle and seat post. As shown in the first post, the default seat post setting has a rearward offset, which means that the saddle position is rather far back. This is a problem for me as I need a zero offset seatpost in order to position my knee properly over the pedal spindle.

As I have previously done bike fitting at LOUE Bicycles, I am able to use the same setup to adjust the saddle position and height on the Birdy for the optimum riding posture. With a rearward offset seat post, it is not possible.

Luckily, this Birdy seat post is cleverly designed such that the saddle rail clamp can be reversed. Basically just rotate the seat post 180 degrees, then slide the clamp to compensate. This effectively gives the seat post a zero/forward offset, which is what I needed.

Birdy stock seat post rotated 180 degrees, with the saddle rail clamp adjusted to give a zero/forward offset. Pardon the messy workbench behind.

Birdy AXS: Bike Geometry and Size Comparison with Fnhon

Before I disassemble the stock Birdy City folding bike for modifications and upgrading, I thought it would be a good idea to study the stock configuration, separated into Drivetrain Overview, Suspension and Brake System, Folding the Birdy Bike, and this post, which is a comparison post.

In this post, I will compare the geometry and size of the Birdy bike (unfolded and folded) with the Fnhon DB12. Other previous folding bike comparisons I have done are:

Java Neo 2 vs Dahon MuEX

Brompton vs Dahon MuEX

Tyrell IVE vs Dahon MuEX

United Trifold vs Brompton

Fnhon Gust vs Fnhon DB12

The reason I am comparing the Birdy to the Fnhon DB12 is because I plan to use the Birdy to replace my Fnhon DB12 as my go-to folding bike. Instead of adding a bike which makes it more difficult for me to choose, I prefer to do a 1-to-1 replacement. It will become my ideal bike for casual riding and also when bringing it to other places by car.

As such, the bike does not need a Brompton's compact fold, nor need to be wheeled around when folded. As long as it fits in a standard car boot it is fine. I do want the bike to be lightweight and fast, with high quality shifting and braking performance.

Overview of the bike shape and dimensions. Fnhon is using 20" 451 wheels, while the Birdy is using 18" 355 wheels (stock condition).

Birdy AXS: Folding the Birdy Bike

Although the Birdy is a folding bike, foldability is not the main feature, unlike a trifold like the Brompton or similar clones like the United Trifold. Rather, it is marketed as a full suspension mini velo that happens to fold as well. The unique Birdy folding method comes from the dual purpose folding joints, which double up as the suspension linkage as well. As such, the folding joints are not seen as a weaknesses in the Birdy frame design, but rather a design that enables full suspension.

I tend to prefer the traditional bifold method, such as those seen on Dahon or similar bikes. The bifold method is easy and does not affect the chain stay length, unlike the trifold method on the Brompton or the Tyrell. This reminds me of the Java Neo 2, which is a unique trifold bike that has a fixed chain stay length, due to the concentric bottom bracket design.

Based on this definition, the Birdy is a trifold folding bike, with the front fork and rear triangle folding inwards. However, the folding process is trickier, while the folded package is not as neat or compact as a Brompton. Anyway, the Brompton is the gold standard and benchmark when it comes to having a compact folded size.

Anyway, let's take a look at the folding process of the Birdy. Although I have tested the bike before, I have not had the chance to study the folding design closely, until now.

A half fold, where the front fork and rear triangle are folded in. Not well balanced though as the seat post has not been put down.

Birdy AXS: Introduction to Birdy City (Suspension and Brake System)

Here is the second part of the Birdy City folding bike introduction. In the first part, the drivetrain was introduced, with all components in the stock condition. In this post, the stock suspension and brake system will be shown.

View of the stock Birdy City from the non-drive side.

Birdy AXS: Introduction to Birdy City (Drivetrain Overview)

Here is a new folding bike for me to modify! It is the new Birdy City by Pacific Cycles, which is the entry level spec for Gen 3 Birdy folding bikes. Although there are many different component grades, all of them have the same frameset. Therefore, if I plan to change everything on the bike, might as well get the entry level model to save some money.

Many years ago, I tried the Birdy when it first came to Singapore, and I was very impressed with the suspension. However, I have never bought the bike as it was quite expensive compared to other folding bike options, plus the folded package always seemed awkward to me.

By chance, I happened to see a great offer by Mighty Velo, which had a good discount on some of the Birdy bikes. There was also an offer by Qoo10, which meant that when I combined the offers, there was a discount of more than SGD 700. This created a pretty irresistible deal, which is why I finally decided to buy the bike.

What's nice is that we can specify the colour of the bike frame for every spec, since the bike shop only assembles the chosen frame with the chosen component spec when you order it. It only takes a few days for them to queue and build up your bike, so the wait time is not a problem.

There are so many nice colours to choose from, but I finally chose this sky blue which looks really nice. In fact it looks very similar to the shade of blue used by Shimano.

Before I remove and modify any components on the stock Birdy City, I will first study it closely, and also do some test riding. This is to allow me to compare the ride feel and performance before and after the upgrades.

Completely stock Birdy City setup with 1x9 speed Sora.

Campagnolo Ekar on Polygon Bend R5

Here is the final post on the Campagnolo Ekar groupset! This 1x13 speed groupset has been installed on the Polygon Bend R5 gravel bike. Check out the pictures below.

Start with the full bike picture. This frame has a really tall head tube and a very sloped top tube, which gives an upright riding posture and a relatively low standover height.