Fnhon DB12: SRAM Force eTap AXS Rear Derailleur

The key component to the SRAM AXS 12 speed drivetrain on the Fnhon folding bike is the rear derailleur. It needs to communicate wirelessly with the shifter, and also shift the chain across the 12 speed cassette. The rear derailleur is the most expensive part of the groupset, as it has many electronics and mechanical components in it.

I chose the SRAM Force AXS, instead of Red or Rival. The Red version is just too expensive, and it has similar features as the Force, except being a little bit lighter due to some carbon parts. On the other hand, the Rival version is a little cheaper and heavier, which is actually a good choice as well. However, the Rival version did not have the Orbit fluid clutch, which I wanted to try.

Comes in a big box!

Way too much empty space in the packaging. This box size might be used for another component, which is why it is so big.

Force logo can be seen clearly on the shiny outer link.

I was surprised to see such a big bulk in the middle of the parallelogram! Apparently this is where the motor and gears are located.

Rear derailleur does not come with an eTap battery, which is sold separately.

The battery will be attached to the rear of the rear derailleur.

At the front, we see the function button and also the LED indicator. This area is pretty bulky as well due to the fluid clutch.

This is a relatively short cage version for road and gravel usage.

Aluminium cage plates

Tall teeth guide pulley, without narrow wide teeth.

Tension pulley actually has narrow wide teeth, to match the chain.

Both the top and low limit screws will touch the aluminum inner link.

This is the Force Wide version, compatible with 36T sprocket, for gravel usage.

Parting lines from injection molding can be seen clearly here, not so ideal for appearance.

The cage goes very close to the mechanism, everything is packed tightly together.

Without battery, the rear derailleur weighs 303 grams.

Here is the battery!

Attaching the battery is very simple, just slot it in and use the latch to lock it in place.

Including battery, the derailleur is 327 grams. The battery itself weighs 24 grams.

Once the battery is attached, and paired to the shifter, the rear derailleur can be operated wirelessly!

How it looks when shifted to the lowest gear. The way the bulky mechanism tucks into the parallelogram is quite clever, since a big tension spring is no longer occupying the space.

A wire links the battery to the motor unit, across the parallelogram.

There is a small spring inside, to eliminate looseness from the parallelogram.

Another view of the wire.

So far so good, the rear derailleur is able to shift normally after pairing with the shifter. It is the first time I am using or studying the SRAM AXS rear derailleur, so there are many new things for me to learn.

An equivalent rear derailleur from Shimano would be the GRX RD-RX815, which is also a gravel rear derailleur, compatible with front double systems, and comes with a clutch. It is a little bit lighter in weight, but otherwise quite similar in terms of function.

Fnhon DB12: XDR Freehub Body

For this conversion of the Fnhon from 1x11 speed to 1x12 speed, the most critical factor is whether I can fit a 12 speed cassette onto the rear hub. There are various 12 speed cassettes, but not all are suitable.

The most common 12 speed cassettes are MTB cassettes, with a large 10-50T or 11-50T, just to list a few examples. However, these are way too big for small wheeled bikes.

As for 12 speed road cassettes of smaller sizes, it is hard to find, except for Campagnolo or SRAM cassettes. To me, Campy is like a niche manufacturer, although they are considered one of the big three alongside Shimano and SRAM. There might be a few other even more niche manufacturers that I do not know of.

That leaves the SRAM 12 speed road cassette as the only viable option (Shimano 12 speed road was not launched yet at this point). This means a XDR freehub body is necessary, to install the 10-36T 12 speed cassette shown in the previous post.

Which was why, before I bought any more new components, I needed to check if the freehub body on my wheelset can be changed or not. To recap, the 451 wheelset on my Fnhon is a custom wheelset, as I could not find a lightweight, Centerlock disc brake 451 wheelset on the market.

Rear hub on the wheelset is a Novatec D412SB-CL, where CL stands for Centerlock.

After doing some research, I found that there are variants of this hub, where the freehub body is the XD or XDR type, instead of the Shimano spline type that I have. This means that it is very likely that the freehub body on this rear hub can be swapped to the XDR type.

I managed to find a replacement freehub body on Lazada, using the limited info from the seller and also my existing hub. Basically it looked like there was a good chance it would fit, so I took a gamble and bought the XDR freehub body which is claimed to be compatible to my current Novatec hub.

Existing 11 speed road freehub body on the Novatec rear hub.

The new XDR freehub body! Last I searched, it is no longer available from the same seller on Lazada.

To remove the freehub body, this end cap/lock nut has to be removed.

Looks a bit different, let's see if it can be swapped successfully.

Original freehub body removed! Ratchet can be seen here.

Once one side of the locknut is removed, the other side slides out together with the axle.

The spacers are of different length, between these two freehub bodies. The longer spacer is for the Shimano spline freehub body.

The Shimano spline freehub body is longer, as the spline engagement stretches all the way to the 11T sprocket.

From another point of view, most of the sprockets on the XDR cassette do not engage the freehub body directly, but are joined to each other instead.

Shimano spline freehub body and spacer weighs 85 grams.

SRAM XDR freehub body and spacer weighs exactly the same. I always hear that the XDR freehub body is lighter, but it is not the case here.

Testing the XDR freehub body on the original axle

Taking the chance to service the rear hub, by cleaning and adding new freehub grease on the pawls and ratchet. Refer to previous PZ Racing and Wheelsport wheelsets.

I tried to reassemble the freehub body, but found that the freehub body could not seat fully into the hub. I panicked a little as I thought it might be incompatible.

Upon closer inspection, I found that there was an extra seal on the freehub body. When I removed the original Shimano spline freehub body, the seal remained on the hub shell, but I did not notice it (refer to picture above showing internal ratchet). The XDR freehub came with its own new seal, which I also didn't notice. So, when I tried to install the XDR freehub body onto the hub shell, there were 2 seals which caused the interference.

Original seal on the left, and the new seal on the right which comes with the XDR freehub body.

Once I took out the extra seal, the freehub body and other parts went on with no problem.

The hub worked normally, and was able to spin smoothly with and without engaging the freewheeling function. I'm glad that I was able to swap the freehub body on this Novatec freehub! Many thanks to Ascent Bikes for choosing a good and widely compatible hub for building this custom wheelset. If not for this swappable freehub body, this 12 speed conversion project would not have been possible.

SRAM Force 10-36T 12 speed cassette. As mentioned in the cassette post, this is a really good ratio to provide a wide gear range and also reasonably small gear steps.

New 12 speed cassette looking good.

The reason why the XDR structure allows a 10T smallest sprocket is due to the smaller integrated lockring (using same lockring tool), and the absence of spline engagement for the smaller sprockets.

If a conventional lockring was used, the diameter would be too big to fit a 10T sprocket.

So far, the 12 speed cassette and the XDR freehub body have been successfully installed on the existing 451 wheelset of the Fnhon folding bike. This has to be the most doubtful part of the modification, as the other components (rear derailleur, shifter, chain) will probably not pose an issue.

Fnhon DB12: SRAM Force AXS 12 Speed Cassette and Chain

My 1x11 speed Fnhon DB11 was completed at the end of 2019, and I have been happily riding it for about 1.5 years. There was basically nothing much that I want to upgrade, since it is already using top level components, such as XTR brake levers and brake calipers, and Dura-Ace/Ultegra Di2 shifting components. I purposely chose an aluminum wheelset as I don't like high profile carbon rims on small wheels due to aesthetic reasons. 

Therefore, this following modification is mainly down to itchy backside syndrome, as there is no real need to modify, nor can it really be considered a substantial upgrade.

I have been wanted to try the SRAM AXS system since it was launched, mainly due to the unique shifter that looks and works differently from others. However, it is difficult for me to use it, as it means I need to change the whole drivetrain ecosystem over to SRAM 12 speed.

SRAM AXS shifter with the unique ergonomics

At the start, it was only the MTB 12 speed system that was available, with a super wide range 10-50T cassette that is only suitable for MTB. Since I had already sold off my MTB due to very very limited use, I don't have a bike that can actually use this 12 speed system.

Alternatively, I could have used the road 12 speed AXS eTap system, but I didn't like the idea of using DOT fluid in my hydraulic brakes, plus I preferred the ergonomics of the Di2 hydraulic shifters over the SRAM road hydraulic shifters.

Then, I came across this SRAM Force 10-36T 12 speed cassette, which looks interesting as it is small enough to be used on small wheeled bikes, which gave me this wild idea to install a 1x12 speed AXS system on this Fnhon folding bike.

First I had to do some preliminary study to make sure that all the 12 speed components are compatible with the bike. The cool thing is that I can use a AXS shifter (for MTB flat handlebar) with a AXS rear derailleur (road short cage type).

AXS Shifter - Fits on standard flat handlebar

AXS Rear Derailleur - To use the road/gravel type, with a shorter cage than MTB spec

AXS 12 speed Cassette - Needs XDR freehub body on the rear hub

AXS 12 speed Chain - Need compatible front chain ring for AXS chain

Spoiler: Yes it all works, as you will be able to see from subsequent posts. The tricky part was converting the rear hub from the existing 11 speed road (Shimano spline) to the SRAM XDR freehub body, which will be shown in a later post.

Before that, let's take a close look at the SRAM 12 speed cassette and chain.

Here is the SRAM Force XG-1270 12 speed cassette

Using my home workshop with some Park Tool items!

This is the Force 10-36T spec, with some pinned sprockets instead of a one-piece machined design on the SRAM RED version.

Only the largest sprocket is black in colour, unlike the older version where the whole cassette is black in colour.

First time I will be installing a SRAM XD or XDR cassette. Still uses the same lock ring tool though.

This 12 speed cassette only fits on XDR freehub bodies.

Only the largest sprocket has splines that engage with the XDR freehub body, plus a screw thread engagement on the inside, similar to that of a freewheel.

Lots of small rivets between the multiple sprockets, transferring the load to each other instead of directly to the freehub splines.

Sprocket sizes are: 10,11,12,13,15,17,19,21,24,28,32,36.

I like the sprocket combinations, as it maximizes the range without making the steps between gears too big. In fact, it is exactly the same as the Sunrace RX1 11-36T 11 speed cassette, just with an additional 10T sprocket at the top.

There is this light grey rubbery layer between the 32T and 36T sprocket. It seems that this is to dampen the driving sound during riding.

The black "spacers" you see between the smaller sprockets are actually rubber rings to dampen the driving sound. The smaller sprockets are actually machined as one piece, so there is no need for spacers between them.

This 12 speed 10-36T cassette weighs just 310 grams, which is lightweight for the size.

I was impressed with the low weight of this Force cassette, as it is lighter than the Ultegra HG800 11-34T 11 speed cassette, which is 337 grams, despite having a wider range and one more gear.

A 12 speed AXS chain is also required, as this AXS system is not compatible with other chains, due to larger rollers being used on the SRAM AXS 12 speed chains. There will be a separate chain comparison post later on.

SRAM Force AXS 12 speed chain

Made in Portugal!

These 12 speed AXS chains have a distinctive look, with the Flat Top design to add some strength, to compensate for the thin side plates.

Weighs 299 grams before cutting, inclusive of the box weight.

It is the first time I am using the XDR freehub body, in order to use this 12 speed cassette. It is new to me, as my previous 12 speed cassettes were using a standard freehub spline, with a top sprocket size of 11T instead of 10T. In the next post I will show how I changed the freehub body to the XDR type.