12 Speed Road Cassette and Chain Comparison: Ultegra R8100 vs Force XG-1270

Quick and simple side-by-side comparison between two different 12 speed cassettes. The Ultegra R8100 is the second-tier road cassette from Shimano, while the Force XG-1270 is also the second-tier road cassette from SRAM. Being at the same grade makes it a fairer comparison, although I think the SRAM cassette costs more than the Shimano cassette.

For detailed information on each of the cassettes, check out their individual pages through the links above!

SRAM 10-36T cassette on the left, with the largest sprocket in black, and others in nickel chrome. 

Shimano 11-34T cassette on the right, with sand blast finish on all the sprockets. Looks very different!

SRAM cassette uses a pinned construction to link all the 12 sprockets together, while the Shimano cassette uses aluminium spiders and loose sprockets.

One way to check if the cassettes are cross compatible is to check the spacing between the sprockets. If they are similar, at least we know that the rear derailleur can shift the chain across the sprockets consistently.

Of course, there are other factors such as the sprocket thickness, teeth profile, the type of chain, the rear derailleur exact movements, but if the spacing don't match, no point checking all the others.

Spacing between sprockets on the Shimano cassette is about 1.8 mm.

Similar 1.8 mm spacing on the SRAM cassette as well. 

With a similar spacing between the sprockets, it might be possible to swap a Shimano cassette for a SRAM cassette, or vice versa. Only by testing it out on the actual bike would it be possible to know how well it works.

SRAM cassette is lightweight at 310 grams, for a relatively large 10-36T gear combination.

Shimano cassette is heavier at 341 grams. But I think it is cheaper as well.

The 12 speed chains are also different. SRAM has its own AXS Flattop 12 speed chain, which has larger rollers that makes it incompatible to many cassettes and chain rings. I made a detailed comparison and study of the Flattop chain, you can check out the measurements in the other post.

Comparison between a Shimano 11 speed (not 12 speed) and the SRAM AXS Flattop 12 speed chain.

One thing I wanted to test was whether I can use a Shimano 12 speed chain on the SRAM 12 speed cassette. If that is possible, I can theoretically widen the gear range of a Shimano 12 speed road drivetrain from 11-34T (max) to 10-36T, which is a big increase from 309% to 360%.

Seems that the Shimano CN-M9100 12 speed chain can rest nicely on the SRAM 12 speed cassette!

Side by side comparison of the 12 speed chains.

Another view of the chains. Different plate shapes, plate thickness, roller sizes, etc.

I didn't do any deeper comparison of the cassettes and chains, as I didn't see anything else worth comparing. Check out the individual posts for details on each of the components.

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.

Shimano GRX Di2 vs SRAM Force eTap AXS: Rear Derailleur

Traditionally, rear derailleurs are either road type or MTB type, and were designed quite differently to meet the different requirements.

Road rear derailleurs are small and lightweight, and have short cages to match the road cassettes. On the other hand, MTB rear derailleurs are built to be tougher and thus heavier, and they also have long cages to match the wide range MTB cassettes. Most importantly, it is equipped with a clutch to prevent chain slap and chain drop when riding on bumpy terrain.

Then, in comes gravel riding, and neither road nor MTB rear derailleurs are completely suitable. Road rear derailleurs are a bit too delicate for gravel riding, and the absence of a clutch causes the chain to bounce too much and result in chain drops. MTB rear derailleurs work a bit better, but are also not completely suitable as they are not suited for closer range cassettes.

Shimano has their GRX range of gravel rear derailleurs, while SRAM has the Force 1x series for gravel setups. Here is a comparison between the two different gravel rear derailleurs by Shimano and SRAM.

There are 4 types of gravel rear derailleurs by Shimano. Either mechanical or electronic shifting, and either front single or front double drivetrains. Pick the one that matches your setup!

GRX Rear Derailleur RD-RX815, which is for 2x11 speed gravel drivetrains, up to 34T cassette size.

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.