Cervelo Aspero: GRX Di2 Rear Derailleur with Garbaruk Long Cage

On the Cervelo Aspero gravel bike, my latest modification is to expand the gear range, up from the existing 11-42T cassette to a larger 11-50T cassette.

I have already received the Garbaruk 11-50T 11 speed cassette, and the rear derailleur cage upgrade kit. Now I will install the upgrade kit onto the stock GRX Di2 RD-RX817 rear derailleur, and hopefully everything fits well!

Stock GRX Di2 RD-RX817 rear derailleur before changing the cage.

Rear derailleur undergoing surgery, with a cage transplant in progress.

I had previously transplanted a Deore XT M8000 long cage onto this GRX rear derailleur before, so this is not new to me. That previous modification was a useful experience that made this upgrade so much easier.

Garbaruk 11T and 16T pulleys installed onto the Garbaruk cage!

It seems to fit well, no problems detected so far.

Stock GRX pulley bolts are used, as they are of the correct length.

Cage transplant complete with new pulleys!

No problem with pulley clearance, since the new guide pulley is the same 11T size as the stock guide pulley.

GRX Di2 RD-RX817 rear derailleur with Garbaruk long cage

Modified GRX Di2 rear derailleur with Garbaruk cage weighs 320 grams, 1 gram less than the stock GRX rear derailleur!

With this Garbaruk cassette and cage modification, the weight was actually reduced while the gear range has increased. More details in the next post!

Cervelo Aspero: Garbaruk Long Cage for 50T Sprocket

In order to match the super wide ratio Garbaruk 11-50T 11 speed cassette that will be going on the Cervelo Aspero gravel bike, I need a compatible rear derailleur.

Given the limits of Shimano Di2 11 speed drivetrain (which is needed for GRX Di2 11 speed), there is currently no compatible rear derailleur. The MTB Deore XT Di2 RD-M8050 can go up to a maximum of 46T, and it is very similar to the GRX Di2 RD-RX817 which I am using.

Therefore, a third party rear derailleur cage is needed to have compatibility with a larger cassette. That was why I need this Garbaruk rear derailleur upgrade kit to make a 11-50T cassette possible with the GRX Di2 11 speed drivetrain.

There are specific rear derailleur cages to match different rear derailleurs, so I made sure to get the correct version to match my GRX Di2 rear derailleur RD-RX817. There is no compatibility with the RX815 version (for 2x11 speed).

New larger pulleys and cage are sold separately, but I needed both.

These may not be genuine Garbaruk cage or pulleys, as they are relatively cheap. Can you spot the typo errors?

To be clear, I bought the Garbaruk cassette separately from the cage and pulleys. The cassette was ordered and shipped directly via the Garbaruk website, while the cage and pulley was from another source. The price difference for the cage and pulleys were quite big when compared to the Garbaruk website. Nevertheless, the quality was good as you can see below.

Aluminium inner and outer cage

Inside view of the cage

2 spacers are used to join the two halves together, before attaching the pulleys.

Engraved words indicate that this cage is compatible to GRX Di2 rear derailleur (RX817).

Garbaruk cage on the left, vs the stock RX817 rear derailleur cage on the right.

Although the pulley to pulley distance does not differ a lot, the Garbaruk cage is a lot longer overall to accommodate the larger tension pulley. This is necessary to increase the chain capacity of the rear derailleur.

Next, to determine compatibility, the fixing point on the cage needs to be compared. There are many dimensions which determine if the cage is compatible or not. From my previous lesson with the Fnhon Ultegra Di2 12 speed, where I attempted to install a TiParts rear derailleur cage onto the Ultegra Di2 rear derailleur, most of the dimensions and design will need to match to ensure compatibility.

Position of guide pulley and stopper looks similar

Similar P axle length and design, which is great news.

Pulley to pulley distance on the stock GRX RD-RX817 is 77 mm. That's in between the Ultegra R8050 and R8150 rear derailleurs.

Garbaruk pulley to pulley distance is 103 mm, slightly longer than the Ultegra R8150 rear derailleur.

Stock GRX cage weight is 34 grams

Garbaruk cage weighs the same at 34 grams, despite it being longer.

So far it looks like the Garbaruk cage will be compatible to the GRX rear derailleur, but I will only know for sure after I install it successfully.

To complete the upgrade kit, I also needed larger pulleys to match the larger cage. Here are the pulleys by Garbaruk.

New aluminium pulleys by Garbaruk. Tension pulley is large at 16T, while the guide pulley is small at 11T.

The new guide pulley remains at 11T, same as stock, to ensure clearance with rear derailleur and cassette. Tension pulley is much larger than the stock 11T.

Stock guide pulley vs new guide pulley. Very different looks despite both being the same 11T size.

Stock plastic pulleys weigh 22 grams

New Garbaruk aluminium pulleys weigh less at just 19 grams, due to extensive cutouts to reduce weight.

The 16T Garbaruk tension pulley has narrow wide teeth, which is surprising. Guess it helps to prevent chain drop from the pulley.

I also noticed that the 16T pulley has teeth that are off centre. You can see more protrusion on this side of the bearing.

On the other side, it is almost flat with no protrusion at the centre. The teeth is biased towards this side. Since there are no instructions, I will figure out the ideal direction later.

On the left is a spare pulley bolt that I have, but it is a lot shorter than the GRX stock pulley bolt on the right.

Short pulley bolt is just 11.9 mm long

GRX pulley bolt is 14.1 mm long

If I use the short pulley bolt, it is not long enough for proper thread engagement.

In the next post, I will write in detail the installation process of fixing the Garbaruk cage and pulleys to the GRX rear derailleur.

Cervelo Aspero: Garbaruk 11-50T 11 Speed Cassette

I had previously modified the Cervelo Aspero from a 2x11 speed drivetrain to a 1x11 speed drivetrain. The gear range was reduced, as the largest cassette that is supported by the GRX Di2 rear derailleur RD-RX817 is limited to 42T.

Although the gear range is well suited to a gravel bike, at 24 to 93 gear inches, I have always wanted a lower gear for steep climbs. This was not possible on the GRX 11 speed drivetrain, until I came across some third party options.

Garbaruk makes conversion kits to expand the gear range, through the use of a longer rear derailleur cage and larger cassettes. Merely changing to a longer cage is not enough, as the movement of the guide pulley needs to accommodate larger sprockets as well.

In this comparison between GRX rear derailleurs RX815 and RX817, you will notice that the front single RX817 rear derailleur has an offset guide pulley to match larger sprockets.

For this upgrade, I got the Garbaruk rear derailleur cage and also their own cassette. Although there are other wide range 11 speed cassettes, such as from Sunrace, the Garbaruk version is the lightest.

Garbaruk cassette, lightweight but very pricey!

11 speed cassette with a gigantic 11-50T gear range! Fits on standard freehub bodies.

Packed in a large pizza-sized box, including the lock ring.

Skeletal design for minimum weight!

Lots of machining done to minimize the weight of this cassette, more details below.

Sprocket Sizes: 11-13-15-17-20-24-28-32-36-42-50

From 11-17T, the spacing is common among wide range cassettes. However, there is a large gap from 17T to 20T, and from 20T to 24T. There is usually a 19T and 21T sprocket, instead of a single 20T sprocket. After that, the gear spacing from 24T to 50T is also commonly seen.

Comparing the Garbaruk 11-50T cassette with the XTR M9000 11-40T cassette and Dura-Ace R9100 11-30T cassette.

Weight of 11-50T cassette plus lockring is just 324 grams which is very light for the size!

The XTR 11-40T 11 speed cassette weighs exactly the same at 324 grams, but it is much smaller. Also, the XTR cassette uses 6 titanium sprockets to lower the weight.

Garbaruk lockring looks a bit different.

Aluminium lockring weighs 4 grams which is standard.

Comparing with the XTR lockring.

Same thread length and design, so nothing special here.

The cassette is mostly hollow! The first 10 sprockets are all machined from 1 piece of steel, with plenty of cutouts to save weight.

Only the first and last sprockets have splines to engage the freehub body!

Last sprocket is engraved to show that this is a 11 speed cassette with 50T sprocket.

I assume that a hollow construction such as this would be easy to clean, as any dirt can be flushed through easily.

Chamfers around the black aluminium cutouts, and minimum connection between the steel sprockets.

The 50T sprocket is made of aluminium and screwed onto the rest of the sprockets. It is also available in a variety of colours to suit your preference.

Sand blasted finish on the steel sprockets look good.

Lots of small connecting bridges between the different sprockets. Reminds me of the Campagnolo Ekar 13 speed cassette!

Small chamfers and teeth shape to help shifting performance.

This Garbaruk 11-50T cassette looks really high quality, with the nicely machined parts and well finished design. It is also one of the lightest, if not the lightest, 11 speed 10-50T cassette.

In fact, it is lighter than the 11-42T cassette that it will replace, allowing me to reduce the Cervelo Aspero gravel bike weight and expand the gear range at the same time!

More posts on the Garbaruk rear derailleur cage, as well as the completed upgrade coming soon.