What are Shimano's SS and GS rear derailleurs?

There are two different models of Shimano rear derailleurs available.

Shimano rear derailleurs are available in two types, SS (short cage) and GS (medium cage), depending on the model. The “cage” here refers to the length of the pulley cage (the unit that houses the two pulleys).

The images above show Shimano 105 series rear derailleurs RD-R7000 on both the left and right sides, but you can see that the pulley cage lengths are quite different between SS (left) and GS (right).

The difference between SS and GS is technically as follows.

• Maximum number of teeth for low/top
• Minimum number of teeth for low/top
• Gear tooth difference from chainring
• Total capacity

To make it easy to remember, SS (short cage) is compatible with cross ratio road sprockets, while GS (medium cage) is compatible with wide ratio sprockets.

It’s easy to remember that SS (short cage) is for cross-ratio road sprockets and GS (medium cage) is for wide-ratio sprockets, but just because the maximum number of teeth is large doesn’t mean that GS (medium cage) is the best choice.

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The points of interest are “low sprocket minimum” and “top sprocket maximum”.

For the GS, the “low sprocket minimum” is 28T, so cross-ratio sprockets such as 11-25T cannot be used. Also, the “top maximum teeth” will be 12T, so lighter sprockets such as 14-28T cannot be used.

Different products have different specifications, even for the same GS and SS.

If you think that all Shimano products have the same specs in GS and SS, that is not the case.

For example, if you compare the RD-R2000-SS rear derailleur of the entry-level CLARIS with the RD-R7000-SS rear derailleur of the middle-grade 105, you will see that the specifications are quite different.

We can see that the RD-R2000-SS is wider and the RD-R7000-SS is narrower. The “low sprocket maximum” of the RD-R7000-GS we saw earlier was 34T, so there is only a difference of two teeth between the RD-R2000-SS and the RD-R7000-SS.

Compatible sprockets vary by product.

As you can see in the table above, even in the same SS series, the CLARIS has the ability to select a larger (lighter) gear for the low sprocket, so you can choose a sprocket with a much wider ratio. It’s an image that makes you cringe when shifting gears.

On the other hand, even if you use a wide ratio sprocket, the 105 has 11 gears, so the difference in gear ratio per gear level will be small, allowing for smooth shifting. In addition, the 105 has a small maximum low sprocket and a large maximum top sprocket, which means that extreme cross ratio sprockets such as 14T-25T can be used.

You can also choose a cross ratio of 13T-25T on the CLARIS, but the 105 with 11 steps of 14T-25T is more cross ratio.

Latest 12-speed components are not divided by GS and SS

For the latest road components, DURA-ACE R9200 series and ULTEGRA R8100 series, which will have 12-speed in 2021, and 105 R7100 series, which will have 12-speed in 2022, there is no GS or SS lineup for the rear derailleur. The rear derailleur is a single product lineup.

This is thought to be because the 12-speed sprocket lineup has a low maximum of “28T or more and 34T or less (equivalent to the GS of the previous generation),” so there is no need to classify the sprockets as SS or GS.

Therefore, when selecting a 12-speed rear derailleur for road use, there is currently no need to use the GS/SS difference as an opportunity.

What is your rear derailleur, SS or GS? How to distinguish

It is difficult to tell whether your rear derailleur is SS or GS, as the latest models do not have a clear model number stamped on them.

The following are two key points to distinguish them.

1. length of the pulley cage (GS has about 3-4 cm between pulleys)
2. shape of the pulley cage (GS has a slightly curved shape)

The difference in the length of the pulley cage between the SS and GS pulleys is difficult to distinguish visually, but it is best to remember that the GS pulley cage will fit another pulley (3-4 cm in diameter) between the pulleys, and the SS cage will not.

Also, regarding the shape of the pulley cage, the GS has a slightly sharper curve than the SS. Sometimes the difference is so small that you can’t tell unless you look at them side by side, but you can tell by looking at them together with the length between the pulleys.

Is it better to choose GS or SS?

Depending on what configuration of gear ratios you want, you can choose GS or SS. For road bikes, SS is basically the most common choice, and for MTB, GS is probably the most common. Most of the standard rear derailleurs for complete bikes use SS.

It is important to note that in some cases, you may want to replace only the sprocket while keeping the standard rear derailleur on the complete bike. In this case, it is necessary to check the number of sprocket teeth that the rear derailleur is compatible with beforehand and replace it with the corresponding one.

It seems that the rear derailleur & sprocket combinations that are not compatible will not fail to work at all, but due to the different length of the pulley cage, it may interfere with the sprocket on the low and top side, or with the chain, and worst of all, it may damage the frame.

We have looked at Shimano’s SS and GS rear derailleurs.

As you get used to riding a road bike, you may want to change the sprocket depending on the scene you are riding in, or upgrade the sprocket for a more comfortable ride. When doing so, be sure to check the model number of the rear derailleur and choose a compatible sprocket.