Sram X.9 Drivetrain
X.9 Rear Derailleur:
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The Sram X.9 rear derailleur comes in three flavors. It is available in a short cage, medium cage, and a long cage. The medium cage pictured here weighed in at 221g.
To pick the right derailleur, you need to know what gears you’ll be using. Ideally you want to use as short of a derailleur as you can get away with in downhill. If you’re interested in learning about capacity see the paragraph below, otherwise you can skip over it.
Derailleur Capacity - Picking the right length derailleur
The equation to figure out a derailleur’s capacity is (Big Ring - Small ring) + (Big cog - Small cog) = Capacity required. These numbers are somewhat interpretive as you can get away with using a smaller derailleur but will have to watch out for bad gear combinations that take up too much chain. Big downhill bikes that often might have a lot of chain pull also can affect which derailleur will work best for you.
Sram derailleurs have the following capacities: Short=30t, Medium=37t, Long=43t
An example - You have a single front 36t chainring with a 11-34t rear cassette.
- To calculate the capacity, (Since you’re running one ring, there is no difference in the big rings)
- Your capacity is just (34 - 11) = 23t
- You need a derailleur that can take up 23t, so you can use the short/medium/long cage derailleur
Another example - You have a 22t/32t front chainrings and a 11-34t rear cassette
- To calculate the capacity, (32-22) + (34 - 11) = 34t
- You need a derailleur that can take up 34t, so you should use the medium/long derailleur.
- If you decide to run a small cage derailleur, you should pay attention to what gears combinations you use as you may break your derailluer or your drivetrain may not shift into all the gears.
Another example - You have a 22t/32t/44t front chainrings and a 11-34t rear cassette
- To calculate the capacity, (44-22) + (34 - 11) = 45t
- You need a derailleur that can take up 45t, so you should use the long derailleur.
- If you decide to run a small/medium cage derailleur, you should pay attention to what gears combinations you use as you may break your derailluer or your drivetrain may not shift into all the gears.
If you’re curious as to which gears will/won’t work for a given derailleur should you choose to go with one that is slightly less than your capacity. You can use the same equation to see what gears won’t work ideally for you by putting the numbers in a chart like this one I’ve constructed for a triple setup (22-32-44) and a 11-34 cassette. There is some leeway in the equation as manufactures typically err on the side of caution.
The derailleur details
The medium cage X.9 derailleur shown here uses an aluminum cage that is strong and has held up well for us. If you get the short cage it is composite (Sram engineered plastic). The X.9 derailleur was redesigned in 2007 and is just as good as an X.0 one in my opinion.
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The cable routing on the Sram X.9 is very good and effectively routes the cable in a clean manner no matter what bike you have with no loop to get snagged or caught by debris. Sram dubs this Direct Route Technology. Sachs first did this before Sram bought them and it’s proven to be a very good way to route the cable.
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The X.9 derailleur is compatible with all Sram 1:1 shifters. The X.9 has hardened pivots which mean these derailleurs are stronger than older Sram derailleurs.
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Perhaps one of the most notable features is that the Sram derailleur body is essentially fixed and will not rotate forward. This means your derailleur body won’t bang or swing forward. This makes for a much quieter drivetrain and is a very nice feature on FSR style bikes where derailleurs often can smack on making an immense amount of noise and potential damage.
Adjusting the limits on the derailleur are done from the side of the derailleur. Sighting in the limits with the screws on the side is a bit harder than Shimano who has them located on the back of the derailleur.
The fin that helps guide the shifter cable to the derailleur is made of plastic composite. The X.9 derailleur’s that we have used haven’t experienced any issues but if you crash hard / often it could potentially be a point of concern and become defunct.
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