GC Cog 40T, 42T & 45T

Compatible cassettes:

The Wolf Tooth Components GC cassette cog is available in two versions: one for Shimano cassettes and one for SRAM cassettes. They are compatible with the following models:

Shimano:  XT 11-36t (CS-M771)

               XTR 11-36t (CS-M980)

               SLX HG81 11-36t - Modification required (must drill out rivets holding the 17t to the larger cogs)


SRAM:  PG 1030, 1050, and 1070 - 11-36 and 12-36 

             X0 11-36t(XG - 1080) - Remove the 14t rather than the 17t


Sunrace:  11-36t cassette -  note that it was not designed for this cassette but the Shimano GC does work ok


Wheel compatibility:  

Compatible with all wheels that we have tested except First Generation Crank Brothers Cobalt and Iodine wheels.


We have chosen to make separate cogs for Shimano and SRAM for two reasons: 1) we design each one for the best possible shifting performance instead of a compromise on both and 2) installation is simplified because no extra spacers are needed. 

Note on “B-screw”: We are no longer shipping a longer screw with each GC.  We have found it is almost never needed with SRAM derailleurs and only needed for about 50% of Shimano derailleurs. We have added it as a separate item in our accessories category. If you think you might need the longer screw, order one separately or just go to you local hardware store and pick up an M4 x 25 socked head cap screw.

It is possible that you will need a longer chain than what is presently on your bike. Make sure that when shifted to the 42T (or 40T) cog, there is still some amount of forward travel possible with the rear derailleur cage. This is especially important on bikes with rear suspension. We have tested with Shimano, KMC & SRAM chains – all function well.


Installation Instructions:

1.  Remove the existing cassette from the freehub.  Set aside the 17T (or 15T if you prefer) cog and a spacer since these won't be reinstalled.



2.  Place the GC cassette cog on freehub.  The side of the GC cassette cog with protrusions should face away from the spokes.

3.  Install the remaining cassette cogs (except for the 17t cog and spacer).  If you are using the 16t replacement cog, the 16t will replace the 15t, 17t and the spacer between them.  Make sure all of the cogs are fully seated before reinstalling the cassette lockring.  Expert tip: rotate the GC cog and the 36T cog fully clockwise before you tighten the lock ring. They will end up there the first time you ride but this will assure the best shifting while you tune it on the stand. Tighten lock ring to the manufacturers recommended value.

4.  Install the wheel on the bike with the chain shifted to the smallest cog.

5.  Adjust the "B-screw" to provide clearance between the top derailleur pulley and the GC cassette cog.  In some cases a longer B-screw will need to be used with Shimano derailleurs to obtain the need clearance.  Turn the screw in far enough so you have more than enough clearance to prevent contact when you shift into the GC cog.  The with the chain in the 42T (or 40T) cog, turn the B-screw out until there is 5-10mm of gap between the pulley and the cog. 

6.  Shift back and forth between the 36T and 42T (or 40T) cog.  The B-screw should be adjusted so there is just enough clearance to shift smoothly between these gears.  To fine tune the the B-screw turn it back OUT 1/2 turn at a time and shift between 36 & 42T until it makes a rumbling noise (upper pulley interfering with the GC cog) or does not shift well. Then turn 1/2 turn back in.

7.  The low limit screw may need to be adjusted counter-clockwise about 1/2 turn since the GC cassette cog is slightly thicker than the 36T cog.

8. Check to see that the chain length is set properly.  With the chain in the largest front chainring and in the GC cassette cog verify that the derailleur still has enough range of motion to take the tension off the chain.  If you have a full suspension bike you will want to verify that the chain does not get tight through the full range of the suspension movement. With the chain is the smallest front chainring and in the 11t cog make sure that the spring on the derailleur is still engaged to keep the chain tensioned.



Q: Does the GC work with all rear derailleurs?

A: The GC 40T works with any Shimano or SRAM 10-speed rear MTB derailleurs. The GC 42T is not compatible with 2011 or older SRAM rear derailleurs due to the location of the upper jockey wheel. The GC 42T does work very well with the newer SRAM rear derailleurs however.  The best ways to tell the vintages of your SRAM rear derailleur is 1) If you have a type 2 (clutch type) rear derailleur it is 2012 or newer and 2) the upper jockey wheel on 2012 and newer rear derailleurs are offset from the derailleur cage's axis of rotation. Long cage derailleurs are recommended when using the GC in 2x drivetrains. 

Q:  Will the GC damage the splines on the freehub?

A:  No, the GC will not cause damage.  The GC is over 4 mm wide at the interface with the splines which provides significantly more surface area to spread out the load compared to the 1.6mm thick individual steel cogs that are on most cassettes.

Q: Can I remove a cog other than the 17T?

A: On some cassettes the 15T can also be removed with good results but the 17T is generally the best choice.  We also make a 16t cog that can be used in place of the 15 and 17 so you end up with a nice smooth transition of 11-13-16-19, rather than 11-13-15-19 or 11-13-17-19.

Q: Will my shifting performance be affected?

A: The shift from 36 to 42 (or 40) is really, really good -- we spent a lot of time making this work flawlessly. The shifting on the smaller cogs may be slightly softer due to the extreme B-screw adjustment. It has never been a problem in testing however. The 40T has a slight advantage in this regard.

Q: Why can't you make a universal fit for SRAM & Shimano cassettes?

A: We considered it but after testing shifting performance, strength and ease of installation, we decided that two different versions was the best solution. No spacers needed with the Wolf Tooth GC!

Q: Can I use the GC with my 2X front shifting?

A: Yes, it works great with 2X, but you will need a long cage rear derailleur to have full use of the cassette in a 2x setup.  If you avoid cross chaining, you can make a medium cage rear derailleur work.  We recommend a minimum front chainring size of 26T with the GC42 or a 24T with a GC40 to avoid excessive torque on the freehub (i.e. don't use a 22T granny gear or you might damage your hub).  If you are a big and powerful rider or are riding a tandem, we recommend you check the torque or minimum gearing specifications on your specific hub.

Q: Can I mix drivetrain component brands (chains, derailleurs, cassettes)?

A: Yes, any combination that works with your 11-36 cassette will also work with the GC 42. Never attempt to use the GC on a cassette it was not designed for however! We have found that overall, Shimano cassettes shift the best, regardless of what derailleur or chain you are using.

Q: Is the GC compatible with all hub brands?

A: We have tested a lot of them and so far they all work. Let us know if you find any that do not work.

Q: Do I need to use a longer B-screw with the GC?

A: For most SRAM derailleurs, probably not. For many Shimano derailleurs, you will need it. Please purchase one with your GC from our web store or from your local hardware store as needed.

Q: How much does the GC weigh?

A: 42T= 86g, 40T= 79g. This is about 10g more than the competition but an aluminum cog is NOT a place you want to save weight! For good shifting and durability, our cog has been designed to be very strong and rigid, not just lightweight. We put on a lot of test miles and added strength where needed based on what we learned. Don't sacrifice performance for a few grams.


Gear charts:


The gear range on an 11-36T cassette is 3.27 (36/11=3.27).  Using a GC42 will increase the range to 3.82 (16.8% more range) which is very useful for bikes setup with 1x gearing.


29 inch wheels


26 inch wheels


27.5 inch (650b) wheels



The gear range on an 11-36T cassette is 3.27 (36/11=3.27).  Using a GC40 will increase the range to 3.64 (11.2% more range).


29 inch wheels

26 inch wheels

27.5 inch (650b) wheels


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