42T GC Cog for Shimano


The GC42 cassette cog is so big that when machining the first batch, the machinist thought he made a mistake!  If being big is cool then the GC42 cassette cog is the coolest cog around.  This cog is made with the precision and finish our customers have come to expect from WTC, and this enables quite possibly the best feeling shift in the cassette.

Be sure to check out the GC tech page for more details. This cassette sprocket is only for use with Shimano brand 10spd XT & XTR cassettes (also SLX if you are willing to drill or cut the factory rivets holding it together). It is NOT compatible with any other brand or model of cassette.  The shift points are properly timed to the tooth locations on the 36t Shimano cogs for optimal shifting performance.

Use of this cassette sprocket requires removal of the 17T or 15T cog & spacer from your cassette. If you add one of our 16T cogs, you will remove both the 17 & 15T cogs.

Note on “B-screw”: We have found a longer screw 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 B-screw, order one separately or just go to your local hardware store and pick up an M4 x 25 socket head cap screw. We highly recommend one of our GoatLinks when using Shimano derailleur -- you will never need a longer B-screw with a GoatLink.

You may need a longer chain than what is presently on your bike. Make sure that when shifted to the 42T 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.

Compatible with the following Shimano 10spd cassettes: XT 11-36t (M771),  XTR 11-36t (M980). Compatible with SLX (HG81) 11-36 cassettes only if you are willing to drill or cut the rivets holding the 17t cog.  The only note on hub compatibility is that these fit extraordinarily tight on certain Stan's No Tubes hubs like the 3.30 and the Easton X4 hubs.  With a little filing and some grease they will go on.

Compatible with Medium and Long Cage rear derailleurs for 1x10 and a Long Cage is required for 2x10.

Made in the USA.

Weight 86g

Note: the GC 42 is not compatible with 2011 or older SRAM rear derailleurs due to the location of the upper jockey wheel. It is difficult or impossible to get satisfactory shifting with the 2011 or older SRAM rear derailleurs so we do not recommend using the GC 42 if you have one of these. The GC 42 works great with the newer SRAM rear derailleurs however.