Wolftooth GC 42 Tooth Cog

1x mountain bike and ‘cross set ups are the trend de jour and there’s some good logic behind it: Ditching the front derailleur, front shifter, and all but 1 of your chainrings is obviously lighter. The set up is also simpler. Forget having to think about which front and rear ring combination provides the best ratio in your current situation (and which ones are redundant), simply move up and down the rear cluster to whatever cog is best.

Of course ditching the front shifting has always been possible but two recent evolutionary options have made the practice much more desirable.

The first is the previously mentioned Wolftooth Wide/Narrow chainrings that allow you to run a single ring without a front derailleur or chain guide but still avoid chain drop in all but the most extreme of situations (editor’s note: I’ve taken a few good spills, including dropping a few feet off a ladder onto my back with my bike landing on top of me, and I still haven’t lost my chain once with the Wolftooth up front).

The other evolution has to do with the number of cogs on your rear cluster. 20 years ago 7 cogs was the standard on higher end bikes. Now it’s 10. Those extra few choices are crucial to offering a decent number of gear options, but until very recently there was still one unsettled issue: Range.

Enter the Wolftooth GC Cog:


Yup, that thing is as massive as it appears.  Eclipsing the rear 60mm disc rotor on most cross country mountain bikes this 42 tooth cog gives you quite the bailout gear.  We’ve found that a 32 or 34 single ring in the front with an 11 tooth cog as the smallest in the back gives ample sprinting support on everything but pavement (where you definitely spin out, but who sprints their mountain bike on pavement?) and shifting from an 11 all the way through to a 42 gives you great range.

A 32 in the front with this 42 in the year, the set up we tested yesterday, allowed us to climb some pretty steep grades with relative ease.  What’s more, shifting into and out of the 42 tooth ring was crisp and precise, though that was AFTER we tested a couple of rear derailleurs.

Before we describe our derailleur issues let’s pass on what Wolftooth says about compatibility:  First of all they make two different GC 42 tooth cogs, one for Shimano and the other for Sram.  They work with current generation 11-36 tooth XT and XTR, and X5, X7, and X9 cassettes.

Secondly, for some of the Shimano applications (like ours) you need a longer b-tension screw (which Wolftooth provides for an extra $1) to dial back the derailleur cage, allowing it to clear the 42 tooth cog.  You need to remove your 17 tooth cog (or your 15, but the 17 is recommended) and its related spacer as you install the 42 tooth cog in it’s place.  Well, obviously the 42 tooth cog goes at the end of the cluster, not in the middle, but you get the idea.

Wolftooth doesn’t explicitly say this but you’ll also want to use a clutch drive rear derailleur with this set up if possible (assuming you have no chain guide up front) to all but eliminate chain drop as mentioned above.

There’s much more great tech info on Wolftooth’s site, including gear charts, but hopefully we’ve covered the basics above.

Here’s the catch that we found with our install:  We first tried this set up with an XTR rear derailleur and it didn’t work out for us at all because the b-tension screw had to be screwed so far into the derailleur that it started to slip under the little metal obtrusion that it is supposed to press against, as the derailleur’s knuckle rotated further back with every turn of the screw.  This meant we couldn’t get the derailleur cage positioned far enough back to clear the 42 tooth cog.

When we tried doing the same thing with an XT derailleur we found that the b-tension screw didn’t have to be screwed as far in because the XT derailleur doesn’t have to be pushed back as far to clear the 42 tooth cog, and as a result the screw didn’t slip underneath what it should press against.  This is because the back plate of the XTR cage, for some reason completely lost on us, actually protrudes a few millimetres past the top pulley wheel and consequently the chain as well, so the plate has to clear the largest cog or risk getting caught up during a shift.  The XT cage back plate has a lower profile than the pulley wheel so as long as the chain that roles along the wheel clears the cog you’re good.

That few millimetres of difference might be entirely what caused our issue trying unsuccessfully to use an XTR rear derailleur with this set up.

However, we have since used this same set up with an XTR rear derailleur successfully.  Unfortunately the 2nd XTR set up was done on a different bike by a different mechanic and has already been handed off to its owner, so we can’t directly compare why one XTR set up worked and the other didn’t.  We wonder if the unsuccessful XTR set up was at least partially due to a slightly flakey derailleur (the b-tension screw was very loose as we threaded it in and may have started to slip and misalign as we tried to set it up properly).

None the less we’re led to believe that using an XT derailleur is the better choice for this set up.  We’ll forward this directly to Wolftooth to see if they have anything to add and if we get a response we’ll post it here.  A response has been received and is pasted further below

We have no experience yet setting this up with Sram components, but if you want to be the first Guinea pig let’s make it happen!

Oh, we should probably mention cost…  It’s $100 for a ring ($89.95 US; darned weak Canadian dollar) and an extra buck for the longer b-tension screw if you need it.  The rings come in black, silver, and anodized red and blue.  We have a few silver ones, Shimano compatible, in now and can easily get more within a couple of weeks if you wish (assuming the manufacturer has them in stock).  We should also mention that Wolftooth makes the same cog in a 40 tooth design instead of the 42 we’re using.

Our set up frustrations with the XTR derailleur not withstanding we really like this set up (well, at least the web editor does; some others in the shop are more cautious) and our very early trials have proved extremely positive.  Hopefully they’ll hold up under more strenuous circumstances.  So far we have every reason to believe they will.

11 speed note:  Yes, we realize there are also emerging 1×11 speed options out there.  We’ve already spec’d a bike with 1×11 stuff from Sram and have another stock 1×11 build in the shop now, and we eagerly await the soon to come 1 and 2 x 11 speed XTR.  For now though using the Wolftooth GC 42 tooth cog is a relatively inexpensive way to get the same range you’ll find on the 1×11 set ups, albeit with one less cog in the middle.

Response from Wolftooth on our XTR issue:

There is no doubt that there are some bike geometries that cause issues, and a flakey rear der might be the cause too (would be my guess given the b-screw was slipping past the stop). Obviously we can’t test every bike frame, but I can tell you that we have had only a few instances like yours where it doesn’t work and there doesn’t seem to be any one cause.

One other interesting thing to note on setting up GCs with XTR is that the newer XTR rear derailleurs have a floating upper jockey wheel. Replacing this with a fixed upper jockey wheel (aftermarket) improves the shifting on bikes where shifting isn’t crisp enought in the lower cogs.

Finally, as you noted the 40t requires a lot less b-screw (stock one in most cases works). Obviously, with less b-screw there will be fewer incompatibilities…none that we have encountered.