Wolf Tooth GC 42t Cassette Cog

Additional Gear Range

And of course, the added gear range provided by the GC42 was nice. Out here in Park City, the additional range came in handy on sustained climbs at altitude and short, steep climbs. Previously I had felt that a 36t cog was just barely low enough and I’d use it all the time on hard climbs. Now, with a 42t low cog, I still use the 36t cog a lot and I use the 42t cog sometimes. The new cog clearly has value, but since I don’t use it all the time, I don’t think I would benefit very much from lower gearing.

Did I miss the 17t cog that needed to be removed to create space for the 42t cog? A little bit.

Removing it created a jump from the 19t cog to the 15t cog (see below for full cog tooth count list). The jump between the two was noticeable when shifting in either direction, but it wasn’t too obnoxious. I found I wasn’t in the 15-19t region of the cassette unless I was moving along at a pretty good clip on a flat or downhill, and in those cases I could usually decide to just go a little faster or a little slower. Even so, I’d recommend that anyone considering adding a 42t cog to their cassette spend a few days paying attention to how often they use the 17t cog. For me, having to do away with it was slightly annoying but not a huge deal. You may feel differently though, depending on where and how you ride.

Wolf Tooth does offer a 16t cog to replace the 17t cog for $14.95. I don’t think I need it, but a rider who spends a lot of time in the 15-19t region of their cassette might want one. See the graph below “Effect of Replacing 17t cog w/ 16t Cog” for the difference between using the 17t and 16t cogs. For this graph, 1 on the horizontal axis represents the smallest cog and 10 represents the largest cog. The change is noticeable, but not too big.

Tom Collier reviews the Wolftooth GC42 Cassette Cog for Shimano, Blister Gear Review.
(Click graph to expand)

Wolf Tooth also offers a 40t cog, though I can’t think of why I’d bother buying it. The jump from 36-42t isn’t extreme and matches the typical progression between gears. If anything, I think the smaller jump from 36-40t would feel a bit odd. Shifting from a 32t cog to a 36t cog is a 12.5% change in gear ratio, while 36 to 42 is 16.7% and 36 to 40 is only 11.1%. I’m usually looking for a bailout gear so the bigger jump is appreciated.

The 42t cog also weighs 86g while the 40t cog weighs 79g, a difference that’s indistinguishable on a bike. The difference in the length of chain required to run either cog is also minimal, so it shouldn’t meaningfully impact chain retention or chain slap.

A Closer Look at Gear Ratios

Below I’ve listed the cog tooth counts for the stock Shimano XT 11-36 10-speed cassette and the same cassette with 40t and 42t Wolf Tooth cogs, as well as the 16t Wolf Tooth cog (replacing the stock 15t cog) with the 42t cog added. I’ve also listed the SRAM XX1 10-42 11 speed cassette that the above configurations try to emulate. Notice that the XX1 cassette still has quite a bit more range than the Shimano cassette with the 42t Wolf Tooth thanks to the XX1 setup’s smaller 10t cog.

Shimano XT M771 11/36: 11-13-15-17-19-21-24-28-32-36 Total Range: 327%

Shimano XT M771 w/ 40t Wolf Tooth: 11-13-15-19-21-24-28-32-36-40 Total Range: 364%

Shimano XT M771 w/ 42t Wolf Tooth: 11-13-15-19-21-24-28-32-36-42 Total Range: 382%

Shimano XT M771 w/ 42t Wolf Tooth & 16t cog: 11-13-16-19-21-24-28-32-36-42 Total Range: 382%

XX1 10-42: 10-12-14-16-18-21-24-28-32-36-42 Total Range: 420%

I’ve also worked up two graphs for folks who prefer graphic representations of information. On each of the graphs below, “1” represents the smallest cog on the cassette and “10” or “11” represents the largest cog.

Tom Collier reviews the Wolftooth GC42 Cassette Cog for Shimano, Blister Gear Review.
(Click graph to expand)

The graph above, Gear Ratio Comparison, was generated assuming the use of a 32t chainring and shows that the gear ratio progression is a bit smoother on both the the SRAM XX1 cassette and the stock Shimano cassette than on the modified Shimano cassette with the 42t Wolf Tooth cog, but the difference isn’t huge.

Tom Collier reviews the Wolftooth GC42 Cassette Cog for Shimano, Blister Gear Review.
(Click graph to expand)

This second graph (shown above), Gear Changes on Different Cassette Configurations (%), shows the percent change in cog size that occurs at each shift. For instance, the second smallest cog on the stock XT cassette is 18% larger than the smallest cog. And on the whole, what this graph illustrates is that a) the gear jumps on the modified XT cassette without a 16t cog are a bit big, b) the 40t Wolf Tooth ring is too small and yields only a modestly easier gear, and c) that the magnitude of the jump in size between one cog to the next varies between and across cassettes.

Durability

Durability of the Wolf Tooth 42t cog has been pretty good. I have probably 200 miles on the cog and it’s showing some minor wear, but I expect I’ll get at least another 300 miles out of it before performance starts to degrade appreciably.

Bottom Line

The Wolf Tooth GC42 Cassette Cog is a winner; it significantly adds to the range of a 10-speed cassette, works well enough to fade out of consciousness, and is a much cheaper upgrade to a 1×10 drivetrain (or in turning a 2×10 drivetrain into a 1×10 drivetrain) than making the switch to a new 1×11 drivetrain. I’ll leave the GC42 cog on my bike until it wears out, and then I’ll get another. The drawbacks are that the setup doesn’t shift quite as well as a dedicated 11-speed drivetrain or cover quite as large a range. They aren’t major, but they are significant enough that when I need a new bike, I’ll seek out one with 1×11 gearing.

Lastly, I do recommend buying the GC42 cog over the 40t version (to get the extra range without real drawbacks), and get it with the extra long screw, just in case you need it.

 

3 comments on “Wolf Tooth GC 42t Cassette Cog”

  1. Nice in-depth review. I hear you on the range advantage of the 42 over the 40, but having tried both, I can say that the shifting with the 40 and the stock derailleur is noticeably better across the entire cassette, since the b-screw doesn’t have to be screwed in so much further than originally intended by Shimano.

    At about 600 miles, I gave up, and went back to a stock XT cassette, since, as you predicted, wear became very significant.

  2. Also, if you have to buy a new cassette to accomodate the WT 40 or 42 tooth, take that cost into consideration. That’s a 100 dollar cassette and a 65 dollar replacement to one of the cogs. Sure, I want a 42 tooth granny, but it’s not worth the SRAM prices and with Praxis’ coming out with a 40t for ~the price of an XT, that’s probably where I’ll land without upgrading to 1×11 (Gx or XT). First world problems.

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