Just when it seemed like Shimano's single ring game was catching up to SRAM's, the Chicago-based component conglomerate miniaturized all other cassettes with its 12-speed Eagle cluster, featuring a massive 50-tooth cog and boasting a wider gear range than many doubles.

This didn't necessarily antiquate the many Shimano 11-42, 11-speed cassettes that came spec'd on bikes around the world, but it sure did make them feel inadequate in comparison—especially for us riders who favor beer over barbells.

If you buy a Shimano single-ring bike off the showroom floor today, there's a pretty good chance that it'll come equipped with Shimano's newer, wider-range 11-46-tooth cassette, but there are still a ton of SLX and XT 11-42 cassettes out in the world. So what's a beer-over-barbell kind of rider to do? Well, normally my advice would be to stay as far away from this One Up 50-tooth Shark conversion kit as possible, even if it offers better range than Shimano's offerings.

The One Up 50T Shark kit is more than just a big ring. It comes with a second, central ring to keep shifting smooth and a new derailleur cage.

For around a hundred bucks you can snatch up an SLX 11-46 cassette and a new chain (which you'll need, because you'll need a longer one and adding links to a chain is a recipe for breaking knee caps on stems). You'll eek out a bit more gear range, and you'll be running a component that's guaranteed to work because it was designed and engineered by a single company.

I don't like cobbling shit together, probably because I lived through the 1990s, when "upgrading" to that Paul derailleur or those Kooka cranks resulted in absolute garbage shift quality. The engineers at Shimano and SRAM work really hard to make their components shift as perfectly as possible, and messing with that by jamming random CNC'd parts into the system doesn't have the best track record.

How many teeth does a great white shark have? You guessed it, 50.

So, as much as I wanted to keep an open mind when I received this One Up kit, which consists of a 50-tooth aluminum cog, an 18-tooth steel cog, and an entire derailleur cage that looked like so many previous failed attempts at upgrading Shimano shifting, it's safe to say I came into it with a bias.

You can imagine, then, how infuriating it was for me when it worked. The fact that I'd gladly recommend the 50T Shark Kit to my closest friends brings me zero happiness whatsoever. I don't like being wrong.

Typically, slapping a giant cog on the back of the cassette results in poor shifting all over the cluster, not just the one shift between brand A and brand B's products. That's because getting the derailleur to shift up into that new big-ass cog requires screwing in the b-tension so much that the guide (upper) pulley runs too far away from the rest of the cluster. The general rule is, the farther away the guide pulley is from the cogs, the slower and less precise the shifting gets.


This is why One Up sells this as a kit with a derailleur cage instead of simple a cog add-on. The One Up cage repositions the guide pulley so it can clear the 50-tooth cog while still running close enough to the smaller cogs for quick, precise shifting.

The Shark Cage is a huge contributor to the efficacy of the kit, but the cogs themselves are doing some heavy lifting too. As mentioned earlier, the kit comes with two. In order to add the 50-tooth to the back of the cassette, you need to make room for it by removing a cog. But if you simply remove one, you're left with 2 things: a larger than desired shift, and mismatched shift ramps. If you look closely at a cassette you'll see how the shift ramps match up between the cogs to deliver the chain smoothly to each.

One Up has some tricks up its sleeve, including an 18-tooth ring to keep the shift ramp equal when adding a 50 tooth on the end.

So, when installing the cassette, you leave out Shimano's 17- and 19-tooth cogs, using One Up's 18-tooth instead, which matches shift ramps, tooth shape and finish so well that if "One Up" weren't stamped into the steel, you'd be hard-pressed to identify it as non-Shimano. The 50-tooth is beautifully done as well, in 7075 aluminum hardened to a T6 temper, with perfectly matched ramping and 8 upshift opportunities per revolution.

It's not the typical hodgepodgery that we've seen in a lot of other cassette expanders. One Up's 50T + 18T Shark Sprocket and Cage is a well-thought-out system, and it performs like one. I've never been satisfied with other cassette add-ons, including other offerings from One Up, but I've noticed little-to-none of the shift degradation that normally accompanies these types of modifications. And after about 1,000 miles, some of which on an e-bike (judge me if you want to), the alloy sprocket has plenty of life left in it.

Two new rings is better than one.

Swapping the Shimano derailleur cage out with the Shark Cage is simple for anyone with some mechanical aptitude, and once installed, is adjusted like any other derailleur. One Up even has thorough instructions on its site to guide users, and shop mechanics doing it for the first time, through the process.

Before you go ordering the kit, though, make sure it's compatible with what you've got. This thing works so well because it's designed to interface specifically with the SLX M7000 and XT M8000 11-42-tooth cassettes. It won't work with anything else, so don't go trying to run it on 40- or 46-tooth cassettes. The Shark Cage is compatible with M9000, M8000, and M7000 derailleurs.

With this kit, One Up offers an excellent, cost effective way to get a lot more (19 percent, to be specific) range out of your cassette. It's not just a way of getting a lower gear, either. It'll allow you to go increase your chainring size by 4 teeth while maintaining the low gear you already have with the 11-42. Personally, I like going up 2 teeth because it yields both higher high, and lower low gears.

Would I do a ground-up build with the Shark Sprocket and Cage kit? Probably not. Don't get me wrong, it's a great way to put parts that you otherwise might get rid of to use, at a fraction of the cost of achieving the same gear range elsewhere. Plus, it doesn't require a different freehub body, which SRAM does, and depending on what you have, it might not even be possible to swap to SRAM XD without getting a whole new hub or wheel. But, if I were starting fresh, I'd probably still opt for SRAM Eagle. It offers an even wider gear range (500 percent opposed to 454 percent), and now that it's available at the GX level, it's pretty affordable.

Still, I'm supremely impressed with the One Up kit, so much that I'm willing to eat my words. If you've already got some compatible parts, this thing is definitely worth the dough.