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by James Huang
March 31, 2017
Photography by James Huang
TECH NEWS BROUGHT TO YOU BY BIKEEXCHANGE
Riders interested in switching to disc brakes on the road have little choice but to get a new frameset and wheels. However, they don’t have to get a complete new groupset, too, as several good cable-actuated disc-brake calipers will get the job done while allowing them to keep their existing gear. One of the latest entries is the Yokozuna Motoko, and as U.S. technical editor James Huang discovered, it’s pretty good — and it isn’t horrifically expensive, either.
The Motoko is a mechanical/hydraulic hybrid that works with standard levers: a standard brake cable links the lever to a small arm on the caliper body, which then operates a hydraulic master cylinder piston. That piston pushes mineral oil through the body to the slave pistons, which then squeeze the pads against the rotor. As compared to purely mechanical disc brakes (like the TRP Spyre or Avid’s workhorse BB7), the claimed advantages of hybrid calipers include increased power, a more positive-feeling lever, and better resistance to weather and road grime.
The concept of a mechanical/hydraulic hybrid is not new. TRP has offered the Hy/Rd for several years now, and both AMP Research and Mountain Cycle promoted the idea back in the 1990s. Even so, it’s only more recently that companies have more finely honed the idea.
There are multiple manual adjustments on the Yokozuna Motoko caliper, including for cable tension and leverage ratio. The latter can be used to fine-tune lever feel and power characteristics, too.
One the biggest advancements is size, and the Motoko is admirably compact. Even as compared to the TRP Hy/Rd — arguably the best of the breed — the Motoko is substantially smaller and lighter. Actual weight per caliper is just 142g with pads but without mounting hardware, plus another 117g for the included 160mm-diameter six-bolt stainless steel rotor — not exactly feathery, but more than 100g lighter per pair than the TRP.
That slimmer design also allows for an open-backed rear window for better airflow over the pads relative the the TRP’s more closed-off shape, plus the Shimano-compatible pads install from the top for easier replacement. A small tool-free adjuster dial adjusts the angle of the arm relative to the piston shaft, too, and users can tweak the lever feel and power depending on the angle chosen.
160mm-diameter rotors are included as standard equipment, but lighter riders may be fine with 140mm ones, too.
As an added bonus, Yokozuna includes its superb Reaction compressionless housing with each caliper — something I consider a virtual necessity for any brake (not just disc brakes) that uses full-length housing. It’s stiffer and more difficult to route than traditional housing, but as the name suggests, it also doesn’t compress linearly under load, which provides much improved lever feel and braking power.
Add in the considerably lower cost of the Motoko compared to the TRP — US$125 per wheel — and it becomes a pretty enticing proposition on paper.
Setting up the Motoko brakes is a cinch, and the simplicity of the design should be familiar to anyone who has worked on traditional cable actuated rim calipers before. Once the housings are cut to length and cables are run, it’s just a matter of loosely installing the brakes on the frame and fork, pulling the lever to center the caliper on the rotor, and then carefully tightening down the mounting bolts.
Bleed ports (painted yellow) are readily accessible, but the company says the caliper should never need to be bled. “Never” seems like an awfully long time, though.
All told, the entire process took less than an hour from start to finish, including swapping rotors and installing fresh bar tape. After taking a few minutes to “season” the rotors with fresh pad material, it was off to the races (so to speak).
Invariably, the question anyone interested in hybrid disc calipers will ask is not only whether they’re as good as fully hydraulic systems (not really), but if they’re a significant improvement over conventional rim brakes. The answer? It’s complicated. The Motoko has some fantastic potential, but Yokozuna has sold it short in one critical area.
Pad clearance is average for a hydraulic disc system. Pad rub was non-existent on the thru-axle-equipped bike used for the majority of the testing.
Power is perhaps where the Motoko gives up the most ground to a fully hydraulic system; there’s simply no ignoring the fact that there’s more hand effort required to produce the same amount of stopping force, both in terms of initial bite and ultimate stopping power. Given the inherent differences between pushing oil through a tube vs. sliding a steel cable through a housing, the Motoko also has a less-fluid feel at the lever.
That said, a careful installation with a well-lubricated inner cable greatly minimizes the friction (almost to the point of being largely insignificant), and the included Reaction housing yields a remarkably positive feel; instead of merely compressing the housing lengthwise as is usually the case with standard housing, pulling the lever harder actually produces more clamping force at the caliper.
The open caliper design allows air to pass in between the pads and rotor to help keep the system from getting too hot. It also allows for finned pads to be fitted for extra cooling capacity.
There’s also outstanding control from the Motoko, and you can more easily (and more consistently) flirt with the limits of wheel lock-up as compared to most rim-brake systems. That advantage grows with degrading weather conditions, too.
Regardless, heat is the Achilles’ heel of hydraulic brake systems, as boiling fluid results in a complete loss of hydraulic pressure, and I certainly started this test with reservations on how well the Motoko would hold up under extended braking given its comparatively tiny fluid volume.
Thankfully, that has turned out to not be an issue, as even a prolonged descent from the summit of Boulder’s Flagstaff Mountain back down into town — a 600m-drop in barely 7km — with the rear brake dragging throughout had no negative effects, aside from a little extra noise and some rotor discoloration.
Yokozuna Reaction housing is built more like derailleur housing with its longitudinal strands. The outer wrap keeps the inner wires from blowing out under hard braking.
That’s especially surprising given the Motoko’s closed hydraulic system, which doesn’t account for thermal expansion like the open hydraulic systems used by TRP on the hybrid Hy/Rd, or the fully hydraulic systems from Shimano and SRAM. The closed nature also means the pads won’t self-adjust over time, although aside from some more extreme weather conditions, that shouldn’t be an issue for most users given the generally slow wear rate of disc brake pads.
Either way, roadies who aren’t accustomed (or comfortable) with the idea of working on a fully hydraulic system will find much to like in the Motoko’s simpler design. According to Yokozuna, the system never needs to be bled (although a few years of use will likely test that claim), and setup is nearly as straightforward as any common cable-actuated rim brake.
So how could the Motoko be improved? It’s simple, really: better pads. While there’s much to like about the Motoko, the stock pad compound just isn’t very good and isn’t likely to blow away anyone coming off of a top-notch rim-brake setup, especially when using enhanced rim sidewall treatments like Mavic Exalith or Zipp Showstopper.
Thankfully, the Motoko uses Shimano-compatible pads (the older XTR standard, to be specific), so there are multiple aftermarket options available. Upgrading to Shimano’s versatile organic disc-brake compound noticeably increases overall power and initial bite, and switching to SwissStop’s superb fully metallic compound increases the Motoko’s capabilities even further (albeit at the expense of greater noise).
Unfortunately, Yokozuna has fitted the Motoko caliper with pads that don’t work as well as they should. Swapping to SwissStop’s sintered metallic compound greatly boosted both initial bite and ultimate stopping power, albeit with a little more noise to go with it. Even standard Shimano organic-compound pads worked better than the stock ones, though.
Sadly, good disc brake pads aren’t cheap, and given the Motoko’s reasonable price, such an upgrade comprises a significant percentage increase. While it’s admirable for Yokozuna to want to keep the cost of entry down, I’d happily spend a little extra up front to extract the full potential.