Stopping on Dirt: Deore XT 4-Piston Brake

Stopping on Dirt: Deore XT 4-Piston Brake

When I think of bicycles, and what I find exciting about them, at least, about the machine itself, my short list of favorite attributes doesn’t include brakes. I suspect I’m not alone. It’s pretty easy to get excited about the frameset, about the control levers, about the wheels, but the brakes? Nah.

But honestly, the brakes are no less important, and arguably more important than the most up-to-date drivetrain. Seriously; after you stop shaking your head, hear me out.

I got up hills just fine on 9-speed drivetrains. I did two weeks in the Alps with a Shimano 105 triple group and it gave me every gear I could need; the 30×27 low gear enabled me to work my way up impatient grades in the Chartreuse, even with legs that were more taxed than a Danish doctor. But here’s the thing: those brakes? Holy cow. You couldn’t pay me to ride them again.

Even the brakes on the Dura-Ace group of that era came up short on ambition. I remember this because they were noticeably less powerful than the original dual-pivot calipers introduced with the D/A 8-speed group. Those things were so powerful some tandem makers were spec’ing them on their bikes and after they were discontinued there was a run on those no less fierce than a discontinued M-series from BMW.

 

Some will argue that braking isn’t an absolute, it is the result of a foundational philosophy, an existential response to the fact that when you go for a ride the last thing you want to do is stop, amiright? And somehow, engineers who didn’t think we could develop the muscle memory necessary to control a brake decided that they would save us from ourselves. Or something.

I’ll never forget my experience of talking with a representative of the venerable Campagnolo who told me that 1980s-era Super Record were meant to modulate speed, not stop on a dime. The thinking, such as it was, had concluded that too powerful a brake would spray havoc through the peloton with crashes caused by overreactive riders braking too hard. Shimano hedged its own bets on brake power with its Servo Wave insert in many mountain bike brake levers. Servo Wave flattened the brake power curve, meaning the harder you pulled, the harder you had to pull to increase braking power. (Servo Wave made a reappearance in hydraulic discs in a way that makes great sense: initial pad movement closes the distance to the rotor with relatively little lever movement and then the Servo Wave slows pad movement to allow more appropriate brake power and modulation. The design helps prevent brake drag.)

This season, for the first time in my life, I believe that between my gravel riding and my mountain biking, I’ve actually ridden more miles on dirt than I have on pavement. No matter what bike I’m riding, no matter where I’m riding, any brake that gives me less braking power than I’d like for the conditions at hand will frustrate me. I end up riding slower.

I hereby submit a braking absolute: in the quest for speed, braking as late as possible and as hard as possible without breaking a tire free is the goal. I don’t want to brake any sooner than I absolutely have to and my ability to let the bike run, no matter what the terrain at hand is. If I know I can get the bike under control in an instant, I can actually release the levers at times. The longer my sense of stopping distance, the more likely I am to just drag my brakes out of self-preservation. It’s the same as fat, dumb and stupid: no way to go through life. (Apologies to Dean Wormer.)

Which brings me, more than less, to the Deore XT 4-piston brake released over the winter. I’ve now had a solid four months of riding it on trails I know intimately. I’ve been running it with 180mm rotors.

Shimano’s website says that the new 4-piston brake increases braking power over the 2-piston brake by just 10 percent. I trust Shimano to tell me the truth about their products; their history is strong. However, I flat-out don’t believe this claim; I’ll get to why soon enough.

The 4-piston brake uses a notably larger pad than it’s 2-piston sibling as well as a different hose and banjo bolt, though the lever is exactly the same. While I’ve seen some 4-piston brakes that feature identically sized pistons, on these the forward piston is 17mm in diameter while the rear is 15 mm in diameter. You can buy just the caliper or the caliper with pre-bled hose and lever. My favorite among the purchasing options? That you can purchase just one brake.

You may have noticed that I didn’t say that a brake can’t be too powerful. I argued that as long as you weren’t breaking a tire free, that any brake that allowed you to brake later and harder was better. That leads me to my one caveat regarding this brake. While Shimano’s web site claims that the new brake is 10 percent more powerful than the 2-piston version, my own riding and comments made by colleagues leads me to think this brake is more like 20-25 percent more powerful.

What I found was that on steep terrain the rear brake was just too powerful. Even on lesser grades I found myself skidding in turns. And I really don’t like tearing up trails.

For me, the answer was to go back to the 2-piston brake in the rear and leave the 4-piston in the front. Now that setup is terrific. So often I feel like I can’t possibly favor my front brake enough, the higher power of the front break doesn’t leave me feeling like I’m only using the front brake. There’s something from my childhood that freaks out if I’m not using the rear brake some. The event in question involved a flying 14-year-old boy.

For bigger riders who go through pads quickly, these brakes would be a wise investment. Anyone racing Clydesdale would understandably want both front and rear, I suspect. Also, riders who have really long descents (I’m looking at you, Park City), these will do a better job of disspating heat. My descents aren’t so long, but they are steep enough to require all the power. All of it.

Online, the caliper alone goes for $125-ish, while with lever it’s going for more like $150.

I’ll keep saying this: to go faster, you have to increase control in a way where you are imparted a sense of confidence.

Final thought: With a brake this strong, you’ll find out how well your tires grip.

 

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6 comments

  1. Don Palermini

    I had to read all the way through to see why the photo (two-piston) was at odds with the headline…

    The way most manufacturers deal with ‘too much rear brake’ isn’t by reducing number of pistons, but by reducing the rotor size. On mountain bikes, it’s not uncommon to have a 180 front paired with a 160 rear (or 200/180) in order to facilitate the perception of equivalent braking. While your novel approach is ostensibly similar in its results, having to think about two different brake pad specs (which tend to be replaced much more frequently than rotors) is just too much for most folks. That said, I know people who run metallic pads in the front and organic in the rear, the thinking being that metallics are ‘grabbier’ (more powerful) and the organics more incremental (modulate-able). Many routes to the same destination.

    On my trail bike I’m running XTR four-pistons with 200mm discs and metallic pads front and rear, and I love the fade-free, one-finger, consistent feel. I guess I’ve trained my rear brake hand to go a little gentler on the lever as I rarely skid unintentionally. While I’ve had many two-piston brakes that I’ve liked very much, I find that the more powerful fours also really help reduce arm pump, and hand/wrist fatigue…just so much power for so little effort.

    To your point, the meatiness of a tire knobs plays a big role in how quickly and controlled your stopping/speed control is.


    1. Author
      Padraig

      I had screwed up on the photos and not all of them loaded as they should. So there’s that.

      You bring up a terrific point, Don; thanks for being part of the conversation. (Don works at Santa Cruz.) Granted, product managers will deal with this issue differently than riders will in the aftermarket. And running different pads or rotors will accomplish much the same goal, and either solution is arguably less expensive than buying a new brake.

  2. George Mount

    Braking is for slow riders;) A set of $35 Dia-Compe calipers with slippery grey pads is all you need (when I weighed nothing).

    1. scott g

      George, a set of Campagnolo Delta speed modulators is in the mail.

      For those who passed AP geometry in school, a set of Paul Touring cantilevers
      can be set to lock the front or rear at will.

  3. Lucien Walsh

    4 pots up front with big rotors, 2 pots in back with smaller rotors. Anyone with track time in a BMW M (or any performance car worth its salt) will be well familiar with this approach.

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