Financial Ruin 101: Installing a Slopestyle MTB Gyro

Introduction

The slopestyle mountain bike is an unquestionably unique amalgamation of a bike. It inherits half its traits from a hardtail mountain bike and the rest from a dirt jump BMX bike, are increasingly difficult to find, and have a relatively bespoke use-case. However for the people who one day wish to own one, and for the lucky amongst us who already do, it’s clear that they are truly special bikes. However, their specialty comes with hefty drawbacks. Namely, sourcing parts for dirt jump and slopestyle bikes is relatively difficult when compared to doing the same for bikes of more popular disciplines such as enduro and downhill. For a year-long student-driven independent project at my school, I decided to combat this issue by fabricating one of these tough-to-find components myself. The part in question? A mechanical disk brake gyro.

What is a gyro, and why does one need it?

If you're reading this guide, you likely are already familiar with what a gyro is—if this is the case, feel free to skip to the next section. However for the uninitiated amongst you, allow me to briefly introduce what a gyro is, and why it exists in the first place. Traditionally, mountain bikes, road bikes, and gravel bikes use one of two types of brakes: mechanical brakes, typically found on older bikes and certain high end road bikes, and hydraulic brakes, which are becoming the standard for their reliability and overall performance advantage. The current state of hydraulic mountain bike brakes are quite good—they’re affordable enough for an entry level rider, require relatively little maintenance, and offer unparalleled stopping power. Essentially, they function by transmitting force from the brake lever through a fluid-filled hose to a piston in the brake caliper, which clamps the brake pads onto the rotor to slow down or stop the bike. For 99% of mountain bikers, this system works perfectly…however for dirt jump and slopestyle riders there exists a slight issue. Tricks are at the core of slopestyle riding, and many of these tricks such as barspins and tailwhips require the bike or handlebars to rotate. Thus, having a cable running from the disk caliper to the handlebars becomes an issue as it inhibits the ability for the bike and bars to properly rotate.

Mechanical disk brake caliper + Caliper

Note: A road/CX specific caliper works best as the cable pull ratio works best with the gyro.

• Avid BB7 Road (purchase here)
• TRP Spyre (purchase here)
• Shimano Sora BR-R317 (purchase here)

*As for the disk rotor, just get whichever one is compatible with your caliper.

Gyro Cables

Note: Both upper and lower cables are required. Essentially all BMX gyro cables will work, just make sure they’re long enough for your frame. For the top cables, purchase the shortest possible cables for the cleanest look.

• Odyssey M3 lower cables (purchase here)
• Odyssey M3 upper cables (purchase here)
• Shadow Sano upper cables (purchase here)

BMX brake lever

Note: Most BMX levers should work fine here, just get whichever one suits your preferences for look/feel. Depending on which type of upper cables your using, you might want to get a gyro specific one like the Odyssey M2 so that you don't run into any issues with the cables interfacing with the lever.

• Odyssey M2 Monolever short (purchase here)
• Shadow Sano medium lever (purchase here)

Gyro Rotor

Note: The position of the threaded holes on the plates are designed to work with a Kink Myriad rotor, however it may work with others since they’re all essentially the same.

• Kink Myriad (purchase here)
• Odyssey GTX-S (purchase here)

Gyro Plates

Note: Designing and machining these was the main focus of my project, and I’ve provided the CAD files below so you can make them if you have the facilities to do so. If not, you could either a.) have the parts made by a company like ProtoLabs or Xometry or b.) use the gyro plate kit from NC17.

• OFFAXIS custom gyro plates (CAD files available below)
• NC17 gyro top and lower plate (purchase here)

Tools + Miscellaneous

• Headset press
• Chain lube
• Cable cutter

For the gyro plates to fit correctly, your bike must have the following:

• Press in ZS44 headset cups. Not integrated headset cups. I used a Cane Creek ZS44/28.6 & ZS56/40 which works great, however any headset that has a ZS44 upper cup will work.
• Enough extra fork steerer tube so that the gyro has enough room for vertical movement. I think around 20mm extra is normally enough. You can check the photos in the steps below to see how much I have on mine.

The lower plate is held in place by the upper bearing cup, so to install it, you first have to remove that cup. To do so, take off your stem/bars + any headset spacers you have, and then slide your fork out through the bottom of the headtube. Be careful while doing this as the lower headset bearing will fall out as well. Make sure to take note of any components that come out during this process and note how they will reassemble. While I'm sure that some $300 specialty headset removal tool exists for use in bike shops, using a screwdriver wrapped in cloth and a sledgehammer works just as well and costs zero dollars. Essentially, all you have to do is turn your bike upside down and stick any long metal object (screwdriver, plyers, socket wrench, etc) through the head tube until it's touching the bottom side of the headset cup. I'd recommend using a towel or something over the metal bit so as not to destroy the bearing plate. Then, just hit it with a hammer a few times on each side until the cup pops out. The attached video above shows how this can be done @ around the 1:50 timestamp (video credit to https://www.youtube.com/@RadCyclist09)

After removing the upper bearing cup, you can slide that cup over the lower plate so that the top of the gyro plate sits about flush with the top of the bearing up. The fit should be slightly loose, and the two parts shouldn't have any friction. Next, sit the bearing cup back onto the frame and align the threaded holes on the gyro plate so that they sit on each side of the headtube evenly. Then, use a headset press to re-press the bearing cup into the frame—making sure that the gyro plate stays aligned throughout this process. If done correctly. the gyro plate should now be sandwiched under the bearing cup and have no play/movement whatsoever. This video by ParkTool explains how to use a headset press for press in headset cups. If you don't want to pay $20 for the tool you can either make one yourself with some threaded rod and nuts or use a hammer and some cloth to whack the cups into place (although this normally works pretty well, it is significantly harder to do with the gyro lower plate installed).

Note: If your frame doesn't utilize a press in headset (check out this site for an explication), then you will have to use drill-in gyro tabs. The rest of this process will still work though. This video (see here) provides an explication for how to drill gyro tabs on a BMX, however it's essentially the same steps for a mountain bike.

Since we had to remove the fork to install the lower plate, now is a good time to reinstall that so that we can arrange the headset stack, add the stem + bars, and the upper plate. Make sure that you put the lower headset bearing back on the fork so that it sits correctly once re-installed, and then slide the fork through the headtube. After doing so put the headset top cover and headset spacers back. Then place the gyro rotor over this upside down (see photos)—this is crucial as if you place it normally then the cable holes won't align. These gyro rotors are designed for BMX, which have smaller head tubes, so when they're used on MTBs (which have larger head tubes) they have to be installed upside down. The stem should then be able to sit directly on top of the upper plate with the threaded holes sitting evenly on each side. Finally, reinstall the headset top cap and make sure everything is sitting tightly and there isn't any play in the headset. This is also a good time to install your new brake lever onto your bars and attach the upper cables from the lever to the threads on the top plate.

Gyros work best with road bike or cyclocross specific brake calipers, so unless you already have one of those on your DJ/slopestyle bike, then remove the existing rear caliper and any cables + brake levers associated with it. For my build, I used an Avid BB7 Road caliper as it's widely used by pros on the FMB world tour, however any of the calipers listed in the materials section should work fine. Installing a road/CX caliper is essentially the same as installing an MTB one—just be mindful that you might need to replace the disk rotor as well. In that case, make sure you acquire and install the correct caliper mounting brackets. Once the caliper is installed, you can thread the barrel adjusters on the lower cables into the threads on the lower plate and connect the cable bits to the slots on the lower part of the gyro rotor. Then, route the cable to the rear caliper. There will probably be too much cable length, so you can remove the sleeve that surrounds the cable and cut it down to your desired length (enough that it will reach the nipple on the brake caliper). Be careful to not cut too much off as it can mess up your ability to correctly adjust and tension the gyro. I actually cut too much housing off mine so the cable doesn't sit super nicely. Luckily, these things cost like $8 so it's not a huge deal if you mess up a bit. Once the cable housing is cut, put it back over the lower section of the cable and attach it to the caliper (see photo). Push the cable through the spot where it's clamped down by a bolt and pull back on the caliper just a little bit so the pads squeeze in. Then clamp down the cable. This should be a good starting point tension wise, however you will likely have to fine tune this later.

MAJOR NOTE: I somewhat screwed up the design of the lower plate and didn't leave fully enough clearance for the lower cable barrel adjusters to thread into the lower plate. Because of this, I actually wasn't initially able to thread them in without them hitting the site of the frame (and thus not threading in). To remedy this, I used a belt sander to remove essentially half the length off the lower part of the barrel adjusters and a small hand saw + a vise to cut half the length off the threaded portion of the screw (see photos for detail). This certainly wasn't ideal and was a complete design mess up on my end, however there is a chance that this clearance issue won't be a problem on other frames. My Trek Ticket DJ has an especially wide/weird shaped headtube. Nonetheless, modifying the files shouldn't be too tough, and it's pretty easy to sand the bolt down as well.

Nice! You're all done...just kidding. Even though all the mechanical components are in place, there is still some fine tuning to do. There are seven points of adjustment that can be used to modify how the brake and gyro interact. You can tighten/loosen the following: The barrel adjusters on the lever, middle part of the upper cable, the two on the top and two on the bottom plates, and the caliper itself (see photos). Essentially this is just trial and error until you find the setup where the brake feels strong and snappy. On the Avid BB7 caliper (which is what I used), there's also an adjustment that moves the brake pads in and out, which is super helpful in getting the bite point just right. Making these micro adjustments can be pretty annoying, but with a little patience it should help the feel of the gyro a lot.

You did the hard work...so go and enjoy it. Show up to your local dirt jumps or skatepark and pretend that you're training for Crankworx slopestyle. Or (more realistically) visit your local pumptrack and just show off how cool your bike is and don't do any tricks. Either way, have fun doing so!