I'd like to see the OPTION for an aftermarket hand brake as well. I ride lots of scooters (as well as motorcycles) and I'm accustomed to having the brake levers at finger's reach. It's an accepted motor memory because of the motorcycle standards all over the world.
The front brake lever (or at least the one on the throttle side) is particularly important in traffic because it's bio-mechanically faster for your fingers to reach that lever (~1-2 inches away) than it is to move your foot position to reach the rear brake lever (or the only/combined brake lever in the Ryker's case). Most riders can "cover" the front brake with a couple of fingers to further reduce reaction times... I do this over 90% of the time in the city, and it has saved my bacon more times than I can possibly count. Covering the rear brake is trickier because of your body position and weight distribution on the bike... covering the pedal means that you're likely RIDING the brake and not COVERING it... which is even more dangerous in traffic (e.g. brake light activated when it shouldn't be, so cagers don't get the visual clue if/when you REALLY slow down).
This is all academic for experienced riders, so I don't mean to lecture or condescend. However, the Ryker is marketed to newer riders (both young and old), that may not have that knowledge or experience. This is another of those deciding safety or usability factors to keep in mind about riding the Ryker. The simple fact of not having a brake to "cover" has already caught me somewhat unprepared a couple of times in Houston traffic.
As for the ISCI hydraulic master/slave actuator solution... it may be tricky to adapt to the Ryker because the brake reservoir, master cylinder, and related switches/sensors are attached to that sliding footpeg assembly. There isn't much clearance behind the side panel for the slave actuator to grab the brake lever. The second complication is the adjustable cam brake pedal pivot (adjustable up/down throw)... where/how to attach the slave actuator arm to the pedal regardless of the users' height selection becomes the dilemma. Spyder's don't have the adjustable brake lever throw, so there is a fixed point to attach the slave cylinder arm to activate the pedal.
The only way I can immediately see a solution, while keeping the full adjustability of the right peg/brake levers, is to put the new (handbrake) master cylinder inline with the existing master cylinder's output (with a check valve, before proportioning/distribution block, and ABS pumps, of course). Honda has used CBS (combined braking system) on their scooters for years... so it can certainly be done. However, that's not a bolt-on kit, and certainly not a good idea for warranty/safety claims because you're violating/modifying the brake system integrity outside of the manufacturer's design. So, hopefully someone else can think outside the box on that solution, or maybe Can-Am can design a factory-authorized (dealer-installed/certified) accessory to address the need/desire for a handbrake.
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QM