Ride-By-Wire Technology: Is It Safe?

Cut the Cable! Let Ride-by-Wire Electronics Give You a Helping Hand

Triumph’s system shows how compact single-plate systems are, leaving more room under the tank.©Motorcyclist

The term “give it some gas” is misleading. Twisting the grip doesn’t squirt more gas into the engine—at least not directly. It simply admits a larger volume of air that then draws more fuel into the cylinder. Managing airflow is what the throttle is all about, and over the decades throttle technology has followed an interesting and cyclical path.

Very early carburetors used a simple butterfly valve to control airflow, and fuel delivery was passive. As air was drawn past various orifices, low pressure in the throat of the carb caused fuel to be drawn from the bowl, mixed with the air traveling past, and fed into the engine.

Over time, carburetor design evolved to better suit more powerful engines and, especially, those with greater dynamics. Simple butterfly-throttle carbs gave way to slide-throttle designs—where the twistgrip pulled a cable in turn attached to a sliding cylinder in the carb throat that acted as a throttle—and eventually to the so-called constant-velocity carburetor, which was a hybrid of butterfly throttle and vacuum-operated slide valve. The rider controls the butterfly, but intake vacuum acting on the slide valve regulates the amount of air entering the engine—this maintains intake-air velocity and helps keep the engine from bogging when you snap the throttle open. This characteristic was especially important as emissions regulations forced ever-leaner jetting.

Servo-controlled throttle plates (shown in gold) manage airflow to the engine.©Motorcyclist

By the early 1980s, fuel injection arrived in a form not unlike the earliest carbs: single-throttle plates for each cylinder (typically) with fuel injected under pressure at or near the intake port. And just as it happened with carburetors, injection eventually morphed to include a second set of throttle plates—not unlike the vacuum slide in a CV carb—for the purpose of improving throttle response and enabling ever larger throttle bodies to permit horsepower increases. If you think about it, both the CV slide and the twin-throttle fuel injection serve to interpret what you are asking the engine to do when you twist the throttle. So for as long as we’ve had CV carbs and dual-throttle-valve injection, we’ve given some control over to the computer.

The next big leap was ride by wire (RBW), introduced to the mass market by Yamaha in the 2006 YZF-R6. This technology is the culmination of what the enginners had been doing mechanically.

Why bother? Especially in a highly tuned engine, choosing throttle-body sizes along with fuel and ignition maps that permit very good rideability and big power potential represents a huge challenge. You want big throttle bodies for peak power, but those get finicky at partial openings. Wouldn’t it be great to have gaping intakes for power but have the intuintive, predictable power deliver you get from smaller carbs or fuel injection? Yes, and that’s where RBW shines.

How it works. In the most basic sense, RBW inserts a computer between your right wrist and the throttle plates. As you twist the throttle—perhaps we should start calling this something else, like a Thrust Request Device—the ECU takes into account engine speed, vehicle speed, gear selection, and other factors. It then decides how much to open the throttle plates based on a few assumptions of how much power you want. This is no longer a one-to-one relationship between your right hand and the throttle plates; the computer knows better and acts to keep power flowing smoothly. Also, for many years, bike manufacturers have used different fuel and ignition maps for each gear in an effort to tailor, usually by trimming back, power in the lower gears. No longer needed: RBW does this automatically, preventing, in essence, full power from ever reaching the rear wheel in the lower gears. What are the other benefits?

Taming power. Manufacturers can now build engines that would be difficult or perhaps impossible to ride smoothly without electronic aids. Traditional engine design separates the “sweet spots” of intake tract, exhaust system, valve timing, and other factors to keep the engine from being too peaky. With RBW, the peak performance can be maintained without rideability issues.

Ride modes. Not only does RBW offer the manufacturer the chance to make peaky engines act like locomotives and offer throttle response that’s smooth and intuitive, but that response can be further tailored. Most RBW bikes have multiple “ride modes” that combine different throttle-response maps and altered thresholds for traction control and ABS. (Some even allow you to reduce maximum power for, say, riding in the rain. Or lending the bike to a friend.) The sportiest modes have the sharpest throttle response, making the engine seem racy and potent. But the same machine can have smoother, more relaxed responses for touring, even duller (softer) throttle response for dodgy conditions, and still other modes optimized for off-road use. You simply couldn’t do that without RBW.

Cruise and traction control. One of the big gains from RBW is easy cruise control and very much improved traction control (see sidebar). Sure, there were cruise controls on non-RBW bikes, but this involved a servo motor opening the conventional throttle, which is a heavy affair with a certain amount of lag in the system. With RBW, the computer maintains a given speed by working the throttle plates directly.

Emissions compliance. RBW systems are better able to meet today’s strict worldwide emissions regulations while maintaining very good rideability. It’s no longer necessary to sacrifice throttle response or power to cut emissions.

Meeting license limitations. In countries where there are power limits for new riders, it’s possible to program RBW to limit peak power to meet regulations. KTM’s 1050 Adventure, not brought to the US, is electronically limited to 95 hp when the base engine is capable of nearly 150. There’s no need to build a new engine for this application; all the work is done by the computer.

Almost universal in cars, RBW has spread quickly in motorcycles, offering benefits for the manufacturer and the rider. Best of all, these are inherently flexible systems. When, for example, Yamaha got it wrong on the first FZ-09s, a remedy was as close as a factory-created “reflash” of the ECU to improve fueling. No need to change parts. No lengthy visits to the service department. Think about that next time you give it some gas.

Traction Control Version 2.0

With RBW, TC is much more flexible, smoother, and effective.©Motorcyclist

A key enabling technology, traction control (TC) has been refined for the last decade-plus. Dissolved to the basics, TC uses wheel-speed sensors to determine if the rear tire is rolling about the same speed as the front. If it’s spinning faster, the assumption is that the tire has broken loose and the computer in charge takes measures to reduce power and regain traction.

Early systems used a combination of fuel cut and ignition retard to reduce power. These are effective tactics but difficult to make smooth in transition; these early systems tended to be on or off, with the resumption of power happening some time after the initial reduction.

Eventually, the manufacturers figured out that reducing the airflow to the engine was an additionally effective means of trimming power, so systems like Kawasaki’s K-TRC use the secondary throttles to partly choke the engine, along with careful reduction in fuel and changes in ignition timing.

Ride by wire changes everything, though, because the primary throttle plates (the only ones in an RBW system) provide the best engine response. They can be used in conjunction with fuel/ignition changes to carefully moderate power to the rear wheel. With RBW, TC is much more flexible, smoother, and effective.

Is Ride By Wire Safe?

Yamaha has an additional mechanical linkage that can force the throttles closed in the event of an electronic failure©Motorcyclist

When you give command of the throttle to an electronic device, you want to know that the bike won’t go all HAL 9000 on you. No need to worry; there are myriad safeguards in place. For starters, modern RBW systems employ dual sensors at the throttle tube or wherever the rider’s commands are picked up. The computer compares the two signals and if they disagree will put the RBW into “limp home” mode. The same is true should the ECU see anomalies in other sensors, including those that tell the computer if the throttles are actually doing what they’ve been commanded to. If any number of critical sensors fall out of range or provide unexpected signals, the system goes into fail safe. Yamaha has an additional mechanical linkage that can force the throttles closed in the event of an electronic failure (see accompanying photo). That’s why some RBW Yamahas still have a traditional throttle spool and cables.

In limp-home mode, the bike will run at a fixed amount of very reduced power—think of it as a high idle—just enough to get you home or to the dealership safely. It might be possible to clear the fault by shutting down with the key and restarting, but a persistent problem should be diagnosed correctly and repaired. And remember that the RBW throttle servos are electrically driven, so snapping the kill switch will cause them to close as well.