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Driving Steer-by-Wire in the Lexus RZ

by Ron CoganMarch 23, 2023
Driving the steer-by-wire Lexus RZ with its aircraft-like steering was easy. Much easier, it turns out, than driving a Saab with a sidestick controller.
Illustration of Lexus steer-by-wire system.

There I was, doing my best to pilot a car around a test track in Sweden without the aid of a steering wheel. My job in this 1992 exercise: Negotiate the twists and turns ahead in an experimental Saab 9000 equipped with a steer-by-wire system and an aircraft-like sidestick controller, similar in concept to that used in Saab fighter jets like the JAS 39 Gripen.

The first few passes around the track were focused and intense, the car jinking far too actively in response to the inputs interpreted from my painstakingly measured efforts with the controller. I was clearly on unfamiliar ground here, quite literally and figuratively since this was my first time on this Swedish test track. But I was determined to get this right, and eventually I did, gaining a sense of the steering and confidently working the stick to turn into a curve, find the apex, and power out smoothly. Then my right-seat observer, a Saab tech with keyboard and display screen in front of him, adjusted sensitivity settings and the car was jinking again. Ahh…part of the learning process.

Lexus RZ Steer-by-Wire

Segue ahead some 30 years – quicker than Tom Cruise graduated from piloting Top Gun’s F-14 Tomcat to Top Gun: Maverick’s F/A-18E Super Hornet – and I’m in an auto-aircraft setting once again. This time I’m in the driver’s seat of an electric Lexus RZ test car equipped with advanced steer-by-wire technology, pondering the steering yoke in front of me.

Coming but not yet available, the steer-by-wire system in this Lexus was calling to me, offering an opportunity to pilot this car around a cone course where expectations were reasonably high that some of the orange pyramids ahead would be sacrificed to the cause, at least initially. But I was not about to repeat my experience with the sidestick controller those many years back, no sir. This would be different.

Lexus steer-by-wire steering yoke.

More Than Just a Yoke

Unlike Tesla’s addition of yoke steering in some Model S and Model X variants, a move that has reportedly caused some driver difficulties during tight turns, Lexus has given this much more thought and a serious dose of elegant engineering. For one, Lexus doesn’t just swap out a round steering wheel for a cooler-looking yoke. In a simple swap, a yoke makes tight turns requiring hand-over-hand steering more of a challenge. However, the yoke in an RZ is not simply a swap, but rather an integral part of a sophisticated steer-by-wire system.

In its steer-by-wire system, there is no mechanical connection at all between the yoke and the car’s rack and pinion steering. It’s all wiring and software backed up by triple redundancies. Software interprets steering input at the yoke and delivers this information to a motor controlling the pinion gear, steering the wheels. What’s important is that the system is speed sensitive and smart, providing a continuously variable steering ratio depending on driving conditions and inputs. The result is confident driving with much less steering wheel travel required than one might expect. Plus, no hand-over-hand steering needed ever, even during very tight turns. Driving this system did require dialing in to its operating nuances, but I figured this out quickly and no cones were harmed during testing.

Lexus RZ electric car.

Auto-Aircraft Tech

As I wrapped up this day’s steer-by-wire mission, I reflected on yet another auto-aircraft memory from years past. Back in the 1990s when GM introduced its swoopy, teardrop-shaped EV1 electric car, the automaker shared that the car’s groundbreaking 0.19 drag coefficient was the same as an F-16 Fighting Falcon, wheels down. The aircraft reference wasn’t surprising since GM had acquired Hughes Aircraft a few years earlier and the automaker was benefiting from a huge aircraft/aerospace brain trust. PR being what it is, we’re not sure if the F-16 aerodynamics comparison was actually accurate but it sure sounded impressive, and it gave us a good point of reference as to how slippery the EV1 really was during the time.

In the ever-changing realm of advanced vehicles and their affinity for aircraft and aerospace tech, what’s next on the agenda? I’ve already experienced Tesla’s “autopilot” and other automakers’ advanced driving tech so check that off the list, until newer iterations come to the fore. I have also driven blindfolded in a test environment during the early years of autonomous driving development…but that’s a story for another time. Maybe a flying car? I think I’ll wait on that.