The RX 400h and the RX 330 look more alike than different, but there are some subtle styling differences. Among them: a new front bumper for increased cooling, a new grille, new fog lamps, new tail lamps with LEDs instead of traditional incandescent bulbs.
The RX 400h also gets specific 18-inch wheels. The wheels are 7 inches wide and the tires are designed to provide grip in corners rather than offer low levels of rolling resistance. This says a lot about the intent of the RX 400h. Lexus could have improved fuel efficiency further with hard, low-grip tires, but chose to enhance handling instead.
The RX 400h uses the fourth generation of Toyota's hybrid system, which it calls Hybrid Synergy Drive, and each generation has been faster and less expensive than the previous. Three electric motors draw on 30 modules of nickel metal-hydride (Ni-MH) batteries. Clever engineering has resulted in efficient packaging of the batteries, which are split into three groups housed largely under the rear seats.
The hybrid powertrain adds just 300 pounds to the curb weight. That's not an insignificant amount of weight, but it's an impressive engineering achievement, and most of the weight is mounted low in the vehicle. Lexus increased the rigidity of the chassis to manage the additional mass. The Lexus RX and Toyota Highlander models are built on the same platform (with modifications) as the Toyota Camry and Lexus ES 330 sedans.
The RX 400h offers the same high levels of comfort found in the RX 330 plus a few notable additions. Brushed-aluminum accents lend a contemporary look. Also, the instruments have evolved: In place of a traditional tachometer, there's an illuminated meter on the left that displays the level of power generated by the hybrid powertrain. The driver can also monitor the gas-electric power distribution on the multi-information display or on the optional navigation system's seven-inch touch panel display.
The cabin is luxurious and inviting. The leather is soft and slightly bunched. Getting in is easy, with no need to either climb up or duck down. The front seats are positioned off the floor at a comfortable chair height and are snug and supportive. Foldable armrests on both front seats provide additional comfort on longer trips. The center console slides forward and back, allowing room for a purse between the front seats.
The instrument panel has three large round gauges. The center dash area is framed in metallic-looking plastic topped with a pair of air vents. The center stack is dominated by the seven-inch display. This screen is used for climate control and trip computer functions, as well as displaying the outside temperature and clock (with alarm). It's also used by the optional navigation system and rear-view camera. The camera is automatically activated when the transmission is shifted into reverse. You can't drive backward by watching the screen, but it's very useful for checking for obstacles that are difficult to see from the driver's seat. The system includes Bluetooth and voice activation. The downside to all this integration is that you have to press two buttons to change the fan speed rather than one. Also, the trip odometer is hard to read. Lexus dealers can program the default settings of many of the functions, so be sure you have them tailor automatic door locking and other features to your preferences.
Audio controls are at the bottom of the center stack. The radio has big knobs for volume and tuning, that are easy to use. The Lexus premium audio is a 132-watt, eight-speaker system with AM/FM/cassette with six-disc in-dash CD changer. The optional Mark Levinson audio system features 11 speakers and 210 watts.
The shifter for the CVT automatic is located on the center dash and follows a mechanical zigzag pattern to make sure you only move it one position at a time. We found it made shifting between reverse, drive, and the lower gears ponderous when we were in a hurry.
The rear seat is contoured for two, though it has belts for three. There's a folding center armrest with cup holders and storage. The rear seats fold forward 40-20-40, the center section providing a long, narrow space for skis, shovels, and fly rods, while still allowing four people to ride in comfort. There is no third-row seat for the RX.
Folding the rear seats down reveals 83.9 cubic feet of cargo space, more than a BMW X5, Mercedes ML350, or Infiniti FX, and just slightly less than an RX 330. The rear seats don't fold perfectly flat, however. The battery packs are housed under the rear seats.
Driving the Lexus RX 400h is quite similar to driving the RX 330. It's smooth and sophisticated, powerful and responsive. Starting out is a bit different, however.
Twist the key and everything on the dash lights up, but there's no sound of an engine starting, only silence. Slide the transmission lever to drive and you can pull silently away on electric power. This is not at all intuitive at first because we're all accustomed to hearing and feeling an engine running before shifting into drive. Shifting into drive when there's no sound, no vibration is a new experience.
At low speeds, the RX 400h is perfectly content to operate in electric-only mode. It's quiet, and you begin to hear things that are normally drowned out by an engine. We found this interesting and enjoyable. It will run in this silent mode in stop-and-go commuter traffic, eliminating the noise and pollution that the cars around you are putting out. The RX 400h maneuvers silently through crowded parking lots as well, where pedestrians often will not hear you coming and therefore won't always get out of the way. Toyota's hybrid system is an electric motor assisted by a gas engine, while Honda's system is a gas engine assisted by an electric motor.
The gas engine starts whenever it's needed to supplement the electric motor. Step hard on the gas pedal and the V6 kicks in quickly and seamlessly. You can barely hear or feel when this happens. It works exceptionally well. All the components work in concert most of the time.
The 3.3-liter V6 is basically the same engine as the one used in the RX 330, but it's modified and tuned to work with the electric motor. It's set up for the on-demand instant restarting used by the hybrid system. Unlike the RX 330's engine, the engine in the hybrid does not use the variable-valve setup because it's not needed and takes up space. There's no starter, no alternator, and no serpentine belt to run all that stuff.
The RX 400h enjoys a 67-percent edge in fuel efficiency over the RX 330 in the EPA's City cycle, earning 30/26 mpg City/Highway. Its 28 mpg EPA Combined rating is comparable to that of the average compact sedan (27.6 mpg); average for SUVs in this class is 15.1 mpg. Lexus says fuel economy is seldom an important consideration for SUV shoppers but that many buyers later become unhappy with the thirstiness of their SUVs after owning them.
More impressive is the absence of environmentally harmful emissions. The RX 400h is rated as a Super Ultra Low Emission Vehicle in California or Tier 2, Bin 3 in other states, confusing designations that describe some of the most stringent emissions ratings in the industry.
But what surprised and delighted us was the acceleration performance of the RX 400h. Stand on the gas and it takes off quickly, whether from a standstill or when cruising. Lexus says the RX 400h can accelerate from 0-60 mph in 7.3 seconds. That's a half-second quicker than an RX 330 and comparable to the Mercedes ML500, which uses a thirsty V8. Lexus says the RX 400h powertrain can generate 3,500 pound-feet of torque at launch.
The RX 400h cruises happily at speed out on the highway and there's plenty of reserve power on tap. When we caught a slower car on a two-lane road, we checked to see it was clear, pressed the accelerator to the floor, and were able to make a quick and easy pass. Safe, quick passing performance was important on Hawaii's Big Island where passing opportunities were limited. Lexus says it takes the RX 400h just 3.4 seconds to accelerate from 30 to 50 mph, at least a solid second quicker than the competition. We were sometimes able to catch the system off guard, however. While coasting down a hill we suddenly nailed the throttle, not a move the car seemed to expect, and there was a momentary lag before the power kicked in. For the most part, though, the RX 400h drives like a powerful and sophisticated SUV.
If we were to nitpick, we'd say it drones a little under light throttle and sound it makes under acceleration isn't entirely pleasing. Also, there's a small amount of torque steer, or something that feels similar to torque steer: Pull up to a stop sign, stand on the gas and make a right turn, and you'll feel a slight tug on the steering wheel or a resistance to turning. But all this amounts to nitpicking and the description of it sounds much worse than the reality.
The RX 400h glides along like it's on a cloud on smooth pavement. The ride is firm but damped. You know when you're on a rough road but the ride is not harsh. The electric steering works perfectly. The steering system uses electrical signals rather than hydraulic fluid and is speed-sensitive, boosting power assist at low speeds for effortless parking. The RX 400h felt composed and responsive on narrow, winding, bumpy roads in the back country high above the Kohala Coast.
The RX 400h was not designed for serious off-road use. The regular RX 330 isn't exactly an off-road vehicle, either, but it handles gravel roads just fine. The RX 400h, on the other hand, should stick to the pavement or risk damaging the hybrid drivetrain.
Slippery surfaces, however, are no problem. The electronically controlled all-wheel-drive system should work very well on wet pavement, snow and ice. One of the three electric motor generators (known as MGR) drives the rear wheels whenever they're needed for improved traction. This electric motor can deliver up to 650 pound-feet of torque to the rear wheels at launch.
The RX 400h also boasts a new generation of vehicle stability systems that are as complex as the gas-electric drivetrain. Vehicle Dynamics Integrated Management, or VDIM, goes well beyond conventional traction and stability controls that simply react to challenging conditions. Instead, VDIM anticipates vehicle instability and makes corrections to stabilize the handling. At the same time, it allows the RX 400h to achieve higher dynamic capabilities.
For the most part the brakes feel normal. That's impressive given that every time you use the brakes they recharge the batteries using a process known as regenerative braking. The brakes on the earliest hybrid cars felt strange. Not so on the RX 400h. The only thing about them we noticed was that it was a little more challenging to modulate the pedal for smooth stops at parking lot speeds.
The 2006 Lexus RX 400h comes as one well-equipped model. It is the premium model in the RX series, adding numerous standard features that are offered as options on the RX 330. The RX 400h comes standard with electric all-wheel drive and all the powertrain features mentioned in this article.
The list of standard features is long: Regency leather interior trim, automatic dual-zone climate control, premium audio, cruise control, automatic headlamps, 10-way power driver's seat, eight-way power front passenger's, leather trim for the steering wheel and shift knob, AM/FM/cassette/6CD stereo, and a power rear liftgate.
Options include DVD navigation with back-up camera, Bluetooth and voice activation, Mark Levinson premium audio with 11 speakers, adjustable front seat heaters, dynamic laser cruise control, DVD rear-seat entertainment.
Safety features include side curtain airbags designed to provide head protection for front and rear outboard passengers. Other supplemental restraint systems include advanced front airbags for the driver and passenger, a knee airbag for the driver, and side-impact airbags mounted in the front seats that are designed to protect the torso, abdomen and pelvis, all of which are important for things like walking. The hybrid system is designed to shut down whenever sensors detect a rollover to reduce concerns from emergency crews about high-voltage power. Also, the fuel tank is much thicker and encased in metal to protect it from damage. All-wheel drive and the sophisticated electronic stability control system (VDIM) are standard, which integrates anti-lock brakes, Brake Assist, traction control and other dynamic safety features. The adaptive front lighting system aims the High-intensity discharge headlamps to illuminate corners as the driver steers into them.