2010 Lexus RX 450h First Drive

A More Efficient, but Much Heavier Hybrid RX

Published: 01/21/2009  - by Erin Riches, Deputy Editor

Our off-road driving route in the 2010 Lexus RX 450h takes us through a neatly manicured meadow bordered by Chardonnay vines. As we ascend a small rise, our right foot resists hypermiling protocol and the hybrid RX's new 3.5-liter V6 starts up, breaking the electric-only silence. Otherwise, the RX 450h shrugs off the adventure and delivers us to the winery's tasting room with nary a dirt clod on its 18-inch wheels.

Last year's Lexus RX 400h wouldn't have put up much fuss, either. But there are dozens of small changes that make the redesigned 2010 RX hybrid feel more at ease with the world.

It's anybody's guess if we'll all be at ease enough to buy luxury crossover SUVs once the 2010 Lexus RX 450h goes on sale in summer 2009. Lexus anticipates the new model will at least match 2008 sales, so expect to see 16,000 of your most environmentally aware friends driving to and from vineyards in this technology-laden hybrid SUV this year.

Putting the 450 in the Hybrid RX
You won't find a mathematical justification for the name change from RX 400h to RX 450h, but it indicates a switch from the old 3.3-liter V6 engine to Toyota's 3.5-liter V6.

The hybrid-specific, 2GR-FXE version of the 3.5-liter V6 resembles the revised V6 featured in the 2010 Lexus RX 350, but it has higher compression (12.5:1 instead of 10.8:1) and runs on the fuel-saving Atkinson cycle. Additionally, its variable valve timing operates only on the intake side.

The Atkinson cycle keeps the intake valves open during part of the compression stroke, so this V6 makes just 245 horsepower at 6,000 rpm and 234 pound-feet of torque at 4,800 rpm, while the conventional version of this V6 delivers 275 hp and 257 lb-ft of torque. In any case, this is a significant increase over the 3.3-liter V6's 208 hp and 212 lb-ft of torque.

Of course, the RX 450h also draws power from its 37-kilowatt, nickel-metal hydride battery pack to power the h-model's electric motors (a 123-kW electric motor for the front-wheel-drive RX and an additional rear 50-kW motor for the all-wheel-drive RX). The battery pack provides 50 hp, giving the 2010 Lexus RX 450h a rating of 295 hp total, up from the 268 hp of the RX 400h. Since torque loads are also higher for this 2010 model, there's now an oil cooler for the front transaxle, which houses two of the three electric motors, along with the planetary continuously variable transmission (CVT).

You'll notice that the battery pack is rated for fewer kilowatts in the RX 450h; the RX 400h's battery pack had a 45-kW rating. But, says Paul Williamsen, national manager of Lexus College (the sales training arm of the Lexus division of Toyota), this doesn't mean the batteries are making less power.

"As an industry, we have still not fixed on all the parameters that we are going to use in the future for rating electric traction systems," he tells us. "We elected last year to lengthen the time window over which we measure peak battery output. That 45-kilowatt number that we published in the past was actually based over a period of time of seven-tenths of a second. It's safe to say the battery is no less powerful than before; we're just rating it more conservatively." (Lexus hasn't disclosed the new time duration, though.)

In fact, Williamsen says the 2010 RX 450h actually gets more power out of its battery pack due to an improved cooling system for the inverter and converters — it's the same setup used on the Lexus LS 600h L.

More Efficient, but So Heavy
Improved inverter cooling is one of many changes that contribute to the RX 450h's better fuel economy. The EPA rates a front-wheel-drive 2010 Lexus RX 450h at 28 mpg city/27 mpg highway compared to 27 mpg city/24 mpg highway for a front-drive 2008 RX 400h. An all-wheel-drive RX 450h comes in at 28 mpg city/26 mpg highway versus 26 mpg/24 mpg for the previous RX 400h.

Other efficiency-enhancing measures for the h-model's powertrain include the addition of cooled exhaust-gas recirculation and an exhaust heat recovery system to the hybrid RX's 3.5-liter V6. This stuff is used on modern diesel engines to reduce emissions, but Lexus says it also provides fuel-economy benefits here. Lexus has also improved lubrication within the front transaxle and fitted various low-friction bearings.

With all these changes, you'd think the 2010 Lexus RX 450h would be getting 30 mpg, but like the 2010 RX 350, the hybrid RX has put on some serious weight.

The front-drive RX 450h weighs 4,650 pounds — an increase of 460 pounds over the RX 400h. Add AWD and you'll be driving around in a 4,810-pound RX 450h — up 445 pounds. As on the regular RX, you can trace the gain to a wider track and structural reinforcements to improve crashworthiness.

Nevertheless, Lexus claims the RX 450h won't be any slower than the RX 400h, which we have timed at 7.2 seconds from a standstill to 60 mph (6.8 seconds with 1 foot of rollout like on a drag strip).

Smoother and Quieter
And, indeed, during our tour of California's Napa Valley, the 2010 Lexus RX 450h gathers speed with the same rapid fluidity as the RX 400h. We also notice that the blending of the power sources is a bit smoother and quieter, particularly when the gas engine is shutting down or restarting. Perhaps this is the result of the two-stage mechanism to absorb torque that the Lexus engineers have added to the transaxle's flywheel damper.

The transmission incorporates hill logic this year, and there are several specialized driving modes, our favorite being the six-speed mode with manual shifting. The CVT's gearchanges are simulated, of course, but the added control is welcome on twisty downhill stretches of Highway 29 near Calistoga.

There's also an Eco mode, which helps you get better mileage by retarding throttle response and reducing air-conditioner oomph. It's livable in slow traffic on cool days, but will drive you nuts at any other time. There's also an EV mode that allows the RX 450h to run on battery power only, albeit for 1-2 minutes at 8-10 mph.

Stops and Steers Better, but Still Not Nimble
As we brake into tight corners, the transitions between regenerative braking and full mechanical braking feel less abrupt than in the RX 400h. We feel more in control when steering, too. The RX's new quicker-ratio electric power steering (EPS) unit provides a modest increase in effort levels as cornering forces build.

Still, the 2010 Lexus RX 450h is not at home on Highway 29. Its excessive weight is apparent when changing direction, and although it has the same double-wishbone rear suspension as the 2010 RX 350, it feels less agile. You can get a sport suspension with revised dampers, bushings and EPS, along with 19-inch wheels and P235/55R19 101V tires, but the benefits are slight.

When the road straightens, though, the RX 450h settles in and delivers a relaxed, serene ride that we simply can't fault.

Remote Touch Me
Aside from its different instrument panel and the battery pack under the rear seat, the 2010 Lexus RX 450h's cabin feels just like the RX 350's and offers all the same amenities. Slick technology like the mouse-operated, hard-drive-based Remote Touch navigation system is even more important in the hybrid RX, though, as it attracts a Gizmodo crowd that revels in technology for technology's sake.

If you spend your work days using a computer, the Remote Touch feels instantly natural. Not everyone works on a computer, of course, yet Toyota learned in focus groups that while the learning curve for Remote Touch is steeper than for a touchscreen, eventually users perceive it to be just as easy to use as the touchscreen.

You can vary the haptic feedback (er, sensitivity) of the controller just as you would with a regular mouse, and there are also volume settings for the cursor (which can be an arrow or a gloved hand) as it tracks across the screen.

The move from a touchscreen to a remote-control-type interface also has allowed Lexus to design a more shapely dash for the RX that spreads out before you instead of getting up in your face. So you no longer have the suspicion that you're driving around in a repackaged minivan with an expensive hybrid drivetrain.

Best of all, at least for Toyota, Remote Touch is cheaper to produce than a touchscreen. You'll eventually see it in all Lexus and Toyota products with a factory nav option.

End Game?
Although it's not any quicker, the 2010 Lexus RX 450h is a better vehicle than the RX 400h. It's a bit more fuel-efficient, and whether you're accelerating, braking or turning a corner, this hybrid RX is a touch smoother and more refined. It feels more like a normal luxury crossover SUV.

Yet the 2010 Lexus RX 450h's extreme poundage seems to be at odds with its mission of efficiency. Maybe hybrids will save us from steaming ourselves in CO2 one day, but not if they weigh 4,800 pounds apiece.

Edmunds attended a manufacturer-sponsored event, to which selected members of the press were invited, to facilitate this report.