Driving impressions: 2010 Lexus RX 350, RX450h

Elsewhere, editor Wayne Cunningham has covered the new styling and cabin features of the 2010 Lexus RX 350 and RX 450h. So I'll comment on the drivetrain and chassis changes.

Let's just say that, at Lexus, "The Relentless Pursuit of Perfection" is not merely advertising hype.

Lexus has obviously been doing something right with its RX, as the midsize luxury crossover is its most-popular vehicle, and the one that defines the midsize luxury crossover segment. But there was room for improvement in both the chassis and powertrain departments. The two previous generations had suspension tunings best-described as "middle-aged, middle-of-the-road American"--soft for comfort, and with plenty of body roll in even moderate cornering. Steering was a touch on the light side, too.

Maybe a generation growing up in sport-compacts is making a difference. Lexus does at least as much customer clinic research as anyone, and changes products accordingly. And the new RX has a much better suspension tuning than its forebears, for improved handling and a better driving experience with no reduction of comfort. The rear suspension change, from struts to double wishbones, may get some credit--as well as extra credit for less intrusion into the cargo area and so greater cabin space--but revisions in spring and shocks rates and careful matching of all suspension components and use of speed-sensitive electric power steering results in a vehicle that is as responsive as many a sports sedan, with very quick turn-in and minimal body roll even when requested to do an IS-F imitation. No, really! No harshness, no thumpiness, no fuss, no muss...and handling response is also a very important safety factor. The crash you can avoid is one you don't have.

Improvements in aerodynamics from the new styling and careful management of underbody airflow--those really aren't skid plates underneath the RX, that sheet metal is there for the same reason race cars don't have lumps hanging out underneath, air management--help reduce wind and road noise, and asphalt sheeting and plastic materials strategically placed and tuned to cancel out resonance at those spots help reduce road noise even more. Polyester felt fender liners eliminate pings from rocks thrown up into the wheel wells. Details, details...must be a Lexus.

And so the interior, in addition to being stylish, ergonomically wonderful, and comfortable, is also relaxingly quiet. The trackball-like controller for the navigation, information, and audio systems is the polar opposite of the counterintuitive devices found in German luxury cars. If you've ever used a computer mouse or trackball or video game controller, no explanation is necessary and no recourse to a 100-page manual.

Drivetrains of both the gasoline V6 RX 350 and gasoline-electric hybrid RX 450h have been upgraded. The 350 gets a bit more power out of its namesake 3.5-liter engine--five more horsepower and seven more pound-feet of torque--but that now goes through a six-speed automatic transmission. Lower first- and second-gear ratios improve acceleration, while closer third through sixth ratios and a higher overdrive in sixth improve driving characteristics and fuel economy. It's quiet and comfortable on the road, as expected. But when the road gets challenging or there is a need to change direction quickly, the new RX just follows orders, with no excessive roll or resistance to directional change.

More impressive was the RX 400h with the newest version of the Lexus Hybrid Drive. It's handling was, if anything, even better than the 350's, despite an extra 300 pounds of mass. The previous RX Hybrid had sometimes inconsistent and nonlinear throttle response resulting from changes in power mode. There was a noticeable jolt when the gas engine came on after being stopped at a light or in traffic, and the addition of electric motor assist during acceleration sometimes provided more power than anticipated by throttle movement. None of this was serious, or even as bad as the non-response of an old precomputer era "slushbox" automatic or long-lag turbo from the '80s, but it did preclude the Hybrid from being a true driver's vehicle.

Not any more. Because the thumps and jolts are gone. If anything, the Hybrid is smoother than its gasoline-only sibling. And noticeably more powerful as well as more fuel-efficient. X amount of pedal travel gets y amount of acceleration, consistently. No surprises.

What's changed? If the basics of the Lexus/Toyota hybrid system are the same, all details are next-generation and mostly lighter, smaller, and more efficient.

The engine is a derivative of the 3.5-liter V6 in the RX 350, but it runs on the Atkinson cycle (like the Toyota Prius), not the Otto cycle of the old RX 400h. That's more efficient, and further efficiencies come from new exhaust gas recirculation and exhaust heat recovery systems that allow quicker warmup and eliminate the need for fuel enrichment to cool the catalytic converter. The heat recovery system allows the engine to be shut off sooner after a cold start, and more often, too.

An improved flywheel damper is the secret to the smoothness of mode transitions in the system. A two-step torque-absorbing mechanism reduces shocks from engine start-up to a negligible amount and is the chief contributor to the RX 450h's driveline refinement.

Power for the hybrid is up, from a combined 268 to a combined 295 horsepower. That bests the RX 350's 275. Both come in front- or all-wheel-drive form, but AWD systems are different. That on the RX 350 is a new electronically activated on-demand system that is lighter and more efficient than previous mechanical systems. As before, the AWD hybrid uses a separate rear motor-generator unit to provide power to the rear wheels when needed.

The RX 350 goes on sale in February, with the hybrid following a couple of months later. Prices have not been announced at the time of writing. Expect to see the enhancements to the hybrid system in upcoming Toyota and Lexus hybrids as well.