Toronto, Ontario - Without a doubt, the RX sport utility vehicle has been a success story for Lexus.

While some other manufacturers produce expensive "halo" cars to bring buyers into the showroom, where other products can then be introduced to the customer in a positive light, the RX has been the beacon that has attracted buyers into Lexus showrooms.

Last year, Lexus sold 4,857 RX 330s and RX 400h hybrids in Canada. The RX 330 accounted for 73 per cent of Lexus SUV sales (14 per cent were RX 400h) and 40 per cent of all Lexus sales in Canada. And for the first time since Lexus came to Canada in 1991, sales of all models broke through the 10,000 level.

In the U.S., 88,101 RX 330s were sold, for a combined total of 92,148 RX 330s.

Photo: Lexus Canada. Click image to enlarge

This is good news for Lexus of course, but equally good for Canada, since most RX 330s sold in North America were built at Toyota Motor Manufacturing Corporation's plant in Cambridge, Ontario. It is the only plant outside of Japan that builds a Lexus vehicle.

The Cambridge plant has been working at full capacity since the RX 330 was introduced in 2003, replacing the RX 300 that had been built exclusively in Japan.

With sales going so well, why tinker with a good thing? Because "Lexus believes firmly in the 'Pursuit of Perfection', so we are continuously looking for ways to do things better," says Kent Rice, Assistant General Manager, Quality Control Engineering at Toyota Motor Manufacturing Canada, the arm of Toyota that builds the RX in Canada.

Rice and his team identified 39 key changes they wanted to make. Five were required by regulations, but "34 are changes we made in response to what RX 330 owners told us they'd like to see improved," he says.

2007 Lexus RX 350 Ultra Premium. Photos: Lexus Canada. Click image to enlarge

Unless you look closely, particularly under the hood, you might not notice much difference between the RX 330 and the RX 350. Items like additional sound insulation in the floor, an invisible laminate in the windshield to reduce interior noise levels, and a quieter air conditioning compressor won't jump out at you. A new steering pump that improves steering feel might impress, but not unless you drive both vehicles back to back.

Buyers familiar with Lexus' navigation screen will immediately notice the much-improved graphics, thanks to the better resolution and clarity of VGA (Video Graphics Array) graphics. Rear seat passengers will be pleased with the larger, higher resolution nine-inch LCD screen for the optional rear-seat entertainment system.

Certainly the biggest change is a new engine, the 3.5-litre V6 that has been showing up in nearly all V6-powered Lexus vehicles, and many Toyotas as well, over the past couple of years.

This is a remarkable powerplant. Bigger and more powerful than the previous 3.3-litre engine, it also delivers better fuel economy. Horsepower increases from 223 to 270, while torque is up from 242 lb-ft to 251 lb-ft. Fuel consumption drops from 12.8 L/100 km in the city to 12.4 L/100 km. Highway consumption remains the same at 9.0 L/100 km; the combined rating is down from 11.1 to 10.9.

Photo: Lexus Canada. Click image to enlarge

The extra horsepower and torque should give the RX 350 better acceleration and a big mid-range boost for improved passing power. Lexus Canada had planned an inter-generational drag race during a Canadian media preview to prove the point, but the plan had to be scrapped when an uncooperative Mother Nature covered southern and eastern Ontario with freezing rain and snow.

But the conditions were more than sufficient to test the RX 350's all-wheel drive and active safety systems. I drove one of the test vehicles from Toronto to Ottawa after the event, a six-hour journey during which I encountered heavy rain, sleet, freezing rain and snow squalls, all happening at the freeze-on-contact temperature of -5 degrees Celsius. (See the accompanying images of the RX 350 after returning to Ottawa.)

Photo: Grant Yoxon. Click image to enlarge

Serious ice build-up on the headlights and windshield required frequent stops along major route Highway 401 to clear the ice … and regenerate the courage to continue. Even the RX 350's standard headlamp washers couldn't remove the build-up.

I can't count the number of vehicles I saw off the road that night. Complicating the trip was a continuously changing road surface - snow-covered, freshly salted, slush-covered and glare ice.

The RX 350 has a new five-speed automatic transmission equipped with an integrated transfer case and a new viscous-coupling-controlled, limited slip differential, replacing the previously all-electronic centre differential. Normally, torque is split 50/50 between the front and rear axles, but under slippery conditions, the limited slip differential directs more power to the axle with the most traction.

We found during our Traction 2006 event, all-wheel drive helps tremendously when accelerating from a standing start, but is not necessarily the answer when turning, avoiding obstacles or stopping. Here, anti-lock brakes, vehicle stability control (VSC) and, above all, good winter tires are essential for safe foul-weather driving.

And the RX 350 has it all. The Lexus moved away sure-footed and without incident on all surfaces. On several occasions hard braking and quick lane changes were required, all accomplished without hearing the bing-bing-bing warning of the stability control system, and, thankfully, without coming close to the 401 median. I had to induce the VSC into action (VSC uses throttle intervention and brakes to correct oversteer and understeer), which I did only once during a U-turn after leaving the highway to clear ice.

Photo: Lexus Canada. Click image to enlarge

That the VSC came into play only when forced says something about the overall stability of the RX platform, but it also speaks to the quality of the rubber under the car - in this case, Bridgestone Blizzak WS-50. But I should also mention that conditions were perilous and I maintained a speed ranging from 70 to 90 km/h for most of the trip. Those that encountered problems that night were often vehicles that had earlier passed me.

As it turned out, the weather deteriorated even more the next day, with high winds and white-out conditions across eastern Ontario. It was a bad day for driving, with two major pile-ups on freeways east and west of Ottawa.

Photo: Lexus Canada. Click image to enlarge

In conditions like that, caution is not enough. The best decision you can make is to just stay home. But when you find yourself driving when you'd rather be sitting at home in front of the fire, it is comforting to know your vehicle has as much safety gear as possible. So if the worst comes to pass, you might have a chance to survive.

The RX 330 equipped with side air bag curtains, standard equipment on the RX 350, received a top five-star rating from the U.S. National Highway Traffic Safety Administration for front and rear passengers in a side-impact collision. In a frontal impact, the RX 330 received five stars for the driver and four for the passenger. The U.S. Insurance Institute for Highway Safety gave the RX 330 its top "Good" rating for a frontal offset impact. Standard passive safety equipment includes multi-stage airbags for the driver and front passenger. The rate of deployment depends on the severity of the impact, passenger weight and the position of the driver's seat on the track. There is also a knee airbag for the driver, large side airbags in the front seats that protect the torso, abdomen and pelvis, and roll-sensing front and rear side curtain airbags.