This is the first turbocharged car Acura has ever made.   Honda has been a leader with small engines and this 2.3-liter turbo is no different.   The turbocharger broadens the power delivery quite a lot from the high-revving Acura TSX four-cylinder, although it doesn't smooth out the engine.   It is slightly quieter than earlier models and takes more effort to hear the turbo whooshing.  

It has no turbo lag and develops 260 pound-feet of torque, though at a relatively high 4500 rpm.   However, a sensitive throttle and fast-responding turbo conspire to keep the transmission busy with upshifts and downshifts on uphill grades, even when driving casually.   Put another way, if your right foot asks for a moderate increase in power and the boost gauge is down low, a gearshift will probably ensue.   Simply selecting S for Sport mode smoothes everything, just remember to shift back into the normal mode so the transmission will use top gear on the highway.  

In the Sport mode, the transmission obeys your manual-shift commands except when you downshift at an engine speed the system thinks is too high, or upshift at one it thinks is too low.   Then at least it tells you that it's rejected your input with a flashing light.   You can manually upshift and downshift in Drive as well, and after a few seconds of no manual input the car will revert to full automatic.  

In heavy stop-and-go freeway traffic, we found it difficult to accelerate smoothly.   It has a drive-by-wire throttle.   We have found many cars with this type of electronic system to have sensitive throttles, and adding a turbocharger seems to magnify the sensitivity.   You can manage the stop-and-go in an RDX smoothly, but its requires more concentration.  

Brakes are solid and offer good feel and progressive retardation, perhaps indicative of the system upgrades for 2010.  

A bigger flaw than a quick throttle or unsettled transmission might be the ride.   A front-seat passenger said she could feel every bump, especially on the freeway.   We could feel them too.   It was like a jolt over the freeway ridges or sharp speed bumps.  

Of course, this firmness in the suspension enables the RDX to perform like a sports car around the corners.   Acura boasts that it will out-corner a BMW X3, which was developed on the Nurburgring circuit in Germany and has a ride similarly biased to performance.   Potential buyers should include road surfaces reflective of their usual travel before deciding how much sport, or comfort, they want.  

We drove one RDX in California then spent a week in another in the Northwest, just in time for snow and ice.   We tested the ABS by slamming on the brakes going down a steep hill with hard-packed snow at 20 miles per hour.   The response was beautiful; it took a long time to get stopped, but we were able to steer anywhere we wanted, without sliding, while our foot was mashed to the pedal.   (In deep snow or dirt or gravel, you can actually stop quicker by locking the brakes, building up little dams in front of the tires, so ABS is not always a great feature in the snow.) We should point out that the P235/55R18 Michelin Pilot tires are considered high-performance all-season, meaning they weren't made for this sort of thing; all-season means three seasons, winter not being one of them.  

Then we went to a slushy parking lot, and tried to cut doughnuts at hard throttle, to test the VSA electronic stability control.   The RDX just turned in tight circles, without much sliding; it was quite amazing.  

A couple days later the slush froze into sheer, lumpy ice and we returned to the bottom of our steep hill.   We charged uphill, and it was fascinating to feel the all-wheel-drive work, and watch the readout on the instrument panel indicate with bars which of the four tires was getting the torque, based on how slippery it was under each tire at any moment.   The all-wheel-drive system, which can send 70 percent of its torque to the rear wheels, struggled for grip, its computer sensors playing the throttle and brakes on and off at four separate wheels at lightning speed, and we made it to the top.   This was very impressive, especially with those high-performance all-season tires that were never intended for dealing with such severe conditions.   With real snow tires, the RDX would be unstoppable in the winter, and we recommend a set for winter climates.  

In winter conditions, it's hard to beat a relatively light high-tech vehicle, with all-wheel drive, anti-lock brakes, electronic stability control, six airbags and xenon headlights, not to mention heated seats and heated mirrors.   Dedicated winter tires should keep you running with the plows.  

The EPA-rated mileage is 17/22 mpg City/Highway for the RDX SH-AWD.   We got 17.6 miles per gallon on premium fuel at an average of 34 mph running stop-and-go on the freeway and 80 mph when the traffic was less crowded, very unfavorable conditions for fuel economy.   We found the fuel mileage similar during around-town driving.   Fuel economy will likely be closer to that 22 mpg EPA Highway rating when cruising constantly at 55 mph.  

The new front-wheel-drive model doesn't handle quite the same around corners where you have your foot on the gas, such as mountain passes and many on-ramp clover-leafs, because it carries a higher percentage of its weight on the front wheels and has no rear drive.   On the plus side it is lighter and rates 2 mpg higher in all conditions.   The top two gears are taller, meaning lower engine speeds for the same road speed and quieter cruising.   While you may coax mid 20s out of it on the highway, fuel economy has never been the RDX's forte.  

Our choice is for the SH-AWD model with its superb all-wheel-drive system.   If it's economy you're mainly after, we'd recommend looking elsewhere.