Acura's Super Handling
Honda's premium brand shows off its all-wheel-drive prowess.
No, SH-AWD is not the easiest to say, but it does explain what Acura has created. The system being used today had its start about 17 years ago when the AWD Honda FS-X concept was introduced at the 1991 Tokyo Motor Show. While that system is not quite the same as what's found on today's Acuras, it was the basis of the current advanced all-wheel-drive system designed not just to keep you going in slick conditions, but also to actually improve handling in any road condition.
To prove their ability of SH-AWD, Acura took us north of Montreal, Canada, to the Mecaglisse winter driving center and pitted its vehicles against some of the best systems in the industry. But before we get to the results of this faceoff, it's important to understand what makes SH-AWD different than other all-wheel-drive systems on the market.
SH-AWD—What Does It Do?
There are many all-wheel-drive systems available in the U.S. market, however they are not all created equal. A typical all-wheel-drive system will feature a front and rear differential with a center differential that can direct power to the front or rear wheels, depending on where traction is needed.
While this is very effective for straight-line acceleration, it has limitations in cornering. To compensate for this, many AWD systems are teamed with traction control and stability control systems to provide yaw control. When the steering wheel angle doesn't match the actual direction of the vehicle, these systems can apply braking to individual wheels to turn the vehicle in the desired direction.
Acura's SH-AWD solves this problem with "torque vectoring." This means that not only can up to 70 percent of the power be directed to the front or rear wheels, power can be applied to individual rear wheels. When cornering, the outer rear wheel can be accelerated up to five percent faster than the front wheels with 100 percent of the rear torque going to that wheel. The result is similar to 4-wheel steering, in that the rear wheels help to point the car in the right direction on dry or slippery surfaces.
We had the chance to experience this for ourselves and found the system to be quite impressive.
Acura set up three venues for the all-wheel-drive matchup. The Acura RL was tested on a circular skid pad with an ice surface covered in snow. A short snow and ice covered course with hills and sharp turns was used to test the RDX, and the MDX was driven on a longer snow-covered course.
All vehicles tested were shod with studless snow tires—the RL wore Pirellis, while the RDX and MDX were fitted with Bridgestone Blizzak tires. The competitive vehicles in each group used the identical tires as those on the Acura models.
When asked why the cars were not fitted with standard tires, we were told that the conditions were so slick that the cars became impossible to drive and the test would have had no value. The conditions on all three courses represented approximately 70 to 80% less grip than dry pavement.
One note about the competitive vehicles that Acura provided—while these tests were not suspect in any way, one needs to keep in mind that Acura was not going to bring any competitive product that performs better than their own vehicles. So while the Acura system appeared better than the competition in all three tests, that's not to say that there aren't other available all-wheel drive systems that would impress as much or more than the Acura system. That said, here is how the tests went.
Of these three vehicles, the Mercedes was the least manageable in the slick conditions. The 4matic system felt crude and car felt very heavy—I was surprised to learn that the Acura actually weighed more. Driving was very unpredictable, with power being cut to stop the wheels from spinning, then returning when unexpected. Even with AWD and ESP, we almost spun the car twice. In conditions such as these, the E-Class would be handful to control.
The Acura and Lexus were similar in their controllability, but the Lexus stability system was much more intrusive. The system provides an audible alert every time the stability control engages. It is possible that this alert can be turned off, but it is easy to imagine this sound causing additional panic to a driver who may already be in a difficult driving situation. However, the Lexus AWD system worked quite well, very predictable and manageable.
The RL with SH-AWD handled the skid pad quite well, with stability control intervention that was unobtrusive, yet you could hear it operating. We did experiment with turning off the RL stability system. The RL was still predictable, but considerably harder to keep on line around the course. This really showed how helpful the electronics can be in a very low traction situation.
We drove the X3 before getting into the RDX. BMW's X-Drive system worked rather well however the X3 tended to push out in the turns where there was a bit of a delay before the stability control brought us back into line. This was especially noticeable on a turn where the apex was also the top of a hill—as we accelerated out of the turn, we would slide to the outside of the course before gaining traction.
Another part of the course that showed a weakness in the X-Drive was a right turn up a somewhat steep, but short, snow-covered hill. While exiting the turn we floored the accelerator until we had traction, but power was cut by the traction control system and coming back on suddenly as we crested the hill.
Taking the RDX out on the course next, the most noticeable difference was that the Acura system keeps you on the desired line by engaging stability control much quicker than the BMW system.
But where the SH-AWD really shined was at the apex at the top of the hill. With the front wheels turned while exiting the corner, the BMW pushed out before its stability system used braking to direct the front end in the right direction. With Acura's SH-AWD system's unique ability to direct power to each rear wheel individually, power was applied to the outside rear wheel as we accelerated out of the corner pivoting the RDX into the direction we were turned. Rather than applying brake to a front wheel to keep us on course, power was applied to a rear wheel for a much smoother and more affective result.
The Acura also excelled at the short hill—power transitioned much smoother and we found the RDX didn't lose as much momentum as the X3. With the SH-AWD system, yaw can be corrected with a combination of power at the rear outward wheel and braking at the front, so less momentum is lost.
The X3 handled this course well, but the SH-AWD in the RDX clearly had the advantage. An interesting competitor to the RDX in this condition would have been the Mazda CX-7, which has very similar engine performance specs to the RDX.
As with the other driving venues, the long course was almost completely snow covered, with a few icy patches. The course was made up of tight turns, steep descents and ascents, and a number of simulated street situations, such as a left turn through an intersection and a stop sign on an icy road.
We drove the Q7 first, starting the course with a simulated left turn through an icy intersection, with the idea of driving through controlled but quickly, so as not to be out of the way of oncoming traffic as quickly as possible. Halfway through the turn we started pushing out towards the "sidewalk" and the quattro system applied brakes to the appropriate wheel to keep us in the turn. However this stopped our momentum at the same time, so while we stayed on line, we were momentarily stopped in the middle of the intersection.
Throughout the rest of the course, the Audi was very stable and predictable, easily maneuvering through the slippery turns. However the stability control was quite intrusive—when a wheel began to slip or the direction needed to be corrected, the braking to individual wheels was often quite jolting, yet it was very affective at keeping the Q7 pointed in the desired direction.
The Acura had a different issue when driving through the intersection. We were able to get through the intersection quickly, but while we were turning smoothly, the MDX would have hit the curb as it pushed out to the edge of the simulated road. In hindsight, accelerating strongly would have likely caused the rear end to pivot as more power was directed toward the outward rear wheel. However with the extremely slick conditions, this may not have had any effect on our trajectory.
The most noticeable difference between these two premium SUVs was how intrusive their respective traction systems were. Where the Audi system was very effective, it was very noticeable when it engaged. The Acura system was quieter and smoother, with course corrections coming from power application in the rear which required less braking to the accelerating front wheels.
Turns could be taken tighter with the SH-AWD, and there was no jolting or sudden braking as we felt in the Q7. We were able to carry more speed with the MDX, however that could also be attributed to the fact that we had learned the course by the time we drove the MDX.
While the MDX did seem to handle the course more smoothly than the Q7, both vehicles are quite capable in snowy, slippery conditions. The Land Rover LR2 would have been an interesting comparison in this particular test.
While Acura may not be the first name that comes to mind when thinking about high-tech all-wheel-drive systems, SH-AWD did prove to be quite effective in the extremely slick conditions in the Great White North.
All-wheel-drive systems from any manufacturer can be very useful when driving in wet or slippery conditions, but with the ability to direct power to individual rear wheels and actually accelerate one wheel faster than the others, Acura's SH-AWD provides improved cornering and handling in a way that no other manufacturer offers. At least for now.
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