Oct 132011
 

The Driving Experience – MR20DE and CVT in the Real World

In the Sentra, the CVT is responsive to the well-calibrated throttle input. The rubber-band feel is greatly diminished. But for those foreign to CVT operation, they might still complain about the “slippery clutch” sensation under hard acceleration.

For those acculturated would enjoy its smoothness and always in the right gear attribute. We don’t have to worry about how the kickdown would jerk the passengers around. We do wish for the 6-spd manual mode features in the Altima, Maxima, and Juke to allow more control.

The engine has good off-the-line acceleration; it gets up-and-go without any drama. It generates sufficient low end torque to slightly chirp the front wheel under hard acceleration from a stop. Noise, vibration and harshness are civilized 90% of the time. As the engine approaches its redline, it becomes more coarse and rough in sound which are typical Nissan characters.

This powertrain combo allows the car to drive like a car with bigger engine. And the driving experience is stress-free. It also moves effortlessly in urban streets and crowded Los Angeles freeways. In translation, this powertrain can propel the Sentra from 0-60 in mid-8 seconds and quarter-mile come high 16 seconds later. Although these are no 370Z performance, but they are comparable to the Sentra’s competitors.

During our ~900 miles test route from San Francisco Bay Area to Irvine, CA, our observed average was 30 mpg which was in line with EPA’s 26 City, 34 Hwy and 29 combined mpg rating.

Suspension – Does semi-independent mean the same as semi-rigid?

The unibody Nissan “C” platform is supported by independent struts in the front and by torsion beam suspension in the rear. Stabilizer bars are utilized in the front and rear, 23mm and 22.2mm, respectively. The torsion beam setup is vastly used in Sentra’s competitors: Chevrolet Cruze, Honda Fit, Hyundai Elantra/Kia Forte, Suzuki SX4, Toyota Corolla… just to name a few.

Torsion Beam Suspension

The common perspectives for the use of torsion beam suspension are generally negative. However, they typically come from petrolheads who actually understand what it is, and by majority in pure performance handling point-of-view. To the ordinary that judge a car by its trunk volume, the torsion beam is simply another component in the car. To them, the beam’s simplicity, rigidity, less cost to manufacture and assembly that eventually result in opening up the trunk to swallow their junk outweighs its limited toe and camber adjustability and freedom of articulation – not that they really know what they are.

But is independent rear suspension (IRS) really necessary for the car in a segment that meant for taking you from point A to B? The answer is: IRS is nice to have but not a necessity if a torsion beam setup is properly designed. The torsion beam is designed to twist slightly. This deflection allows the right-and-left wheels to move independently to some degree. Therefore, the torsion beam system can be considered as semi-independent system which is good for relatively smooth road surface like what you typically encounter in your day-to-day commute.

Nissan’s history in beams
The current torsion beam setup is much simpler than the multi-link beam setup Nissan used in the past. The torsion beam is only connected to the chassis at two points. The integrated trailing beams are mounted to the rigid beam brackets at the bottom of the rear passenger floor that provides both lateral control (side-to-side axle movement during cornering) and longitudinal control (straightline).

In comparison, the multi-link beam consists of a more cumbersome lateral link similar to Scott-Russel lateral locator link. Functionally similar to a panhard rod, the lateral link is a second member connecting the torsion beam to the chassis to provide lateral control. This link is cleverly designed by Nissan to reduce unsprung weight and some of the shortcomings in the original Scott-Russel design. The Multi-link Beam’s longitudinal control is provided by the integrated trailing flange that is mounted to the weaker beam brackets and bushings at the bottom of the rear passenger floor.

The torsion beam design has made the beam brackets much stronger to take on higher lateral load without the need for the lateral link. The beam brackets and bushings are the gate keeper for proper handling in the torsion beam setup. The geometric design of the beam movement dictates the roll steer. As the beam moves through the suspension travel, the geometry would allow the beam to point to the direction of the turn to induce roll understeer, which in effect allows the rear to rotate less as the body rolls resulting in gradual, easy to maneuver understeer.

Compared to the B15, the torsion beam allows for greater negative camber in the rear; one-half of a degree is gained in the B16. The coil springs and shock absorbers are now mounted separately. The shock absorber mounting angle, and placement at the far end of the beam in the B16 enhance anti-squat geometry, lateral control, further reduce intrusion in the trunk space, and increase negative camber as suspension travel shortens.

Braking

Stopping mechanism comes from 11.02- x 0.94-in vented discs front and 9.0-in drums in the rear. It is equipped with four-channel Anti-lock Brake System (ABS) and Electronic Brake Force Distribution (EBD).

The single-piston floating front calipers are capable to halt the Sentra from 70mph in 200 ft. The brake pedal has the modern cars’ lightness. Fortunately, the pedal is easy to modulate and provides sufficient feedback. The Bosch supplied ABS is rough and unsettling which explains the fairly lengthy braking distance.

Ride and Handling

On the ground, the contact patches come from a set of P205/55R16 Bridgestone EL400-02 standard touring all-season tires on 16- x 5.5-in steel wheels with our much hated hubcaps. The EL400-02s are the norm for original equipment but Bridgestone will have a hard time selling them retail. The EL400-02s have been around since 2006. There are so much better tires out there with lower retail price. On the Sentra, the EL400-02s have very low noise level and offers stable handling and smooth ride.

Putting all the above theory aside, it can’t really out handle or be as mod friendly as the B13 SE-R. During spirited driving in the twisties, its tall driving position exaggerates the body roll. The fact is that the body roll is properly controlled by allowing the suspension to do its work since the B16 has much stronger platform. Thus it is easy to explore its handling limit as natural mild understeering is the result and is accompanied by heavy front tire squealing under quick change of direction. On the spec sheet, the Sentra generates 0.79 lateral g-force in skidpad and 64.3 mph in the slalom.

In comparison to its little brother, Versa, the Sentra has the reluctance to turn, feels more stubborn and less agile. Perhaps our handling evaluation might not truly depict its handling characteristics since our particular tester has alignment problem – it pulls to the left quite severely.

During urban commute, pavement imperfections are nicely absorbed based on our stiff suspension calibrated backside. To ones who can only reference softness by their ultra soft mattress, they might judge the Sentra as a bit harsh or bobbles too much. The rear suspension however has the tendency to visit the bumpstops over speed bumps.

The feedback and road feel through the steering wheel is average for being an electro-assisted unit. It weights appropriately and has natural ratio of 16.4:1 with 2.9 lock-to-lock turn and 35.4 ft turning radius. The 0.35 coefficient of drag does hamper its straightline stability at freeway speed under crosswind conditions.

Interior

The instrument panel layout is very legible. Controls are well-placed and intuitive to use. The front seats are comfortable for long journey, accompany by a standard 160-watt 6-speaker sound system that offers crisp mid and deep bass. Although the Sentra is assembled along with the Versa, lower build quality and workmanship is noticed in the Sentra. Perhaps it is because Versa is a global product, and Sentra is for America markets only.

Compared to B15, rear legroom is now significantly improved by the 5.9-in increase in wheel base that only lengthened the overall length by 2.3-in, keeping parallel parking at ease. Passenger compartment volume has also swelled by increase in width and height of 3.2-in and 4.0-in, respectively. Trunk space is now 13.2 cu-ft, at 1.5 cu-ft increase. The Sentra has obtained NHTSA’s safety rating at 5 out of 5 stars for both frontal and side crash tests.

Overall Impression

Scoring System:
Powertrain Performance & Refinement
6/10

Handling & Ride Characteristics
6/10

Brake Performance & Feel
6/10

Comfort & Workmanship
7/10

Features & Technologies
6/10

Will I buy one factor
3/10.

My recommendation factor
3/10

Afterthought

Despite our love for Nissan and to show our unbiased nature, the Sentra might not be a car that we would recommend. Other lawns are greener is true here. Sentra’s competitiveness is fading in an alarming rate. Take a look at the 2011 Hyundai Elantra for features, styling and workmanship. Check out the 2011 Ford Focus for its Europeaness, handling and fuel efficiency. Consider Government Motor’s bail-out funded, Korean-built, Chevrolet Cruze for its direct injection turbo engine. The upcoming B17 Sentra would necessitate major innovations. End

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