Six Star Magazine Six Star Magazine Spring 2015 | Page 30

The strength of FWD is in normal driving

While RWD vehicles can perform at a

the available traction under hard acceleration

conditions, when the front wheels are needed

very high level when it comes to acceleration,

and when cornering. This characteristic

only for gentle power delivery and cornering.

there can be other challenges. In cornering,

gives the average AWD vehicle the potential

Under strong acceleration, weight transfer sees

RWD vehicles tend to oversteer, meaning the

to be more stable in all conditions.

the nose of the vehicle lift and this can lead to

back end of the vehicle can slide sideways.

torque steer and loss of traction.

This can be an alarming situation for the

Meanwhile, in the corners, FWD vehicles

driver and one that can be difficult to control.

tend to understeer; the driver turns the

Also, in low-traction conditions, RWD

wheel to follow the corner, but the car goes

vehicles can become unstable because the

straight instead. In slick or loose conditions,

rear wheels handle all the power delivery.

FWD vehicles can suffer because the front

Due to the fact that full-time AWD

wheels need to handle power delivery,

vehicles are able to divide the power delivery

cornering and most of the braking, with

responsibilities among all four wheels,

significantly less traction available.

they have the ability to capture more of

Part-time AWD offers
part of the solution
A part-time AWD system operates in 2WD
mode (FWD on most vehicles) most of
the time and then automatically switches
to AWD when conditions warrant. This
type of system was once favoured by some
manufacturers because it offered fuel savings
over full-time AWD systems. While this
may still be true of some manufacturer’s
AWD systems, decades of engineering
experience and fine-tuning have made Subaru
symmetrical full-time AWD systems both
lightweight and ultra-efficient.
As with 2WD systems, on-demand AWD
systems are at their best when the demands
are limited. But when conditions require
power to be sent to the other two wheels,
challenges arise.
First, the power-splitting mechanism of
the on-demand AWD system is generally
limited to helping you get going when
starting to accelerate in a low-traction
situation. When driving in slick conditions
at higher speeds or on a very long and curvy
road, the on-demand system can struggle
to keep pace with the circumstances. If
conditions change suddenly, this system
may not be able to react quickly enough to
avoid potential hazards.
While on-demand systems only respond
to a loss of traction, full-time AWD systems
are always engaged and always active,
making them the most effective and safest
solution for all possible driving conditions.
These systems are also particularly adept at
handling unpredictable driving conditions,
when immediate response is critical.
Full-time AWD maximizes available
traction right from the start by sending power
to all four wheels and maintaining power

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