An effective way to identify a nicely balanced Subaru WRX is to listen to the
cries from the front and rear tyres. Push a standard WRX through a corner and
you'll hear the outside front tyre howling for relief. It screams: "Hey, I'm
copping all the load here - gimme a break!"
But the Whiteline enhanced 'P-Rex III'
MY03 WRX is utterly different. When you tip this sucker into a corner, both the
front and rear outside tyres share the pain equally and, as a result, the
chassis is much better poised and balanced.
Instead of being forced to drive around the WRX's inherent understeer, the
driver of the Whiteline MY03 has much more flexibility. Sure, you can make the
thing understeer into a corner if you provoke it, but overall the chassis is much more
adaptable. A mid-corner throttle lift-off will bring on a gentle
oversteer. Oh, sorry - you don't like oversteer? Simply spend 5-minutes
adjusting the rear dampers and swaybar and you'll have it balanced just the way
you like it.
P-Rex III's handling can be configured to suit any driver
Interestingly, tyre grip becomes relatively lacking when you've got the
chassis balance and control of the Whiteline upgrade. You see, the standard Bridgestones
are fine on the stock WRX, but the sheer cornering loads that the Whiteline car
can generate means the car would really benefit from a stickier set of tyres - in dry
Jim Gurieff from Whiteline explains: "We always configure
our handling kits on the car's original tyres. This lets us find the correct
balance and we can raise tyre grip levels from there."
The Whiteline P-Rex III MY03 is the company's in-house development and
testing vehicle, which has been subject to extensive road and track trials.
"This car wears pretty well everything we can throw at it," says Jim.
talking 40mm adjustable struts, adjustable front and rear swaybars, anti-lift
kit, rear camber kit - you name it!
The Base Handling Kit
The platform for P-Rex III's suspension upgrade is the so-called Handling
Kit, which is designed to give buyers the biggest "bang for buck". With no
optional extras, the Handling Kit gives you upgrade swaybars, an anti-lift kit
and a rear camber adjustment kit.
Depending on its intended market, we're told the GD-series WRXs uses solid
front and rear swaybars measuring 19mm and 20mm respectively. Whiteline replaces
these with 3-position 'blade' adjustable 22mm solid bars at the front and rear
(part numbers BSF33Z and BSR36Z). There's some interesting test data related to
the fitment of the 22mm rear swaybar. With absolutely no other changes, G-circle
tests saw mean average lateral Gs increase from 0.83 to 0.855 and the maximum
attainable speed increased from 33 to 39 km/h.
Front-end grip is further enhanced with Whiteline's proven anti-lift kit
(part number KCA359). The anti-lift kit comprises replacement front control arm
mounts fitted with a relatively low-compliance bush. The mounts are engineered
to relocate the control arm pick-up to deliver additional castor, while the
low-compliance bush reduces alignment variation during cornering. In the case of
a WRX (which is fitted with MacPherson front struts) castor is essentially the
angle that the front struts lean back from vertical. The benefit from additional
castor is greater camber while cornering (greater 'dynamic' camber).
Whiteline claims their kit delivers an extra 0.5 degree positive castor in
static conditions and around 1.0 degree in dynamic conditions. Reduced bush
deflection (in comparison to the factory bushes) is the reason for the kit's
greater dynamic castor. Unlike the earlier GC-series WRX, fitment of the
Whiteline anti-lift kit to a GD-series WRX necessitates a pair of spacers that
allow clearance against a so-called "crumple brace". This brace is said to
enhance crash performance and has no stiffening effect from a handling point of
Whiteline's Words On Castor
Six reasons why "too much castor is never enough"...
- Maximise tyre contact patch during roll
- Improve turn-in response
- Increase directional stability
- Maximise tyre contact patch during
braking and acceleration
- Improve steering feel and self-centre'ing
Increase dynamic negative camber (on turn)
Why increase castor before camber?
- Camber doesn't improve turn-in, positive caster does
- Camber is not
good for tyre wear
- Camber doesn't improve directional stability
adversely effects braking and acceleration
The final component of the Handling Kit is an adjustable rear camber set
(part KCA414). The more serious your intent, the more camber you should dial in
- Whiteline suggests a "Touring" rear camber angle of -0.75 degrees, a "Sport"
setting between -1.0 and -1.25 degrees and a "Race" setting up to -2.5
The base Handling Kit retails for AUD$837 plus fitting (which typically
involves about 3 ½-hours labour).
P-Rex III's Optional Extras
In addition to the Handling Kit, P-Rex III has served as a test bed for a
range of other items that are separately available.
Most importantly, P-Rex III has been the test bed for Whiteline's new range
of Group 4 coil-overs. Jim says these offer a "true" 40mm internal diameter and
feature 10-position adjustable bump and rebound force. The 60mm ID springs are
carried on height-adjustable platforms and use relatively mild spring rates -
300lb at the front and 225lb at the rear. Unlike the factory struts, the Group 4
units are non-inverted - this means the adjustment mechanism is at the top of
the strut and is much less exposed to mud, etc. Unlike many other "converted
rally" designs on the market, the Whiteline Group 4 shocks are also specifically
designed for road use and reputedly do not require regular maintenance.
The standard WRX rear swaybar mounts have been known to fail when rear sway
stiffness is significantly increased. To avoid this situation, P-Rex III carries
Whiteline's 'unbreakable' heavy-duty mounts (part number KBR22). The standard
swaybar links are also replaced by extra heavy-duty alloy links (KLC26), which
offer improved strength as well as providing more direct swaybar actuation.
Jim says there's a relatively limited amount of toe adjustment on the rear
wheels of a GD-series WRX. Rear toe-out is generally desirable on a WRX, so
Whiteline has fabricated an adjustable front parallel link that should be fitted
in conjunction with a replacement lockwasher. The lockwasher prevents the
factory rear toe adjustment mechanism from shifting during normal use. Toe
adjustment is then performed through a replacement front parallel link (part
number KTA107). This adjustable link allows ample toe adjustment and virtually
eliminates any chance of toe change in normal driving. Note that low-compliance
replacement bushes should also be fitted to both lateral links.
Whiteline's P-Rex III has also been treated to front and rear strut braces
(part numbers KSB599 and KSB511). Jim comments that the GD-series Impreza is
much more rigid than the previous GC-series Impreza, but strut bracing can still
make a noticeable improvement.
In addition to those mentioned
above, Whiteline offers a number of optional extras. However, Jim says most are intended for hard-core motorsport use and
cause a considerable NVH trade-off. These items include a 'motorsport' anti-lift
kit (with an extra-firm bush), rear sub-frame lock kit, diff support lock kit, a
heavy-duty steering rack mount kit and a camber adjustment rod for the rear.
In our brief drive we were extremely impressed by the ride/handling compromise of P-Rex III -
even with the dampers nearly fully 'wound up' the ride remains more supple than,
say, a factory MY02 STi. As discussed, handling balance is vastly improved and
can be tailored to suit your specific driving style. Turn-in is crisp (without at any time being nervous ), mid corner-balance is exceptional and the power-exit
traction of the AWD Rex rounds out a very impressive package.
And the price, you ask? Well, brand new Group 4 adjustable coil-overs will
set you back AUD$3390. Inevitably, the new struts form bulk of the overall
price. Add to this AUD$837 for the Handling Kit, AUD$388 for both the front and
rear strut braces and AUD$287 for the adjustable rear toe arms and you've
scraped in just under AUD$5000 (plus fitting). Five grand isn't chicken feed,
but this is still an excellent purchase for anyone serious about street/weekend
racing their Rex.
MY03 WRX Variations
You may be wondering what the differences are between the MY03 and MY02 WRX
"There have been a couple of small changes," says Jim. "The rear spring
platform has been altered and the angle of the rear strut - which suffered
stiction problems in the '01 and '02 - has been changed."
Other than that, the
fundamental MacPherson strut layout remains the same. Inverted mono tube dampers
- which Jim says are little more than a marketing tool except in competition use
- are also carried over from the MY01.
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