A new dimension in suspension
BY MARTON PETTENDY | 29th Aug 2001
The adoption by Holden of what it calls Control-Link Independent Rear Suspen-sion and other suspension tweaks stand out as the biggest technological advance made by VX/WHII, ones that brings a range of welcome ride, handling and stability benefits.
Specifically, the extra link reduces the rear wheel's variation of toe (the direction in which the rear wheels are pointed) movement during rear suspension compression and rebound, resulting in improved handling precision and greater stability through better location of the rear wheels.
Adapted by Holden engineers from a proven Opel design first seen in the Omega around the time VT appeared, fitment of the extra toe-control link in either side of the rear suspension necessitated the addition of locater points on Commodore's horseshoe cross member.
Holden stops short of dubbing the new suspension a multi-link system - rather a development of Commodore's semi-trailing arm arrangement.
Unlike the heavy but more sophisticated double wishbone IRS used by upmarket Ford Falcons, Control-Link IRS will be standard across all Commodore and Statesman models, but not the ute.
"With VX Series II, we again set ourselves the challenge of creating a truly competitive edge in the area of ride and handling," said Tony Hyde, executive director engineering and design, at the launch.
"I can say with all confidence that once you've had the opportunity to drive these cars, you'll discover for yourself that we succeeded in meeting that challenge." Identical to the set-up already employed by HSV's GTS, the adjustable toe-control link is complemented by model-specific suspension geometry changes.
The static camber of the rear wheels on VX/WH cars has been reduced (from 1.5 to 0.5 degrees), as has the static toe setting (from 0.1-degree toe-out to 0.32 degrees toe-in).
Holden claims these adjustments optimise the benefits of the control links, but the fact is previous VX/WH models' pronounced negative rear camber and toe-out settings are simply no longer required with the superior new system.
Control-Link IRS also brings with it the ability to make more accurate rear toe settings during production, and the ability to adjust rear toe during service if necessary.
Anti-roll bar diameters are also revised with the aim of building in more understeer to go with the better-sorted rear-end.
The front stabiliser bar diameter in Executive, Acclaim, Berlina and Calais models is increased by 1mm, while the rear anti-roll bar diameter has decreased by 3mm. Similarly, the rear stabiliser bar in S, SS and Caprice models has decreased 3mm in diameter while the front-end remains unchanged.
VX/WHII sedans with optional Country Pack suspension will carry increased ride height and ground clearance courtesy of increased front/rear spring rates, while rear stabiliser bar diameter increases by 3mm. Wagons fitted with Country Pack suspension get a rear stabiliser bar with 2mm smaller diameter. Holden also used Low Speed Tuning technology to improve the ride comfort on Series II Commodore Executive, Berlina, Acclaim and Calais models.
The LST method includes the use of spacers in the valving shim stack of the rear shock absorbers to return tighter control during low-speed suspension operation. The rear shock valving in Country Pack models has also been revised to match the increased spring rate.
"The reduction in variation of toe during suspension movement has improved straight-line and turn-in precision," said Mr Hyde.
The addition of the control links is accompanied by a reduction in the static camber of the rear wheels. This change improves rear wheel traction, and the overall handling feel.
"The result of these (stabiliser bar) changes is that the VXII has improved stability, particularly in fast, sweeping corners, with mild understeer characteristics. Gravel road stability is also improved, with a higher rear grip level and progressive breakaway at the limit of adhesion," he said.
Finally, a revised tyre construction, produced after consultation between Holden and Bridge-stone engineers, is said to aid the increased- diameter front stabiliser bar in promoting a sharper and more accurate steering feel, especially on-centre.
The new tyre should combine with the decreased negative camber to address complaints of excessive rear tyre wear since VT was launched.
Series II also heralds standard traction control for the S Commodore sedan, leaving only the Executive sedan and wagon without it. But there's still no traction control for Ute and, though Mr Hyde didn't rule it out in future, the omission of Control-Link IRS limits VUII's engineering improvements to the addition of standard ABS for the base utility.
Though it's not mentioned anywhere in the VXII press material, Holden also admitted to fiddling with the ECU's torque mapping in Gen III V8 models fitted with an automatic transmission. Mr Hyde said it was a case of better matching the engine's torque curve with the four-speed's shift points, with aim of making them "softer".
Of course, VUII benefits from across-the-board VXII range updates like new cruise control and indicator stalks, standard alarm system (but the base ute misses out), new badging and new optional metallic paint colours.
But there's precious little else new for VUII buyers.
DRIVE IMPRESSIONS:
Commodore S and SSHOLDEN'S sportiest Commodores, the S and SS, have received the least Series II attention, but it's at this end of the performance spectrum that the real benefits of Control-Link IRS become most evident.
Steering precision has never been a Commodore strong point relative to Falcon - either during turn-in or mid-corner. But a blast in facelifted S and SS sedans revealed a vast improvement in the FE2-equipped Commodores' ability to maintain a cornering line without the constant steering corrections required by its predecessor.
Yes, the new tyres and thinner rear swaybar play a roll in producing crisper turn-in with more understeer at the limit, but the biggest advance is the improved steering feel and response as a result of better road-holding at the rear.
Commodore's steering is still wooden but thanks to the rear-end's vastly improved grip level, mid-corner stability and more predictable at-the-limit behaviour, it's no longer vague or confidence-sapping.
Berlina/Calais
THERE is little to distinguish Holden's luxury short wheelbase cars from the Executive/Acclaim in driving dynamics, but Holden's claims of higher rear grip levels and more progressive "breakaway" were borne out by a dirt-road stint in a Berlina wagon.
The VXII simply felt less willing to break traction and more predictable when it did so.
Commodore Executive/Acclaim
EXPERIENCED Commodore-spotters will have trouble picking entry level VXII models externally.
But the changes are more noticeable once you get inside the cabin. Behind the wheel the biggest discernible difference is the new switchgear.
More tactile and simpler to use than before, the new cruise and indicator stalks have a more substantial feel than the flimsy items dished up previously.
Ride/handling differences are not readily apparent until the pace picks up, but even the base Commodores feel better planted to the road out back and have better off-centre steering feel.
And that applies to the wagon as well as the sedan, which also seemed to benefit in grip terms over the wet and greasy drive route.
Statesman/Caprice
HOLDEN'S long-wheelbase cars have never had a stability problem, but the compliant new IRS makes them feel even more glued to the road and less prone to getting their not insubstantial bulk off track over bumps or under heavy braking.
Superior rear-end toe control gives the WH an even greater feeling of solidity on the road, and somehow there's both a sense of better road holding and less rolling mass through better integration of suspension and tyres.
Read about the new Commodore's market analysis, pricing and equipment levels in our New Models section