GM Rethinks MacPherson Strut

General Motors Co. adds a new front suspension to the redesigned-for-'10 Buick LaCrosse, virtually eliminating the torque steer inherent to front-wheel-drive vehicles and improving overall drivability.

Called High-Performance Strut, or “HiPer Strut” as GM has branded it, the new setup comes as standard equipment on top-of-range LaCrosse CXS models.

The rollout of HiPer Strut coincides with the launch of LaCrosse models with a 2.4L Ecotec 4-cyl. gasoline direct-injection engine, which received a Ward's 10 Best Engines nod this year.

So far, the only other GM vehicle to receive HiPer Strut is the high-performance Opel Insignia OPC in Europe. The suspension was added to the OPC last year.

With the Insignia coming to the U.S. as the new-for-'11 Buick Regal sports sedan, odds favor the high-performance Regal GS show car receiving HiPer Strut when it gets green-lighted for production as expected later this year.

Outside of GM and Ford Motor Co.'s Focus RS in Europe, which the Dearborn, MI-based auto maker markets as “RevoKnuckle,” few auto makers employ this suspension approach due to cost.

For that reason, HiPer Strut will remain on premium vehicles at GM for the near future, says Jim Federico, chief engineer and vehicle line executive for the LaCrosse.

“It's not a cheap part,” he tells Ward's during a test drive for the suspension and new 4-cyl. engine in Virginia. “There's some money in it. We will have to price for it.”

In addition to reducing torque steer, HiPer Strut also is designed to isolate unwanted feedback from bumps and rough surfaces in the roadway, as well as improve steering precision and cornering performance in wet and dry conditions by keeping more of the tire patch on the roadway.

Federico says the goal of HiPer Strut was to make a McPherson-strut design work like the short long-arm setups of rear-wheel-drive vehicles. It also shows mechanical advancements remain in chassis technology, despite the proliferation of electronic assistance.

HiPer Strut retains the traditional MacPherson-style strut design, but GM reduces the length of the spindle assembly by adding a second ball joint on top of the steering knuckle. The shorter spindle length reduces negative camber, putting more tire rubber on the roadway and greatly reducing torque steer.

The second ball joint also de-couples the steering knuckle from the strut, which helps isolate unwanted feedback from the road.

The lower control arms are then attached to a rigid subframe, which is bolted to the body structure with four isolators to further damp noise and vibration.

The unique setup also improves the ride quality of larger wheels, such as the 19-in. variety found on the LaCrosse.

Federico says once costs come down, HiPer Strut could be particularly effective on small cars with big wheels — a styling element highly sought after by auto makers.

“It is more costly, it adds more mass, but it gives Buick what it needs,” he says. The extra ball joint, bushings and accompanying hardware add 18-22 lbs. (8-10 kg) to the vehicle.

Testing a LaCrosse with HiPer Strut against similar models without the technology, the system effectively eliminates torque steer resulting from the 304-hp V-6.

Under full acceleration, a HiPer Strut-equipped LaCrosse exhibits none of the disturbing pulling or tugging sensations in the steering wheel a driver might experience with so much power going to the front wheels.

WARDSAUTO.COM

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