I know, I know. But I didn't name it. Let's try to move beyond that, shall we? The 2010 Buick Lacrosse CXS will be the first of perhaps many GM vehicles to get the new Hiper Strut front suspension. What is Hiper Strut?
In short, it's a complete rethink of the tried-and-true MacPherson strut suspension. At first glance, it looks similar. There's a strut, there's a lower control arm and the stabilizer bar connects to the strut body.
But, critically, the Hiper Strut does not rotate with the tire as you steer the car. The spring and damper only move up and down. The upper steering pivot does not reside in the top mount, high in the fender well. Instead, the Hiper Strut (HS from here on -- I'm tired of saying it) has a new upper ball joint jutting out at the bottom of the strut body (yellow, above far left). That little yellow link amounts to a stubby upper control arm and the front knuckle pivots on it's own as the wheels are turned.
This has several benefits: The kingpin offset and the kingpin angle are reduced. The scrub radius is diminished. Torque steer should be less of a concern. Steering precision should increase. Tire wear should be easier to manage. On the negative side (theoretically, anyway) self-aligning torque (and therefore natural steering effort buildup) may actually decrease. But this may not be noticeable if the power steering assist curve is tuned correctly.
Here are some more graphics, provided by GM ...
They've changed colors on us, but the little link and upper ball joint are more obvious here. You can see how the front knuckles (light blue) will turn left and right while the strut stays still.
Everyone loves a good explosion, and this is a good one. It's a bit of a brain twister at first, but if you stare at it long enough you'll see that the lower control arm has no lower ball joint. The fork at the bottom of the strut does not -- can not -- pivot left and right relative to the LCA. Instead, a lower ball joint is bolted to the fork, partway up from the bottom.
I know what you're thinking. Isn't this similar to the Ford RevoKnuckle, the trick strut front end they put on the high performance Ford Focus models they sell in Europe, but not here?
Yes, it is kinda sorta like that. Here are some RevoKnuckle graphics...
The method is different, but the main points are the same. The strut does not rotate, there is a new upper ball joint, and the kingpin geometry and scrub radius improvements are similar.
Same concept, different way of getting there. Even though the RevoKnuckle came before, the GM HS is going to make it into the US marketplace first.
But both of these modified strut suspensions came late to the party compared to Toyota. Over in Japan, something called Super Strut suspension has been available on a variety of Toyota hot-rods since the mid-80s, beginning, if I'm not mistaken, with the much-loved AE86 Sprinter/Levin. We know it here as the Corolla GTS, but Toyota Motor Sales USA deemed the Super Strut too expensive and declined to offer it on US models.
Though the goals were the same, the Super Strut was quite different. A short link between the lower arm and the strut actually generated a camber change as the wheel moved up and down by moving an upper ball joint in and out.
To get the reduced scrub radius, Toyota used the dual pivot setup with two lower ball joints and two links instead of a single LCA, just like we see on a lot of cars today. The strut in this case still turns with the wheel, but this setup is arguably lighter than the HS and the RevoKnuckle. I'm not sure how rigid the Super Strut remains over the long run, though. Those intermediate links can't be allowed to develop any slop if they are to hold the wheel in place properly.
In any event, interesting riffs on the standard strut front suspension are possible, but GM's Hiper Strut is going to be the first (of these three ideas, at least) to make it to these shores.
mark19 says:
07:31 PM, 04/ 2/10
very interesting, reminds me of the scrub radius on a double wishbone setup on the 90's civic. so we can now get cheaper suspension parts, and still get a better scrub radius. It was obvious Honda got rid of the double wishbone setup on the civic as it does cost more than a macpherson. that's another argument. hope this makes ford bring it here soon as their competition GM just did.
roadburner says:
07:53 PM, 04/ 2/10
Cadillac's version will be called the ADHD Strut.
firstwagon says:
01:07 PM, 04/ 3/10
Since it's going on an existing model I would be curious to see a back to back test, old vs new.
See if the difference is major or minor to the driver.
dg0472 says:
04:04 PM, 04/ 3/10
@firstwagon,
Autoblog says it's pretty noticeable:
http://www.autoblog.com/2010/03/25/quick-spin-2010-buick-lacrosse-cxs-gets-hiper-w-video/
roadburner says:
08:35 AM, 04/ 4/10
Dan, how do you think those designs compare to the "double pivot" design that BMW first introduced on the E28 5 Series in 1981? At the E28 introduction BMW claimed that the design reduced brake dive and improved transitional roll response- all while permitting a small positive scrub radius(which BMW considered beneficial).
firstwagon says:
06:03 PM, 04/ 4/10
Thanks dg0472
good article, just what I was wondering about.
perceptive1 says:
07:28 AM, 04/ 5/10
@firstwagon
"Since it's going on an existing model I would be curious to see a back to back test, old vs new.
See if the difference is major or minor to the driver."
Yes!
formenow says:
03:30 PM, 05/13/10
I just love the graphics on this picture
norm_peterson says:
06:35 AM, 09/ 2/10
Since the strut is no longer involved with steering, that should remove the small torque about the strut axis due to endlink loading from what the driver feels at the steering wheel as he corners. I'm curious if, or how, that is being compensated - I'm assuming that with conventional struts that the effect is made to add a tiny bit of understeer.
Dan?
Norm
2slow says:
02:49 PM, 02/23/11
The BMW double pivot design creates a "virtual ball joint" at the intersection of the two links. This allows the virtual ball joint to move further out than a physical ball joint could package. Unfortunately, moving only the lower end of the kingpin does not allow for a short spindle length (distance from wheel center to the kingpin in rear view) BMWs are typically rear drive so they have less of an emphasis on spindle length and it's effect on Torque steer. The Hiper Strut allows both the upper and lower pivot to move outboard, reducing spindle length.
chikoo says:
01:56 PM, 09/16/11
This is so basic.
I am surprised this was not done ages ago.
Sort of proves how slow the auto industry is to make progress underneath the skin.
Mr. McPherson comes out with a strut that turns with the wheel and everyone went gaga over it.
I am glad the new GM is changing that approach.
Good Job!