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by Hib Halverson

The Bad Dip, Inch-by-Inch

Enough of the deep-geek stuff. Let’s go back to the R/H Loop at Milford and examine what Magnetic Selective Ride Control does when one traverses the "Bad Dip" at 120 miles per hour.

First we need to know how much ground is covered in a given time. At 120, you’re covering 176 feet every second. MR takes about 10-mSec to respond and in that time the car only moves 21 inches. From here on, the best guy to explain what happens is Mike Neal.

Mike Neal offers a blow-by-blow...oops...bad words...let’s say, a millisecond-by-millisecond account of what MR does when the car crosses the Bad Dip. Image: author.

"In a basic sense, MR tries to maintain body movement in a plane in space as the car moves forward. Calculations taking place in the controller are always trying to achieve that end.

"When you enter the dip, the wheel position sensors, seeing the wheels falling down into the dip, give a signal to the controller that a large body event is taking place. The controller determines the next thing the body will do is pitch down.

"Before the body can be pulled down, MR goes very soft on the rebound damping, not only to let the wheels fall into the dip, but to let the springs actually push the wheels into it. Without MR, you’d have heavier rebound damping which would tug the front end into the dip. MR avoids that by turning down the rebound. Again, sky hook is trying to keep the body in a flat plane.

"Once the tires near the bottom of the dip, the body wants to fall into it, too, so MR gets very stiff on the compression damping. It takes much longer for the body to move down on the suspension because compression damping is, now, very stiff.

"When you start coming up, out of the dip; the controller sees the suspension starting to be shoved up into the body. To keep the body from pitching upwards, sky hook sets the shocks very soft on the compression side, so the suspension will easily move up but not pitch the body up as you come up, out of the dip on the other side."

Consider carefully what Neal just said: as the car starts out of the dip, Magnetic Selective Ride Control switches through nearly its full range of compression damping, from very stiff to very soft. It does this in around 10 milliseconds while the car, traveling at 120 mph, moves about two feet...amazing!

"As you finally clear the dip," Neal continues, "you might have some, secondary, cyclic motion taking place which pitches the body. The controller sees that, sky-hook-calculates, then applies whatever appropriate level of compression and rebound damping to properly damp those motions."

"This is just what the body control strategy is across this one bump. At the same time, the system may be doing wheel control and stability enhancement, too. MR’s actions are never simple. It can be using several different algorithms to control varied types of suspension movement simultaneously."

Star Wars? Rocket science? You bet.

On the Road with MR

Blasting across dips at 120 is an extreme exhibition of Magnetic Selective Ride Control’s abilities even borderline-crazy C5ers shouldn’t try at home. So, what kind of driving will make you glad you ordered MR on your 2003 Coupe or Convertible?

"If you’re on a smooth road," Mike Neal told us, "while you’ll notice better isolation, it’s advantages to handling are minimal. It’s on roads which cause large ride events and body motion where it has huge benefits.

"If you’re trying to get around a track that’s smooth, like Road America, a ‘billiard table’ having no great heaves and undulations, MR has a minor effect.

Magnetic Selective Ride Control is standard on all 50th Anniversary cars and optional on any 2003 Coupe or Convertible.
Image: Chevrolet Communications.

"But, go to a place like the Nürburgring in Germany where it’s like the asphalt was laid down after little or no grading or smoothing–lots of dips and undulations–and you’re takin’ every turn at 100 mph or faster. It doesn’t take much of a ride event to really unload the car by heaving it, pitching it around and rolling it. In a place like that, MR is a huge advantage.

 MR doesn’t offer the sporting driver that much on a flat track, like this section of the Milford Proving Ground, other than a little less body roll in transitions as MR dials-up the roll damping. Shown here is Darin Dellinger at the wheel of a base 03 Coupe.
Image: author

At about the same spot on the track we see Mike Neal in a 50th Coupe with MR. Note less body roll. Image: author.

"With MR, you don’t have to wait for the body to settle before making your next steering input because the car is already transitioned, ready for the next maneuver. In that kind of ride environment, MR greatly improves the Corvette’s handling."

Nürburgring, huh.

Uh well...that ain’t in the Registry’s budget this month. Nevertheless, to fully appreciate MR, I had to find something beyond structured tests at a proving ground in Michigan.

Two thousand miles southwest, I found that on roads I know well. North of downtown Los Angeles are the San Gabriel Mountains. About eight miles into the San Gabriels on State Route 2, hang a left on L.A. County N3. Stay on that for about 30 miles and you end-up at the desert town of Palmdale but you’ll have been over some of the better high-speed touring west of Nürburgring.

The ’03 I was driving, a loaded 50th Convertible with an automatic, was the perfect choice to see how MR works in the real world. After you go left on N3, there’s less traffic and the road gets rougher, not potholes and broken pavement, but heaves and undulations of different depths, heights and lengths. There’s a few Nürburgring-style, bumpy, 100 mph turns, too.

The author, at speed on County Road N3 in Southern California’s San Gabriel Mountains. Star Wars meets the 50th Car in the real world. Image: Gary Peterso

It was easy to feel MR making a difference. Compared to a base car, it was like night and day. Considering this was a performance sports car, the ride was quite plush and the isolation quite good.

Even compared to the previous RTD system, MR has improved wheel control over the higher frequency (10-15 Hz) ride movements because it can bring more damping authority to bear and it can switch between damping levels quicker. The system effectively damps the big heaves, pitches and rolls that come from bumps and dips or low spots on the edge of the road. If dips at the Grounds weren’t enough, 30 miles, hauling-ass over N3 sold me on MagneRide.

Does MR have short comings? Really high frequency (17-20 Hz or better) stuff, such as little ripples on concrete highways or washboard/chatter-bump surfaces are a slight problem. In a straight line, the ride is a little harsh and, when ripples’ frequency approach that of the vehicle structure, you can hear kind of a subdued rumble. At high speed and at high lateral acceleration over chatter bumps, the car wants to skate sideways.

MR seems to be less effective in damping this kind of harshness presumably because, even with a 10mSec response, with the car moving fast, it can’t react quick enough to bring the most ideal damping to bear. While this harshness is a shortcoming, the types of surfaces that cause it are fairly rare.

In fact, this might not be entirely an MR issue. The stiff sidewalls of C5s run-flat tires amplify this type of harshness to the suspension. Rumor has it that C6 will have a new, Goodyear EMT with vastly improved harshness qualities and that might solve this problem.

On relatively smooth roads near the car’s limits in abrupt transitions and turns at high lateral acceleration, a MR car’s base springs and stabilizer bars show their inadequate roll stiffness. Sources tell us that DIY tuners can trade a little isolation to make up some of this roll stiffness deficit by adding Z51 stabilizer bars to MR cars. A C5 in the hands of a talented, aggressive driver will react well to that change.

Hard core racers, autocrossers and very aggressive street drivers will still want either Z51s or Z06es, both of which have higher rate "stab" bars along with stiffer springs and fixed-valve shocks tuned specifically for motorsports.

After all this discussion of MagneRide, I keep coming back to this one, overriding and persuasive thought: It’s pretty damn amazing to be able to drive a C5 really hard into a high-speed sweeper on a rough road and not have the car upset by bumps, dips or rises. Yeah, you might get ABS and even see a little Active Handling, but the big thing that makes the car more predictable and handle so well when going really fast over rough stuff is MR.

Clearly, we are not the only ones who think this. Just before the C5 Registry magazine deadline for the print version this article, Popular Science magazine announced Magnetic Selective Ride Control as the winner of its prestigious "Best of What's New" award in the Automotive Technology category for 2002. This award recognizes products or technologies that are a significant step forward in the category.

About a month before we posted the longer, Internet version of this story on the C5 Registry web site, the December 2002 issue of the Society of Automotive Engineers magazine, Automotive Engineering International, named MagneRide one of its "Top 10 Technologies" for 2002.

Award-winning Magnetic Selective Ride Control–yeah, a bit Star Wars it is, but it sure works well.


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C5 Registry Magazine, the C5 Registry web site and the author would like to thank Team Corvette’s Mike Neal and Dave Caldwell, Delphi’s Darin Dellinger and Beth Lewis and Lord Corporation’s Dr. Lynn Yanyo for special assistance in preparing this article

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