C4 Corvette's Selective Ride Control - Six Steps for a King's Ride - Page 3 of 3

The Inside Story of C4's Shock Absorber Revolution, Selective Ride Control

© 2009 by Hib Halverson
No use without permission, All Rights Reserved

Road Testing Rebuilt/Revalved SRC Shocks

Several years ago, we found both front shocks leaking on our 1995 ZR-1. As the car had less then 50,000 miles on it, no doubt this was caused by the valve seal durability issue discussed earlier. We contacted Bilstein and they told us that rebuilding would include new piston rod assemblies having a revised seal package. Since we drive this ZR-1 hard on the street, they also suggested revalving so we ordered Bilstein's Moraca valving.

Click image for larger view Bilstein Technician, Lou Lauerenzana, begins assembly of one of our SRC dampers. Image:  Author	Click image for larger view Here, Lauerenzana fills one of our shocks with damper oil just prior to its reassembly. Image:  Author	Click image for larger view This big machine is a 'shock dyno' which Lauerenzana uses to test one of our freshly rebuilt, front dampers. The machine is instrumented with sensors which send force and velocity data to the PC in the center. Image:  Author

Occasionally a rebuilt shock, when first installed, will set a time-out code. This is caused by stiffness of the new bypass valve shaft seals. It takes a little time to loosen up the seals such that actuator movement quickens to within the range the SRC controller required.

The effect revalving the shocks had on the car's handling was dramatic. In the lower valving ranges, the wheels more aggressively damped and, as a result, the "floating" one often feels from the OE valving's weak rebound control was gone. Once in a while, this car gets autocrossed and it often gets driven hard over windy mountain roads. That the upper SRC ranges are noticeably stiffer, offering better control during aggressive maneuvering, was a welcome improvement. This stiffness was especially noticeable (and desirable!) at high speed in road racing "track day" events.

After testing the car in both autocross and road race environments, our opinion is: the revalving definitely improves the car's feel and response in transient maneuvers. On a ZR-1, the change in rear rebound, alone, is worth the cost of revalving.

We've run the car about 30,000 street miles since the Moraca revalving and our opinion of its ride is positive-but with qualification. The more aggressive, street/track valving degrades ride quality. Even with the SRC selector switch in "Tour", ride is more firm than was the stock valving. While we, here at the CAC, like this car's ride on the street, other people who think they need motorsports-derived shock valving but know they don't want a firm ride over tilt-slabbed highways, potholed roads, harshness crossing tar strips and so forth, should stick with the stock valving.

Now that you've read the disclaimer, know that those who race or who regularly drive hard on the street will benefit greatly from revalving. In fact, we've been wondering what took us so long to do this to the car. Where will our ZR-1 project go from here? Well...now, we want to upgrade the car's springs, stabilizer bars and front lower control arms to Z07 level.

And Finally

"It was always my favorite system," Scott Allman said about Selective Ride. "We didn't feel we need to go to these complex real-time damping systems and could keep it to basically a 'state device' and meet all the performance requirements.

"Roads don't change fast enough in their mean excitation that you need real time damping. I guess you could justify it on, say a Cadillac, if your trying to get that last iota of ride comfort, but if you were doin' the Corvette, you're looking for a level of control authority which is a step above your standard sedan and you don't need to have a real-time variation to get the handling effect you're looking for."

Admittedly, Allman is somewhat biased because SRC was, for the most part, his baby. After driving C5s and C6es with ride-adaptive shocks, we're not sure we fully agree with Scott's view of Corvette not needing more advanced systems. There is a large block of Corvette buyers wanting the car for its image, not for its performance and those folks demand a soft ride.

Conversely, we share Scott Allman's view that, from an at-limit handling perspective, some of the systems which came after SRC, namely "Selective Real Time Damping" or "RTD" (both the bi-state, 1996 version, and the continuously-variable, 1997-'02 version) offered less damping bandwidth than Selective Ride. This made them a poor value to Corvette customers interested in the best handling performance for his or her dollar.

It was not until 2003, when GM introduced RPO F55, "Magnetic Selective Ride Control" ("Magnaride" or "MR") did Corvette get an uplevel suspension damping system that exceeded Selective Ride Control's bandwidth in both ride and handling.

The Corvette Action Center would like to thank Dave McLellan, retired Corvette Chief Engineer; John Heinricy, retired GM Director of High-Performance Vehicle Operations and Scott Allman, Principal Engineer, Harley-Davidson Vehicle Dynamics Group and Bilstein of America for their support during the research for this article. This story was adapted from an earlier piece published during 2006 in Corvette Enthuaist magazine. The CAC is grateful to CE Editor, Andy Bolig, for making it possible for us to post our version of this article.

Sources:

Bilstein Corporation of America
13102 Stowe Dr.
Poway CA 92064
800 537 1085
www.bilstein.com/index1.php

Corvette Central
Box 16
Sawyer MI 49125
800.345.4122
www.corvettecentral.com

Doug Rippie Motorsports
Suite 2
1117 Highway 25 North
Buffalo MN 55313
763 477 9272
www.dougrippie.com

Helm Inc.
14310 Hamilton Ave.
Highland Park, MI 48203
(800) 782-4356
http://www.helminc.com

Tom Henry Racing
5886 Route 8
Bakerstown PA 15007
877 866 7278
www.tomhenryracing.com

Bosch Diagnostics
2800 South 25th Avenue
Broadview IL 60155
www.boschdiagnostics.com

Vette Brakes and Products, Inc.
7400 30th Av. North
St. Petersburg FL 33710
800 237 9991
www.vbandp.com