Like building a good foundation of a house, the first place to start when you modify your C5 is the suspension. The very first thing you need to do is determine how you are going to use your Corvette. The way you drive your car determines what kind of suspension modifications are best suited for you. For example, if you plan on taking long weekend trips to the country, you want a smooth-riding car that is fast and comfortable. If this car is only to be used as a drag car, you want to get maximum weight transfer over the rear wheels. Finally, if you plan on attending track events or road races with your C5, then you need to concentrate on balance and neutral handling. As mentioned in Chapter 2, C5 Corvettes were available with five suspension options during their eight-year production. Two were performance oriented (Z51 and FE-4) cars designed for autocrossing and weekend road-racing track events.
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Fifth-generation Corvette suspensions were built with four major components: shocks, sway bars, springs, and an aluminum controlarm suspension system. All Corvettes have been fitted with aluminum upper and lower-control arms and suspension uprights since 1984. The materials are lightweight and durable. The suspension uprights are interchangeable in the front and rear because they are the same design, but the front and rear control arms are different. The control arms are referred to as an unequal-length design. That means the upper and lower arms are different lengths. This design is found on all fifth-generation Corvettes. Corvettes are well known for their outstanding handling, and this unequal-length control arm design is one of the reasons. Composite transverse leaf springs were first fitted to Corvettes in the rear of all 1981 models. Lightweight and inexpensive to build, these springs eliminate the coil steel springs usually found in most car suspensions. Another advantage of composite springs is that the suspension height can be adjusted by turning the ride-height screws. These screws are located at the corners of each front and rear spring. Front composite springs were introduced to Corvette in 1984. All Corvettes built since 1984 have composite front and rear springs. While all C5 composite springs look the same, their differences are found in their spring rates. In other words, how stiff is each spring? Base suspension cars have the lightest spring rates, and the 2004 Commemorative Edition Z06 has the stiffest spring rates. All Z06 models were equipped with a 10-percent stiffer spring than the Z51 handling package. This added roll stiffness and reduced rear squat under hard acceleration. The stiffer the spring, the more firm the ride. Again, you need to decide what kind of driving you want to do with your C5 to make the best spring-rate decision. Shock absorbers control the amount of up and down movement the suspension makes over bumps and dips in the road. Shock absorbers also help the tires maintain contact with road during hard cornering. The F45 and F55 suspension options are fitted with electronically adjustable shock absorbers. The FE4 fitted on all Z06 models had the stiffest shocks offered on production C5s. The Z51 sports-handling package available on all non-Z06 Corvettes used shocks built by Sachs. Z06s also used shocks built by Sachs. Shock valving was changed in the Z06 in three areas. Low-velocity suspension movement was increased at all four corners. GM suspension engineer Mike Neal said, “adding low velocity damping slows body roll, firms the ride a bit, and improves the front suspension’s response in transient maneuvers, such as quick lane changes or autocross chicanes.”
Sway bars are attached to the frame and supported by rubber bushings. Each end of the bar is attached to the front and rear lower control arms via a plastic or aluminum link. Aluminum links were introduced in the 2002 model year for the FE4 and Z51 suspension options. The thicker the bar, the less lean your Corvette exhibits in a hard corner. The stiffest sway bars were offered on the Z06 high-performance packages from 2001 to 2004. In 2001, a higher-rate, front sway bar was introduced on the Z06. The new bar was increased to 1.181 inches, up 0.055 inch from the 2000–2001 Z51 bar. Wheel alignment specifications were changed for the 2001 Z06 because of the new Goodyear F1 Supercar non-run-flat tires. Camber of -0.75 degree was a huge increase over other C5s. This setting is used at all four wheels. These Goodyear tires work best with a static negative camber. According to GM suspension engineer Mike Neal, “The more pliable sidewall of the F1 Super Car tire allows that much negative camber without an adverse effect on tire mileage.”
The 2001 Z06 had one final upgrade that we need to discuss. It was a more advanced Active Handling system. Designated AH2, it was a significant improvement in a system that was already good. The key changes made affected sideslip angle and rear-brake stability control, and improved coordination with traction control. The system was also fitted with a competitive mode. The improved sideslip angle control means the system can sense if a driver is too slow to react or is overreacting in a corner that exceeds the cars limits. The Active Handling system applies the right amount of differential braking to maintain the car’s balance. The AH2 is better coordinated with traction control, which uses either rear-brake intervention and engine torque limiting to control rear-wheel spin. Compared to AH1, the revised Active Handling’s use of traction control is skewed more towards rear brakes than engine controls. The result is less engine “sags” and better engine response after a traction control incident.
Selecting Springs, Shocks, and Sway Bars
Street: In my opinion, C5 Corvettes equipped with the F45 or F55 suspension options offer the best ride compromise. Both suspension options give the driver three suspension settings on the console. A simple flick of the switch from Tour, Sport, or Performance allows the driver to change the stiffness rate of all four shock absorbers. The F55 option became available in 2003 and is called “Chassis Continuously Variable Real Time Damping” (CCVRTD) suspension, or MagneRide. MagneRide shock absorbers utilize magnetorheological (MR) fluid inside the shock assembly. This fluid is a synthetic liquid with carbon iron particles (97% to 99% iron) that provide electromagnetic properties. The shock’s dampening changes when these particles are subjected to a direct-current magnetic field strength. The MagneRide controller is a dualprocessor unit capable of making 1,000 adjustments per second in all four shocks. The controller receives wheel movements via position sensors and the wheel movement data; the controller determines body motions (pitch, roll, and lift). Non- MagneRide Corvettes (1997–2002) equipped with F45 can be upgraded to F55 option. You can add GM Performance part number (PN)12499507, the C5 Corvette MagneRide Shock Upgrade kit. This upgrade kit uses the existing F45 wheel position sensors, driver select switch, and main suspension system wiring harness.
Drags: The classic drag-racing photo shows a car starting its race with its nose high in the air and the rear tires firmly planted on the ground. Frontengine, rear-wheel-drive cars tend to have more weight on the front wheels, so the trick is weight transfer.Corvette owners who drag their cars usually mount their battery in the back. Hardcore drag racers install narrow front tires on 5-inch-wide rims. Typical tire sizes are 5.25 x 16 on the front and 11.50 x 16 cheater slicks on the rear. Racers also use lightweight front brake rotors and calipers to reduce unsprung weight on the front wheels. Front and rear springs are usually from the FE1 base suspension package that allows the nose of the car to rise in the air and transfer weight to the rear wheels. Modified automatic transmissions are a favorite Corvette drag-racing tool. The C5 hatchback is also popular with Corvette drag racers. The large rear hatch window puts a lot of weight over the rear wheels. Engine choices start with street stock LS1 or LS6 engines all the way to twin-turbo, 1,000+ horsepower, 427+ cubic-inch engines. Elapsed times and trap speeds at the finish line are falling every day, so go to your local drags and find out what people are turning in their Corvettes.
Autocross: Autocrossing started in the early 1950s and has grown to a very popular weekend sport. The SCCA sanctions the Pro Solo and Solo autocrossing series each year. Local SCCA clubs across the country hold autocross events in their areas. Autocrossing is usually a pretty safe sport. Traffic cones are set up in a large parking lot or airport runway. The cars that negotiate the course the fastest win their class. Each driver is assessed a time penalty for every cone they knock down. The trick is to drive quickly and smoothly and not take out any cones. Car preparation varies: street-class rules are very limited in what you can modify on your Corvette. Street Prepared classes allow limited modifications to your engine and suspension. Drivers of all classes are required to wear helmets. The 2001–2004 Z06 is the car of choice in the Stock category. The cars are nimble and have enough power to do well on longer courses. In Street Prepared, the 1999–2000 FRC and 2001–2004 Z06s are very popular. The FRC is much less expensive to purchase and most of the suspension and engine parts are going to be changed in Street Prepared. The Z06 does have a closer ratio gearbox, which is an advantage on shorter courses. Autocrossing really teaches drivers car-control in a safe environment. The sport accepts both young and older men and women. It is a good way to exercise your Corvette on the weekend, and I recommend starting with the SCCA website for more information on track events and regulations.
Road Racing: There are several ways to road race your Corvette. You can race your Corvette in local track days or Car & Driver’s One Lap of America. In addition, you can compete in SCCA’s amateur racing series or race in the SCCA SPEED GT World Challenge series. Track days are held at various race circuits around the country. The organizers charge a daily fee, give your car a safety inspection, and determine your driving skill. Depending on your skill level, they either let a qualified driver ride with you or let you drive alone. If your car and engine are modified, the safest place to see what your car can do is on a closed racetrack. Some Corvette tuner shops offer track-day support services, for a fee, for which they prepare, store, transport, and maintain your car at the track. MTI Racing in Marietta, Georgia, is one example of a tuner that provides this service. MTI Racing attends track days around the South each year. They bring a support trailer and mechanics to help their customers maximize their track time. Their trailer is equipped with brake pads, rotors, tires, oil, fluids, and parts to keep you car running during the weekend. MTI Racing also offers driving instructions to help clients maximize the performance of their Corvettes and improve their driving skills. The Car & Driver One Lap of America is usually held in mid May to early June. Car & Driver magazine sponsors the event. Much like autocrossing, Corvettes can run in the street-class or modified category. A C5 won the event overall in 2003, and Corvettes are usually sprinkled among the top finishers. As outlined in Chapter 1, this is a grueling event that takes a lot of physical stamina and superb driving skills. The event usually visits 10 to 12 racetracks located around the country in six days. A fast, comfortable, reliable car usually does well. Check out the rules and schedule at Car & Driver’s website.
Again, the SCCA offers a wide variety of amateur racing classes for Corvette drivers. The showroom stock category, called T-1, is the least expensive. The C5 is an excellent choice to race in the T-1 category. The best C5s for this are the 1999–2000 FRC and the 2001–2004 Z06. The SCCA allows competitors to install the factory GM Performance Parts T-1 package, which includes better shocks, larger sway bars, heavier springs, and a transmission cooler. However, once you have committed to this kind of racing, your car is not usually streetable. In order to save weight, some interior accessories are stripped from the car. Complete roll cages make it difficult for passengers to use the right seat. Mandatory fuel cells have to be installed for safety, and other safety items must be added for track and driver safety. Like the autocross series, each SCCA region holds races, and the drivers who accumulate the highest three points per category are invited to the annual runoffs. GM engineer John Heinricy drove a 1999 FRC to several T-1 National championships. He has won a total of five National Championships driving Phoenix Racing C5 Corvettes.
The SPEED GT racing series is an all-out racing series sanctioned by the SCCA. Each event is 50 minutes in length and is televised on the SPEED channel in a one-hour show. The SPEED GT Corvettes are all-out racing cars. All of their interiors have been stripped and filled with regulation roll cages. Most of the Corvettes running in this series are re-bodied C5s. Specifically, they are the boxcars built by GM from 1999 to 2001. The regulators have allowed the Corvette competitors to install the newer C6 Z06 body panels onto the old chassis. The new body is better aerodynamically and is more appealing to the race fans. But underneath beats the heart of my favorite Corvette, the C5.
Installing Front and Rear Composite Springs
Now that we have covered the various ways to race your Corvette, let’s use a real-world example of how to install a new set of composite springs into your C5. We visited MTI Racing in Marietta, Georgia, to watch them install new composite springs in a C5. This particular C5 had recently been upgraded with a 550-hp, LS2 engine package. The stock Z51 suspension system worked well with the original 345-hp LS1 engine. However, with the new LS2 installed, MTI’s owner, Reese Cox, thought this car needed improved handling. During a test drive, Reese noticed the front end rising dramatically under hard acceleration. The nose also dipped under hard braking. Reese didn’t feel the car’s suspension was up to the task of handling such an increase in power. Reese, a former road racer, knew that the owner was going to use this car for street use and track events. The owner needed a compromise in handling and ride. Reese decided to install Vette Brakes & Products (VBP) Extreme front and rear composite springs. Reese told me that top Corvette teams use 1,200- to 1,300-lb spring rates in the front of their cars! However, he recommended installing a VBP 850-lb front and a 750-lb rear spring in this car.
MTI Racing installed VBP PN97320 Extreme 850-lb front and VBP PN97344 Extreme rear 750-lb springs. The MTI team attacked the spring installation like the pros they are. The first thing they did was park the car on a flat surface and measure and record the ride height at each corner of the car. Removing the front spring was more involved and took the most time. The front spring rests on top of the lower control arms and is mounted above the engine cradle. The rear is bolted underneath the lower control arms. The front spring needs to be pulled through the engine cradle for removal.
The rear spring is just unbolted and drops straight down away from the car. Having the car on a lift and having all the right tools made this a quick conversion. MTI started the project by removing the C5’s front brake calipers. To do this, they used a 15-mm box wrench to remove the upper and lower caliper bolts that hold the unit to the suspension upright. Once removed, the caliper was stored on the upper control arm. Next, they placed a floor jack under the front suspension for support when they removed the upper control arm bolts. Before they removed the upper control arm bolts, they removed the 10-mm brake-line bolt located directly below the upper control arm. This prevents bending the line when the upper control arm is loosened.
Next, they removed the four 15-mm upper control arm bolts. Once this was completed, they removed the two 13-mm lower shock absorber retaining bolts. Next, they loosened the 18-mm tie rod end bolt and gently tapped it with a hammer to break the knuckle free from the joint. Next, they placed a floor jack under the car’s lower control arm to lower the unit. MTI used PB spray lubricant to help remove the screw in the front spring height adjuster. This has to be removed before taking the spring out of the car. They removed the four 13-mm spring shackle bolts attached to the front engine cradle. The old factory Z51 spring was removed. The new VBP 850-lb front spring was ready for installation. They reversed the removal procedure to install the new spring. They torqued the bolts per the Corvette Shop manual specifications.Moving to the rear spring, MTI placed an 18-mm socket on the lower rear spring adjuster bolt and a 21-mm wrench on the upper adjuster nut. Then they loosened the rear spring adjuster. Before they could completely remove the nut, they placed a jack under the spring and removed the O-ring retainer on top of the adjuster. Next, they removed the nut and lowered the jack to remove all of the tension from the spring. Then they placed the jack stand under the middle of the rear spring and removed the four 13-mm spring shackle bolts.
The new VBP spring was ready for installation. They reversed the spring removal procedure to install the new VBP rear spring. The bolts were torqued per the Corvette shop manual specifications. They reinstalled the wheels and checked to make sure the car sat even at all four corners. They used the screw-type adjusters to bring the car to the previously measured ride height.Once the car was back on the ground, it was time for a test drive. We were surprised at how well the car rode. In spite of the much higher spring rate, the Corvette absorbed bumps without any major jarring or thumping. Reese took the car out for a test drive and agreed with my assessment. Under hard braking, front dive was minimal and the nose remained flat even when it was under hard acceleration. We think the car is now very capable of utilizing its new power more effectively.
Installing Coil-over Front and Rear Springs
Coil-over springs are designed to replace the factory transverse composite leaf springs. Road-race drivers believe that these springs provide more suspension adjustments when setting up a car to race at a new track. These springs are not inexpensive, but do have their place in the right competition settings. The system is pretty simple. A coil spring is placed over the shock. The spring sits in a cradle, which bolts to the frame at the top of the suspension and is secured to the lower Aarm with bolts. The cradle has a large adjusting nut that is turned to increase or reduce the individual spring rate. To install the first step is to follow the composite front and rear spring removal process. Follow the installation instructions and torque specifications provided by the coil-over spring manufacturer.
I recommend staying with the original shocks installed at the factory unless you are going to be doing high-performance driving. Each suspension option was designed around the shock that was installed for that particular car. However, if you decide to change the shocks, it is a straightforward job. You need a jack, safety stands, and a good toolbox to complete the change. The front factory shocks are held in place with two 13- mm bolts that are secured to the lower control arm. The top of the shock is held in place with one 15- mm bolt. The rod of the shock goes through a hole in the top shock tower frame. The 15-mm bolt on top of the shock secures a washer and a rubber bushing. The radiator overflow tank and windshield washer tank must be removed to gain access to these bolts. Snap-on makes a special, double-D wrench that must be inserted into the top of the shock tower rod. This allows you to loosen the 15-mm bolt while the double-D keeps the rod from turning. Some people secure this rod with vise grips, but often it destroys the threads on the shock.
The rear shocks are secured with one large 15/16 bolt at the bottom and two 13-mm bolts on the top that are attached to the frame. In both jobs, wheel removal is a must in order to have enough working room for the project. The most aggressive factory shock for the C5 was installed on the 2004 commemorative edition Z06. These shocks are a good value for the money. They work very well on an older Z06, FRC, or cars equipped with Z51 suspensions. The front shocks are GM PN10339944 and the rear is PN10339945. These shocks provide good car control, and dollar for dollar they are hard to beat.
Remember, when installing high-performance shocks, be sure to review your driving requirements. Aftermarket shocks are available as a replacement for the factory shocks, or you can find extreme-high-performance units that give you maximum adjustability. Some gas shocks have lines attached to them. These lines are hooked to a braided line that ends at an auxiliary cylinder. The cylinder has an adjustment screw to allow you to finely tune your ride. Coil-over shocks can also be adjusted for ride firmness. The adjustable coil springs and adjustable shocks on a coil-over suspension provide an endless number of adjustments.
The stock C5 with the Z51 handling option is a very stable platform, with 345-hp under the hood. But if you start pushing over 550 hp at the crank, your suspension performance suddenly becomes critical. Fortunately, MTI Racing’s owner Reese Cox has spent a lot of time at racetracks driving Corvettes. We decided to tap his experience and learn how to improve a modified C5’s braking and handling. He suggested replacing factory Z51 factory sway bars with ADDCO’s tubular 35-mm front/25- mm rear sway bars.
He told us cars steer more precisely through corners with these bars. Because they are tubular they are also lighter. They also make the car more stable at higher speeds and provide excellent emergency maneuvering. To change C5 sway bars, the first step is to remove the sway bar end links with an 18-mm wrench and a number 6 Allan wrench. Next, use a 13-mm wrench or socket to remove the four bolts that hold the bar to the frame. MTI Racing Technician Chris Iverster installs the new ADDCO 35- mm front tubular bar onto the test C5. A 13-mm socket is used to install the four sway bar bushing brackets to the frame. Tighten these bolts to 43 ft-lbs of torque. MTI installed solid Z06 end links that replaced the stock plastic end links. Tighten the links to 55 ft-lbs of torque and remove the four 18-mm upper and lower rear sway bar bolts. The two 18-mm endlink bolts are also removed. The bar can now be removed from the car. The new ADDCO rear tubular bar can be installed. The lower sway bar bolts are tightened to 71 ft-lbs of torque. The upper bolts are tightened to 49 ftlbs of torque. The end links are tightened to 52 ft-lbs of torque. The car is now ready for a test drive. The bigger bars did not have an adverse effect on the car’s ride. However, turning into corners was very crisp and instant. We did not experience any body lean, no matter how hard we pressed the car in a corner. This is a very worthwhile upgrade over the optional Z51 factory sway bars. The finished car felt very precise, and a flick of the wheel provided instant response to the driver. We feel confident knowing that the car’s handling is now more precise with the addition of these sway bars. Lowering the C5 Corvette
C5s can be lowered about 1 inch in the rear and 3/4 inches in the front with the stock bolts if you have the Z51 suspension. If your car is equipped with the base suspension (FE1) or the Continuously Variable Real Time Damping (F45) suspension, lowering the car makes it ride stiffer. You can use the spring jackscrews to lower the car as much as they allow. Then road-test it, and if you don’t like the ride, simply crank up the adjustment. This does not damage the shocks because the F45 system “sees” the decrease in ride height. Keep in mind that F45 cars have base springs. Softly sprung cars may have more of a problem with lowering than Z51s. You can lower the FE1 and F45 about 1/2 inch in the front and rear safely. Adjusting both front and rear bolts to their maximum gives you approximately 3/4 inch in the front and 1 inch in the rear. While this does not sound like much, it makes the car look and feel a lot lower. This puts the air dam 2 inches off the road after the procedure. You might consider either cutting off the lower 1 inch of the air dam or raising the car about 1/2 inch so it won’t scrape so much. Before lowering your car, measure the height of the front and rear wheel wells from the ground through the center of the wheel. It should be somewhere around 27-3/8 inches in front and 28- 5/8 inches in the rear. Write down these numbers.
Lowering the Rear
With the car parked on a level surface and the front wheels blocked, jack the rear of the car and support with two jack stands. It is actually easier to do the lowering if the wheels are removed, especially when it is time to measure the bolt height to ensure that the car is level (you might want to remove the wheels now also). At each end of the transverse leaf spring, locate a long bolt, with the threaded end pointed upward.
You should see about 1 inch to 1- 1/2 inches of exposed thread on the bolt (this is on the top of the leaf spring). Using an 18-mm socket and ratchet on the bottom of the bolt, tighten (clockwise) until only two or three threads are exposed on the top part of the bolt. Use an 18-mm wrench to hold the top nut in place as you turn the bolt. Leave two or three threads exposed before it contacts the nut. The nut has a small “C” clip on it so it won’t back out. It takes about 5 minutes per side to lower the rear about 1 inch. It is a good idea to measure the exposed threads on each side to ensure they are the same.
Lowering the Front
The car definitely has to be raised in the front. With the car safely raised, on jack stands, and with the front wheels removed, find the end of the transverse leaf spring next to the shock. Locate the 10-mm end of the ride height adjustment bolt. It has a retainer clip. With some suspensions (like the F45) it is easier to get at the top of the bolt if the lower shock absorber bolts (13 mm) are removed so the shock can be moved out of the way. Using a 10-mm socket on the top of the stud, turn counterclockwise (like unscrewing—even though you are not, you are just on the opposite end of the bolt so it looks that way) until tight. Back off the bolt about a 1/8 to 1/4 turn to ensure it does not freeze in place in case you want to raise the car at some future date. Reattach the lower shock mounts, put the wheels back on, and remove the jack stands.
At this point, the car may not appear to have been lowered very much. Take it for a drive around the block and allow things to settle. Then, with the car parked in the same spot, re-measure the height of the wheel wells as above. The difference between the two measurements is the amount the car was lowered. Make sure that both sides of the front and rear are the same measurements. Adjust as necessary. Drive the car for a week or so, then have the alignment checked by a good shop. Align as necessary. If the car feels like the suspension is riding on the rebound bumpers, you may be too low. The best fix is to raise the car by about 1/4 inch and test-drive it again.
Written by Walt Thurn and Posted with Permission of CarTechBooks