Fine tuning the suspension | Project Chevrolet C5 Corvette Z06 Part 9

Update by J.G. Pasterjak to the Chevrolet Corvette Z06 project car
Jan 27, 2022

Our Corvette had become a technological tour de force–or something close to that, anyway. It had more aero. More grip. More brakes. It even looked like a real race car, too. 

Then one small thing threated to bring us all the way back to Square 1: tires rubbing on the fenders, with that excitement happening at a buck-25 on the high banks of Daytona. 

 

Handling Tweaks

Back in the April issue, we detailed the rationale and process for replacing our car’s factory transverse leaf springs with RideTech coil-overs. In addition to offering some theoretical benefits, the coil-overs came with lots of anecdotal evidence showing that they’re just flat more driver-friendly than the transverse leaf springs. We were also attracted to how easy they would make spring rate changes, coupled with a wide availability of spring rate choices. 

[How to replace Corvette leaf springs with coil springs | Project Chevrolet C5 Corvette Z06 Part 7]

We found ourselves needing to take advantage of those benefits when a wheel and tire upgrade sent us in search of some fine tuning to maximize our newfound grip.

First, let’s talk about that rolling stock. Our Corvette, like most Vettes made in modern times, came from the factory sporting wider wheels at the rear of the car. The hot track setup, though, is to run the same size at all four corners, so we used 18x10.5-inch wheels not just at the back of our C5 Z06, where God and the Corvette’s designers intended, but also at the front of our car. Then we wrapped those reproduction alloys with 315/30R18 BFGoodrich tires–we used the Rival S for autocross and the R1 S on track. 

Our OEM replica wheels were a fantastic budget alternative, since they were readily available and fairly inexpensive. We shopped around and sourced ours from multiple vendors to assemble two full sets, paying less than $125 for some of those wheels. 

While this rolling stock did technically accept our 315mm tires, the installation required a bit of a stretch. A 315mm tire is really happier on an 11-inch-wide wheel, which allows the sidewall to sit closer to vertical and helps with transient response. But while our 315mm tires were wide, we really wanted to run 335mm tires–the widest Rivals available–on the rear. More rubber is usually better than less, right?

Our Momo RF-20 wheels looked boss but stood a little proud of the rear fenders thanks to our fat BFGoodrich tires. Our solution involved a set of generic fender flares purchased via eBay and a little quality
drill time. Photography Credits: J.G. Pasterjak

So we found ourselves upgrading to a gorgeous set of Momo RF-20 wheels. These flow-forged wheels–18x11 inches up front and 18x12 in the rear–weigh in at less than 26 pounds apiece. That’s the same as our replica wheels, but remember, the Momos are wider. Ours retail for about $500 each, and in our book that’s pretty darn good for a highly customizable set of wheels: Choose your size, bolt pattern, offset and color. 

Our front wheels feature 52mm of offset, while the rears have 59mm of offset. We went in knowing that we’d be right at the limit, yet could always tweak fitment with spacers. And we did need to run spacers: 1.5mm up front and 6mm out back. (The front spacer was required to clear our Wilwood brake hats, so the next time we mount up tires, we’ll simply have a local machine shop remove a bit of material from the wheel mounting surface.)

Once we mounted our 335mm rear tires, though, they stuck out past the fender lips by nearly three-quarters of an inch. So we covered them with a set of $25 eBay flares–which look better than they have any right to for that kind of coin.

Moving our 315/30R18 BFGoodrich tires from the 10.5-inch-wide wheels to the 11-inch-wide wheels flatted out the tread, instantly putting more rubber on the road. The sidewalls now sat closer to perpendicular, too. End result: a happier tire. Photography Credit: J.G. Pasterjak

Everything seemed fine and dandy until we hit the high banks of Daytona during an Optima event. Once we got north of about 125 mph, the downforce pushed the rear fenders onto the tires. And that’s bad.

Another problem cropped up at the same time: All that rear rubber was producing a lot of lateral grip–so much of it, in fact, that our Corvette’s once benign handling was thrown off. The car now understeered during all phases of cornering. While this allowed us to get to full throttle earlier on corner exit, during turn-in and through the middle of the corner we frustratingly had to wait on the chassis. 

 

Sam to the Rescue

Our solution–like the solution to so many other Corvette-related problems–came with a call to Sam Strano of Strano Performance Parts. Sam knows a thing or three about Corvette handling, and he has the stack of Solo National titles as both a driver and a builder to back up his advice. He’s also incredibly open with information: Sam has no setup secrets or proprietary information, he simply offers ideas to help drivers succeed. 

One of the best things about running coil-overs on a Corvette? Lots of spring choices. Coil spring open a wealth of tuning opportunities that just don’t exist with the stock transverse leafs. Photography Credit: J.G. Pasterjak

After a few chats, we came to the conclusion–or at least the hypothesis–that between the aero-induced squat and the grip-induced push, our car needed a bit more rear spring rate. The RideTech kit had shipped with 700 lbs./in. front and 600 lbs./in. rear springs, which perfectly complemented our 315mm square tire setup. The increased rear grip, however, seemed to demand more spring.

Sam advised we install 750 lbs./in. coils out back, and was able to deliver the proper set of Hyperco springs within three days of our conversation. It’s reassuring having someone who can not only discuss possible solutions, but deliver them as well. We had the parts in our hands almost before we could even sweep out the garage and get the car jacked up. 

After our first session on the high banks of Daytona, we spent a lot of time cleaning rubber debris from our rear wheel wells. (Note how nicely our neck fits inside those new flares, though.) Quick tip for C5Corvette owners: The next time you remove your rear shocks, replace the upper bolts with studs and nuts. This makes removal and installation orders of magnitude easier. Photography Credits: Tom Suddard (Corvette on jacks), J.G. Pasterjak

The uprated springs seem to be a success. We haven’t been back to Daytona yet–even though it’s just across town, it’s not like we can run laps whenever we please–but our testing has revealed improved handling, especially through the middle of turns, where the car now carves a line better than before. Mid-corner adjustments can now be made with the steering wheel, meaning we don’t have to wait around until the tail end of the turn and attempt to fix things with the gas pedal. 

 

More to Do

Did you catch that mention of our Wilwood brake hats? They call that foreshadowing; look for a future installment detailing our full Wilwood setup. Plus, there’s more aero to cover. We’ll also discuss some of the safety upgrades that give us a little more reassurance on track. Look for all this and more coming soon.

 

Strapping Young Lad: Proper Tie Downs for Our Corvette

Did we mention how handy it is to know Sam Strano when you own a Corvette? That became clear when he recently busted our humps after seeing a picture of the car lashed down to its trailer, where we had run the tow straps through the wheels. 

We replaced our flapping, generic tie-downs with a set specifically designed for the Corvette. Photography Credits: J.G. Pasterjak

“I can fix that for you,” Sam said, before even asking the length of our trailer or the current tie-down configuration. Naturally he had the proper setup in stock. 

A few days later–and after a less than $300 charge on our credit card–a set of Mac’s Tie Downs arrived. They perfectly fit the Corvette and feature ends that properly hook into the car’s factory frame slots. Loading and unloading the car is now a breeze. The ends of the straps no longer flap in the wind, while the smooth release action of the Mac’s ratchets can be operated with just one hand. 

Remember that tow straps are very much a wear item, and their condition should be taken seriously and monitored, much like a safety harness or other item whose webbing can degrade after prolonged exposure to UV rays and the elements. (Likewise, don’t forget to store tow straps out of the sun, and take some time to regularly clean and lubricate them.)

Our take-home advice, no matter what car is on the trailer: If you plan to tow the same vehicle frequently, invest in a fitted set of straps. You’ll find it’s worth the expense when you work with properly fitting straps, whether you’re taking your time loading up at home or trying to get on the road at a dark, rainy race track.

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