Dec 1, 2018 update to the Chevrolet Corvette Z06 project car

Project Z06: Keeping Our Alignment Stable

Getting a suspension aligned and keeping it aligned are two different challenges. Recall our talk about static and dynamic alignment a few pages back, and let’s see how that applies to maintaining our Corvette’s performance alignment.

First, let’s talk about our static settings, because even if we set them to a certain measurement, they may not stay that way. Toe settings are unlikely to creep, but paint marks on the tie rods can easily reveal any slipping parts. Plus, those reference points can be used to index settings.

Caster settings, however, are subject to some creep depending on how they’re adjusted, especially on MacPherson strut cars. On our Corvette’s A-arm suspension, caster is adjusted via shims placed beneath the control-arm mounts, so there’s no chance of anything slipping. If a shim falls out, we probably have bigger problems. But on a strut car, caster is sometimes adjusted by moving the upper strut mount through slotted holes. Since this setup doesn’t employ any sort of positive stops, these connections are subject to slippage under the extreme loads of track driving or autocross. Adding additional fastener retention strategies like Nord-Lock washers can be a good idea in these situations, and a few dabs of paint can be used to reveal any slipping.

Camber adjustments are also subject to movement in cars that use slotted or oversized holes. And here’s where we ran into a potential problem. Our Corvette’s camber is adjusted via the eccentric bolts used to locate the inner pivots of the control arms. Camber is only secured by the clamping force of those bolts. Add in the lack of positive stops and the relatively soft aluminum subframe, and there’s a chance that something will move when pushed too hard.

Meet the Fix

Our solution to this issue came via the AMT Motorsport Adjustable Camber Kit. It features machined aluminum bolts that are beveled, thus providing adjustment cams that are incapable of slipping once tightened.

Not sure if these parts are up to the task? When AMT’s machines aren’t cranking out Corvette parts, they’re building microtolerance military and medical hardware. As a bonus, the $350 kit–which provides adjusters for the entire car-allowed us to achieve even more negative camber than before.

Now we needed to address another issue: keeping our desired alignment settings predictable as the suspension moves about. The biggest culprits behind dynamic alignment variances are typically the rubber bushings used to isolate suspension members from the chassis. Most OEM bushings do a great job of controlling noise, vibration and harshness, but as cornering loads increase, so does their deflection, causing vital suspension bits to move relative to the chassis through more than their desired axes.

To find out how much movement was actually taking place, we set up a simple experiment. We took a set of stock C5 control arms and applied some force to deflect the bushings. Just 500 pounds of force compressed the stock rubber control-arm bushings 0.025 inch. Extrapolate that movement at the chassis/arm pivot point into potential deflection at the contact patch–which could be separated from this point by even more rubber bushings–and you see that even on a world-class sports car, rubber bushing deflection can cause notable dynamic alignment change.

The solution is a bushing material that constrains suspension arm movement to the desired axes. Materials like polyurethane and Delrin are commonly used to make performance-oriented bushings, since they provide a solid base for pivoting while resisting compression. They’re still somewhat plastic, however–a plus in terms of reducing noise, vibration and harshness, but a performance compromise nonetheless.

Bearings, however, are not at all plastic. Spherical bearings limit the motion of the suspension components to only the desired directions while allowing for zero unwanted slop or deflection. They also reduce friction in the desired movement arcs.

AMT Motorsport provides a solution here in the form of a complete monoball bearing kit for Corvettes–C5 through the current car. Step one is to remove the stock control arms and send them to AMT, where they’re stripped, inspected and prepared for the bearing kit. The bearings are then pressed into heated arms; when the arms cool, the bearings are locked in for a zero-tolerance fit. The bionic arms can then be reinstalled.

The transformation is immediately noticeable. C5 Corvettes, oddly enough, are not blessed with the best steering feel considering their capability. Eliminating their notoriously weak rubber control-arm bushings goes a long way toward sharpening steering response, improving control during loaded cornering, and providing helpful feedback to your hands. It also keeps dynamic alignment spot-on, making for predictable breakaway tendencies that are welcome in a car with such high limits.

The tradeoff is a lack of noise and vibration isolation. Let’s face it, metal on metal is not as soft as metal on rubber. Still, we’d call the $2500 bearing setup “streetable” for the occasional drive to the track or autocross. It’s probably not ideal for a daily driver, but it won’t automatically preclude the occasional drive on the street. For the performance gain, we’ll tolerate a little bit more noise.

Stay in Line

Time to actually make some changes to our Vette. We started by setting the camber. Our BFGoodrich g-Force Rival S tires prefer a lot of camber, so we delivered. (When you start grinding the outside edges, you’ve gone too far.) The AMT hardware allowed us to max out the fronts at 3.5 degrees of negative camber. At the rear, our testing revealed that our car is happiest when set one notch from max, meaning 2.6 degrees negative. Tire wear seems pretty ideal with that much camber, while any more would cause wheelspin issues.

Then we set our caster. We picked the side with the most and simply equalized the other, so we’re running 5.75 degrees. While increasing caster also increases stability, adding too much to the Corvette starts to eat away at the amount of static negative camber.

Finally, we set the toe. We started with zero all around for our baseline and planned to adjust as needed. If the ground is wet, or if we’re running higher-speed venues where we want slightly more benign manners, we’ll toe in the rear slightly— maybe 1/16-to â…›-inch total. If we want a little snappier turn-in, or if we’re running lower-speed venues featuring tight turns, then we’ll set the rear straight ahead and maybe toe out the front just a bit. Since we indexed our tie rods with paint markings, we’ll always be able to return to our base settings.

This latest round of hardware has given our Corvette a new, stable suspension, but there’s still some more work to be done. Corvette purists, please cover your ears as we announce our next step: We’re going to replace the stock transverse leaf springs with some coil-overs. Stay tuned.

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