As Corvette owners, we are blessed with significant factory adjustability on the range of camber that we can get from the car. Most folks have to buy aftermarket camber plates, eccentric balljoints, and the whole rest of it to try and gain some negative camber for the sake of racing.
Regarding the reason for camber, in short, it's to help keep the tire as much || as possible during cornering, versus having the outside tire leaning over into positive camber during a turn. Not only does it improve your grip, but it helps wear your tires more evenly if you're racing a lot.
So if the C5 has camber adjustment, why the need for a camber kit? Two reasons:
First, and Hardbar's reason for creating these, is that adjustable camber, by definition, can move. Huh? Well, the factory eccentric bolts are built with the heads 'offset', so when you turn them, they move in a slotted hole, moving the lower control arms in and out, which changes your camber. This is great for the street, but when you're racing, if you hit an FIA curb hard, or drop a wheel into the dirt, or various other things, that can jolt the eccentric hard enough to move, which will change your camber, and as a result, your toe. This is undesirable, since you *really* want to be sure of what your car's going to be doing at 100+mph speeds!
Second, and my reason for getting these, is that the factory eccentrics do not allow the full range of adjustment that the slotted hole might otherwise provide. Nearly every racer I have talked to agrees that about -1.5* of camber in the rear of the car would be about ideal, but getting more than about -1.0* to -1.2* is quite hard for most.
In my '97, I was only able to get about -0.8 to -0.9, depending on the height of the car. For the sake of street driving, I run my car higher than most autocrossers, and so I'm handicapped even a bit more. Note that stiffer springs and bars will let you run the car lower in autocross, without having rubbing troubles.
Since my rear camber is the only place I was having trouble, I only installed the rear shims, but installing the fronts would be similar.
As far as actual numbers, don't take these as gospel, but most autocrossers I've talked to favor around -2.5 front, -1.5 rear, with maybe a little more in the front on some cars. Road racers like somewhat less in the front, -1.5 to -1.8, depending on the track, setup, and whatnot. Those are at least some guidelines to get started as you start asking other folks that know more than me!
Installation Notes - Removal
This installation took me around four hours the first time, which meant about 3 hours of fighting with the left side, and about 30 minutes to do the right, once I had figured out the tricks.
First, get your car up on stands however you prefer to do this, and pull the wheels you'll be working on.
If you look at the lower control arm, and follow it in towards the frame, where it mounts, you'll see a rubber bushing, and a bolt that goes through the subframe, through the bushing, and a nut on the opposite side. In the front, there is one of these at each point, so you can control camber and caster. In the rear, there is only one, at the front mounting pt. of the A-arm. (fig. 1)
When you loosen the eccentric to remove it, the control arm will want to flop inward towards the center of the car. On the nut-side of the bolt, there is also another circular plate that will want to come out with the bolt, and make sure to remove that as well.
Because of the weight and/or spring tension on the control arm, it will be nearly impossible to move the bolt much, especially in the tight space between the fuel tank and the rear subframe.
So, to make things easy, you can fashion a small support out of some 2x2 wood, that will hold the control arm in place, and remove the preload, so you can pull the bolt right out, and slap the new one in. You have to cut a small notch out of the wood, since the available space between the rear control arm and the leaf spring are tight enough that the 1.5" thick 2x2 won't quite fit. I chose a short piece of 2x2, since it would stand up on its own, and I then wouldn't have to balance it while moving the jack into place under the control arm. Once that is built and ready, the trick that takes a few minutes is getting the height juuuust right to remove the preload, and to not create more by jacking up the control arm. The support is pictured in fig 2, and its use in fig 3.
The eccentric bolt pulls out towards the front of the car, right into the way of the fuel tank and fuel lines. Just keep worrying it out until it pops free - you might have to hold some lines out of the way with your hand.
Installing the new Bolts
Since every car is different - manufacturing tolerances, ride heights, and things like that, the downside of these shims is that getting to your target alignment might take a few different tries in the shim size/offset. The kit is made up of 12 pieces of aluminum, 6 squareish, and 6 that are half-circles. Holes are drilled in a spot that is hoped to give you close to your target camber range. Cars might not even by symmetrical - as in my case - so you may have to install some different sizes from Hardbar on different sides of the car.
Since the replacement bolts are longer than the factory ones by just a skosh, I found that putting them in the front, facing towards the rear of the car, was impossible. so, I installed them the other way, but kept the square bushing in the rear, and the round one in the front, as indicated by hardbar's directions, which have pictures and are quite good. (I'm simply covering the tricky parts that helped me get it done faster)
To install the bolts with the shims on them as I did, first put a washer on the bolt, and then the square bushing. Remember, the hole goes towards the outside of the car, and make sure to orient the shim properly so that it will line up with the half-circle shim that will go on the opposite side. Push the bolt through (which should still be easy if you have the wooden support in place), and then put the other shim on, a washer, and then the nut, loosely.
Space is tight enough under the car that you'll have to tap the bolt back and forth a bit to get things lined up so that you'll be able to rotate both shims to get into their proper place. (Figs 4,5) Since the control arm flopped inward when you removed the factory shim, you'll now have to pry it outwards as much as possible. I used a medium-length pry-bar set from Sears, as in fig 6.
This might be fairly easy, as it was on the right side of the car, or it might be an absolute two-feet, muscles straining, cursing effort, like it was with the left side of the car. Just keep working at it until you get the shims locked into the machined indent in the subframe, and then tighten down the nut on the bolt to keep everything in place. The Nylok nuts should stay in place quite well, but torque everything down nicely with your 21mm wrench and socket, to make sure it all stays in place. (figs 7,8,9)
Results & Impressions
There isn't a whole lot to be said here, either, but I'll throw some notes out there:
On the first try, using the kit for -1.5* camber in the rear, I came out with -1.2 and -0.85* of camber. Wha? Well, this is for a couple reasons. First, as I said, my car is relatively high, especially compared to a T1 car, like Hardbar runs. When your car is lower, the control arms are already further along in their camber curve, and you can get more static negative camber. Second, some cars just seem to be off a bit, and it looks like mine is.
Since I had to buy a complete kit from Hardbar (my only complaint), I had some shims good for around -2.5* camber in the front of the car lying around, so I tried one of those in the RR to try and increase that camber up to a degree or more. I haven't gotten the car aligned yet, but I should be close, and if not, I'll try some new shims from Hardbar.
The pieces are nicely matched, and the hardware is good quality and metric (thank god). Dennis Bauer of Hardbar was tireless in answering my questions via phone - although a bit slow via e-mail - and has offered to ship me new shim sizes free of charge until I can get the alignment evened out. If I can get to the -1.2 to -1.3 level that most Z06's seem to be able to get to, then I'll be happy.
One final note - these aren't listed on hardbar's website, so it is probably best to just call and talk to one of the fellows there.
fig 4 - front shim with bolt loose.
fig 5 - rear shim with bolt loose.
fig 7 - front installed
fig 8 - installed front 2
fig 9 - installed rear shim