When it comes to getting around a corner better, one of the first things to change is tire camber. Back in 1967, most standard Camaros came with a Uniroyal Laredo 7.35x14 tire on a 5-inch-wide rim. Tread width was a whopping 4.5 inches! The main thinking of engineers at that time was to set the car up with lots of understeer so it would never spin out. If the driver slammed on the brakes and jerked the wheel, they wanted the car to just plow into whatever was ahead rather than spin out, roll over, or cross over into oncoming traffic. Hanging corners at 1g was never part of the thought process.

Most Camaros have a front weight percentage of 52 to 58 percent depending on engine type, equipment, and modifications. This high front weight percentage puts extra lateral load on the front tires when cornering. When negotiating a slalom, tire lateral loads are at their highest because the mass of the car is shifting side to side. This makes running a slalom toughest on cars with high front end weight, narrow front tires, or poor camber curves.

Tire Performance

Tires need negative camber to perform their best. Tire companies have test data that tells them the ideal amount of negative camber for a given load. This test data is closely guarded and not shared with the public, so specific data for a specific make of tire is not available unless you want to pay some big bucks to have your own tires tested at CALSPAN like some pro race teams do. In general, we know a few things about what a tire wants in the way of camber. Adding negative camber helps the tire generate more grip for a given load, it takes pressure off the outer shoulder of the tire and moves it inward, spreading the load more evenly across the whole tread area. It also lowers the slip angle and reduces turning effort. Slip angle is the difference between where a tire is pointed and where it is actually going. The more it's sliding, the higher the slip angle. When we want to increase cornering grip, more negative camber is the primary adjustment to get the tire in a more optimum part of its performance curve.

Geometry

Figure 1 shows a common first- and second-gen Camaro suspension layout. The upper control arm is usually 75 percent as long as the lower control arm. On a stock Camaro, the arms are nearly parallel at ride height, making for very little to no negative camber gain in bump (dive) or roll. As the wheel goes up, the top of the tire is pulled in more. The tire pivots around the Instant Center, (IC) but the IC moves inward towards the centerline of the car in bump due to the angles and lengths of the control arms. The usual way to increase negative camber gain is to lower the upper control arm's inner pivot point, use a taller spindle, or install extended upper ball joints. Placing the upper control arm at a steeper angle improves camber gain but can increase side scrub at the tread and alter roll center height and movement. More on that some other time.

Way back in 1967, the first road race ever won by a Camaro was engineered and driven by Dick Guldstrand. Guldstrand lowered the upper control arm mounting points, increasing negative camber gain in bump and roll. This is often called the "Guldstrand Mod," and Guldstrand still sends out templates with the hole locations to those who ask. But even with this lowered pickup point, the amount of camber gain is not enough to make up for body roll. To make up for that, additional static negative camber was used. Anywhere from 2 to 3 degrees of negative camber is used for all-out autocross Camaros. The third-generation and later-model Camaros have a more limited amount of adjustment room. Generally, the more negative camber gain per inch of bump your suspension has, the less static negative camber you need to start with.

Camber Thrust/Toe

Another interesting force created by increased negative camber is camber thrust. Figure 2 shows a tire with negative camber of 3 degrees. If we extend lines from the top and bottom of the tire, they intersect at what's call the Instant Center. Excluding a few other factors, this is the center of a circle the tire will try to roll around. Imagine the lines as a cone. The cone would roll around in a circle with a radius of about 40 feet. Since the tire can't roll around in the circle it "wants" to go in, it pushes inward on the suspension. This makes the car drive like it has excessive toe-in and toe must be reduced accordingly to compensate. If stock toe settings of 3/16-inch are used with -3 degrees negative camber, both tires will push inward and can even push hard enough to raise the front of the car a little or wear the outside shoulder of the tire. It's not uncommon to set toe-in at zero or even toe-out to tune in faster steering response for autocross. First-gen Camaros generally tolerate less toe-out than second-gen Camaros, which have a tendency to toe-in under bump, first-gen's toe will toe-out a lot. Third-gens and later have better steering geometry.

No Free Lunch

So where's the downside? Why doesn't every car come from the factory with two or three-degrees negative camber? Or why don't they set the suspension geometry to have lots of negative camber gain? Just like there's "no free lunch," you pay for all that cornering joy by wearing the inside edges of your tires while driving on the freeway. You also have the tires tugging on the steering wheel because they want to turn. The car will feel a little more nervous like it's waiting for your command to turn, and then it's gonna turn! Generally, a more aggressive camber curve will raise the front roll-center, which will have a stiffening effect on the front in-roll. When the tire changes camber more, the roll centers move more. On corner exit and track out, you are on the gas and the front end lifts. All that wonderful negative camber gain reverses and becomes positive, so you can have power-on understeer.

Tuning Tips

The best way to get going with camber settings is to assess how aggressive you need to be. Not everyone needs -6 degrees camber like Indy Cars run.

Here are some tips:

First and Second-gens

  • Street driven, stock with no mods, occasional corner carving: -0.5 to -1 degrees negative.
  • Street driven, geometry mods, but like curvy roads: -0.5.
  • Autocrossing/Track, no geometry mods: -3 to -4.
  • Autocrossing/Track with geometry mods: -2 to -3.
  • Heavy street, occasional Autocross/Track, a lot of geometry mods, run hard: -1.5.

Late-Models

Newer Camaros, like third-, fourth-, and fifth-gens, usually cannot get more than -0.75 degrees camber unless they are lowered. If so, they can get about -1 degree. I'd max out the negative camber setting and set as much positive caster as possible within the factory adjustments. Be sure to reset toe-in. On a third-gen you can mark where the factory settings are, slide the strut inward, and rearward all the way for an autocross, then push it back to the stock settings for street use.

Further refinement comes from tire temperature readings, lap times, and tracking tire wear. Every car and tire combination will be a bit different, so hitting the track is the only way to optimize your settings.

SOURCE
Pozzi Racing
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www.pozziracing.com