![\"\"](\"http:\/\/www.rhoadescamaro.com\/build\/wp-content\/uploads\/2010\/11\/DSC09325.jpg\" "\\"DSC09325\\"")
<\/a><\/p>\nThe angle, a bit over 8 degrees (90-81.7=8.3) is the “kingpin inclination” (KPI) or “steering axis inclination” (SAI) angle. \u00a0It is basically, the angle from vertical about which the knuckle rotates when steered.<\/p>\n
There are pros and cons to this angle being big or small. \u00a0One pro, is it ends to reduce the “scrub radius” that some people say is a bad thing. \u00a0It also provides a centering force akin to positive caster.<\/p>\n
A con though, is that it produces positive camber in the outside wheel – i.e., if you turn right, the left front wheel will get positive camber just from turning. \u00a0The higher the KPI, the more positive goes the camber. \u00a0This is a Bad Thing.<\/p>\n
Can’t change KPI in this class, really requires a whole new knuckle. \u00a0But we can fight this Bad Thing with a Good Thing, and in our case that Good Thing is positive caster.<\/p>\n
Caster is the same sort of angle as above, except as viewed from the side. \u00a0Positive caster produces negative camber on the outside wheel when turned. \u00a0 The more positive the caster, the more negative camber gain.<\/p>\n
Autocross has some fairly tight maneuvers, ones that often require large amounts of steering angle input. \u00a0Long wheelbase cars like the Camaro have to use even more steering input around given radius corners (see \u00a0CVD 4 – Skidpad<\/a><\/em> for some explanation), making it all the more important that, to the maximum extent of our rules-bound ability, we minimize any unfavorable consequences of turning the wheel.<\/p>\n Many modern cars use a lot of caster. \u00a0The Porsche 911 GT3 uses upwards of 8.5 degrees; some Mercedes-Benz come from the factory with over 11 degrees. \u00a0 Heck, even the latest Mustang uses 7 or more. \u00a0Lots of sporty cars made in the last 20-30 years provide 5-7 degrees.<\/p>\n Most people don’t believe me when I tell them what the Camaro’s base caster setting is. \u00a0Here’s photographic proof, from my Chevrolet Chassis Service Manual, (far right column):<\/p>\n That’s right, the factory caster setting is positive 1\/2 degree, plus-or-minus 1\/2 degree. \u00a0Meaning potentially zero degrees positive caster! \u00a0So with over 8 degrees of KPI\/SAI, there is almost no positive caster to counteract that positive camber gain on the outside front tire.<\/p>\n Just another facet of how bad the first-gen Camaro’s front suspension is from the factory. \u00a0\ud83d\ude42<\/p>\n So, to try to nullify this Bad Thing we’ll add some positive caster to the equation. \u00a0Common thinking amongst most of the first-gen Camaro guys is that “4 or 5 degrees is enough”…which of course means that I’ll be aiming for at least twice that much! \u00a0\ud83d\ude42 \u00a0The thing is, even at about 8.5 degrees of positive caster, its beneficial effects are only canceling out the detrimental effects from the KPI. \u00a0A first-gen Camaro with 12 degrees of positive caster will only see about the same positive effect from caster, that a “normal” car would get with 6-7 degrees.<\/p>\n Adding all this caster isn’t a trivial endeavor either. \u00a0 There’s a few side effects that must be managed.<\/p>\n One is an increase in steering effort. \u00a0I’m a big believer in providing the driver with a stable, precise, sensitive, and consistent platform upon which to operate. \u00a0 If we require the driver to use big muscles to dance the car through the course, we can’t expect the driver to have a lot of precision touch in his inputs. \u00a0To help enable this, I plan to run power steering. \u00a0An excellent race seat will hold the driver in, without any stabilizing forces through the wheel. \u00a0This should enable “fingertip” steering wheel forces, enabling the driver to maintain a much better feel for the front tires. \u00a0I believe the power steering ratio on the Z28 was also a bit quicker, which I like – it’s also harder to be precise when you have to produce huge turns of the wheel in a small amount of time.<\/p>\n The other side effect is it can change your wheelbase. \u00a0 The traditional (and FSM-specified) way of adjusting camber and caster on these cars is to use shims on the upper control arm’s inner attachment point. \u00a0Use of shims at both ends produces negative camber, and their use at one end or the other changes caster. \u00a0The threaded upper bolts are long enough to produce large amounts of change. \u00a0This method of caster adjustment moves the upper ball joint “back”, and if the hub is centered between the upper and lower ball joints, moves the wheel centerline back half that distance.<\/p>\n The problem here, is the whole wheel is moved back in the wheelwell, and with the amount of caster I plan to add, doing it all with the upper arm, would move the wheel back more than 1\/2″. \u00a0I want to be able to run very very low, and do everything I can to reduce or eliminate rubbing with the big 265-section front tire. \u00a0The Camaro’s inner fender has the most vertical room right at the stock front wheel centerline, which means I need to keep the wheel centered to maximize how low I can go.<\/p>\n To keep the wheel centered, but still produce large caster values, means I need to also move the lower ball joint forward, while moving the upper ball joint rearward. \u00a0If I move each equal amounts, the wheel stays centered in the wheelwell, and I get to enjoy the yummy KPI-canceling positive caster.<\/p>\n Since I’m spending my custom control arm allowance on replacement upper control arms, I have to stick with the stock lower arms. \u00a0However, there is an allowance for replacement offset bushings. \u00a0So long as these offset bushings don’t contain any more metal than stock, I can use them to produce some of this same caster gain. \u00a0You can see in the pic below, how the mount axis goes through the bushing cylinders at an angle – this produces a clockwise rotation (in top view) of the driver’s side lower control arm, moving the lower ball joint forward.<\/p>\n<\/a><\/p>\n<\/a><\/p>\n