Chassis Basics
In order to tune your car, we would recommend that you understand your suspension system. This page aims to help you with the basics in stock car racing terminology and fundamentals.
Camber
Camber is simply the amount of "lean" your tire has. it is measured in positive and negative numbers. If the top of the tire is leaned into the car, it's negative camber and if the top leans out, then it's positive camber.
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Postive camber for the left front tire and negative for the right front. You tune this based on the amount of temperature split from inside to outside of your tire. This can be up to 25 degrees of split depending on your tire manufacturer.
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*Hotter on the inside of the RF and hotter on the outside of the LF is what you are looking for.
Caster
Caster is the amount of "lean" or angle the spindle has. This is set with the top of the spindle further back as compared to the bottom. You can look at the upper and lower ball joints to make the comparison, but should be measured with a caster gauge doing a steering sweep, following your gauges procedure.
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Positive caster is when the upper ball joint is further toward the back of the car as compared to the lower.
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Why do you want caster? It angles or cambers the tires as steering input is given. It gives the driver a responsive feedback from the steering wheel and it helps to turn the car because it loads the LF tire more as more steering is added because it decreases the dynamic crossweight or "de-wedges" the car as steering is added.
Caster Split
Caster Split is the difference in positive caster from the RF vs the LF. The more caster split you have, the more the car will want to steer itself into the turn. Typically a 2 -3 degree split from right to left is set. This means that the RF has more positive caster than the LF by 2 -3 degrees.
Cross-Weight
and Wedge
Cross weight and wedge are the same thing, just different terms. When we think about cross-weight usually we think about it when the car is at a static state, or at ride height. Dynamic cross-weight exists too, but measuring it is difficult as you need a pull down machine to measure the wheel loads under compression, so we will think about it at ride height.
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Increasing cross-weight increases the pre-load on the RF and LR corners as compared to the RR and LF corners of the car. When adjusting cross-weight you want to make sure of a few things:
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Car is full of fuel
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Tire pressures are at hot PSI settings
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Car is at the ride height settings you want to race at
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Sway bar settings are consistent (some cars have pre-laod on the sway bar and some only set dynamic pre-load)
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Suspension geometry is set; including trailing arm angles, bump steer, caster, camber, toe, differential square, 3rd link angle, pinion angle etc.
Basically, setting cross-weight is the last thing you will do.
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Increasing cross-weight will tighten your car and decreasing cross-weight will loosen your car. An old rule of thumb was to have the same amount of cross-weight as equaled to the left side weight. This isn't the case anymore as suspension systems have advanced and bump springs and bump stops dramatically alter the dynamic cross weight.
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Cross-weight is still important however, because it is a continually tuneable option for you at the race track that will help you gain a balance in your tire temperatures.
