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The total resistance to body roll provided by springs and anti-roll bars, measured in pounds per inch of wheel travel or Newton-meters per degree. The distribution of roll stiffness between front and rear axles is the primary tool for tuning handling balance.
Adams' Chassis Engineering explains the practical relationship: "The best way to control camber changes caused by body roll is to limit the roll angle by changing the roll stiffness of the suspension. The two most common means of controlling the roll stiffness on any given car are via the springs and the stabilizer bars." He illustrates the trade-off: "if a car had a front spring rate of 700 lbs-inch and a roll angle of 2 degrees, and you wanted to reduce the roll angle to 1 degree, you'd need to install 1400 lbs-in. front springs. This would double the roll resistance." He adds the critical performance insight: "cars that corner faster will need more roll stiffness to control the roll angle" — a car on race tires cornering at 1.0G will have 33% more roll angle than the same car on street tires at 0.75G, assuming the same roll stiffness.