Roll stiffness

Roll stiffness is a measurement of a vehicle or axle's resistance to chassis roll. Total roll stiffness for an axle is calculated by adding up the roll stiffness of all elastic suspension components. On a typical vehicle, that may include the springs and the anti-roll bars. However, as of 2025, we do not use anti-bars, so our total roll stiffness is equivalent to our spring roll stiffness. Each axle has its own roll stiffness. The vehicle has a total roll stiffness as well which is found by adding the roll stiffnesses of each axle.

Roll stiffness is used to calculate lateral load transfer distribution.

Corner Spring Roll Stiffness

Spring roll? Yum! Corner spring roll stiffness on a given axle is determined using the following:

$k_{\theta }{}_c{}_s=1/2\times k\times M{R}^2\times t^2$

• k_{theta cs} is the contribution to overall roll stiffness by the corner springs
• k is the linear spring stiffness
• MR is the motion ratio between the corner spring and the displacement of the wheel center
• t is the tract width of the axle

Anti-roll Bar Roll Stiffness

The estimated torsional stiffness of an anti-roll bar on a given axel can be calculated using:

$k_a{}_r{}_b=\frac{\pi D^{4}G}{32l}$

• k_arb is the torsional stiffness of the anti-roll bar
• D is the diameter of the anti-roll bar
• G is the anti-roll bar's material's shear modulus
• l is the anti-roll bar's effective length

The ARB roll stiffness is determined using:

$k_{\theta }{}_a{}_r{}_b=k_a{}_r{}_b\times M{R}^2\times t^2$

• k_{theta arb} is the contribution to overall roll stiffness by the anti-roll bar
• MR is the motion ratio between the twist angle of the anti-roll bar and the wheel center displacement

Sources

Simplified steady-state lateral load transfer analysis for spring rate and anti-roll bar selection | Kelvin Tse