Vehicle assumptions / geometry
Mass inputs are per corner. Spring motion ratio is wheel movement / spring movement equivalent used as kwheel = kspring × MR². ARB dimensions and adjustability are checked against current manufacturer data. Absolute axle roll-stiffness values in Nm/deg are estimates unless explicitly identified otherwise.
Comparison
FLLTD derivation
FLLTD includes elastic roll couple distribution, sprung-mass geometric load transfer through the roll centers, and unsprung-mass geometric load transfer. It is intentionally not the same quantity as front roll-stiffness distribution.
Calculation notes
Spring conversion
1 lb/in = 0.1751268 N/mm
Wheel-center spring rate = installed spring rate × motion ratio²
Tire-compliant corner rate = (kwheel × ktire) / (kwheel + ktire); axle ride rate = 2 × corner rate
ARB conversion
ARB axle roll stiffness is represented in Nm/deg. Where manufacturers publish only dimensions or percentage changes, the database value is marked as an estimate.
Equivalent wheel rate = 2 × Kφ × 57.2958 / (track² × 1000), in N/mm.
Both values are shown because they describe the same bar in rotational and linear terms.
Axle spring roll stiffness
Kφ = kcorner × 1000 × track² / 2 × π/180, in Nm/deg.
Roll gradient
Roll gradient = sprung-mass roll moment per g / total roll stiffness.
About / assumptions
This calculator is intended for comparative analysis and is not a vehicle setup prescription. Spring and anti-roll-bar specifications are based on the best available manufacturer and technical-source data. Where an absolute anti-roll-bar rate is not published, the displayed axle roll stiffness is an engineering estimate based on available dimensions, relative-rate information, and suspension geometry.
Always verify component specifications for your particular model year and part number.
Spring and anti-roll-bar library reviewed September 2026.