Stabilizer bar (anti-roll bar)

01

Set the section, steel and bar rate

Wittek and co-authors from ThyssenKrupp Federn und Stabilisatoren and the Silesian University of Technology note that the inner section of a loaded stabilizer bar contributes little, which is why tubular bars were developed to save weight. For equal stabilization a tube needs an outer diameter about 6.5% larger than the solid bar and saves about 40% in weight; realistic weight saving does not exceed 45%, and the ratio of outer diameter to wall thickness should not exceed 6.5 to 7.5. Solid bars are made from heat-treated steels to DIN 17200 and 17221, and tubular bars primarily from micro-alloyed 26MnB5 and 34MnB5, hot or cold bent. [1]

Their test bar was a Ø23.5 × 3.6 mm tube in 34MnB5 (Rm = 1700 MPa), hot bent with a 50 mm bending radius, oil hardened and tempered. Listed data: stabilizer bar rate 41.6 N/mm, end force 3575.7 N, spring deflection 2s of 86.0 mm, bearing distance 616 mm ±2, leg distance 1024.1 mm ±2, maximum equivalent stress 890 MPa, conductive heating to 940 °C and 856 °C before hardening. The bar failed early because proeutectoid ferrite formed at the bending radii; ferrite depth above 0.15 mm led to fatigue fracture. [1]

NHK Spring's hollow stabilizer patent explains that seam-welded tube from roll forming reaches a wall thickness ratio (wall thickness ÷ outside diameter) no higher than 0.15–0.17, and that seam-welded tube can save 50% or more in weight against a solid bar when the design stress allows. Its method cold-draws the tube to a ratio of 0.20–0.27 and a tensile strength of 800–1,000 N/mm², bends it cold, anneals it at 300–450 °C and shot-peens it, giving 20–30% weight reduction; it names SAE 1541 as a steel example and limits carbon to 0.17–0.45 wt%. [2]

For solid bars, the NHK Spring and JFE patent on stabilizer steel records carbon steel such as S48C and spring steel such as JIS SUP9 in conventional stabilizers, and notes that stabilizers of 1000 MPa or more have been developed. [3]

Editorial calculation: torsional stiffness of a round section is proportional to its polar moment, π(D⁴ − d⁴)/32. For the 23.5 × 3.6 mm tube (inner diameter 16.3 mm), (23.5⁴ − 16.3⁴) ÷ 23.5⁴ ≈ 0.77, so it keeps about 77% of the stiffness of a 23.5 mm solid bar; the solid bar with equal stiffness is about 22.0 mm, against which the tube is about 6.8% larger in diameter and about 41% lighter — consistent with the paper's figures. Its D/t is 23.5 ÷ 3.6 ≈ 6.5, and 41.6 N/mm × 86.0 mm ≈ 3,578 N matches the listed end force. [1]

Give the supplier the vehicle and axle (front or rear), required bar rate or roll stiffness, 3D drawing with bend radii, leg and bearing distances, solid or tubular section and outer diameter and wall thickness, steel grade and tensile strength, end form (eye, flattened or ball-joint mount), bushing and bracket positions, fatigue test load and cycle target, coating and corrosion test, and quantity.

02

Prove fatigue life, shot peening and corrosion protection

The JFE and NHK Spring patent describes the production route as cutting hot-rolled stock, hot bending, hardening and tempering to strength, shot peening the surface and finally coating for corrosion protection; coating raises the material to about 180 °C. Stepping stones cause dents and coat peeling, corrosion then starts fatigue cracks, and low-temperature toughness matters in winter when corrosion is severe; in its tests a specimen with absorbed energy below 40 J/cm² at −40 °C was rejected. [3]

NHK Spring's hollow-bar examples all target durability of 150,000 cycles or more at the same displacement; a solid bar quenched and tempered to 1,270 N/mm² met it, a hollow bar from seam-welded tube with a 0.16 wall ratio reached only about 1/4 to 1/3 of the solid bar's durability, and tube below 750 N/mm² tensile strength can break before 150,000 cycles. Shot peening at 300–400 °C right after annealing gave durability at the level of the solid bar, and internal shot peening before bending is an added option. [2]

Meritor's tubular stabilizer patent notes that shot peening the outside creates compressive residual stress, but the nozzle cannot reach the whole inner surface near the bends, so fractures in peened tubes start on the inner surface; it proposes autofrettage, pressurizing the sealed tube to put the bore in compression. [4]

The ThyssenKrupp test rig accepts bars up to 1100 × 350 mm and 10–25 mm in diameter, with end forces up to ±4 kN, ±40° oscillation and 0.5–4 Hz. [1]

Bushings: NHK Spring's bushing patent describes a vulcanized rubber bush bonded to the painted bar and held by a bracket bolted to the body. Water between bar and bush, or very low temperatures, can let an unbonded bush slip and make noise, and mud, sand or salt water entering the gap can break the bar's coating. It names JIS G 4801 spring steels SUP3, SUP6, SUP7, SUP9, SUP9A, SUP10, SUP11A, SUP12 and SUP13 for the bar. [5]

Ask for the fatigue test method (rig, load or angle, frequency), cycle target and results on production bars, shot peening coverage including bends and bore, decarburization limits, hardness, coating system, stone-chip and corrosion test, low-temperature impact data, and bushing type (bonded or loose) and material.

03

Compare what suppliers offer

The reviewed suppliers list stabilizer bar bushings only; none was found to list the stabilizer bar itself.

When requesting quotations for bars, ask each supplier for its bending, heat-treatment and peening process, steel certificates, fatigue and corrosion test reports and drawings. For bushings, ask for rubber compound, bore size matched to the bar diameter, bonded or loose design and bracket drawing.

04

Trace the stabilizer bar assembly

This is a functional reference built from the sources cited; it is not one maker's design.

05

Fill the specification fields with values for your vehicle

A stabilizer bar quotation needs values for your vehicle. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

06

Send the axle, geometry and proof requirements together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Vehicle: [model; front or rear axle]
Rate: [bar rate or roll stiffness]
Geometry: [drawing; bend radii; leg and bearing distances]
Section: [solid or tube; OD; wall]
Steel: [grade; tensile strength]
Proof: [fatigue load; cycles; peening; coating; corrosion test]
Bushings: [compound; bonded or loose; brackets]
Quantity: [units]

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