Suspension and steering systems
Published with permission from the Federation Internationale de l' Automobile.
ARTICLE 10: SUSPENSION AND STEERING SYSTEMS
10.1 Sprung suspension:
10.1.1 Cars must be fitted with sprung suspension.
10.1.2 The suspension system must be so arranged that its response results only from changes in load applied to the wheels.
10.2 Suspension geometry:
10.2.1 With the steering wheel fixed, the position of each wheel centre and the orientation of its rotation axis must be completely and uniquely defined by a function of its principally vertical suspension travel, save only for the effects of reasonable compliance which does not intentionally provide further degrees of freedom.
10.2.2 Any powered device which is capable of altering the configuration or affecting the performance of any part of the suspension system is forbidden.
10.2.3 No adjustment may be made to the suspension system while the car is in motion.
10.3 Suspension members:
10.3.1 With the exception of minimal local changes of section for the passage of hydraulic brake lines, electrical wiring and wheel tethers or the attachment of flexures, rod ends and spherical bearings, the cross-sections of each member of every suspension component, when taken normal to a straight line between the inner and outer attachment points, must :
- intersect the straight line between the inner and outer attachment points ;
- have a major axis no greater than 100mm ;
- have an aspect ratio no greater than 3.5:1 ;
- be nominally symmetrical about its major axis.
The major axis will be defined as the largest dimension of any such cross-section.
10.3.2 When assessing compliance with Article 10.3.1, suspension members having shared attachment points will be considered by a virtual dissection into discrete members.
10.3.3 No major axis of a cross section of a suspension member, when assessed in accordance with Article 10.3.1, may subtend an angle greater than 5° to the reference plane when projected onto, and normal to, a vertical plane on the car centre line with the car set to the nominal design ride height.
10.3.4 Non-structural parts of suspension members are considered bodywork.
10.3.5 Redundant suspension members are not permitted.
10.3.6 In order to help prevent a wheel becoming separated in the event of all suspension members connecting it to the car failing provision must be made to accommodate flexible tethers, each with a cross sectional area greater than 110mm². The sole purpose of the tethers is to prevent a wheel becoming separated from the car, they should perform no other function.
The tethers and their attachments must also be designed in order to help prevent a wheel making contact with the driver's head during an accident.
Each wheel must be fitted with two tethers each of which exceed the requirements of 3.1.1 of Test Procedure 03/07.
Each tether must have its own separate attachments at both ends which :
- are able to withstand a tensile force of 70kN in any direction within a cone of 45° (included angle) measured from the load line of the relevant suspension member ;
- on the survival cell or gearbox are separated by at least 100mm measured between the centres of the two attachment points ;
- on each wheel/upright assembly are separated by at least 90° radially with respect to the axis of the wheel and 100mm measured between the centres of the two attachment points ;
- are able to accommodate tether end fittings with a minimum inside diameter of 15mm.
Furthermore, no suspension member may contain more than one tether.
Each tether must exceed 450mm in length and must utilise end fittings which result in a tether bend radius greater than 7.5mm.
10.4.1 Any steering system which permits the re-alignment of more than two wheels is not permitted.
10.4.2 Power assisted steering systems may not be electronically controlled or electrically powered. No such system may carry out any function other than reduce the physical effort required to steer the car.
10.4.3 No part of the steering wheel or column, nor any part fitted to them, may be closer to the driver than a plane formed by the entire rear edge of the steering wheel rim. All parts fixed to the steering wheel must be fitted in such a way as to minimise the risk of injury in the event of a driver's head making contact with any part of the wheel assembly.
10.4.4 The steering wheel, steering column and steering rack assembly must pass an impact test, details of the test procedure may be found in Article 16.6.
10.5 Suspension Uprights:
10.5.1 The suspension uprights must be made from a permitted aluminium alloy. Particulate reinforced aluminium alloy matrix composites are forbidden.
10.5.2 The loads from the suspension members and wheel bearings must individually and entirely be carried by the suspension upright. Exceptionally up to three suspension members may be connected together by titanium, aluminium alloy or steel components before their load is passed into the upright.
10.5.3 Suspension uprights may not protrude beyond:
‐ A vertical plane parallel to the inner face of the wheel rim and displaced from it by 120mm toward the car centre line.
‐ A radius of 180mm from the centre of the wheel when viewed from the side.
The above measurements will be made with the wheel held in a vertical position.
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