Basic Suspension Geometry: Introduction

The safety, stability, handling and performance of a vehicle depends on many factors. One of the most important aspects of these characteristics is the design of suspension and steering systems. BMW vehicles are known for their superior handling and road holding performance.

The design of the BMW suspension systems is a key factor in achieving these goals. Suspension geometry is defined as: "The angular relationship between the suspension, the steering linkage and the wheels - relative to the road surface."

Fig 1: Identifying Design Of BMW Suspension Systems

Courtesy of BMW OF NORTH AMERICA, INC.

There are several alignment geometry angles which relate to the suspension components and steering linkages including:

• Caster
• Camber
• Toe-In/Toe-Out
• Steering Roll Radius (steering offset)
• Steering Axis Inclination (SAI) and Included Angle (IA)
• Toe Out on Turns
• Thrust Line and Thrust Angle

All of these angles influence:

• The ease with which the vehicle can be steered
• The overall vehicle stability (handling, tracking and safety)
• Tire wear

The suspension geometry for any given vehicle is a result of the design engineers development of the vehicle and the design criteria for that particular vehicle.