Steering Roll Radius (Steering Offset)
The steering offset is the distance between the point of contact of the projected line drawn through the steering axis to the road surface and the center point of the tire contact area (foot print). The roll radius is the distance between these two lines.
- A positive roll radius exists when the steering axis line is inside the center line of the tire.
- A negative roll radius exists when the steering axis line is outside of the tire center line.
When the Steering Roll Radius is excessively positive, stability during braking is reduced. When the Steering Roll Radius is excessively negative, the directional stability is reduced and there is reduced feedback to the driver through the steering wheel. BMW vehicles are designed with a slightly positive Steering Roll Radius. This gives the driver a better "road feel" without compromising braking stability.
Steering Roll Radius is not adjustable, but can be influenced by improper tire and wheel combinations. Wheels with incorrect offsets can compromise handling characteristics. Scrub Radius is another term used to describe Steering Roll Radius.