Ackerman Steering and Racing Oval TracksMany racers are becoming aware of Ackerman Steering geometry and are concerned with how it influences their race cars. Conventional Ackerman Steering was developed around 1800 AD. Yes, 1800, not 1900. The Ackerman concept is to have all four wheels rolling around a common point during a turn.

                                                 

The example above shows that the inside front tire must turn a larger number of degrees than the outside front tire for this principle to work.

Ackerman Steering Theory

The theory was originally developed for wagon designs to keep them from skidding crushed stone driveways.

Modern race cars will use this as a baseline and then adjust the closeness to true Ackerman in order to maximize traction. For best efficiency, keep it as close to true Ackerman as possible. See next 4 slides to help with the geometry.

Ackerman Linkage Set Up

Top View

Rear Mounted Rack with 4 Wheels

Ackerman Linkage Set Up

Top View

Front Mounted Rack with 4 Wheels

Ackerman Linkage Set Up

Top View

Front Mounted Rack with 3 Wheels

Ackerman Linkage Set Up

Top View

Rear Mounted Rack with 3 Wheels

Top View of Toe-in

Positive Toe

Zero Toe

Toe-in angle “a” is the angle of how much the wheels point in. Negative toe is when the wheels point out. Rear wheel production cars have 5-20 of toe in and front wheel drive cars have up to -20 degrees of toe out to compensate for drive forces and bushing compliance. For maximum efficiency with a rigid suspension, toe should be kept to near 0 with slight toe-in if the vehicle steering feels darty.

aa

Front view of camber.

Negative Camber

Zero Camber

Camber angle “c” helps keep the flat part of the tire in contact with the road during hard cornering. Production cars are generally -3..0 degrees. For max efficiency keep this as close to 0 as possible.

Front Viewcc

Caster and Caster Angle

Positive Caster is the distance that the contact patch of the tire follows with regard to the point at which the steering axis contacts the ground. Caster determines straight line stability as well as self-centering feel. The caster distance for an has less to do with efficiency but has a lot to do with steering feel. Try to set caster at 1” in front of the contact patch. Negative Caster can lead to steering instability.

Front View of Kingpin Anglek

r

Kingpin angle “k” is the angle from the front view that goes through the steering axis. Kingpin angle influences on center feel and straight line stability. “r” is the kingpin offset or steering offset. “r” influences steering feel and dictates forces applied to the steering during braking. For maximum efficiency, minimize “r”, but do not have “k” above 7 or so degrees. Large values for “k” create high steering effort.