Steering Geometry Flashcards
What are the two aims of a steering system?
- Centre point steering
- When cornering all steered wheels must turn about a common centre
What is splaying of the wheel?
The turning in or out of the wheel due to forces of the vehicle and the road
What is the scrub radius?
(AKA Offset)
Distance between the centre point of king pin and wheel contact points
How is the large scrub radius problem overcome?
By varying steering geometry by:
- Wheel camber
- King pin inclination
- Dished Wheels
What is KPI?
(AKA king pin inclination)
Tilting in of the king pin
What are Negative camber advantages and disadvantages?
Advantages:
- Camber angle reduced when cornering
- Sensitivity through tyre is reduced (helps to keep the vehicle in a straight)
Disadvantages:
- Offset is increased
- Heavier steering
- Increased tyre wear
What are positive camber advantages and disadvantages?
Advantages:
- Lighter steering
- Offset reduced
Disadvantages:
- Cone effected
- Wear on the outer edge of the tyre
What is positive and negative camber?
- Positive: Wheel tilts out at the top
- Negative: Wheel tilts in at the top
What is negative and positive offset?
- Positive: When the wheel centre line meets the KPI/SAI below the road surface
- Negative: Where the angles meet above the surface
If there is no king pin what replaces the King pin inclination?
Swivel axis inclination
How do we counteract inward and outward splaying?
- Splay in = Toe out
- Splay out = Toe in
How should the vehicle be moved prior to using a tracking gauge?
Backwards then forwards (Forwards always being the last movement)
What checks need to be done before using a tracking gauge?
- Check tyre size, pressures and wear
- Check wheel bearing play
- Check front suspension for wear and damage
- Check the run out of the wheels
What methods of introducing caster are there?
- Moving the upper wishbone
- Offset centre bolt
- Underslung
- Overslung
What are the two ball joint splitters?
- Tapered wedge
- Clamp and screw
What are the two main ways a slip angle can affect a vehicle?
- Oversteer
- Understeer
What is the slip angle?
The difference between the intended line of travel and actual line of travel
What are the forces affecting slip angle?
- Cornering
- Camber
- Wind
- Weight
What happens to the steering if you have too much negative caster?
The steering becomes heavy
What is positive and negative caster?
Positive - Kingpin tilted to the rear at the top
Negative - Kingpin tilted to the front at the top
What can cause oversteer?
- Increasing the load on the rear of the vehicle
- Lower than recommended rear tyre pressure
- Large load transference from the inner rear wheel to the outer rear wheel when cornering
What can cause understeer?
- Increasing the load on the vehicles front
- Lower than recommended front tyre pressures
- Large load transference from the inner front wheel to the outer front wheel when cornering
What is front wheel alignment also known as?
Tracking
What does a ‘Toe out on Turns’ test measure?
Alignment of track arms
What will distortion of the track angle cause?
- Misalignment
- Incorrect wheel angle
What would happen if wishbones are of an equal length?
When road deflections lift the wheel the track will vary but camber wont
How can almost true rolling action be achieved?
- Inclining steering arms towards each other (ackerman angle)
- Line projected from each king pin meet on the centre of the vehicle ahead of the rear axle
What can cause the vehicle to pull to one side?
- Incorrect front wheel alignment
- Unequal track rod adjustment
- Incorrect steering angle
What is steering ‘shimmy’?
A rapid oscillation of the front wheels causing the steering linkage to shake from side to side
What can cause steering shimmy?
- Excessive play in the steering box
- Excessive play in the ball joints or king pin
What is steering ‘wander’?
The vehicle tending to swerve side to side, making controlled steering difficult
What can cause steering wander?
- Excessive negative caster angles
- Excessive play in steering joints
- Tight ball joints, kin pin or steering joint
- Incorrect steering box adjustment
