Design Position of Wheel Center Flashcards
What is the Wheel Base
Distance in the vehicle’s xz plane between the center of tire contact at the front and rear wheels
Wheel Contact Point
Intersection between the roadway and the wheel’s center plane
Long Wheel Base Influence
More room for passengers
Improved ride comfort
Improved safety
Shorter Wheel Base influence
Better Maneuverability
Lower Cost
Lower Weight
Typical wheelbase values
2100 - 3500mm
Ratio wheelbase to vehicle length
0.6 +- 0.07
Track Width
The distance in the yz plane between the centers of the tires’ contact on a single axle.
Wide track width influence
Better driving behaviour
Reduced vehicle roll
Improved design aesthetics
Narrow track width Influence
Less stability
Increased vehicle roll
Less room for passengers and powertrain
Track Width values
1210 - 1600mm
Ratio of track width to vehicle
0.8 to 0.86
Can the track width change during driving
Yes, camber changes and suspension kinematics effects during suspension compression and extension can change the contact path so it changes the track width
Vehicle Center of Gravity
Imaginary point at which the vehicle’s entire mass can be concentrated; position varies with vehicle loading
What does low CoG result in
Good handling and driving safety
Reduced vehicle pitch and roll
Reduced wheel load fluctuations on inclined surfaces
Higher CoG results in:
Increased rear axle load on inclined surfaces
Typical values of CoG
1000 to 1750 mm behind the front axle, 300 to 750mm above the road
What is Wheel Travel
Wheel travel is the displacement
s of the center of tire contact, also
known as spring travel or
suspension travel.
How is the wheel travel measured
It is measured from the neutral position.
Positive during jounce (suspension compression)
Negative during rebound (suspension extension)
Typical values of wheel travel
60 to 100mm for compression
70 to 120mm for extension
By which parameter is wheel travel described
- Camber angle
- Diagonal spring angle
- Roll center
- Toe change
- Camber change
What is Toe Angle
Angle in the road surface plane between the vehicle’s longitudinal axis and the center plane of the wheel
What does the toe angle influence
Straightline stability, cornering behavior, and suspension tuning
Toe out meaning
C > B; the distance between the front of the wheels is bigger than the distance between the back of the wheels
Toe in meaning
C < B; the distance between the front of the wheels is smaller than the distance between the back of the wheels
Typical Values of Toe angle
Front axle of rear-wheel-drive car 0°to +30’
Front axle of front-wheel-drive car -30’ to +20’
rear axle -20’ to +20’
Wheel camber meaning
Angle between the wheel’s center plane and a plane perpendicular to the road surface including the line of intersection between the road surface and the wheel’s center plane.
What does Camber influence?
Lateral dynamics, aligning torque, and suspension tuning
Positive camber
The top of the wheel is further outboard than the contact
patch
Negative Camber
The top of the wheel is more inward than the contact patch
What does negative camber influence
It improves the wheel ability to transfer lateral forces during a curve
Large camber angle influence
Increases tire wear and rolling resistance
Why does the camber angle remain positive during straightline driving
To suppress steering wheel vibration but should be as small as possible
Roll Center meaning
The point in the axle;s yz plane about which the vehicle body rolls
Does the roll center point change
It changes during jounce and rebound
High roll center meaning
Less body roll due to shorter lever arm
Low roll center (at or below road surface)
Reduced camber and track width changes during jounce and rebound
Typical roll center values
80 to 250mm at the rear axle
0 to 130mm at the front axle
Steering angle
The angle between the vehicle’s x-axis and a line formed by the intersection of the wheel’s center plane and the road surface
Max steer angle
30deg to 43deg in both directions
Larger max steer angle?
Reduces vehicle’s turning radius and improves parking capabilities
What is the steer angle limited by
The clearance space in the wheel wells.
Tire/Wheel Slip Angle
The angle between the wheel’s velocity vector along the wheel center plane and the wheel’s actual direction of displacement at the tire contact patch.
When does the tire slip angle occur
Mainly when lateral forces are acting on the center of tire contact
