1. Chassis System
Chassis is the systems between the body and the road and includes frame/sub-frame, suspension (front and rear), steering system, brake system, wheels and tires
The scope of suspension design is the choice of basic geometry for optimum wheel location, the mounting of suspension members to the body (including the use of sub-frames), the springing medium, and the provision of damping of vertical wheel movement
The scope of steering design is the optimization of front suspension geometry for steering, the choice of steering system, the provision of power assistance, the satisfaction of safety requirements
The scope of brake system design is the choice of friction system, the design of the operating linkage, the provision of servo assistance, the satisfaction of safety requirements, the provision of anti-lock braking and other enhancements such as emergency brake assist.
The choice of wheel and tire size, choice of wheel material and tire configuration, choice of spare wheel configuration or “run flat” technology

2. Suspension System Requirements
Allow each wheel to move vertically to provide ride comfort, while constraining its movement in other directions to maintain stability and control. Vertical wheel movement from the datum position compresses a spring keeping wheel movement within limits, although bump and rebound stops are provided should the limit – normally set by the space constraints of body design – be reached. A damper ensures that the subsequent spring movement (an oscillation) is quickly reduced to zero.
The other most important secondary aim of suspension design is to keep all four wheels as nearly upright as possible at all times, not only when traveling across uneven surfaces but also when the body rolls during cornering. A conventional car tire delivers optimum grip for cornering, braking and accelerating when it is upright. In practice it is impossible to achieve this ideal constraint without resorting to extremely costly and space-consuming measures, and current suspension systems are in most cases concerned to approach it as nearly as possible.
In some cases, as with the use of trailing arms at the rear of front-driven cars, the inevitable camber change and reduced grip during cornering is exploited as a means of reducing understeer – but overall cornering grip is also sacrificed as a result.

3. Suspension System Requirements
Another important requirement is that the weight of the unsprung mass i.e. wheel, tire, hub and suspension assembly at the “road” end of the spring, should be as low as possible. The lower the weight is relative to the weight of the body (the lower the ratio of unsprung to sprung mass), the less the body will react to any wheel movement, and the better the tire will be maintained in contact with the road surface, to the benefit of both ride comfort and road holding
The task of the suspension linkage which attaches each wheel to the vehicle body is to keep the wheel as nearly upright as possible in all circumstances (zero camber angle) and pointing in the desired direction (nominally parallel to the vehicle centre line, except when the front wheels are being steered), regardless of the unevenness of the road surface which causes the wheels to move vertically, and of the attitude of the vehicle body which may move in pitch, roll, and heave (pure vertical movement) according to the forces acting at its centre of gravity.
The importance of keeping the wheels as nearly vertical as possible is that this gives the tires the best chance to operate efficiently, with minimum rolling resistance. Many competition cars deliberately run positive (top-inwards) camber to achieve maximum cornering grip but the rate of tire wear and the additional rolling resistance when running in a straight line are unacceptable in most road-going cars.

4. Primary Functions of Suspension
Support vehicle weight.
Keep the tires in contact with the road.
Control vehicle’s direction of travel
Maintain correct wheel alignment, important in vehicle handling
Reduce effect of shock loads with the use of springs, dampers and bushings
Maintain correct vehicle ride height

5. Types of Front Suspension
Usage
Cost and Weight
Package
Control
McPherson Strut
Small FWD Cars
Light & Not expensive
Compact Ok
SLA or Double Wishbone
Luxury Cars
Heavier & expensive
Not compact
Good
Solid Axle with Leaf Springs
Heavy Trucks
Heavy & not expensive
Minimum

6. McPherson Strut Suspension
Lower Link
Lower Ball Joint
Stabilizer Bar
Camber Bolt
Strut
Rubber Bushes
Tyre
Top Mount
Link
Brake Disc
Wheel Rim
Bump Stopper
Spring
Rubber boot
Wheel Bearing
Wheel Cap
Wheel Mounting Bolt
Drive Shaft / Spindle
Lock Nut
Heat Shield for Ball Joint (To protect from Brake Disc heat)

7. Features of McPherson Strut
Upper control arm in double wishbone is eliminated
Provides anchoring of tie rod on knuckle
Combines the following parts into one assembly to provide wheel control
Spring Seats
Springs, Bump stoppers
Rebound Stopper
Link for mounting Stabilizer Bar
Lower the Forces on BIW-Mountings
Provide Better Space at the side to mount transverse Engine & Gear box
Better Space for Front Crash Members & Crumple zones

8. Advantages of McPherson Strut
Disadvantages
Less favorable kinematic characteristics
Forces & vibrations transferred to inner wheel-arch panel which is relatively elastic
Difficult to insulate against road noise
Friction between piston rod & guide impairs the springing effect
Critical to package [Gaps between Tyre & damper, Springs & Wheel-arch]
Ground Clearance critical
Advantages
Combination of several parts into one assembly
Upper transverse link replaced by top mount
Occupies less space
Transverse engine mounting possible
More space for front crumple zone

9. Double Wishbone Suspension
Lower Link
Lower Ball Joint
Stabilizer Bar
Rubber Bushes
Tyre
Top Mount
Upper Control Arm
Brake Disc
Knuckle
Spring& Damper
Wheel Mounting Bolt
Upper Ball Joint
Tie Rod
Brake-Rod
Steering Gear

10. Features of SLA or Double Wishbone
Has 2 control arms (upper & lower) connected to the steering knuckle by ball joints (UBJ & LBJ)
Upper control arm in double wishbone is shorter than lower arm which helps control the camber angle to desired level during body roll
Spring, shock and anti-roll bar are attached to LCA
Steering arm is attached to the knuckle

11. Advantages of Double Wishbone Suspension
Disadvantages
More complex than McPherson Strut
Short spindle SLAs tends to require stiffer bushings at the body, as the braking and cornering forces are higher. Also they tend to have poorer kingpin geometry, due to the difficulty of packaging the upper ball joint and the brakes inside the wheel.
Long spindle SLAs tend to have better kingpin geometry, but the proximity of the spindle to the tire restricts fitting oversized tires, or snow chains. The location of the upper ball joint may have styling implications in the design of the sheetmetal above it.
Advantages
Kinematics can be controlled easily
Provides good camber compensation during vertical movement
Pitching movements can be balanced i.e anti-dive, anti-squat possible
Toe-in, Camber & Track change can be controlled optimally due to variety of control parameters 11

12. Front Suspension Parts
Strut /
Damper
ARB
Spring
Steering Tie-rods
Suspension Bush
Ball Joint
Lower Link
Knuckle
Tyre
Wheel rim
Sub-frame
Corner Module
Drive Shaft / Bearing
Subframe 12

13. Types of Rear Suspension
Usage
Cost and Weight
Package
Control
Twist Beam
Small FWD Cars
Light & Not expensive
Compact Ok
Multi-Link
Luxury Cars
Heavier & expensive
Not compact
Good
Hotchkiss
Trucks
Heavy & not expensive
Minimum

14. Twist Beam Rear Suspension
TA : Trailing Arms CB : Cross Beam
B : Pivot Bushes S : Coil Spring
D : Dampers E : Top Mount
T : Torsion bar P : Panhard Rod TA CB B S D E T P
Welded Rigid Connection 14

15. Features of Twist Beam Suspension
Very compact package
Inexpensive to manufacture, assemble/disassemble.
Eliminates several parts: control arms, anti-roll-bar, etc.
Twist axle acts as a anti-roll-bar
High stresses in the welds 15

16. Advantages of a Twist Beam Suspension
Disadvantages
Exhibits compliance Oversteer tendency
Torsion & Shear stress in Cross member
High stress in weld seams
Advantages
Whole axle easy to assemble & dismantle
Requires very little space, easy to package spare tire, fuel tank, etc.
Spring-Damper assembly is easy to fit.
Control Arms & Rods are eliminated.
Wheel to Spring Damper ratio favorable.
Less unsprung mass
Cross member acts as a anti-roll-bar
Negligible toe-in & track change
Low camber change under lateral forces. 16

17. Twist Beam Rear Suspension Parts
Strut /
Damper
Spring
Tyre
Drum
Drum Brake
Twist Beam
Unitized Bearing
Packaging
Suspension Bush
Wheel rim
Twist Beam Module 17

18. 3-Link Rear Suspension Top Mount Coil Spring Damper Sub-frame
Longitudinal
Link
Transverse
Links
Pivot
Bushings 18

19. 3-Link Rear Suspension Parts
Strut /
Damper
Spring
Tyre
Drum
Drum Brake
Unitized Bearing
Suspension Bush
Subframe with Multilink Suspension
Multi-Link Suspension 19

20. Features of 3-Link Rear Suspension
Relatively expensive
Requires more space
Easier to control wheel movement with 3 links
Longitudinal link picks up longitudinal loads
Transverse links pick up lateral loads 20

21. Advantages of 3-Link Rear Suspension
Pitching movements can be balanced i.e 100% anti-dive, anti-squat possible
Toe-in, camber, track change can be controlled optimally due to variety of control parameters
Disadvantages
Costly as compared to twist beam and other suspensions due to increased number of components, links, bushings & bearings
Higher production & assembly costs
Higher degree of tolerance control required to maintain geometry 21

22. Hotchkiss Rear Suspension22

23. Hotchkiss Rear Suspension
Suspension Bush
Tyre
Wheel rim
ARB Bush
Hotchkiss Suspension
Shackle
Parabolic Leaf Spring
Conventional Leaf Spring
U Bolt 23

24. Features of Hotchkiss Rear Suspension
Simple in design
High weight
Easy to assemble
Provides good pay load carrying capacity
Robust in design 24

25. Advantages of Hotchkiss Rear Suspension
Simple with very few parts
Easy to manufacture & assemble
Robust design
High load carrying capacity
Disadvantages
High weight of suspension i.e high unsprung mass.
Occupies More Space than other suspension types 25

26. Wheel Movements Controlled by Suspension
Jounce & Rebound
Roll
Toe in/Toe out
Left or Right Steer
Camber
Spin

27. Axle/Vehicle Jounce & Rebound
At Ride Height
In Jounce
Spring Compression
Spring Extension y z
Rear View y z
At Ride Height
In Rebound

28. Axle/Vehicle Roll y z At Ride Height Axle Roll Spring Compression
Body Roll
Rear View y z

29. Wheel Camber
Wheels with no Camber
Wheels with Camber y z
Rear View

30. Wheel Toe in/Toe out
Wheel Toe-in
Wheel Toe-out y x
Top View

31. Wheel Steer
Wheel RH Steer
Wheel LH Steer y x
Top View

32. Suspension Geometry in Wheel Jounce
Assembly
Ride Height
In Jounce
Lower Control Arm
Upper Control Arm
Lower Ball Joint
Upper Ball Joint
Body Pivot
Note:
Wheel at original position (pink)
Wheel in jounce (blue)
Original control arms (solid)
Control arms in jounce (dotted)
Note wheel camber y z
Rear View

33. Suspension Geometry in Wheel Rebound
Assembly
Ride Height
In Jounce
Lower Control Arm
Upper Control Arm
Lower Ball Joint
Upper Ball Joint
Body Pivot
Note:
Wheel at original position (pink)
Wheel in jounce (blue)
Original control arms (solid)
Control arms in jounce (dotted)
Note wheel camber y z
Rear View

34. Steering Geometry Error in Wheel Jounce
Note:
Wheel at original position (pink)
Wheel in jounce (blue)
Original tie rod (solid)
Tie rod in jounce (dotted)
Note geometry error
Tie Rod
Steering arm
Ball joint
Ideal Location for body ball joint
Ideal path for steering
arm ball joint
New position for body
ball joint
New path for steering y z
Rear View

35. Steering Geometry Error in Wheel Jouncez
Ideal center
for tie rod on body
Center for
Short tie rod
Center for long tie rod
Steering arm
ball joint at ride height
Steering arm ball joint at
jounce
Ideal path
Short Tie
Rod Path
Long Tie
Ball joint
Pulled out
Pulled in
Rear View

36. Steering Geometry Error in Wheel Jouncez
Steering arm
ball joint at ride height
Ideal center
for tie rod on body
Ideal Tie Rod
Center above
Ideal
New Tie Rod
Ideal path
New Path
Ball joint
Pulled out
Steering arm ball
joint at jounce
jounce
Rear View

37. Steering Geometry Errors
Position of Tie Road to Body Joint
Steering Arm Ball Joint Position
Steering Geometry Error
At ideal center
On ideal path
None
Inboard towards wheel
Pulled in towards body in jounce or rebound
Toe-in (link ahead ) Toe-out (link behind)
Outboard towards body
Pulled out towards body in jounce or rebound
Toe-in (link behind) Toe-out (link ahead)
Below ideal center
Pulled out jounce and pulled in in rebound
right steer (behind) left steer (ahead) in roll
Above ideal center
Pulled in in jounce and pulled out in rebound
right steer (ahead) left steer (behind) in roll

38. Suspension Roll Center
Roll center is defined as a location at which lateral forces developed by the wheels are transferred to the sprung mass
Each suspension has a roll center
Lateral forces can be applied to the sprung mass at the roll center without causing suspension roll
Each suspension has a roll axis about which un-sprung mass rolls when a pure moment is applied
Vehicle roll axis is the line joining the roll centers of the front and rear suspensions

39. Roll Centers z x

40. Roll Center for 4-Link Solid AxleFy
Upper Link UL
Lower Link LL
FyLL
FyUL a b
FyLL/FyUL = b/a
FyLL+FyUL = Fy
Top View
Side View y x z x

41. Roll Center for 3-Link Solid Axle
Top View
Side View
Track Bar y x z x

42. Roll Center for Hotchkiss
Side View
Roll Axis z x

43. Roll Center for Positive Swing Arm SLAFU Fy FL Fy
Rear View y z

44. Roll Center for Negative Swing Arm SLA

45. Roll Center for Parallel Arm SLA

46. Roll Center for Inclined Parallel Arm SLA

47. Roll Center for McPherson Strut

48. Assignment Determine roll center for your suspension
Determine suspension envelope in y-z plane for your suspension