shobote
SHO Member
There's a company called Whiteline that engineers full suspension kits and makes anti lift kits for front and all wheel drive cars; a pdf file exists on their whiteline.com.au 5Th December 2003
Revised version
Discussion Paper
Effect of Whiteline Anti-Lift Kit (ALK)
Revised 5th December 2003
Jakub Zawada B.E. (Mech)
5Th December 2003
Revised version
Introduction to Anti-Dive and Anti-Lift
“Anti” features in suspension systems are a characteristic that can be used to influence
the stiffness of the front or rear suspension under traction forces (under braking or
accelerating).
The individual terms are relatively straightforward and self-explanatory with the “anti”
reducing or totally restricting the characteristic (lifting or diving). In the front suspension
there may be levels of anti-dive during braking and anti-lift during accelerating
(assuming traction to the front wheels is present), similarly in the rear there could be antilift
during braking and anti-squat during acceleration.
It should also be noted that these characteristic can also be reversed into a “pro”
characteristic (as in pro-lift at the front under braking).
Anti features can only be implemented under the influence of the braking or accelerating
forces at the wheels, for example a rear wheel drive vehicle cannot have an anti-lift
characteristic in the front (as there is no drive to the front wheels).
These characteristics do not change the steady state load transfer (during braking or
accelerating) at the tire contact patch. The load transfer during steady state acceleration or
braking is a function of the wheelbase, CG height, and the braking force.
100% of anti-dive or anti-lift would give no deflections of the suspension (from the static
ride height) during braking and accelerating. It does this by passing the extra load during
accelerations through the suspension components instead of the spring. Similarly 0%
anti-dive would pass the entire load through the spring giving maximum deflections.
Anti-dive and anti-lift are calculated by the position of the side view instant center; this
imaginary point in space is generated by the geometry of the suspension system.
The Effect of the Whiteline Anti-Lift Kit (ALK)
The % anti-dive or lift in a suspension system (the Subaru WRX front end for example) is
a function of the position of the side view instant center (SVIC). This SVIC is the pivot
point for the side view swing arm (also the pivot point of the suspension at that instant),
which is a line drawn from the tire contact patch to the instant center (under braking – for
acceleration it is drawn from the wheel center).
The slope or angle of this swing arm (effectively the position of the SVIC) describes the
amount of anti-dive and anti-lift present in the suspension system.
5Th December 2003
Revised version
The SVIC is found by the intersection of two lines. The first is the projection of the lower
control arm, say through the chassis mounts behind the front wheels, the second
line is the normal to the axis of the strut tower at the top of the strut, projected behind the
front wheel in the case of the Subaru WRX.
(Note: to be absolutely correct these lines should be projected onto the wheel center
plane, so any lateral drop or rise in the control arms will effect the SVIC position.
However in most cases the control arm angles are usually low, or flat when looking from
the front of the car, and give minimal effect)
The diagram below shows the SVIC and swing arm details for the Subaru WRX.
Together with the position of the SVIC, the wheelbase, CG height, % front torque (for
anti-lift under acceleration) and % front braking (for anti-dive) are required to calculate
the amount of anti features in the front suspension.
With the ALK fitted to the WRX, the rear mount of the front lower control arm is
lowered by approximately 20mm. There is also a castor change present by moving the
mount outwards, this adds positive castor to the suspension.
The effect of this component results in the following anti-dive and anti-lift properties in
the Subaru WRX, expressed as percentages in the following table.
5Th December 2003
Revised version
Standard WRX WRX with ALK
Wheel Base 2530 2530 mm
CG Height 600 600 mm
% Front Braking 70 70 %
% Front Traction 60 60 %
SVIC Height 457 26.2 mm
Swing Arm Length 5949 11495 mm
% Anti-Dive 22.7 0 %
% Front Anti-Lift* 6.5 -6.1 %
* Negative value denotes pro-lift
As can be seen from the table, the anti-dive reduces to 0% from 22.7% and the anti-lift is
reduced to a pro-lift value of 6.1% from 6.5% anti-lift.
Effect of Anti-Dive and Anti-Lift as Modified by the Whiteline ALK
As mentioned previously if 100% anti-lift or anti-dive is incorporated then all the
longitudinal load transfer experienced under braking and accelerating will pass through
the suspension components (namely the control arms) leaving the springs unloaded with
no deflection present (from static ride height). 0% would pass the entire load onto the
spring giving maximum deflections.
This can be used to stiffen the suspension system under braking or accelerating.
In the case of the Subaru WRX fitted with the ALK, the suspension system becomes
softer during braking and accelerating actions, as both anti-dive and anti-lift have been
reduced. A softer suspension will give rise to larger deflections.
An experiment was then set out to show that this was the case. A standard Subaru WRX
was used initially and deflections were captured using a digital video camera during
acceleration runs. The same WRX was then fitted with an ALK and the procedure was
repeated again. The results are shown in the following table.
5Th December 2003
Revised version
Whiteline ALK Test - 23.10.2002
Standard WRX
Measure A Measure B Ratio Distance Average (mm)
980 740 0.76 529 517
890 650 0.73 511
890 650 0.73 511
Standard WRX with ALK
Measure A Measure B Ratio Distance Average (mm)
900 690 0.77 537 535
870 660 0.76 531
910 700 0.77 538
Measure A = (700mm) Bottom of Sill to black trim below door Mirror
Measure B = Bottom of wheel to guard in Video
Average is actual bottom of wheel to guard distance
As can be seen from the table with the ALK fitted the WRX had a higher wheel (bottom
of wheel) to guard height indicating higher deflections present.
This concurs with what is expected with the modified anti-lift percentages being reduced
(to pro-lift in this case).
A softer front suspension during acceleration and braking will even out the load on the
front tires, giving a higher total cornering load available or more front-end grip. This will
lead to less understeer when cornering under power or brakes.
Another way of looking at this is that under power or brakes the effective spring stiffness
is lower, reducing the front-end anti-roll resistance, hence reducing weight transfer at the
front and less understeer.
Softer front rates will also allow better wheel tracking over rough roads, keeping the tires
in contact with the ground.
The drawback of the ALK is that there is an increased amount of deflections or pitch; this
can affect suspension geometry if there is a very large amount of pitch. However the
ALK adds additional castor that will more than cover any reduction in castor due to
excessive pitch during braking.
5Th December 2003
Revised version
Additional Discussion – Anti-Dive and NVH
Many sources describe that too much Anti-dive in the front end of suspension systems
can have adverse effects. Anti-dive percentages of more than 50% are rarely seen in
vehicles without very careful design to the suspension systems (for example noncompliant
bearing type joints on the suspension), and some recommend (“Tune to Win”
Carroll Smith) no more than 30% be used as even this much will have an undesirable
effect.
The effect of Anti-dive is to increase the loading of the suspension components and
suspension bushes. This increases deflection in the system that can affect the geometry
(for example reducing castor under braking), and also increases friction in the bushes,
which could lead to suspension lockup and less than adequate wheel tracking over the
ground.
Such “stiction” and load transfer through the control arms into the chassis all work to
raise the levels of NVH (noise vibration harshness). By decreasing the anti-dive from
23% to 0% with the ALK, any NVH associated with the anti-dive in the Subaru WRX
has been removed, therefore assuming all things being the same (apart from the
installation of a Whiteline ALK) there should be less NVH present.
This gives scope to increase the bush stiffness in search of enhanced suspension
geometry control. Therefore it is can be possible to stiffen the bushes of the front
suspension without raising the NVH level when the car is fitted with an ALK.
Conclusion
With the ALK fitted to the Subaru WRX, a softer suspension will be present during
braking and accelerating. This will help traction, as the wheel will be able to track the
ground more precisely. Also in terms of balance the front end will have a proportionally
lower roll resistance during traction or braking, aiding in reducing the power understeer
effect that is present in these cars.
Revised version
Discussion Paper
Effect of Whiteline Anti-Lift Kit (ALK)
Revised 5th December 2003
Jakub Zawada B.E. (Mech)
5Th December 2003
Revised version
Introduction to Anti-Dive and Anti-Lift
“Anti” features in suspension systems are a characteristic that can be used to influence
the stiffness of the front or rear suspension under traction forces (under braking or
accelerating).
The individual terms are relatively straightforward and self-explanatory with the “anti”
reducing or totally restricting the characteristic (lifting or diving). In the front suspension
there may be levels of anti-dive during braking and anti-lift during accelerating
(assuming traction to the front wheels is present), similarly in the rear there could be antilift
during braking and anti-squat during acceleration.
It should also be noted that these characteristic can also be reversed into a “pro”
characteristic (as in pro-lift at the front under braking).
Anti features can only be implemented under the influence of the braking or accelerating
forces at the wheels, for example a rear wheel drive vehicle cannot have an anti-lift
characteristic in the front (as there is no drive to the front wheels).
These characteristics do not change the steady state load transfer (during braking or
accelerating) at the tire contact patch. The load transfer during steady state acceleration or
braking is a function of the wheelbase, CG height, and the braking force.
100% of anti-dive or anti-lift would give no deflections of the suspension (from the static
ride height) during braking and accelerating. It does this by passing the extra load during
accelerations through the suspension components instead of the spring. Similarly 0%
anti-dive would pass the entire load through the spring giving maximum deflections.
Anti-dive and anti-lift are calculated by the position of the side view instant center; this
imaginary point in space is generated by the geometry of the suspension system.
The Effect of the Whiteline Anti-Lift Kit (ALK)
The % anti-dive or lift in a suspension system (the Subaru WRX front end for example) is
a function of the position of the side view instant center (SVIC). This SVIC is the pivot
point for the side view swing arm (also the pivot point of the suspension at that instant),
which is a line drawn from the tire contact patch to the instant center (under braking – for
acceleration it is drawn from the wheel center).
The slope or angle of this swing arm (effectively the position of the SVIC) describes the
amount of anti-dive and anti-lift present in the suspension system.
5Th December 2003
Revised version
The SVIC is found by the intersection of two lines. The first is the projection of the lower
control arm, say through the chassis mounts behind the front wheels, the second
line is the normal to the axis of the strut tower at the top of the strut, projected behind the
front wheel in the case of the Subaru WRX.
(Note: to be absolutely correct these lines should be projected onto the wheel center
plane, so any lateral drop or rise in the control arms will effect the SVIC position.
However in most cases the control arm angles are usually low, or flat when looking from
the front of the car, and give minimal effect)
The diagram below shows the SVIC and swing arm details for the Subaru WRX.
Together with the position of the SVIC, the wheelbase, CG height, % front torque (for
anti-lift under acceleration) and % front braking (for anti-dive) are required to calculate
the amount of anti features in the front suspension.
With the ALK fitted to the WRX, the rear mount of the front lower control arm is
lowered by approximately 20mm. There is also a castor change present by moving the
mount outwards, this adds positive castor to the suspension.
The effect of this component results in the following anti-dive and anti-lift properties in
the Subaru WRX, expressed as percentages in the following table.
5Th December 2003
Revised version
Standard WRX WRX with ALK
Wheel Base 2530 2530 mm
CG Height 600 600 mm
% Front Braking 70 70 %
% Front Traction 60 60 %
SVIC Height 457 26.2 mm
Swing Arm Length 5949 11495 mm
% Anti-Dive 22.7 0 %
% Front Anti-Lift* 6.5 -6.1 %
* Negative value denotes pro-lift
As can be seen from the table, the anti-dive reduces to 0% from 22.7% and the anti-lift is
reduced to a pro-lift value of 6.1% from 6.5% anti-lift.
Effect of Anti-Dive and Anti-Lift as Modified by the Whiteline ALK
As mentioned previously if 100% anti-lift or anti-dive is incorporated then all the
longitudinal load transfer experienced under braking and accelerating will pass through
the suspension components (namely the control arms) leaving the springs unloaded with
no deflection present (from static ride height). 0% would pass the entire load onto the
spring giving maximum deflections.
This can be used to stiffen the suspension system under braking or accelerating.
In the case of the Subaru WRX fitted with the ALK, the suspension system becomes
softer during braking and accelerating actions, as both anti-dive and anti-lift have been
reduced. A softer suspension will give rise to larger deflections.
An experiment was then set out to show that this was the case. A standard Subaru WRX
was used initially and deflections were captured using a digital video camera during
acceleration runs. The same WRX was then fitted with an ALK and the procedure was
repeated again. The results are shown in the following table.
5Th December 2003
Revised version
Whiteline ALK Test - 23.10.2002
Standard WRX
Measure A Measure B Ratio Distance Average (mm)
980 740 0.76 529 517
890 650 0.73 511
890 650 0.73 511
Standard WRX with ALK
Measure A Measure B Ratio Distance Average (mm)
900 690 0.77 537 535
870 660 0.76 531
910 700 0.77 538
Measure A = (700mm) Bottom of Sill to black trim below door Mirror
Measure B = Bottom of wheel to guard in Video
Average is actual bottom of wheel to guard distance
As can be seen from the table with the ALK fitted the WRX had a higher wheel (bottom
of wheel) to guard height indicating higher deflections present.
This concurs with what is expected with the modified anti-lift percentages being reduced
(to pro-lift in this case).
A softer front suspension during acceleration and braking will even out the load on the
front tires, giving a higher total cornering load available or more front-end grip. This will
lead to less understeer when cornering under power or brakes.
Another way of looking at this is that under power or brakes the effective spring stiffness
is lower, reducing the front-end anti-roll resistance, hence reducing weight transfer at the
front and less understeer.
Softer front rates will also allow better wheel tracking over rough roads, keeping the tires
in contact with the ground.
The drawback of the ALK is that there is an increased amount of deflections or pitch; this
can affect suspension geometry if there is a very large amount of pitch. However the
ALK adds additional castor that will more than cover any reduction in castor due to
excessive pitch during braking.
5Th December 2003
Revised version
Additional Discussion – Anti-Dive and NVH
Many sources describe that too much Anti-dive in the front end of suspension systems
can have adverse effects. Anti-dive percentages of more than 50% are rarely seen in
vehicles without very careful design to the suspension systems (for example noncompliant
bearing type joints on the suspension), and some recommend (“Tune to Win”
Carroll Smith) no more than 30% be used as even this much will have an undesirable
effect.
The effect of Anti-dive is to increase the loading of the suspension components and
suspension bushes. This increases deflection in the system that can affect the geometry
(for example reducing castor under braking), and also increases friction in the bushes,
which could lead to suspension lockup and less than adequate wheel tracking over the
ground.
Such “stiction” and load transfer through the control arms into the chassis all work to
raise the levels of NVH (noise vibration harshness). By decreasing the anti-dive from
23% to 0% with the ALK, any NVH associated with the anti-dive in the Subaru WRX
has been removed, therefore assuming all things being the same (apart from the
installation of a Whiteline ALK) there should be less NVH present.
This gives scope to increase the bush stiffness in search of enhanced suspension
geometry control. Therefore it is can be possible to stiffen the bushes of the front
suspension without raising the NVH level when the car is fitted with an ALK.
Conclusion
With the ALK fitted to the Subaru WRX, a softer suspension will be present during
braking and accelerating. This will help traction, as the wheel will be able to track the
ground more precisely. Also in terms of balance the front end will have a proportionally
lower roll resistance during traction or braking, aiding in reducing the power understeer
effect that is present in these cars.
