Tales of a 3.9 litre Tdi Bushie Ute

Bushie Suspension

In spite of the cost of living, it’s still popular” – Kathleen Norris

 

The following two quotes (in italics) from CODE LS9, and CODE LS10, referring to suspension modifications were copied from pages 41 and 49 of the Queensland Code of Practice for Vehicle Modifications, Version 2.6 | July 2015.


High Lift – 50mm to 125mm (Design)
CODE LS9
1. Scope
Code LS9 provides for the preparation of designs that may be approved by Registration Authorities for use by other signatories or modifiers. The designs under Code LS9 cover the design of vehicle lifts in excess of 50mm but not more than 125mm.

Vehicle lifts that do not exceed 75mm, and are achieved by modification of the suspension and fitting of alternate tyres and rims only (do not include a body lift) do not require certification under the LS9 code. Any person performing this type of modification must ensure the modified vehicle meets all the technical requirements of the LS9 and LS10 sections of this code, however no formal certification or lane change test is required.

Code LS9 does not apply to ADR category L-group vehicles, including motor cycles.

1.1 Designs covered by the Code LS9
The following is a summary of the designs that may be prepared under Code LS9:
• Design of modifications that combined result in the vehicle being raised by more than 50mm but less than 125mm from the original as manufactured height;
• Design of front suspension modifications using different struts or uprights;
• Design of independent rear suspension modifications using different struts, trailing arms or uprights;
• Design of a conversion using a complete suspension assembly from a different vehicle model;
• Design of a complete rear suspension assembly using components from different vehicle model(s); and
• Alternative wheel and tyre specifications for vehicles with modified axles or suspension.

1.2 Designs not covered by Code LS9
Designs that are not covered under Code LS9 are listed below:
• Design for vehicles originally equipped with ESC that have not been approved by the vehicle manufacturer or proven through testing;
• Certification of the actual physical modification of particular vehicles (this is covered by ode LS10);
• Design for modifications that raise the vehicle body more than 125mm from the original s manufactured height (lifting vehicles beyond 125mm is outside of the scope of the QCOP); and
• Design for modifications that raise the vehicle body more than 50mm from the original as manufactured height on vehicles that have had the wheel track reduced from the as manufactured width. Modifications to these vehicles will only be considered on an individual application basis.


High Lift – 50mm to 125mm (Modification)
CODE LS10
1. Scope
Code LS10 covers modifications that result in a vehicle lift of more than 50mm but not more than 125mm.
The conversions may be carried out in conformity with designs approved by a Registration Authority under Code LS9.

Vehicle lifts that do not exceed 75mm, and are achieved by modification of the suspension and fitting of alternate tyres and rims only (do not include a body lift) do not require certification under the LS9 code. Any person performing this type of modification must ensure the modified vehicle meets all the technical requirements of the LS9 and LS10 sections of this code, however no formal certification or lane change test is required.

Code LS10 does not apply to ADR category L-group vehicles, including motor cycles.

1.1 Modification covered under code LS10
The following is a summary of the modifications that may be performed under Code LS10:
• Modifications that result in the vehicle being raised by more than 50mm from the original as manufactured height;
• Front suspension modifications using different struts or uprights;
• Independent rear suspension modifications using different struts, trailing arms or uprights;
• Conversion using a complete suspension assembly from a different vehicle model;
• Fitment of a complete rear suspension assembly using components from different vehicle model(s);
• Installation of body lift kits; and
• Fitting of alternative wheel and tyre specifications for vehicles with modified axles or suspension.

1.2 Modifications not covered under code LS10
The following is a summary of the modifications that may not be performed under Code LS10:
• Modifications to vehicles originally equipped with ESC that have not been approved by the vehicle manufacturer or proven through testing;
• Design of the modification of particular vehicles (this is covered by Code LS9);
• Modifications that do not have a design in accordance with the requirements of Code LS9;
• Modifications that raise the vehicle body more than 125mm from the original as manufactured height (lifting vehicles beyond 125mm is outside of the scope of the QCOP); and
• Modifications that raise the vehicle body more than 50mm from the original as manufactured height on vehicles that have had the wheel track reduced from the a manufactured width. Modifications to these vehicles will only be considered on an individual application basis.


To avoid confusion due to differing common usage for some terminology, definitions used here are:

  • Compression is the direction, upward, of wheel or suspension travel, for dampers (shock absorber), it is the action of returning from an extended state
  • Rebound is the direction, downward, of wheel or suspension travel, for dampers it is the action of returning from a compressed state
  • Bump is the displacement from static ride height in the compression direction
  • Droop is the displacement from static ride height in the rebound direction

Suspension changes were necessary to accommodate the axle swap from Land Rover to Toyota Landcruiser HZJ105R units.

For the rear suspension, the Land Rover upper control arms are retained, but lower control arms are heavy duty replacement Nissan Y61 Patrol arms.

Suspension height is raised approximately 50 mm above stock Land Rover height. In Queensland the suspension height of four wheel drive vehicles can be raised 50 mm and not require a modification plate.

The approximate static ride height of standard suspension springs for an unladen Land Rover are 260mm front, and 320mm rear. When the chassis is level, the rear spring perch is approximately 40mm lower than the front spring perch. This difference together with the taller rear spring, probably allows for spring deflection when load is added, which increases the force on rear more than front springs. The specifications for the Land Rover 120 list the chassis height at the rear bearing supports as 781mm unladen to 669mm laden, a range of 112 mm.

The suspension spring’s job is to support the weight yet allow free movement of the supporting members (wheels, tyres, axles), to utilise the inertia of the suspended mass to transmit as little terrain variation as possible to the vehicle occupants. The softest spring allows the easiest movement of the supporting members, but it needs to suspend the chassis on the supporting members at the desired static ride height. The spring rate should be neither too soft, or stiff.

Springs react to load changes by deflecting, with the force increasing or decreasing as the wheel travels up or down following the terrain. They store, then release the energy during each bump event. The damper doesn’t react to the load change, only to the velocity and its job is to dissipate all of the energy from the bump into heat, which can occur during either, or both, of the bump and rebound strokes. The spring rate doesn’t affect the amount of energy that the damper has to contend with. For best results with soft springs the damper needs to convert most of the energy to heat during the bump stroke and a lesser amount during rebound. That swings toward the converse requirement as spring rate is increased.

The undamped natural frequency of the suspension springs provides a reliable comparison for ride comfort. Higher natural frequency indicates a stiffer, harsher ride. The natural frequency of the rear springs should be greater than that of the front springs. The following list is a guide for natural frequency and use (high performance road and race cars would use somewhat higher numbers).

  • General on and off road use; 1.350Hz front, 1.688Hz rear
  • Fast four wheel drive tracks, <50 kph; 1.100Hz front, 1.350Hz rear
  • Slow four wheel drive tracks, <25 kph; 0.750Hz front, 0.930Hz rear

The undamped natural frequency of a spring is:

fn = 0.5 x square root [spring rate / load]
where:
fn is natural frequency in Hz
spring rate is in N/mm
load is in kN

Bushie Ute has Firestone reversible sleeve air springs for both front and rear suspension. The front air springs are Firestone assembly order number W01-358-9327, and the rear air springs are Firestone assembly order number W01-358-5429. These air springs have a more durable construction compared to the type Land Rovers have used for many years. Benefits of reversible sleeve air springs include:

  • ride height and level can be maintained when the load is changed
  • ride is more comfortable no matter what the load because undamped natural frequency stays fairly constant (air pressure, thus spring rate, changes with load)
  • tractive effort on low traction surfaces is optimised by adjusting the pressure in the air springs, thus the down force at the tyres (i.e. total grip is maximised when all driving wheels have equal down force)
  • ability to change the spring height has many advantages on difficult off road tracks

Firestone recommends selecting air springs that support the design load and height with air pressure between 400 and 600 kPa, and not exceed 700kPa. They also advise that lower operating pressures increase durability.

The front W01-358-9327 air springs were used both front and rear with my old Range Rover and are popular for Jeeps, and Land Rovers in the USA, but they don’t have sufficient load capacity to retain the rear axle load rating and GVM from the Land Rover 120 donor.

 

 

W01-358-9327 Static Data Chart

 

W01-358-9327 Dynamic Characteristics

 

Two reasons for choosing W01-358-5429 air springs for the rear suspension are:

  • They have been proven as arguably the best air springs for Nissan Patrol utes
  • The piston shape is very well suited to vehicles with this amount of sprung and unsprung mass

The piston in this air spring is shaped to reduce the change in spring rate of reversible sleeve air springs during bump and rebound travel. The trapped air is compressed during bump travel, and expands during rebound travel, thus increasing or reducing the air pressure. The spring force is the product of air pressure times effective area, and the effective area changes as bellows rolls up or down on the piston. The effective area is approximately the mean of the bellows and piston cross sectional ares at the position where the bellows rolls on the piston.

W013585429

1T14C-7 Data Sheet

 

 

A common misconception with air springs is that it is thought that inflation pressure adjusts the ride height.

This is not the case with reversible sleeve air springs. Changing the ride height involves removal or addition of air into the bellows. If the load hasn’t changed, the pressure difference as the height changes is negligible while the “rolling lobe” remains on a nearly parallel section of the piston because the change to the effective diameter is so small.

Changing the load on the air spring will change the air pressure. Load = pressure times area. In the case of reversible sleeve air springs the effective area/diameter is approximately the mean of the piston diameter and the outside diameter of the bellows, both taken at the position of the rolling lobe.

 

effective-diameter

 

When a change to the force acting on the air spring extends or compresses the spring from the static ride height, the volume, pressure and temperature of the trapped air will change, in accordance with the natural laws for gasses. Spring rate is the change in force divided by change in height.

With air springs, the spring rate increases if the load increases, and vice versa.

The spring rate increases if the volume of trapped air is reduced. Since the effective area doesn’t change significantly when the spring height change is relatively small, the spring rate can, for practical purposes, be taken as a function of the height of the air column trapped in the bellows. Increasing the static ride height and thus the height of the air column will reduce the spring rate.

If the spring is changed to one with a different diameter, but the load and air column height remain the same, the pressure and volume of the trapped air both change. The spring rate is greater for a larger diameter air spring when the height of the air column and load are same compared with a smaller diameter air spring.

When the volume of air is trapped in the spring, the spring rate becomes progressively higher as the spring is compressed, and progressively softer as the spring extends. This behavior is desirable in most cases.

The exception is when maximum bump travel is required, for maximum vertical wheel travel on difficult off road obstacles. The trapped air can simply not be compressed enough. One solution is to release some of the trapped air from the compressed spring. Another is to connect an external reservoir to the air spring, which effectively increases the volume of trapped air. A guide/rule of thumb to allow full bump travel is for the volume of the external reservoir to be about double the volume of the air spring at static ride height.

The external reservoir will reduce the spring rate, but if the flow rate between the spring and reservoir is controlled, say by the small diameter of the connection, its effect will be reduced at highway speeds when roll stiffness is required but provide a softer spring rate and full vertical wheel travel for slow off road situations.

An “Airock” system constantly monitors vehicle speed, pressure in each air spring, and the output value from each ride height sensor. It allows two driving modes, “on road” and “off road”.

Above a preset road speed the Airock system automatically adjusts the ride height of the springs to the “on road” height. On a highway, “active mode” controls body roll or pitch due to cornering or braking forces. It doesn’t adjust spring heights at low speed, e.g. for speed humps.

A second ride height can be preset, activated only at low speed, for travel over rough off road tracks. To allow difficult obstacles to be negotiated, the spring heights and pressure can be adjusted in “manual mode”. The arrow buttons adjust forward or rearward pitch and left or right roll. Diagonal pitch can be adjusted by pressing an adjacent pair of buttons at the same time. Pressing the √ plus an ⇑ or ⇓ button will raise or lower all springs together. The X button returns all springs to their preset height.

User Controls In-Dash

Because the donor Land Rover was never equipped with anti-roll bars, there is no legal requirement for them. However they will be fitted if road testing shows they are needed.

Land Rover installed air spring suspension, which they call EAS for electric air suspension, in some models. The following file, in pdf format, is a copy of the workshop manual for the EAS system used in the early 90’s.

Range Rover 1990-1994 Air Suspension