For me, the motivation was a combination of all of the above.

My own range Rover, a 1986 EFI Vogue, was in standard road going trim when I purchased it.  It was fitted with a front spoiler, aluminium bull bar (good for mounting spotlights only), after market alloy wheels, and a rear mounted nudge bar.  I doubt very much that it had ever seen a bog hole or steep hill climb.

The event that forced my hand, and started me on the road of suspension modification, was when I purchased a set of Hankook RT01 MT 31"x10.5" tyres, mounted on a set of white spoke rims.  The combination of larger, wider tyres, mounted on rims with a greater offset, and a set of rear suspension springs that had already with stood 130,000 miles of punishment, resulted in my new tyres being dealt to buy the razor sharp edges of the wheel arch surrounds.

The easiest solution to this dilemma would have been to follow the same path that so many Range Rover owners take.  Simply fit a set of 50mm lift springs.  However, I felt in the long run, that this would be a compromise (but certainly a cheaper solution than the one I took).

The Range Rover design engineers have millions of dollars to spend on research and development, along with the necessary equipment to design, build, and test their design modifications.  If a suspension left was as simple as adding a 50 mm lift spring, why wasn't it a factory option?

Let the Design Begin

At first glance, fitting a 50 mm lift spring looks harmless enough.  However, several problems exist.

1. The 50 mm lift spring has a higher spring rate than a standard spring.  During hard out offroading, or when carrying heavy loads, this can be a bonus.  However, the increase in the suspension stiffness can reduce axle articulation.
2. The 50 mm lift spring is manufactured from a spring wire of approximately 2mm larger in diameter than a standard spring.  If you compare the lengths of a fully compressed standard spring with that of a 50 mm lift spring, he will find that the 50 mm lift spring is approximately 20 mm longer.  In practice, this will result in 20 mm less upward axle articulation.
3. If left unmodified, the shock absorbers are no longer sitting at mid-stroke when the vehicle is at rest on level ground.  They are extended by an extra 50 mm.  This will mean that, when fully crossed up, the axle dropout will be reduced. 

Remembering that the fully compressed spring height of a 50 mm lift spring is also 20 mm longer than standard (as detailed above), again when fully crossed up, the spring will bottom out while the shock absorber still has approximately 20 mm of travel left.  This is wasteful.

The solution to the above problems lies with the lengths of the shock absorbers.  If you are happy with the heavier spring rate of the 50 mm lift springs, then you need new shock absorbers with a 20 mm longer compressed length, and a 50 mm longer extended length.  The closest compromise I have been able to find are the Old Man Emu shocks designed for the Nissan Patrol long wheelbase.  However, new shock absorber mounts will need to be manufactured, as the end fixtures are not the same as those for the Range Rover.

As you are beginning to see, by making one small modification, a whole host of complications exist.

Personally, I wanted more then 50 mm of lift.  Because of the 100 inch wheel base, and a long overhang, the Range Rover suffers when negotiating steep break-overs and deep trenches.  The door sills and the rear quarter body work usually takes a beating.  I wanted to get more clear air between the bodywork and the hard stuff.

Reading the American magazines and assorted web sites revealed that they were doing lifts of as much as 150 mm.  Modifications to these extents are usually extremely expensive.  Not wanting to over do it, I said my goal at a 100 mm lift.

In Search of a 100mm Lift

In Light of the above issues I set myself the following guidelines:

1. Obtain a lift not exceeding 100 mm.
2. Retain the softer spring rate of the original specification springs.
3. As a minimum, maintain the original axle articulation dimensions by fitting extra length shock absorbers, or by utilising the original shock absorbers with redesigned mounting locations.
4. Try to keep the conversion as simple as possible.  Where possible, the lift should be able to be removed at a later date to restore the vehicle to its original specifications.

Many hours were spent lying underneath the Rover trying to decide the easiest and most economic method of achieving my guidelines.  The conclusions I came to where as follows:

1. Fit new 40mm lift King springs with a fabricated 60mm packer. The 40mm lift springs are manufactured from the same diameter spring wire is to the original Range Rover fitment, hence maintaining the same fully compressed spring height.
2. The 60mm packer for the front spring would be fabricated such that the shock absorber mounting, and stroking, would remain as per the original.  This is possible because the front shock absorber is mounted inside the spring.  Hence, when the packer lifts the spring, it also lifts the shock absorber.
3. New upper shock absorber mounts would be required in the rear, mounted 100 mm lower than the original.
4. New, longer brake lines would be required due to be increased distance between the chassis and the axles.
5. Because the 100 mm of lift would drastically change the king pin angle in the front axle, the front radius arms would require resetting.  If the kingpin angle is not restored to the original specification, the vehicles on road derivability would be seriously affected.

Part 2

In summary of part 1, I had decided on a 100 mm suspension lift, achieved by fitting 40 mm lift King springs, 60mm spring packers, repositioning the rear top shock mounts, and resetting the front swing arms.

Let the Modifications Began

Fixing the first two issues were easy.  Two new spring washes and a drive shaft catcher bolted through the floor pan were quickly install.  However, the modified swing arms seemed to have all the expects scratching the heads.  Numerous phone calls to Wellington concluded that if I could supply a materials testing report, complete with the signature of a suitably qualified person, which stated that the structural strength of the swing arms had not been severely affected, they would allow them to pass.

I phoned Heated Treatments Limited and spoke to their Quality Engineer.  He was more than happy to carry out some comparison hardness testing between the heated and unheated areas on the swing arms.  This was duly completed, and revealed that the original steel hardness was approximately 17 Rockwell C, and the heat affected steel was approximately 15 Rockwell C.  (For any other you who have an understanding of steel hardness, the swing arms are manufactured from very soft steel.  They have probably been designed this way so that they act as a crumple zone in the event of an accident)

The Quality Engineer was more than happy with the results and supplied me with a certificate to that effect.  This in turn satisfied the Certifying Engineers.

Part 3

The key to off road performance of any vehicle is "balance".  All things have to work in harmony with one another.  This includes everything from the driver input to the tyres that touch the ground.

The function of the suspension system is to keep the tyres on the ground at all times.  If the tyres lose contact, traction is lost, and you lose forward momentum.  This may seem all too obvious, and I am not trying to tell anyone how to suck eggs, but this is all too often overlooked when carrying out suspension modifications.

As with any modification, the proof is always in the pudding.  Up until the first off road excursion, I had no idea as to whether or not all the calculations and hard work was going to pay off.  There was always the fear that I may have weakened the integrity of the original set up.  I had to rebuild my confidence, and overcome my fear of breaking something.

My confidence grew after each consecutive off road excursion.  A number of these were conducted in the Rotorua and Taupo areas, and I cringed at the thought of having to be towed home from so far afield.  But to date, no part of the suspension modification has failed or caused me any real concern.  (Except for the CV joint fitted to the front drive shaft.  Due to some over zealous greasing I managed to push out one of the grease seals which bound up the joint)

The Range Rover's performance off road has been outstanding.  At this stage I have no more axle articulation than a standard spec'd vehicle, but I do here 100mm of extra ground clearance, which is a big help considering that the Range Rover suffers from a long rear overhang. The combination of the 40mm lift King springs and the standard length Koni shocks work extremely well.  I think the slightly softer spring rate over the 50mm springs is an asset.  To date I have only ever bottomed out the suspension system two or three times, and that was always at a very high speed and my own silly fault.  The Koni shocks are superb, and if you can afford them, they can't really be beaten for performance.  Getting the shock absorber dampening correct is just as important as the right spring rate.

I have also fitted "polly air springs" to the back to help when carrying heavy loads, and I also run these pumped up to about 20psi when driving on road to help stiffen the rear springs and reduce the body roll.