Height ?

High is not always good.

Key

Red horizontal line represents the centre of gravity.

Red vertical lines represent the wheel travel movement. (Although in real life the axle drops in a curve)

Red dots on the chassis is where the control arms are mounted to the chassis.

Red dots in the wheels is the centre of the axle

Blue dot represents the wheel centre if different to the red centre of axle dot.

Standard

When a vehicle is sold from the dealership, the vehicle will drive well, be very subtle and comfortable and easy to get in to. Because your first impressions helps them sell a vehicle. That said the vehicle is quite capable off road and is extremely safe. Little tyres, low centre of gravity and light weight.

What happens when you become more adventurous and want to explore up north or just go further than the very easy bush tracks or even just carry a heavy load.. Now we are starting down the world of modified vehicles. What affects do modifications have on your 4WD.

 

 

How the vehicle is affected by springs.

The more you raise a vehicle the more unstable it becomes. The centre of gravity isn’t the only thing that changes. The higher the vehicle is raised the shorter the wheel base becomes and the caster is reduced. Caster is the line between the two king pins in relationship to the ground. And if the suspension system is not set up correctly it is quite possible to have next to no down travel and heaps of up travel.

When you raise a live axle 4WD, most people assume the wheel is directly below where the wheel used to be but that is not true. As you can see by the illustration below the suspension pivots from the round red dots on the chassis. So when you raise a vehicle the wheels swing inwards.

Coil raise 50mm

The first accessory sold is suspension. A good set of springs and shockers. We only recommend raising a standard vehicle by 40mm to 50mm from standard. This is a pretty safe modification. As you can see the centre of gravity is only slightly raised and the wheel base and caster angles are only slightly altered. This is where most 4WDers stop.

 

BLK and 50mm

But some want to add larger tyres. This means more guard clearance as the tyre is so much larger than the original. One of the better ways to gain guard clearance is to install a body lift kit. By doing this all the steering geometry achieved from the 50mm spring lift is unaltered as only the body is raised off the chassis. This will have an effect on the centre of gravity as seen in this illustration. All of this can be engineered as long as your car doesn’t have SRS air bags.

 

Dropper and 50mm

Now a Discovery 2 for example has SRS air bags and cannot be altered. It is illegal to install a body lift kit in this situation. Although not as safe, it is allowed to install a dropper kit. This is a kit that instead of raising the body off the chassis drops all the suspension downwards off the chassis. This option will fit the larger tyres under the vehicle but has two major alterations. The centre of gravity is raised a lot further as the chassis, engine, gearbox, transfercase, steering box and everything else attached to the chassis is raised. The wheel base is also decreased further as the axles swing further away from the chassis. We make a dropper kit for the Discovery series 2 and we have gone to great lengths to make our kit as safe as possible. But it is not as safe as a body lift. We have exaggerated the effects on these illustrations but if you compare the images from above you will see a higher centre of gravity and a shorter wheelbase.

 

Drop boxes

I believe these to be very dangerous. A drop box gives excellent ground clearance as only the wheels are lowered. So the diffs and axles have heaps more clearance than just fitting larger tyres. The centre of gravity is raised similar to the dropper kit with all the body and chassis weight been raised. BUT the wheel base is decreased even further as you can see in this illustration. The red dot in the centre of the shaded wheel is where the centre of the wheel would be using a drop box, the blue dot is where the centre of the wheel is with the drop box. A drop box has massive effects on the wheelbase and how the vehicle handles. Along with a list of other issues as well.

Tubbing

This is by far the best way to build a vehicle if possible. This is done by making the inner wheel arches larger for the tyre clearance and not raising the vehicle above the 50mm spring lift. Although quite involved the end product is better than all the options listed above. As you can see the centre of gravity is nice and low. The tyres give better ground clearance and the wheel base in un-altered.  This ticks all the boxes but is not always achievable.

 

 

In real life we converted a Disco S2 fitted with a 50mm spring lift and a dropper kit to a tubbed vehicle. Note when we tubbed this vehicle we had to alter the wheel base by a four inches.