Last updated 28/09/2017
Do you need a lift? According to some, one of the most important modifications to any 4WD is the installation of after market suspension lift kit. Is this really true? Is after market suspension universally a good idea?
Why So Low Out Of The Factory?
Why are vehicle manufacturers bringing out their independent front suspension (IFS) four wheel drives with so little ground clearance? Just a little bit more would be great. It doesn’t need to be huge, just enough to keep the belly off the ground in a typical rut. It seems that standard vehicles can bottom out in the ruts even on an easy track to popular family beach and camping spots. Why not give us a few more centimeters to clear those tracks?
It’s not a matter of cost. What’s it take to increase ground clearance slightly? A tighter pre-load wound up on the spring? The cost is practically zero. Do vehicle manufacturers have shares in after market suspension companies? Are they just being stupid?
There is a good reason – the ride height is purposely chosen in a IFS vehicle to minimize CV angles and minimize failure rate. The drive shafts on a stock vehicle are designed to be perfectly level and the CVs to be completely straight when the front wheels are straight. With straight CVs, wear is minimized and longevity and reliability are maximized. The front wheels spend the vast majority of their time pointing straight ahead, so with level drive shafts the CVs are only significantly worn during the small fraction of a vehicle’s life spent turning corners or when on uneven terrain.
As soon as you lift a vehicle the CVs start wearing out more than they otherwise would. Not a bit more. A lot more. Driving straight ahead is wearing them out due to the non zero angle. So instead of wearing out a small percentage of the time, they are wearing out all the time. The wear is constantly accumulating, increasing the risk of a future failure.
The CVs in a stock vehicle are less likely to fail for two reasons:
1. They will be less worn so will be stronger when faced with a potential failure event, such as a shock load when offroading.
2. Any potential failure event will occur at a lower CV angle, reducing the stress on the CVs.
People often associate a failure with what they were doing at the time. Instead of holding the suspension lift accountable, they’ll blame the fact that they were tackling a demanding track at the time. Or they were showing off and driving too hard. Actually failures have many contributing factors which accumulate over long periods of time. As soon as you lift your vehicle the wear is accumulating and potentially contributing to a future failure. See this article for an explanation on how failure works.
To reduce the risk of CV failure, the differential can be lowered when installing a suspension lift. This reduces the CV angles. Ground clearance will be lost directly under the diff, however ground clearance across the rest of the vehicle will be improved, as well as approach angle and the ability to fit larger diameter tyres. This is no different to installing a suspension lift on a vehicle with live axles. The differential ground clearance is not changed for live axle vehicles.
Get After Market Suspension For Better Performance
After market suspension manufacturers often claim their products afford superior handling and performance. One of the key parameters that determines a vehicle’s handling is its centre of mass. Take a look at a Ferrari or Lamborghini. They are low. Raising a vehicle’s centre of mass degrades its handling, increasing body roll, increasing rotational inertia, deteriorating steering feel and increasing the risk of rollover. So right off the bat, all other things being equal, a lift kit will degrade handling.
Apart from lowering the centre of gravity, the other way to enhance handling, given suspension geometry and linkage design is already fixed, is stiffer suspension (with matched shock absorbers). After market suspension is often stiffer than factory suspension. Stiffer springs means they will sag less under the load of the vehicle, providing lift. Stiffer springs also have increased load carrying ability. Many after market springs are provided for increased load carrying so again they’ll be stiffer than stock springs. Stiffer springs do enhance steering response and reduce body roll. But stiffer isn’t better. The vehicle manufacturer could have easily fitted stiffer springs without additional cost. The spring stiffness is a compromise between handling, load carrying ability, passenger comfort, articulation and traction over bumpy terrain. The vehicle manufacturer picked a stiffness they thought was the best compromise. Stiffer springs aren’t superior quality, they simply offer different advantages and disadvantages. So in my opinion you wouldn’t get after market suspension because it’s universally better in terms of performance. It’s different. Get it if you want to carry heavy stuff or you want increased ground clearance and articulation. If you want superior on-road handling you’d lower your vehicle and fit stiff springs.
We’ve already discussed how lifted suspension negatively impacts CV reliability. What about the reliability of the suspension itself? The stock suspension is reliable. It’s simple and the geometry is well constrained to ensure it stays safe. There isn’t much that can go wrong. Imagine how many hundreds of thousands of vehicles the manufacturer sells, most running stock suspension. Mining, agriculture, rental vehicles, commercial fleets – they’re all stock. For the small fraction of vehicles running after market suspension, in my experience they account for a disproportionate quantity of failures. Over extension of ball joints, impacts between various suspension components due to flawed suspension travel, strut failures, mounting bolt failures – these are problems I’ve seen in vehicles with after market suspension (in addition to CV failures). Maybe it’s because those vehicles are driven over tougher terrain and with heavier loads. Regardless, stock suspension is reliable in my experience. I wouldn’t get after market suspension for the purpose of increased reliability.
Shock absorbers wear out so it’s possible that after market shock absorbers could last longer. So maybe you’d consider after market shock absorbers if you wanted greater life out of them. However the slow deterioration seen in shock absorbers is not something that will see you stuck out in the bush. If reliability is defined as simply being able to drive then longer lasting shock absorbers don’t really offer enhanced reliability but will offer better performance on bumpy surfaces compared to worn factory shock absorbers.
What About Lifting Live Axles?
Installing a suspension lift on a live axle still degrades handling through increased centre of mass and worsens reliability of UV joints but not to the same extent as CVs in independent suspension. Although universal joint angles are increased, the change in angle is much less when compared to the same lift height on independent suspension and the effect on wear and longevity is much less. This is why live axles are preferred for extreme offroading. They can be configured for huge lift and articulation without effecting strength as much.
Do You Need Big Flex for Going Offroad?
With open differentials it pays to have good flex in your suspension so that all wheels maintain firm contact with the ground. With differential lockers (or traction control) it doesn’t matter if you lift a wheel. The grounded wheel will have more traction because all the weight is on that wheel, and it will receive all the torque through the diff locker or traction control. If you want to maintain driveability on road and minimize increasing the center of mass of your vehicle you are better off getting selectable diff lockers than changing the suspension to get more flex.
If you are doing hard core trails then more flex does have advantages. It keeps the vehicle more stable which is useful if for example you are pushing the limits of traction and inclination. Lifting a wheel causes instability where the vehicle may rock back and forth, potentially triggering a loss in traction or worse a rollover.
When To Get After Market Suspension
In my opinion you should get after market suspension if you want to carry heavy loads for long periods of time and / or if you want improved off road performance through increased ground clearance, articulation, flex, approach angle and departure angle. Another reason is if you want to fit larger diameter tyres to your vehicle. Get some experience with your vehicle before deciding on a lift kit. Does the rear end feel saggy and sloppy when you’re fully loaded? Are you bottoming out on the tracks you usually drive on? If you answer no to both of these questions then maybe you don’t need after market suspension.
Lift your vehicle by the minimum you can get away with. This keeps the centre of mass as low as possible, minimizes negative effects on reliability and hopefully keeps your 4WD legal. Increasing lift increases wear on your CVs disproportionately. A small lift doesn’t make much difference. A large lift means you’ll probably break CVs every so often.
For me, the front end on my hilux was a bit too low for what I wanted to do. It would often beach itself too easily in soft sand and would clip the ground on relatively tame rocky trails. I also didn’t want to lose ground clearance when fully loaded for touring. So I got a small lift – 40mm. And I got stiffer rear springs rated for constant heavy loads. The lift I got is below the 50mm lift limit enforced in most jurisdictions in Australia to keep it legal. Remember you must keep the total lift below the limit. This means suspension lift + body lift + lift garnered through larger diameter tyres must be less than the maximum allowable lift according to the law in your state or territory.
Types of Lift
There are a few ways of lifting your vehicle. Some legal, most not. I’m no expert on vehicle modification laws so do your own research. This is my interpretation of the limited and possibly inaccurate information I’ve come across regarding suspension lift in Australia.
Strut spacers: This is a spacer between a coil strut and the strut mount. It shifts the entire assembly down. This introduces potential problems with over extension of suspension components / steering linkages and bump stops no longer adequately limiting travel. I understand strut spacers to be illegal.
Spring over: This is where leaf springs that have been designed to run under an axle are re-positioned on top of the axle, providing a lift equivalent to the thickness of the axle. I understand spring overs to be illegal.
Extended shackles: This is installation of longer shackles on leaf spring suspension. I understand extended shackles to be illegal.
New springs / struts / shock absorbers: This is the only way that I know of to provide a true suspension lift legally without getting engineering certification, as long as certain requirements are met like not exceeding maximum allowable lift height. New springs will be longer and / or stiffer, providing the lift. Shock absorbers are also replaced to suit the spring rate and travel.
Body Lift: This involves installing spacers where the body fixes to the chassis. It does not improve ground clearance but does provide extra room to fit larger diameter tyres. It is not a suspension lift. I’m not sure on the legality of body lifts. A body lift will increase the twisting force that the mounting surfaces experience. This increases the risk of mount failure during an accident.
Air Bags: These are pressurized bags that provide lift assistance for your existing suspension and are used to adjust ride height and stiffness. The air pressure in air bags can be adjusted to suit different loads and conditions. Their adjustability is what makes air bags superior to other suspension arrangements. The problem with air bags is that they may load the chassis at a position where it is not designed to take that load. Chassis failures have occurred as a result of air bags. Use them for fine adjustment of your springs rather than as a substitute for springs designed to carry the load. Air bags may or may not be legal depending on how they impact suspension travel.