Arguably the most popular 4WD topics around the camp fire are either tyres or suspension, or both. Now that we have fitted a heap of vehicle protection gear to our Ranger, which has added considerable weight, our truck is a bit low to the ground and the skinny wheels and road tyres look out of place. In this next installment of our Ironman 4×4 Bush Truck build, we fit an up-rated suspension system.
Of all the accessories that you could possibly fit to your 4WD pride and joy, a fully matched suspension upgrade kit is one of the most expensive. Although your replacement bull bar looks good when you approach your vehicle in the parking lot, once you’re driving, it is largely unnoticed. The same can be said about your canopy, side steps, rear bumper and tow-bar, the underbody plates, and that winch hiding inside the bull bar. Your spotlights are useful only at night.
Your suspension, however, gives you constant feedback with every metre travelled − and there can be few things worse than a beautifully kitted out 4WD that drives badly.
I often speak to folks who have been promised a magic carpet ride, and, having parted with a considerable amount of hard earned cash, end up with a vehicle that is disappointing to drive. This relatively minor mistake can cause one to hate a vehicle which is otherwise very good. There are cases where the suspension product itself is not very good, and no amount of magic is going to improve that situation. In most cases, however, I find that the incorrect type of suspension upgrade is fitted and often a very unrealistic expectation is created in the vehicle owner.
To better understand why a suspension upgrade is often an absolute must for your 4WD, let’s briefly look at the basics. The vehicle suspension system consists primarily of springs and shocks. These major components pretty much determine the ride quality of the suspension system. Less prominent goodies such as control arms, bushings, shackles and U-bolts have little effect on ride quality. Wheels and tyres also form part of the suspension system of your vehicle, because of the flexible nature of the rubber tyres. We’ll cover this next month.
The primary function of the springs in a suspension system is firstly, to keep the chassis and body of the vehicle at a predetermined ride height above the wheels and axles, and secondly, to insulate the vehicle cab (where you sit) from the up-and-down movement of the wheels and axles over undulations in the terrain on which you are travelling.
The springs absorb road shocks and irregularities, and carry the weight of the vehicle, its passengers, and any load. Note that the vehicle body and chassis are above the spring, and the wheels and axles are below the spring.
The two major types of spring commonly used in 4WD vehicles today are the leaf spring and the coil spring.
Leaf springs are one of the earliest types of spring used on automobiles, and remain a popular choice for the rear of most pickups. These leaf springs are pretty robust, and due to their two-stage design, carry heavy loads better than coil springs can. However, they are less comfortable than coil springs, which are now found on the front of almost every bakkie currently available and are even starting to make an appearance on the rear of some of the latest dual-cabs.
A major advantage of a leaf spring over a coil spring is the fact that it also locates the rear axle and keeps it in place. With coil springs, the axle has to be located by means of a number of radius arms. Leaf springs are therefore used only on solid axles, whereas coils are used on both solid axles and independent suspension designs.
In very simple terms, shock absorbers dampen the up and down movement of the vehicle’s springs and therefore that of the axles and wheels. This ultimately controls undue movement of the body. They should be referred to as ‘Dampeners’ but we call them ‘Shock Absorbers’ because, when they work properly, they seem to smooth out the ride. Strictly speaking, though, the springs absorb the road shocks and the shock absorbers absorb this energy from the springs in the form of heat.
This is the fundamental idea behind how your suspension works: travelling down the road, you hit a speed bump and the wheels and axle are thrown up into the air. The spring is compressed or deflected, and it now has a huge amount of energy stored in it. The spring expels this energy by expanding again, forcing the wheels and axle to crash back down onto the road surface. The result is an uncomfortable jolt inside the vehicle − and, more importantly, a loss of traction while the wheels are jumping up and down.
When you add a shock absorber which absorbs the energy stored in the spring before it can expel it, there is much less of a jolt. The wheels are also in contact with the road surface more of the time, improving handling and safety. I have always found that uncomfortable 4WDs can be made to give a much better ride by merely fitting uprated shock absorbers. These control the springs better and induce a smoother, more controlled ride. Note: there is a difference between ‘softer’, and ‘more comfortable’.
Types of shock absorbers
Most shocks on modern 4WDs are twin-tube, hydraulic, gas-charged, telescopic shock absorbers – gas shocks for short. The inner pressure tube is top-filled with hydraulic oil. The working piston inside the shock moves up and down through this oil, encountering varying degrees of resistance because of the valves inside the piston.
As the shock is compressed, the shock shaft starts to displace hydraulic fluid from the inner pressure tube into the outer reservoir tube. The outer reservoir tube is two-thirds filled with hydraulic oil. The upper third of the outer reservoir tube is filled with nitrogen gas, under some pressure. The oil being displaced out of the inner tube compresses this gas, as hydraulic fluid cannot be compressed. The gas puts the hydraulic fluid under pressure, which raises the boiling point of the fluid and goes some way to preventing the oil from aerating and causing the shock to fade. (A fading shock has less control over the spring, causing poor handling and a bad ride.) The hydraulic oil which is being heated by the up-and-down movement of the piston cools down somewhat, due to the fact that it is in contact with the outer casing of the shock at the bottom two-thirds of the shock body.
Foam cell shocks are similar in design to gas shocks, with one fundamental difference. Both the inner and outer tubes are top-filled with oil. There is a neoprene-type foam bladder in the outer reservoir tube, hence ‘foam cell’. There is no nitrogen gas charge inside the shock. Oil displaced by the shock shaft as it enters the inner pressure tube now compresses the foam cell, as opposed to nitrogen gas. As the hot hydraulic fluid is now in contact with the entire length of the shock body, more cooling takes place, preventing overheating. Foam cell shock absorbers typically have 50% more hydraulic fluid than their nitrogen gas equivalent. I have always felt that foam cell shocks were a tad smoother than nitro gas shocks. At Ironman 4×4, we offer nitro gas as well as two versions of the foam cell shock absorbers.
Nitro Gas shock absorbers are all-rounders, good for most applications. The Foam Cell shocks are harder to punish due to their much larger oil capacity, and the Foam Cell Pro shocks are enormous beasts with double the oil volume of the equivalent Nitro Gas shocks. They are very sporty and very capable.
So what is wrong with the original suspension on your 4WD?
For the most part, not much. There are certainly a few glaringly-poor standard suspension systems on modern 4WDs but, for the most part, they are pretty good. Spare a thought for the poor suspension engineer at the motor company, though. He has to design a suspension system that has to be good in as many applications as possible. Whether you are travelling alone in your unladen double-cab bakkie down a country road, or shaking down one of the Kgalagadi’s notorious gravel roads with your wife, two kids, and everything including the kitchen sink in the back and on top of the roof, and towing that new Jurgens Explorer, the standard suspension system has to attempt to be good enough. The reality is that this is virtually impossible to achieve with conventional steel spring suspension.
There are several reasons for wanting to upgrade one’s standard suspension. A lifted truck with big wheels and tyres hardly ever looks bad. Increased ride-height can improve off-road ability when done correctly, too. Many people who buy a bakkie for the first time after having driven a sedan, are looking for a ‘softer’ ride. Once you start fitting permanent accessories on the nose, and gear on the back, the loss in ride height needs to be addressed. A full replacement bull bar, winch and second battery can easily add up to 150kg on the nose of the vehicle, and cost you a good inch in ride height. Some folks have a permanent drawer system, recovery gear, tyre repair equipment, fridge and slider, tools, etc, all under a steel canopy in the rear of the truck. This will drop the ride height in the rear, too, and we haven’t even loaded the chairs, chops or beer yet! It is even harder to address the problem if you occasionally carry very heavy loads or take on heavy towing.
What is the fix?
From the outset, it is important to bear in mind a couple of fundamental things regarding handling and ride quality. A firm spring will carry more load, but will be more uncomfortable when the load is removed, making the vehicle handle poorly. It may also then cause the vehicle to lift too high. A softer spring will be more comfortable, but will give rise to more body roll, adversely affecting handling; and it will not be able to carry much load. Neither of these can be fixed by a good shock absorber. It is a team effort. It is very important to ensure that the correct springs are chosen for your application and then to match them to the correct shock absorber, for correct control. This will ensure that you are happy with the ride quality of your 4WD.
Configuring the front of your 4WD is pretty easy. You either have accessories fitted to the front, or you do not. These accessories are normally fitted once and are not taken off the vehicle with any regularity. The more accessories you fit to the front, the heavier the springs will have to be. Almost all current 4WD SUVs and pick-ups have coil springs out front. The solid-axle variants (which include the 70 Series Land Cruisers and the Jeep Wrangler) have radius arms and panhard rods locating the axle, and separate coil springs and telescopic shock absorbers doing the suspension work. The other vehicles are mostly independently sprung, with upper and lower control arms locating the front wheels. The front spring sits over the front shock absorber, and this is referred to as a strut. This design is found on all current non-70 Series Toyotas (Fortuner, Hilux, Prado, and Land Cruiser 200), Ford Ranger and Everest, Isuzu KB and MU-X, Mitsubishi Triton, Pajero and Pajero Sport, Nissan Navara, VW Amarok, Mercedes X, Mazda BT-50 and others.
At Ironman 4×4, we’ve tried to make spring selection a bit easier by coding our springs with the alphabetical suffix ‘A’ to ‘E’ where applicable. For example, the Ironman part number for the coil spring on the front of our Ranger Bush Truck is FOR001A, or FOR001B, or FOR001C. FOR is obviously for FORD, 001 is the model specific part number (current model Ranger) and the A, B or C determines the spring rate, with A being the lightest and C being the heaviest. A single-cab Ranger with no accessories on the front, and needing a bit of a lift, would get the FOR001A spring; whereas a double cab with just a bull bar could use the FOR001B spring. Our Bush Truck has the Full Monty, and we therefore had to fit the FOR001C spring to get the most lift possible to compensate.
Thus, when selecting your front spring, you need to establish what accessories will be fitted to the front of the vehicle, as this determines the correct grade of spring. It becomes an issue when the suspension upgrade and the fitment of the accessories do not happen at the same time. In such a case, the accessories should always be fitted first, and then, when your budget allows, have the suspension upgraded.
A word on front spacers
Not a good idea! (Four words, actually, but no less truthful.) With the up-and-down movement of the front wheels on these independent-suspension 4WDs, the limits of the up-and-down travel are important, and are accurately determined during the design of the front-suspension geometry. The limit of the upward travel of the front wheel is normally determined by a rubber bump stop. When the wheel has reached this upward limit and this rubber bump stop comes into play, there still has to be some remaining degree of compression of the strut. When a spacer is fitted between the top of the strut and the chassis, it not only induces additional lift but critically compresses the strut further by the thickness of the spacer. On many current 4WDs, a 30mm spacer on top of the front strut will cause the strut to reach maximum compression before the bump stop comes into play. At maximum compression, there is nowhere to go. The spring is solid, and it is all metal on metal, resulting in a possible broken front shock, cracked chassis and some chipped teeth.
When you are articulating the front end of your 4WD off-road and hanging the wheels in the air like a pro, the limit of the downward travel of the front wheel is determined by the length of the front shock. This downward limit ensures that the front CV shafts are not forced into an angle that is more than they were designed to handle. It also ensures that the inner CV joints do not pull out of their housings, causing expensive damage. More importantly, though, this downward limit also ensures that the upper and lower ball joints in the upper and lower control arms, which locate the front wheels, are not extended past their maximum operational angles. Should this happen, they could pull out of their housings or snap off. This will dislocate the front wheel, and then nobody is going anywhere. At speed, it will be catastrophic. Fitting spacers to the top of the front strut effectively increases the total length of the strut assembly, which allows the front wheels to be able to drop down further, past the maximum downward limit, and potentially cause the aforementioned problems.
On the rear of most modern SUVs and pick-ups, there are either coil springs or leaf springs. Coil springs are in general favoured on wagons, as they are touted to be more comfortable, while bakkies generally carry load more regularly and thus use leaf springs. As with the front coil springs, the rear coils from Ironman 4×4 are graded ‘A’ through ‘E’ where applicable.
As most SUVs and double-cabs are also the family transport, the majority of them do not carry much load on a daily basis. When the weekend or the annual holiday comes around, things change. This makes spring selection a bit more challenging. As an example, fitting a ‘C’ rear spring to an empty Fortuner is going to make it look like a dragster, and drive pretty poorly. However, when the annual holiday comes around, it will carry anything you can chuck at it with ease. This is not a desirable situation.
Fitting a ‘B’ spring here will do the trick, as it will give a nice lift but not too much, it will still have a decent ride, and, when the holiday comes round, it will carry the luggage and all else better than the standard suspension would. You will still notice that the wagon is loaded, but it will not be as pronounced. If you are fortunate enough to have a dedicated Bush Wagon, you can fit the heavier rear spring and leave all your off-road touring gear loaded.
Towing presents its own unique set of challenges. Tow-ball weights, trailer/caravan weights and trailer/caravan loads are much debated, but little understood. Personally, I steer clear of towing anything that looks like it will give me a headache. What I can say, is that a huge number of people try to fix towing problems by fitting heavy-duty suspension at the rear of their tow vehicles. In most cases, this is merely masking a problem, not fixing it.
On the rear of our Ironman Bush Truck we have leaf springs. I must admit that I have always been quite impressed by the ride quality of the current Ford Ranger in standard guise. The guy in charge of suspension design for this truck deserves a ‘Bells’. It strikes a really good balance between comfort, control and loadability, more so than any other truck on the market.
Modern leaf springs still seem quite rudimentary by design and application – half elliptical blades stacked on top of each other in diminishing lengths from top to bottom. For good measure, add a couple of really thick, less-curved ones to the bottom to help carry additional load. I’m afraid I have over-simplified here, as leaf springs are quite complex when you start to delve into the science behind their design. Suffice to say, after more than 100 years, they are still around. They must, therefore, be doing a good job.
Leaf springs found on the rear of bakkies are typically two-stage leaf packs. The upper stage is a collection of thinner curved leaves stacked on top of each other. They decrease in length as you move down through the pack. The second stage is normally one or two thicker, flatter blades that come into play only once the first stage has been flattened somewhat by the load, and come down to rest on the thick second or ‘overload’ stage.
On some original-equipment leaf-spring designs, the second stage is cambered up quite close to the first stage. What typically happens is that, even with no load on the rear of the bakkie, the first stage could be forced down onto the second stage by mere road undulations. The thick second stage bounces the first stage back into the air with a jolt that is felt as harshness from the rear. Bakkies ride better with a bit of a load on the back. We again use ‘A’ to ‘E’ on our Ironman 4×4 leaf springs to determine spring rate. What we do with our ‘B’ rated leaf spring is to give the first stage more camber and lift it away from the heavy second stage. We also tend to flatten the second stage out a bit to give more clearance. It is instantly more comfortable. The downside, of course, is that the rear of the vehicle will sag further under load before the second stage comes into play.
On the Ford Ranger, our leaf spring numbers are FOR002A, FOR002B and FOR002C. On a vehicle looking for a more comfortable ride when carrying no load, we would use a FOR002A leaf spring; for a daily driver carrying occasional light to medium loads, FOR002B; and, for vehicles carrying a constant 300kg and more, we’d use FOR003C.
What did we fit to the Ironman 4×4 Bush Truck?
On our Bush Truck, we fitted a bull bar, a winch with synthetic rope, heavy-duty recovery points, and the heavy-duty underbody protection plate kit. This caused a loss in front ride-height of just over an inch – around 30mm. As mentioned previously, we fitted the heaviest of our front coils. For the rear springs, I went in a totally different direction for the sake of a bit of R&D (research and development).
Ironman 4×4 recently launched a new helper spring product called the Ironman 4×4 Add-a-Leaf helper spring kit. This kit basically consists of two short cambered taper spring blades. These blades are added to the standard vehicle spring pack and are installed between the first and the second stages of the rear leaf spring pack. What this essentially does is add a significant amount of spring rate and camber to the first stage. It gives a good 50mm of lift, and helps keep the first stage away from the nasty second stage. It rides very nicely when the truck is empty, and it can carry a good load with ease. It is also half the price of conventional replacement leaf springs.
Once we had fitted the suspension, the truck was about 40mm taller than standard, which is a perfect outcome. I’d had some concerns about the outcome of the suspension fitment, as the Ford Ranger in Automatic guise can suffer from propshaft vibration. This is caused by the fact that the vehicle has a two-piece propshaft, and any suspension lift results in a more acute angle between the rear half of the prop shaft and the front half. This is most often cured by fitting a spacer kit between the chassis and the centre bearing of the propshaft. This drops the centre bearing down and straightens the propshaft. I am happy to report that my Bush Truck has no such issues.
For the shock absorbers, I went with our top-of-the-range Foam Cell Pro units. These are arguably the largest shock absorbers available that will fit the Ranger without modification. The standard rear shocks on the Ranger have a piston diameter of 24mm; the Ironman 4×4 Foam Cell Pro shock piston diameter is a whopping 45mm.
While the increase in diameter is 88%, the increase in the surface area of the working piston of the shock is 250%. This means that the graphing for the damping and rebound can be very finely honed and calibrated to ensure supreme ride-control. I’d initially fitted the comfort-valved shock absorber part number on the rear, as I was afraid the ride would be too firm. After a couple of weeks, I decided that the rear was a tad too soft, and opted to fit shocks with the stiffer valving. It was a big improvement, and the ride is still superb.
Next month l discuss fitting wider wheels with bigger tyres – which match the plastic over-fender trims which have widened the body of our truck a bit. Once we had done this, we realised we needed to have a bit of a look at the standard brakes, and knocked on the door of some serious brake specialists for help.
By Mic van Zyl