Pretty much every ute on the market utilises leaf springs for the rear suspension. Why? Leaves are old as buggery, noisy and offer about the same ride quality as a billy cart with a milk crate for a seat. And that’s before you fit an aftermarket, higher-rated spring pack to handle the touring loads and towball weight from your caravan. Spoiler alert: heavier rates do not improve unladen ride quality, in fact, things get much worse.
Look, it’s not all bad in leaf-world. They’re still the number one choice when it comes to carrying a load and sheer simplicity. Not much else comes close for the money, it’s just that they’re pretty ordinary when it comes to, well, everything else. Ride quality ain’t great, off-road flex leaves a lot to be desired (no pun intended) as standard, and generally they’re just a massive compromise. Jack of no trades, master of one.
But if you’re chasing an upgrade that solves pretty much all the traditional leaf-pack problems, then it’s time to take a Bo Peep at parabolic springs, my friend. They’re comfier, quieter, offer better articulation and don’t lose out on load carrying.
What is this magic?
No magic, just a really clever application of metallurgy and physics… so yeah, it pretty much is magic, I guess. Whatever, let’s jump in.
A traditional, semi-elliptical leaf pack is made up of several layers of spring steel that are designed to flatten out when a load is placed in the tray. This is the “spring” action of the pack. Each individual leaf in a pack is slightly different in length. The longer ones bend with less load placed on them, and the shorter ones take more effort to compress. Think of it like trying to break a stick over your knee. The shorter it gets, the less leverage is available and the more difficult it becomes. It’s the same principle.
This is what’s called a progressive spring rate. It’s nice and supple in the first part of the spring travel but takes progressively more load to move as the spring resists the downforce from above. What does this mean in layman’s terms? This means that leaf springs generally don’t flex heaps or offer much in terms of ride comfort, but boy, can they take some weight. So, both bad and good at the same time. Schrodinger’s suspension, if you will.
Each individual leaf in the pack is a uniform thickness along its length and is stacked from short ones on the bottom to longer ones on top. It’s simple, it works, and it has been done for, like, the last few hundred years. When it comes to supporting heavy loads, leaf springs are your guy.
Enter the parabolic spring…
However, parabolic springs are the (relatively) new gunslinger in town, and frankly, they’re a big improvement in more than one area.
Rather than being a uniform thickness (when looked at from the side), parabolics taper out from their thickest point in the middle to their much thinner ends. This has several advantages, from needing fewer leaves in the pack to allowing for a much comfier ride and a few other pluses, too.
Lower weight = more GVM to play with
With a traditional leaf pack, the more individual leaves there are (i.e. the thicker the pack is), the higher the load the pack can support. With parabolics, however, the individual leaves work much more efficiently at distributing the given load along its length.
Basically, this means you only need two or three leaves per pack, cutting down on weight significantly and allowing it to be added in other more important areas without unduly affecting your GVM rating. You’re getting the same load-carrying ability from a lighter, more efficient spring. Kind of like driving an AU Falcon vs. a brand-new Ferrari. I mean, they’re both cars, but one is a lot lighter, faster and better than the other (talking about the AU, obvs).
Quieter operation = a greater appreciation of the band Crazy Town
I don’t care what you say, the song ‘Butterfly’ will never get old, and pumping it while driving with the volume turned up to eleven is one of life’s true pleasures. Of course, that pleasure is mitigated somewhat when your suspension is banging and clanging with every individual bump in the road like a toddler left alone with a saucepan and rolling pin.
Traditional leaf packs may have a thin piece of anti-friction material in between the metal layers, but they can and do wear out, and the leaves are free to slap against each other like dodgem cars piloted by the vision impaired. When travelling down corrugated or bumpy dirt tracks, this can quickly drive you mental, and not even the soft strains of Crazy Town can bring you down off the ledge.
Parabolics, by their design, are not in contact along their full length and, as a result, are orders of magnitude quieter, not to mention are much less prone to dust and mud contamination – a common cause of corrosion. Chalk up another W for modernity.
Better ride, increased comfort, and non-bruised kidneys ftw
I could give you a strongly worded dissertation on such heady topics as ‘inter-leaf friction’ and the ‘relation between initial spring travel and the rapid expansion of effective spring rate’ here, but that’s way less fun than drawing eyebrows on a photo of Peter Dutton, so I won’t keep you from doing that for long.
Let’s just say that parabolics give near-coil spring levels of comfort during the initial phase of suspension travel – aka the phase of travel that soaks up minor bumps on the road – and, as such, offer much higher levels of comfort while underway.
And no, they don’t suck for towing or carrying heavy loads
Even though the parabolics are a lot more supple and willing to articulate over traditional leaves, the true genius of the design is that they can still do leaf spring stuff, or to put it simply, they can still handle heavy loads. This is why they’re perfect for towing and carting a family’s-worth of holiday gear.
The rate of spring compression soaks up smaller bumps with no worries while simultaneously being able to take a bunch of ball weight or having the canopy loaded up with a pallet or two of BMX bikes, the 12-burner BBQ and that marble dining table one of the in-laws asked you to pick up on the way back from your trip because you’re too much of a coward to say no.
The brass tacks
I’ll level with you here. There are a lot of considerations when selecting a leaf spring set-up for the back of your tow pig. Leaf pack performance is a hell of a rabbit hole, and they can be modified and customised to flex like a Russian gymnast, carry heavier loads than a Russian strongman or put the power down like Vladimir Putin descending an escalator. They can even do a couple of those things at the same time. But, and it’s a big one, when comparing a stock leaf pack with a parabolic version, the parabolics not only win the race, but have iced down, given an interview to Channel 7, signed some autographs and are on the bus home by the time traditional leaves cross the line.
As always, however, consult your local suspension expert about what will work for your specific set-up.
It should also be noted that there are a lot of parabolic springs on the market. As with any mod to your tow rig, it pays to shop around and find the right fit for you and your vehicle. For our money, Terrain Tamer are the go-to. They’ve done the hard yards over a lot of years with plenty of research, development, design and manufacturing to bring one of the most modern, technologically sound and stringently proven parabolic springs in the game. They even use their own special grade of spring steel to make these things work exactly like it says on the box.
You can find out more at www.terraintamer.com
Tell `em we sent ya!
Read next: