Parabolic Leaf Springs with Fitting Position Rear Axle for FOTON TUNLAND P201 4WD

Parabolic leaf springs for the P201 4WD TUNLAND do the same job as a conventional pack with fewer leaves and a fraction of the friction.

For a 4WD that runs empty through the week and loaded on weekends, that difference shows up every time you drive it.

What Are P201 4WD TUNLAND Parabolic Leaf Springs

A parabolic leaf spring is built from a small number of leaves, each machined thicker through the centre and tapering toward both ends.

That taper follows a curve rather than a straight line, which is where the name comes from. The shape spreads bending stress evenly along the full length of each leaf instead of letting it concentrate at any point.

Because the stress is distributed properly, each leaf can be longer and thinner than a conventional one carrying the same load. Fewer leaves do the work, and a parabolic pack can replace a conventional pack carrying ten or more.

The leaves are also spaced so they only touch at the ends and at the centre, held in alignment by brackets that do not clamp them together along their length.

What Is Parabolic Suspension

Parabolic suspension is simply a leaf sprung setup running parabolic springs rather than a conventional multi-leaf pack.

The mounting points, the shackle, the U-bolts and the axle all stay the same. What changes is how the spring responds to the road beneath it.

A conventional pack resists small inputs before it begins to flex, because every leaf has to overcome friction against its neighbours first. A parabolic pack has almost none of that friction, so it starts moving with the road surface immediately.

That is the whole difference, and it is why the ride change is noticeable from the first corrugation.

P201 4WD TUNLAND Parabolic Springs vs Leaf Springs

Conventional multi-leaf and parabolic are both leaf springs, so the comparison is between two designs rather than two different things.

A conventional pack has every leaf in full contact with the one above and below. Those surfaces slide against each other as the spring flexes, and the friction between them resists the movement.

That friction has one genuine benefit, which is self damping. A multi-leaf pack resists its own oscillation to a degree a coil spring cannot manage on its own.

Everything else about that friction is a cost. The spring feels firm over small bumps, the leaves squeak once the coating wears away, water and grit sit between the surfaces and corrode them from the inside, and the pack is heavy.

A parabolic pack removes nearly all of that friction. It responds to inputs a conventional pack absorbs, it stays quiet because the surfaces are not rubbing, and corrosion between the leaves is far less of a problem when there is a gap instead of a contact face.

Parabolic Leaf Springs vs Normal Leaf Springs for Your P201 4WD TUNLAND

Articulation is where the difference matters most off road.

A parabolic pack flexes further before anything binds, which keeps the wheel loaded on uneven ground where a stiffer conventional pack would lift it. A loaded tyre is a tyre doing work, and that is what gets a vehicle through a rutted track.

Weight is the other factor that separates them. A parabolic pack matching a conventional one for load capacity weighs around a third less, and almost all of that saving is unsprung mass sitting below the springs.

Less unsprung weight means the suspension has less mass to accelerate over every bump, so the wheel follows the surface more closely and the dampers have less work controlling it.

On a vehicle running close to its limits, weight removed from the springs is weight freed up for payload.

P201 4WD TUNLAND Parabolic Leaf Springs Pros and Cons

The honest version, because parabolic is not automatically the right answer.

On the positive side: a considerably better ride unladen, more articulation, less noise, less corrosion between the leaves, a lighter pack and more available payload. Multi-stage behaviour means comfort when empty and support when loaded.

On the other side: a parabolic pack costs more than a conventional one. It relies more heavily on the shock absorbers, because the self damping that inter-leaf friction provided is gone. And some designs have clearance limitations around the overload leaf at full articulation, which matters on a vehicle used hard off road.

The deciding question is how your P201 4WD TUNLAND is actually used. A ute permanently loaded to its limit and never run empty gains less from the comfort advantage, since it sits on the loaded part of the range the whole time. A correctly rated conventional heavy duty pack can suit that better.

Where parabolic earns its money is the vehicle that alternates between empty and loaded, covers distance, and spends time on corrugations.

Why Parabolic Springs Need Good Shocks on Your P201 4WD TUNLAND

This gets left out of most descriptions and it matters.

Losing inter-leaf friction means losing the self damping that friction was providing. The spring now moves more freely in both directions, and controlling that movement falls entirely to the dampers.

Factory shocks were valved for a spring that damped part of its own movement. Fit parabolic springs under tired or standard shocks and the vehicle can feel loose over undulations, which is the dampers being asked to do more than they were specified for rather than the springs failing.

The same parabolic pack with appropriate shocks rides considerably better than the conventional pack it replaced. Fitted over worn ones it can ride worse than standard.

Have the shocks assessed when the springs are being chosen rather than afterwards.

Spring Steel and How Parabolic Springs Are Made

Manufacturing matters more on a parabolic spring than on a conventional pack, because each leaf is carrying more of the load.

The leaf starts as spring steel bar and is drawn to a varying thickness along its length, thick through the centre and tapering toward the ends. That taper is rolled rather than machined, and how accurately it is formed decides whether stress spreads evenly along the leaf.

Formula 4x4 springs use high grade carbon spring steel in the SUP9 and SUP9A grades, which is the material class suited to sustained cyclic loading rather than one made to hit a rate on day one.

Hardening and tempering are what decide the finished toughness. Heat treatment that varies across a batch produces a pack where one leaf carries more than its share, which is how a spring sags without anything visibly breaking.

Because a parabolic leaf carries more load per leaf than a conventional one, every one of those steps matters more than it would on a pack with ten leaves sharing the work.

Military Wrap on a Parabolic Spring Pack

A parabolic pack could theoretically run as a single leaf, and most use at least two for a specific reason.

The lower leaf carries a full military wrap at each eye, where it wraps completely around the eye of the main leaf above it.

If the main leaf fails, that wrap contains it and keeps the axle located rather than letting the spring separate and the axle move. On a pack with only two or three leaves, that redundancy matters more than it would on a conventional stack.

It is a small detail that does not affect how the spring rides and matters a great deal on the day something breaks.

P201 4WD TUNLAND Parabolic Spring Load Ratings and Lift Heights

Parabolic springs are specified by constant load the same way the rest of the leaf spring range is.

Constant load means the weight permanently added to the vehicle rather than what the vehicle weighs empty. A canopy, drawers, water tank, fridge and recovery gear move a ute up through the bands faster than most owners estimate.

Choose a rating below what you carry and the pack sits lower than it should under load. Choose far above it and the ride advantage you paid for disappears when the tray is empty.

Front and rear are rated separately on vehicles with leaf springs at both ends, since the front carries accessory weight while the rear carries payload.

How Parabolic Springs Behave Under Load in Your P201 4WD TUNLAND

A parabolic pack is progressive rather than linear, which is what lets one spring work empty and loaded.

Unladen, only the main leaves are doing anything, and the spring is soft enough to absorb inputs a conventional pack would transmit straight through.

As load increases the leaves deflect toward each other and the second leaf starts contributing, raising the effective rate.

Push further and a free floating overload leaf engages, which sits below the pack and makes no contact until the suspension compresses under weight.

That gives three stages of response from one assembly, which is why a parabolic sprung vehicle rides well empty without sagging under load.

Handling and Torquing P201 4WD TUNLAND Parabolic Leaf Springs

New U-bolts go on without exception, since the originals have stretched permanently and will not clamp as they did.

Check the fixed pin head seats fully into the locating hole in the axle seat before the U-bolts are tightened, because that head is what holds the pack in position on the axle.

Handle the springs carefully all the way through fitting. A parabolic leaf is thinner through most of its length than a conventional one, and marking or gouging the surface creates the stress point a fatigue crack starts from.

Retorque the U-bolts after the first few hundred kilometres once the pack has bedded in.

Have a wheel alignment done afterwards, since the ride height change moves the geometry straight away.

Find Parabolic Leaf Springs for Your P201 4WD TUNLAND

Select your P201 4WD TUNLAND to see the parabolic leaf springs available for it across the load bands and lift heights. Work out what the vehicle permanently carries before choosing a rating, and have the shocks looked at while the springs are being specified.