My Stockman Pod Extreme has worked very well across a range of on-road and extreme off-road situations. But recently I upgraded the Cruisemaster XT Freestyle suspension to better suit the operating weight of the Pod.

Usually I drive quite conservatively with the Pod, as all my required camping equipment is stored in the internal drawers and there is no reason to shake it up. But recently, while driving quickly to avoid a storm, I noticed that the suspension on the Pod Extreme was not working effectively.

Gross Vehicle Mass

The Stockman Pod Extreme has a Tare Weight of 440kg and is rated to a maximum GVM of 1250kg.

Usually I don’t carry over 800kg of load on the Pod which would reach the maximum GVM. I believe that the total operating weight of my Pod is actually around 950kg, which is well short of the maximum GVM.

It might seem like very little difference between my actual operating load and the GVM, but in practice it means that the springs are substantially stiffer than are really necessary to work at the operating load of less than 1000kg.

So why doesn’t Stockman specify a lower rated system from Cruisemaster for the XT Freestyle suspension fitted? This is because there is no lower weight rated option available, so they’re already using the lightest specification available.

XT Freestyle Spring Specification

A little research (calling the spring manufacturer, King Springs) reveals that Cruisemaster use a standard design “coil-over” spring in their XT Freestyle systems. The key measurements are a spring free height of 10” and an internal diameter of 2.5”, with ground flat ends.

A few years ago King Springs stopped making coil-over springs in their Kings Performance Springs (KPS) range, hence Cruisemaster now special orders its XT Freestyle springs. So we can’t use King KPS springs as an option.

As noted the lowest rated spring option available from Cruisemaster is for a GVM of 1200kg. This rating is created by using 550lb per inch springs. This figure is noted on the screen printed serial numbers on the existing Cruisemaster XT springs.

Calculating Optimum Spring Rate

As noted the operating weight of my Stockman Pod is around 950kg. This is based on a) calculating the aggregate weight of the contents, and b) measuring the existing spring deflection.

The existing spring deflection is about 40mm under operating load, with the spring being about 210mm at rest. There is about 55mm of clearance between the bump stops.

Using this information, it is possible to calculate what the full load deflection of the spring should be, and then to calculate what the spring rate could be reduced to, whilst keeping actual deflection less than the standard full load deflection.

For my operating weight of 950kg, it would seem that the ideal spring rate is about 400lb per inch.

Following fitting of the 400lb per inch springs, the spring deflection at rest has increased by only 10mm, so the ride height is 10mm lower, and this suggests the calculation was correct.

Eibach Coil-over Springs

As Kings no longer produces the KPS range, I needed to find an equivalent 10” stack and 2.5” internal diameter spring set. It turns out that Eibach produces an appropriate 400lbs per inch spring, as well as many other spring rates, in the correct sizing.

I used Ian Boettcher Race Parts, in Queensland, to supply the parts, and they delivered the correct Eibach Springs very quickly.

Fitting the Coil-over Springs

To fit the replacement springs into the XT Freestyle suspension system the lower bolt from the damper needs to be removed, and then, if the Pod frame is raised, the swing arm will droop to allow the spring to be easily exchanged.

There is no need to remove the trailer wheels, provided that the trailer body can be lifted high enough to allow the trailing arm to fall open sufficiently for the spring to be removed.

Refitting is the reverse of removal, but some thread locker should be applied to the damper bolt retaining nuts.

Conclusion

Fitting lower rated springs to the XT Freestyle suspension in a Stockman Pod Extreme tunes the spring rate to the lower actual working mass of the very light Pod Extreme.

As Cruisemaster doesn’t provide this option, but does use standardised coil-over spring sizes in the XT Freestyle suspension, it is relatively straight forward to do your own calculation, and get your springs properly tuned to the actual trailer GVM.

Historical Update

Resulting from this blog, I have heard on good authority that in the past Stockman used to use softer springs in their Extreme Pods. But many prospective customers demanded higher load capacities (to the detriment of ride quality) from their Pods, and Cruisemaster ceased to offer lower load rated suspension systems (at a guess, possibly related to King Springs closing production of their coil-over KPS range). So as a result all the production Pod Extremes are now delivered with a 1250kg GVM rating.