XT Air Singel with Twin G35

How to choose the right spec for my Cruisemaster XT Freestyle suspension Kit.

The Cruisemaster XT range of suspension kits is the most versatile caravan/trailer system available on the market today, giving you more options to specify the suspension kit that is perfect for your needs.

Now in it’s 6th generation the XT Freestyle gives you mores options than before – both in terms of the design specs and choices of style.

To work through the choices available, we have broken this down into a number of areas to consider:

  1. Single axle or Tandem Axle?
  2. XT Coil or XT Air?
  3. What ATM rating?
  4. Drop Axle or Straight?
  5. Brakes type?
  6. Chassis to Face dimension?
  7. Spigot Size?
  8. Stud Pattern?
  9. Trailing Arm Finish?

Important Notes:

A. As the trailer designer – we recommend you always refer to Bulletin  VSB1 – Building Small Trailers for matters relating to Compliance. Your trailer will need to be certified by an engineer prior to Registration and we recommend you use a suitably qualified engineer to design the chassis and choose the suspension kit.

B. Rather than build your chassis and then choose a suspension it is recommended that you choose your suspension and then use the relevant Installation Guides on the XT Product page to design the chassis to suit it.

  1. Single or Tandem Axle?

This decision is related to how much weight you want to tow – and may be simple if your trailer is very small (0-2000kgs) or very large (3000-4500kgs) – but in the weight range from 2200 to 2800 kgs you could choose 1 or 2 axles.

Single axle systems are cheaper, lighter and easier to manoeuvre whereas tandem systems are more stable on the road and may sustain less damage if you get a tyre blowout on one side.

2. XT Coil or XT Air?

There is no doubt that in terms of protecting both your caravan/trailer and its contents you cannot beat XT Air suspension. It will cost more ( approx $1400 more for a medium tandem system) and you may also wish to have an air control kit to manage your airbag pressure. It also has the benefit of being able to adjust the air pressure (within reason) to modify the ride performance and level or lower the trailer when you arrive at your destination.

On the other hand the XT Coil system may suit those of us wanting a simpler suspension. Each XT Coil setup uses a twin rate spring system with X5K King Springs that is designed to provide excellent ride performance at or close to the ATM rating of the trailer. Unlike the XT Air system there is no adjustment if you are carrying a lighter load so you will need to estimate your weights carefully to select the right XT Coil rating.

3. What ATM rating?

This is defined as ‘the total mass of the laden trailer when carrying the maximum load recommended by the ‘Manufacturer’.’ Click here to see more relevant weight definitions.

The XT System has a range of ATM ratings as detailed here

The ATM rating you select for your suspension will need to take into account your tow vehicle’s towing capacity and will determine the payload you are allowed to carry when you have finished the build. It is advisable to estimate the tare mass of the finished product and the payload you require before determining the ATM rating of the suspension.

Once the ATM has been selected this will be important in all other aspects of the chassis design, including drawbar certification, wheel rim selection, tyre selection, wheel studs etc

4. Drop Axle or Straight?

Another key feature of the XT range of suspension is its option for a drop axle in the design. This effectively lowers the chassis by 65mm when compared to the straight axle making access easier from the ground.

Straight vs Drop axle comparison

The Installation guides on each Cruisemaster XT product page have all the info you need to ensure your chassis is designed perfectly for your XT suspension system.

5. Brakes type?

Whilst most caravans use 10 in or 12in drum brakes, some customers choose Cruisemaster 12 in ventilated disc brakes due to their superior performance and less likelihood of overheating and fading. Please note disc brake options are only available on 102 mm and 110 mm spigot diameters.

The ATM rating will largely determine the size of drum brakes required – as a guide an ATM over 1500 kgs per axle would necessitate a 12 in drum brake system.

Both 10in and 12 in drums are available in Cruisemaster, Alko and Dexter brands.

6. Chassis to Face dimension and Wheel Offset?

The ability to choose the chassis to face dimension allows you to locate the wheel rim where you want it in the wheel arch of the trailer. Cruisemaster kits can be made with a chassis to face range from 175mm to 260mm though please note at high ATM ratings it is recommended to avoid the largest chassis to face dimensions if possible. Ideally

  • For single axle kits with an ATM of 2600kgs the c/f dimension should be 210mm or less
  • For tandem axle kits with an ATM of 4500kgs the c/f dimension should be 200mm or less
  • See note below regarding using positive offset wheels to reduce the effective chassis to face dimension

Other factors to take into account when choosing the chassis to face dimension are the clearance of the tyre in the wheel arch and next to the chassis rail and the wheel rim offset. While most caravan/trailer wheels are zero offset – ie the face is directly in the centre of the tyre – if you are matching the wheels to your tow vehicle it is likely to have a 40-50mm offset which can be allowed for by calculating the chassis to face dimension.

7. Spigot Size

The part of the axle hub that protrudes through the wheel rim is referred to as the spigot and is measured where it meets the drum face. Cruisemaster XT kits are made with various spigot sixes depending on the brake setup. The most common spigot sizes with 12in drums are 93mm, 106mm and 110mm. With disc brakes the spigot is 102mm or 110mm and with 10in drums the spigot size is 65mm or 78mm.

The goal is to match the spigot size (say 106mm) with the central bore of the wheel rim (say 106.2mm) so that the rim is perfectly located and carries the full weight of the trailer rather than only the wheel studs. This is essential where the load rating is high.

The alternative is to use a spigot smaller than the central bore of the rim and then to use tapered nuts to keep the rim centrally located. But in this case the studs are carrying all the weight and they must be specified to be capable of doing this or they will fail.

Spigot Options

8. Stud Pattern

Cruisemaster XT Suspension kits are manufactured with a range of stud patterns allowing you to select the pattern to suit your rims. The most common options are listed below and if you require a different stud pattern please let us know what it is and we will see if it is possible with your kit.

9. Trailing Arm Finish

Why not add some personality to your XT suspension with a range of attractive colours as detailed below

Premium powder coating includes sand blasting, Corro-Zinc pre-coat application then top coat whereas the standard powder coat includes basis preparation and top coat. Trailing arms can also be supplied bare (blue steel) if you prefer to paint them.

We hope this guide helps you through the many choices available with the XT suspension system. If you have any queries regarding Cruisemaster products please contact us here and we will be pleased to help.