Basic knowledge about frame extension.

The base for towbar or rear carrier

Are you in looking for a frame extension for your motorhome? Perhaps you are curious about its purpose and the process for retrofitting one?

Welcome to our blog at X-CAMPING post where we cover the most asked questions about frame extensions, including their selection and installation. Since over 60% of motorhomes are constructed using the Fiat Ducato chassis, and an additional 10-15% use the identical Citroen Jumper and Peugeot Boxer, we will refer to the Fiat Ducato as the base vehicle throughout.

What is a frame extension? What is its function?

Motorhomes, including A-Class, Class C, and camper with overcab bed, provide optimal comfort in compact spaces. To create a sense of spaciousness, motorhomes must also offer ample space, which can be achieved by expanding the living area.

The motorhome body is fixed on the base vehicle's chassis. It is necessary to extend the chassis to provide support for the rear garage and to maintain the stability of the vehicle.

In this case we call it a frame extension. For most motorhomes with a living unit that extends beyond the original frame of the base vehicle, a frame extension is necessary. A frame extension's key role on a motorhome is to provide support for the overhang and the rear garage.

Depending on whether a motorhome is fitted with a towbar from the manufacturer or not, it is referred to as a load-bearing or non-load-bearing frame extension. Vehicles that are retrofitted with a towbar almost always require a load-bearing and non-load-bearing frame extension.

Load-bearing frame extension

A load-bearing frame extension forms the basis for additional equipment. These are usually trailer hitches, motorcycle carriers, bicycle carriers, jacks, rear boxes or other load carriers. A non-load-bearing carrier looks very similar to a load-bearing carrier, but there are some features that make them different.

How can I recognise a stable frame extension?

A load-bearing frame extension usually consists of two parallel C-profiles or, less commonly, rectangular profiles with a wall thickness of 3 mm or more. When a frame extension is retrofitted, it is identified as such and provided with a nameplate. The nameplate also contains most of the information on the load capacity of the frame extension, i.e. tensile load, support load and D-value. The following illustration shows a supporting and a non-supporting frame extension.

How do I select the right frame extension?

In order to choose the right frame extension for motorhomes, it is important to have the following basic knowledge about your own motorhome.

• Which base vehicle do I have, e.g. Fiat Ducato X250?
• Which frame does the motorhome have, e.g. standard frame, low frame or ALKO chassis?
• How long is the overhang, measured from the end of the frame to the rear wall of the rear garage?

Why is that important? Here is the answer. A frame extension consists of the following main components:

• From vehicle-specific adapters that match the frame of the base vehicle, e.g. Fiat Ducato flatbed, Ford Transit ALKO lowbed, Renault Master standard frame. The adapters are both frame and vehicle specific, so it is important to distinguish between them when retrofitting a frame extension.
• And from the side members, which are matched to the length of the overhang. The side members are usually the same for one frame extension manufacturer and fit on several adapters and therefore on several vehicles. They only differ in length, which depends on the length of the overhang

What options are there for extending frames?

When searching for information on the right frame extension for my motorhome, I come across dozens of terms that are predefined for different frame types. In most cases, these are synonyms that describe one and the same thing. To dispel any doubts, here is a brief explanation of frame types (chassis types) and frame extensions for motorhomes:

ALKO-Chassis

ALKO-chassis, also known as lightweight chassis or low frames, are typically hot-dip galvanized and have slotted holes along the chassis. In contrast to standard frames, which feature a leaf suspension and rigid axle, ALKO chassis come with independent suspension and sprung torsion bars.

Fiat Camping Car Special (CCS) chassis

The wide-track frame, low frame, flat frame, or Fiat Camping Car Special (CSS) is a unique feature exclusive to Fiat Ducato vehicles. Essentially, it is a standard ladder frame that has been halved, resulting in a lower frame height of a few centimetres. Another feature is that the base plate of the body is securely affixed to the frame, for instance, by means of adhesive, rivets, or, on occasion, screws.

Standard frame, Euro chassis or ladder frame

The frame is a standard frame that looks like every platform trailer. The frame is often referred to as a ladder frame. The Fiat Ducato is also referred to as the EURO chassis.

Advantage of X-CAMPING universal towbar

Some frame extension and towbar manufacturers provide diverse adapters for CCS and standard frames, but at X-CAMPING, our adapters suit the Fiat Ducato frame without distinction, regardless of the frame's type, be it a standard frame, Euro chassis or ladder frame, wide-track frame, low frame, flat frame, or Fiat Camping Car Special frame.

To illustrate the difference between CCS and normal frames, here are two pictures showing the difference.

Retrofitting the frame extension - the procedure

Now that we have learned how to choose and buy a frame extension, let's proceed with the main objective of the process, which is to assemble it. As previously stated, buying a frame extension is only beneficial if coupled with another component, such as a towbar or another rear carrier, which is typically a towbar. Here, we explain how to install a frame extension with a trailer coupling from X-CAMPING, which you can perform by yourself.

If retrofitting a trailer coupling with a frame extension is required, follow these steps for installation:

Completeness and feasibility check:

Although this step may appear trivial, it could save an abundance of time and hassle. Therefore, ensure to examine that all components are in place as directed in the assembly instructions. To achieve this, follow these three simple steps:

1. Please refer to the installation instructions and seek clarification from the seller or installer regarding any work that you are unsure or do not understand.
2. Arrange all components to visualize installation and ensure sufficient length of side members.
3. Ensure that there are no cables or other mounting devices that hinder the attachment of the towbar to the vehicle.

Once the device's completeness and individual assembly processes have been verified, proceed with the actual mounting process. During the mounting of individual components, ensure that they are easily screwed on. Tightening all screw connections is the final step of the assembly, which occurs after aligning the towbar and frame extension.

Fitting the frame adapter

Firstly, the adapters supplied are screwed onto the original chassis of the base vehicle. Our model is a CCS special chassis of the Fiat Ducato X250 L4 - MKF3. On this Ducato, there are four M10 x 120 bolts. The installation of the frame adapters is the same for both Fiat frame types, i.e. CCS and normal frame. The only difference is that an additional hole must be drilled in the vehicle frame for the Fiat Ducato X250 with Eurochassis.

The frame adapters are mounted on the outside of the original longitudinal members. To ensure that the adapters are sufficiently stable, additional counter brackets and reinforcement brackets are fitted on the inside.

Mounting the side members

The base frame's side members act as the actual bridge for the overhang length of the motorhome. The length of these side members is dependent on the length of the rear garage or the free overhang of the camper body. The figure below provides a schematic representation of the distances and clearances that require consideration when calculating the length of the base frame.

The approximate length for the Fiat Ducato X250 can be found in the table.

The actual length of the frame extension should be taken slightly longer in order to shorten it to the desired length if necessary. Please note that the ball of the trailer coupling must have at least 65 mm clearance to the rear wall or rear bumper.

Fitting the reinforcements

The base beams of the frame extension should be fortified in accordance with their length. Up to 750 mm, no supplementary reinforcing elements are needed. For lengths ranging between 750 and 1400 mm, unique profiles are employed for strengthening. These profiles are introduced into the base frame profiles. When the length exceeds 1400 mm, the frame extension ought to be reinforced with diagonal braces.

Length of frame extension	Base frame	Reinforcement profiles	Diagonal braces
0 ≥ 750 mm	Yes	-	-
751 ≥ 1400 mm	Yes	Yes	-
1401 ≥	Yes	Yes	Yes

 

Fitting the trailer coupling and installing a cable set

A cross member usually completes the frame extension and forms an adjustable towbar in most cases. The trailer coupling, also known as variable, is adjustable in width at the very least. This is because the coupling is fit onto the base frame either from the inside or outside, depending on the situation. While selecting a towbar, it is essential to ensure that it adjusts in at least two, preferably three directions, that is, in width, height, and length.

The variability of the trailer coupling is particularly advantageous when aligning complete trailer couplings.

A cable set is crucial even though it is not included with a towbar. You can fit the cable set now or later on.

Alignment and tightening

In the "Completeness and feasibility check" section of the instructions, we stated that you should only tighten the bolted connections at the end of assembly. This is to ensure proper alignment of the trailer coupling. Make sure to note the ball height of the coupling, which should be between 35 and 42 cm. For motorhomes with a long overhang, the upper limit must be observed and a range of 40 to 42 cm is recommended. If not secured, some alignment between the frame extension and the towbar is still possible.

On some vehicles, the ball height in this area cannot be set without additional adjustment. In this case, special side plates are used to move the trailer coupling up or down accordingly.

At X-CAMPING, the grid panels are available in three different versions:

• Three holes version
• Four holes version
• Five holes version

After alignment, tightening of all screws and a functional check, the clutch can be used.

Follow-up inspection

Although many people forget it, a very important point when retrofitting any towbar, especially for motorhomes, is the follow-up inspection.

After driving about 1000 km with a trailer or rear carrier, it's advisable to inspect every towbar regularly. This includes examining the screw connections. To facilitate quicker detection of any loose connections during subsequent checks, the screw connections should be marked with paint when the towbar is installed.

Installation example Fiat Ducato 130 Multijet Sunlight A69 year 2011

As an example of retrofitting the trailer coupling and frame extension, we show a video of the installation of a complete set on a Sunlight A69 motorhome based on a Fiat Ducato 130 Multijet built in 2011. The vehicle is an overcab bed built on a standard frame (ladder frame). The vehicle was not equipped with a load-bearing frame extension ex works. The overhang of the rear garage was 96 cm, so that a frame extension without additional reinforcement would have been sufficient.