If the wheel base is to be modified or if the overhang is to be extended, the material quality and dimensions of the lengthening piece must correspond to the chassis frame (St 12.03). Functioning, smoothness and free movement of instruments and operating equipment as well as the stability of supporting parts must not be impaired by the performed modifications.

Cut-outs in the backwall of the driver’s cab must be provided with an enclosing frame. The remaining diagonal struts and cross-beams are to be reinforced by junction plates and are to be welded to the inserted frame.

The distance between cab and attachment must be at least 50 mm.

Frame modifications

• The permitted axle loads must not be exceeded. It is also required not to fall below the permitted minimum front axle load.
• Attach the underrun protection as explained for standard vehicles.
• Extend the subframe up to the frame end.
• Check the function of the towing device.
• Reinforcements must be available for desired towing device.

The side rails are hollow profiles (cap profiles). If it is required to drill, the appropriate operations may only be performed in the specified areas.

It is not permitted to drill:

• At the upper and lower belt of the chassis frame. Exceptions are boreholes at the rear frame end. However, these boreholes must not lie in the area that are reserved for the supporting functions of the rear axle. In addition, they must not be applied to parts that are attached to the frame.
• In the range of profile modifications of the frame side-rails (frame drop and frame indent).
• At force-application points (e.g. directly at the spring brackets).

In special cases, it is permitted to drill boreholes in the crosspiece of the frame side rails.

• Distance a: at least 20% of the frame height
• Hole separation b: at least 50 mm
• max. bore diameter: 15 mm

Grind and ream after drilling. Before usage, distance bushes must be welded in.

Perform wheel-base extensions of the longest standard base. If the wheel base is to be modified, the next larger standard wheel-base is to be used and shortened. Reinforce the intersecting point with sheet-metal shoes.

Wheel-base modifications based on displacing the rear axle are not permitted.
Separation points are not permitted in the area of:

• Force-application points
• Axle guiding and axle spring-suspension
• Profile modifications

After the wheel base modification, the chassis has to be reinforced by a continuous subframe.

Moments of resistance required for the subframe:

• Up to the max. standard wheel-base: <nobr>30 cm³.</nobr>
• Above the max. standard wheel-base: 15% increase.

The wheel-base modification results in an altered turning circle and changed weight values.

Wheel base modifications lying within the range of the minimum/maximum standard wheel-base, require no special permission.

• If wheel-base modifications are to be performed, the drive-shaft arrangement and length must correspond to that of a comparable standard vehicle.
• The diameter and wall-thickness of the drive-shaft must correspond to that of the standard vehicle.
• If required, use several drive shafts with intermediate bearings.
• The inflection angles <nobr>(ß1 = ß2)</nobr> must not exceed 6° . Deviations impair operating life and noise level.
• Counterbalance drive shafts before mounting them.

Volkswagen AG does not provide information on the road/braking/steering behaviour of vehicles whose wheel bases were extremely changed.