Why carry out a trailing third axle conversion?
Fitting additional axles only takes place for one reason, to maintain legally compliant axle weights when using a vehicle for its intended purpose.
As with all chassis modifications the main reason why an additional trailing axle, commonly known as a 'Tag' axle, would be fitted is to cater for a gap in the manufacturers product range where there is no new standard line built product to the correct specification available or to increase the carrying capacity of an existing vehicle. In both of these cases the addition of a lifting 'Tag' axle is a relatively simple exercise, however due to availability or possibly cost it is unlikely the additional axle will be manufactured by the original chassis supplier.
The base specification of the donor chassis will dictate the extent of work required which, assuming the original wheelbase does not require modification, could also involve the fitting of a chassis liner, an end of frame extension or an independent EBS module.
Depending on operational requirements the additional axle will be fitted with either single or twin wheels and tyres, which are usually the same size as those fitted to the drive axle.
