Why carry out a leading 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 leading axle would be fitted is to cater for a gap in the manufacturer's product range where there is no new standard line built product available to the correct specification or to increase the carrying capacity of an existing vehicle. In both of these cases the degree of difficulty encountered when installing the new axle will be dependent on the base specification of the donor chassis. Due to the specialist nature of the axle required in this situation it is unlikely it will be manufactured by the chassis supplier.
When fitting a leading axle, due to the proximity of the prop shaft the axle beam used for this type of conversion has a special profile, so as not to interfer with the drive line, plus it will usually be fitted with a restricted lift facility. The common description for this arrangement is a 'mid lift' axle.
The base specification of the donor chassis will dictate the extent of work required which, assuming the original wheelbase does not require modification, this could also involve the fitting of a chassis liner, an independent EBS module or repackaging the ancillary equipment fitted by the chassis manufacturer to provide the working space required to accommodate the axle and its attachments.
The additional axle will be fitted with single wheels and tyres, however the choice of tyre size will ultimately be dependent on the customers operational requirements and the geometry of the finished installation.