It is a total of 50mm rise, but the following is what the actual rules say 'The tyre diameter must not be more than 50mm larger or 26mm smaller than that of any tyre designated by the vehicle manufacturer for that vehicle.' and 255/65/16 is what is on the plate in my car so that immediately rules out 235/85/16 and then:
4.11 LOWERING OR RAISING VEHICLES
None of the codes in VSB 14 allow for the raising of any vehicle where the wheel track has also been reduced. These vehicles are subject to individual approval on a case-by-case basis.
Raising the height of the vehicle may be performed without certification providing the overall increase in vehicle height is not more than 50mm. This may be achieved as a single modification such as the installation of a 50mm lift kit, or by a combination of smaller lifts as described below:
- the fitting of body blocks or lift kits (50mm maximum if no other modifications resulting
in a change of vehicle height are performed);- suspension modification, (50mm maximum if no other modifications resulting in a
change of vehicle height are performed);- changes to tyre size (maximum change in tyre size diameter of 50mm); or
- a combination of the above that results in a change of vehicle height not exceeding
50mm.

