Thread: Tyre legal limit

Now I don't know about any of you, but for a fair while now I have been under the impression that the largest increase in tyre size permissible without an engineer approval is 15mm on diameter.

However as I am currently investigating what size to go up to and how to keep my insurance intact I have come across this little beauty....


4.2.4 Overall Nominal Diameter
The overall diameter of any tyre fitted to a passenger car or passenger car derivative must not
be more than 15mm larger or 26mm smaller than that of any tyre designated by the vehicle
manufacturer for that model.
The overall diameter of any tyre fitted to:
 4WD passenger vehicles specifically designed for off-road use (typically MC ADR
category). All wheel drive (AWD) vehicles including those AWD vehicles that may be
certified as MC ADR category, (also commonly known as soft roaders) are not
included in this category;
 4WD goods vehicles and their 2WD equivalents if the chassis and running gear are
essentially the same as the 4WD version (N ADR category); or
 any medium weight goods vehicle (NA2, NB ADR category).
Must not be more than 50mm larger or 26mm smaller than that of any tyre designated by the
vehicle manufacturer for that vehicle.


Off-Road Passenger Vehicle (MC)
A passenger vehicle having up to 9 seating positions, including that of the driver and being
designed with special features for off-road operation. A vehicle with special features for
off-road operation is a vehicle that:
 Unless otherwise approved has four wheel drive; and
 Has at least 4 of the following 5 characteristics calculated when the vehicle is at its
Unladen Mass on a level surface, with the front wheels parallel to the vehicle’s
longitudinal centreline, and the tyres inflated to the Manufacturer’s recommended
pressure:
 Approach Angle of not less than 28 degrees;
 Break-over Angle of not less than 14 degrees;
 Departure Angle of not less than 20 degrees;
 Running Clearance of not less than 200mm; and
 Front Axle Clearance, Rear Axle Clearance or Suspension Clearance of not
less than 175mm each.

This is from the horses mouth, these quotes I copied exactly from the Govt Dept of Infrastructure and Transport website, this is not just hear-say!

What this means for me is I can put 245/75-16 tyres on my disco without engineer approval, bonus!

In Victoria the changes are that anything greater than a 50mm change in roof height needs to be engineered. How you elect to get that 50mm is up to you.

The largest tyres that can be engineered for the road are 33" and an overall change to roof height of up to 150mm. So, I'm needing engineer approval. Since I have to get it I'm going to make it worthwhile ... hello 2" body lift and 33" tyres.