Wheels up to 26mm wider than the largest optional wheel recommended by the vehicle manufacturer for the vehicle can be fitted without the need to notify the RTA. The overall diameter of the wheel and tyre combination must be no more than 15mm over the largest diameter wheel and tyre combination specified for the vehicle and not more than 15mm below the smallest diameter wheel and tyre combination specified for the vehicle.
When fitting a larger wheel & tyre fitment the combination of the replacement fitted unit MUST stay within the mudguard. Also when viewed directly from the top of the mudguard to the ground, with the tyre & wheel unit facing in a straight ahead position, the tyre & wheel MUST not be visible.
Influence of Smaller Offsets to Standard Fitment
If the new wheel is wider than the wheel fitted originally by the vehicle supplier, clearance could be reduced between the vehicle's bodywork and or suspension.
There is obviously a limit to how much of a width change you can make without adversely influencing legal requirements, which require the wheel and tyre unit to be covered by the mudguard and not protrude from the vehicle's bodywork.
Smaller offsets will create a scrub radius, which may affect the handling of the car, but there are a number of reasons why you may need to choose a smaller offset, which are in the next slide.
- To compensate for a wider wheel: A wider wheel with an identical scrub radius as the original wheel, will be positioned closer to the suspension components. If the wheel is too wide, it will not fit. To compensate, you would choose a smaller offset to move the wheel away from the suspension or inner bodywork.
- A smaller offset than the original will set the wheels outward, so that the stance of the car becomes wider and stability is increased. In some applications, the benefits of this stability are greater than the drawbacks of the scrub radius change and the driver may make this compromise.
- Smaller offsets than original fitments, move the wheels outward so they have a tendency to fill out the wheel to provide improved looks. Vehicles set up for show, more than performance, will often choose a lower offset wheel. If the offset is too small the sidewall will rub the inside of the external bodywork.