There are a few technical aspects to fitting wheel spacers, so I'm making videos where possible to help guide people through the process. I hope these blog posts and videos help develop an understanding of what's required to be safe and what is needed to pass local Low Volume Vehicle Testing Association (LVVTA) certification in New Zealand.

There's always much discussion on wheel spacer safety online and opinions given so freely given on whether to use them or not. The reality is that many OEM manufacurers such as Porsche (911) and Alfa Romeo (164) have some history of supplying them as a factory component to allow certain wheel combinations etc. They're also present in motorsport as a tuning device and can be used as a suspension tuning and grip finding element which can ultimately be the difference between winning and loosing a race.

Here is a picture of a TCR car upright and hub. This is a professional level world touring car series. As you can see these hubs are designed with an extended wheel centering boss that is about 30mm long. Standard road cars are generally equipped with 10-15mm long centering bosses. This combined with long motorsport style studs allows for the use of multiple slip on spacers which comin in various widths which are then stacked to give the desired offset. This shows that as long as the engineering is correct even the stacking of wheel spacers is safe in a motorsport environment.

Anyway the point being that wheel spacers are safe as long as they're engineered correctly and fitted correctly. The most important aspects of this are that the spacer sits flat against the vehicle hub, the wheel sits flat against the spacer and the fasteners are of a suitable length to enable the appropriate engagement of wheel nuts either meeting or exceeding OEM specifications. 

The other requirement for LVVTA certification is that wheels and tyres are within the confines of the vehicle bodywork. ie: they sit inside of and don't rub on the bodywork of the car and that the inside of the wheel also does not foul on any suspension, braking or inner guard comonenets. The extent to which you can get away with aspects of this is a one on one discussion with your LVVTA certifier.

Have a look through the video and hopefully it provides a good guide including the fitment of longer studs.