I am aware he asked about the safety, but given that OP stated he was looking to buy them and fit them; it's the right thing to do letting he/she know the legality of the intent. I'm going to go by QLD road rulings given the differences betwee state RTAs. SRI/CAI: A SRI/CAI setup is not illegal as long as: a ) the filter is securely fastened to the vehicle (no zip ties, needs to be a proper bracket) b ) the vehicle continues to comply with ADR 28 (now superseded by ADR83) (external noise) c ) the vehicle continues to comply with ADR 37 (emissions control) Also the filter does not specifically need to be enclosed; however you may need to do so in order for the vehicle to comply with ADR 83. Vehicle noise levels range from 76-81; for reference a passenger car 65 mph at 25 ft is rated around the 77db mark. HID: As you have said, HIDs are not illegal provided that they don't provide undue glare (re: Blind) other road users (ADR46) and the light provided must only be white light only. For compliance, this means proper lenses (no, not adjusted standard lenses); projector lenses and self-leveling ones if necessary. Just because lots of people do it, doesn't make it any less legal. Rims/Tyres: Like most states you can only go so far in terms of increase or reduction, in your example (going from 5.5 to 8) is also illegal as it is more than the 1.3x allowance. However, http://www.tmr.qld.gov.au/~/media/c792a0c9-92b1-43ee-933b-7bdd8b20842f/pdf_modification_motor_vehicles2.pdf doesn't state that flaring the guards is illegal, it just states that the wheel must protrude past the wheel arch/flares OR past where it would usually protrude past (if the wheels originally went past the vehicle). I confirmed this some time ago when I emailed them regarding guard rolling (he referred to the guards as 'mudguards'): I completely agree with you regarding the point about many modified cars being safer than standard cars but that doesn't give us an excuse to do non-legal modifications to the car <_< After all, hoons/car enthusiasts (we're all the same) rate on the top of Society's Most Wanted list second only to paedophiles.