Cup-A-Likes are nice
Join Date: May 2012
Location: United Kingdom
County: West Sussex
Ok...here goes...again, I've posted this numerous times but they're not always easy to find.
I've run 18s with std & Eibach springs.
Firstly lowering does NOT cause clearance problems as it just 'uses' up the first part of the suspension travel, it doesn't alter the later part where the clearance problems occur.
Bump stops are a must, even if the cars sits on them when stationary....they do compress & there's not that much movement anyway.
It would help immensely if people would also state what tyre sizes they're using as it's the tyre width/height that causes the rubbing....as well as the wheel positioning....ET/spacing.
The 'correct' 18" size is 225/40 to keep it as near to a 225/45 17. New tyres have taller tread & this can cause rubbing compared to worn tyres when clearance is minimal. If 225 17s don't rub why should 225 18s....same tyre width, it's all down to the wheel position/ET. If you really want to play it safe stick with the std ET of 30.5.
The 18s I used had an ET 40 BUT spaced 12mm giving an ET of 28 with absolutely no clearance problems. Originally I fitted 16mm spacers, giving ET 24, & the rears rubbed....fronts were fine.
So somewhere between ET 28 & ET 24 is the safe limit, I'd stick to 28.
I also ran the ET 40 rears unspaced, while waiting for the 12mms to arrive, & also had no problems.......so I can't understand how Spukey's are rubbing on the inner edge.....he hasn't stated his tyre size though.
Also tyres aren't exactly the same size when comparing different makes, only small ammounts but when a couple of mm is all it takes to clear or not....I think you get my point.
In the past I used to also calculate the wheel's increased J/width into the differing ET when comparing against std 7.5 J ET 30.5 225/45 17s but this was incorrect as it's the tyre width + ET/spacing that's important. The wheel width is only really critical if still using 17s for inner clearance of the springpan but again ET/spacing can usually overcome this. Larger rim diameters easily clear the springpan as my ET 40s proved.
So to summarise, 225/40 18s ET28 should be fine.