I have an IS F-Sport AWD and have stock wheels with spacers now (25mm f&20mm r, effectively making the rims 18x8 et20 and 18x8.5 et30), no rubbing at all on stock height. I'm looking at a set of rims, they are 18x8.5 et33 and 18x9.5 et38 with 245/40R18 and 275/35R18. Sadly the offsets and sizes that fit our cars well usually comes way more pricier.

Tried a few fitment calculator and the front would be fine, wondering if the back is good as well? I may lower the car with RSR down in the future, if it becomes no good I can also go with 235/40R18 and 265/35R18 to stay within 1% variance.

Some second thoughts/opinions please?

 

Funny you post this cause I'm looking at going to almost the exact same setup...18x8.5 +35 and 18x9.5 +38.
Your +33 in the front is not an issue at all...I wouldn't give it a second thought.
My only comment is the tires may be a little on the big side, but at stock height you should be fine. If you lower it, depending on how much, then it can be an issue with the tires rubbing.
I'm also looking to run 235/40/18 and 265/35/18.
Technically it's still safe to use the F Sport tiring sizing (225/40 and 255/35) on the 8.5 and 9.5 rims respectively, but I'm more about the better fitment with upsizing to the next size.
My completely illogical thought on the tires is why have wider rims just to run the same skinny stock tire sizes lol! I know it doesn't make sense...hence why it's illogical.

 

Hey there, thanks for checking in.

I don’t have plans to lower the car yet since the winter is around the corner. Bridgestone tires I’m running now has a relatively thin sidewall as well. Sounds like I’m good for now then!

One more thing, how aggressive you think the front offset can be without rubbing on stock height? If possible, I would keep my spacers (I have 25 and 20mm ones) or get some 15mm ones to keep the front flush.

 

With the new rim specs you plan on getting, using your existing spacers are out...it's way too aggressive...your IS would be a Go Kart at that point lol
Even 15mm is out...you'd be down to 3-5mm spacers at best. I would say for the front a 3mm would be fine for sure...you'd have to test a 5mm out to see what it looks like. If you could fit a 3mm on the rear without issue, that would probably be the max i would go...considering the next size would likely be 5mm.

 

Yeah...it says on the fitment calculator that my new setup with 18x8.5 et33 would give 4mm of fender clearance in the frontcomparing to what I have now, so 5mm will be fine. Not looking to add spacer in the rear though. I was thinking about 15mm because they are the thinnest spacer available with bolts on them. Using anything 10mm or less would require original bolts to be replaced with longer ones which I'm not a big fan of doing so, correct me if I'm wrong...

(Question on the side: what rims are you looking into? I'm looking into a couple of them with similar specs. Maybe we are looking into the same set or rims lol)

 

For the front spacer, if you try a 5mm, while it may work vertically, I would also check when you turn the wheel. Likely everything will be fine at stock height, but as you turn the wheel with it spaced out further, it changes the clearance between the tire and the fender liner.
Once again...these are only precautionary suggestions...as I mentioned, at stock height everything will likely be fine.

With regards to thickness of the spacer, there is a formula of 1.5 with regards to the wheel stud and wheel nut...meaning...once the wheel nut can cover 1.5 times the width of the stud with the length of the treads, then you're.
For a simple example...if the wheel stud was 10mm wide (or thick), then the wheel nut would have to capture the treads over a distance of 15mm of the stud to be safe. So a 5mm spacer is the max you can run with a stock stud and nut.
Right now I have 6mm spacers in the front, so I'm technically over that 1.5 formula, but I haven't had any issues for 2 years now. But I use a custom made spacer that fits the bolt pattern, hub on the car, and bore of the rim perfectly...and quality aftermarket nuts.

The rims I'm looking at are from a Canadian manufacturer, so I'm not sure if you get them in the US.
The company is GTS Wheels...but I'll save the model number for my build post update tomorrow when I pick them up ;o)
No rubber yet...waiting until March/April...hopefully winter is done by then.
Another company I liked while looking around is JNC...specifically the JNC014 in a square setup...but the offset was only +30, so the rear would have issues.
And yet another company was SuperSpeed...specifically the RF05RR.
I try to go offbeat with my selections to give some originality...but nothing against the mainstream rims...they all look wonderful, and offer a variety of finishes to give that uniqueness.

 

Thanks for the input, didn't know thin spacers have that exception. Sadly the rims I like the most comes only in offsets like +35 or +30 in the rear, I'll have to keep looking.

 

I feel your pain!

 

sometimes I feel like pulling the trigger regardless of the offset then work the quarter panels to make them fit lol