School me on tire vs rim fitmet
 

Admittedly, I know squat about tire/rim fitment, but I have run in to an issue.

-I bought new rims for the car, they're 18x8.5(outside) and 7.5(inside)
- Proper tires for these guys are 215/40

This set up will fin nicely under the wheel wells without needing to roll the fenders. BUT, it's damn near touching the springs on the inside of the rim and tire.

Having never run in to this issue, I'd imagine I need some kind of spacers to change the offset. I've found 15,25,and 30mm spacers to be the most common.

If I add say, the 25 in the front, and 30 in the back, I will need to roll the fender and or get flares/some kind of widebody. I can roll the fenders but do not want to allocate $ for widebody stuff.

Can I get away with a skinnier tire? If so, can anyone do the math on the spacer used vs tire sizes? I don't want the "stretched VDUB" look, but if I can get away with using a tire thats 7.5" at the least, and able to fit with the spacer, i'd like to do so.

I really don't know what the stock offsets are, the rim is an ADR M-Sport, 4x114.3. The car is a 1990 240sx.

i would bet the offset is around 40 or 45 for those cookie cutters

It's 43mm. Any idea on what the max offset is on a s13 using a 8.5 wheel so i can get the spacers?

by outside vs. inside i imagine you mean edge to edge vs. mount to mount
if so you have 7.5" wide wheels. wheel width is not edge to edge. my 17x9s measure 10" across. anyway

look through the wheel/tire fitment thread
http://www.zilvia.net/f/showthread.php?t=129865

if you're confused or lazy just use an online calculator
http://www.1010tires.com/WheelOffsetCalculator.asp

find a comparable example...
http://www.zilvia.net/f/showpost.php...7&postcount=85

then compare
7.5 +43mm - 30mm = 13mm effective
vs
8 +5mm front and 9+15mm rear

plug in the numbers and voila
front: 7.5 +13mm has 11mm more outside clearance
rear: 7.5 +13mm has 17mm more outside clearance

of course actual clearance varies depending on tire size and alignment and suspension set up but you get the general idea
tire fitment isn't precise because different brands in the same size don't all sit exactly the same.

anyyyyyyyway imo sell them and get something else
18x7.5 looks bad regardless of how they fit. way too tall to be that skinny