Will these wheels fit my car? How does offset work?
 

I want to buy some wheels for my car but have questions on the tire size, offset, and wheel. The wheels have a 5x100 lug patter and are 18x9.5 with a +38 offset. The tires I want to run are 235/40/R18, or 225/40/R18. Can someone explain to me how offset works or if this setup will work. Thank you.

Holy eff you're gonna get flamed.

We need some more info on the topic if it works. You can fit this, yes.

However, are you lowered on springs or coilover? do you want a flush setup, can the wheels stick a bit outside of the fender or do they have to be inside etc etc.

Offset is always telling you the space from the center of the wheel in one way. Higher Positive offset gets the wheel inside the fenders, while lower positive, or even negative offset gets the wheel further outside. Offset is always in mm.

For example, an 8.5" wide wheel with +35 offset is about flush. If you make it an 8.5" +45, it will be 10mm more inside the fender. An 8.5" +15 on the other side will be 20mm more outside of the fender (and therefore poking out of the fender)

Wheel wide does factor into this aswell. An 8.5" and a 9.5" wheel differ in size 1" or 25.4mm. Now since the offset is the space from the center (middle) of the wheel, you have to split this in 50%, as the wheel will be 0.5" wider to the inside, an 0.5" wider to the outside.

Now if you combine wheelwide and offset, you can play with those figures.

So if an 8.5" +35 wheel is about flush in the front, an 9.5" +38 wheel will be about 9.5mm outside the fender (1" Wide difference = 25.4mm / Divide by 2 = 12.5mm / Substract 3 (differnce 38/35 offset) equals 9.5mm.

This can be solved with lowering the car or adding camber to it.

As for tire size, first figure is always tire wide, secound is % wide to hight, 3rd figure is the wheel size. So a 245/35/18 is 24.5cm wide, 35% of 24.5cm high (so 8.5ish cm) and for 18" wheels.

A 9.5" wheels is 24.1cm wide (1" is 2.54cm) so a 245 tire will be about flush with the wheel, and is the minimum you should go for. This depends a bit on tire brand as not all have the same tireflank size.

Hope this helps a bit to get you started

Only american wheels use offset, the rest of the planet uses the metric system. true story.

Right now I dont have any coilovers. I want the wheels to sit flush with the fender. I plan on getting coils later but my goal with the coils is not to be slammed I just want it to go a little lower.

Also why are 18s disliked on the brz

Weight

It's gonna poke at stock height. Lower it like 2 inches and it'll be flush.

So with all that being said would a 18x9.5 et35 fit on stock suspension?

yes, but they will poke out... a lot.
http://www.ft86club.com/forums/showthread.php?t=7535

If you read my text you would actually know.

Quote " if an 8.5" +35 wheel is about flush in the front, an 9.5" +38 wheel will be about 9.5mm outside the fender (1" Wide difference = 25.4mm / Divide by 2 = 12.5mm / Substract 3 (differnce 38/35 offset) equals 9.5mm."

And as explained in the text aswell, offsett is in mm, so a +35 is 3mm more "outside" than a +38, so a 9.5 +35 will be about 12.5mm outside the fender in the front