Ok so I've spent a lot of time searching and reviewing calculation tables and such for wheel fitments on our cars... this on my.is. Yeah yeah, I know, but they have the calculations. Still, I wanted to run my thoughts by you guys here.

The wheels I'm interested in are offered in both +48 and +32, and only in 8". I'm not worried about going wider, 8 inches of wheel is fine, since the tires can fluctuate and make more or less width as needed/wanted.

So I'm thinking that going +48 is the better idea. It will mean the wheel lip will be pushed outward another 14.7mm (a little over half an inch) from where the stock IS wheel lip is.

So let's see... I'm trying to run calculations for both 18" wheels and 19" wheels, and tires to match. Here is what I've come up with:

Front:
19x8 +48 235/35
18x8 +48 235/45

Rear:
19x8 +48 245/35
18x8 +48 245/45

Someone on the other forum already verified a few years back that 19x8 +45 (what, a 2mm difference from +48? :P) with 235/35 fits on both front and rear with no problems, and someone else verified that the rears could be a bit wider. This is where I get the thought for 245 width for the rears. And for 18's, this is why I say 45 series. Based on what has been said elsewhere, this sounds about right. But as always, if someone knows better, by all means chime in.

If the above specs for both 19 and 18 seem good, then all I need to do next is decide if I want to go 18's (save money, get better wheel protection, more suspension from taller tire), or 19's (look slick, but spend more money on both tires and wheels, run a greater risk of bending from a minor pothole).

Your thoughts are requested

 

I personally would go with the tire size that matches closest to OEM, this way no need to 'guess' actual driving speeds, etc.

and it doesn't hurt ride quality, if the tires are coordinated with OEM, than you will be fine.

I suggest playing around with different sizes than those listed, since the smallest difference was <4% and it is recommended to stay with +-3% difference both ways.

Good luck. And i would rock the 18s personally, 19s look nice, but as you said more risk, pricier tires, etc.

I had 18s on my ES300 and they looked great and filled the wheel wells nicely, and it is a bigger car than the IS300, and now another IS is rocking out the same set in my city [he bought my old rims]

 

Someone on the other forum suggested:

for 19's... 235/40 in the front and 245/30 in the rear

for 18's... 235/40 in the front and 245/35 in the rear

Sound more reasonable?

 

i have 225/40/18 all around. they are flushed with my fenders... perfect.

 

what offset wheels? And close-up pics?

 

18x8
Offset: 40mm
Backspacing: 6.10"
Bolt Pattern: 5-114


let me see if i can find some close up pics..

 

no close up pics.. sorry..

 

Okay, lets just get this out in the open first:

THERE IS ABSOLUTELY NO ADVANTAGE IN THE IS300 TO RUN THE SAME WIDTH WHEELS WITH STAGGERED TIRES!

Alright. I'm good. Now, the more the offset goes *towards* zero, the further it is pushed *out* and away from the center of the vehicle. So, an 18x8+35 will be further out than an 18x8+45.

Secondly, a 245/45r18 tire is more than 2" taller than stock. Heck, a 245/40r18 is still an entire 1"+ taller than stock tire diameter. A 245/35r18 is the same diameter as stock 215/45r17. The whole purpose of retaining stock tire diameter is so that your speedometer stays ACCURATE and also so it will actually fit on the vehicle without rubbing issues.

Thirdly, you will NOT want to run a 245 width tire on an 8" wheel, as it's bulgy, funky looking, and handles poorly as it is the IMPROPER tire width for the width of the wheel. A 225/40r18 is where you should live, if you so choose to buy 8" wide wheels. If you go with 8.5" wide wheels, then sure! Go with the 245's. You will notice significantly poorer handling because of the large, bulgy sidewall.

The proper tire sizing for stock wheels is 215/45r17. For 18" wheels, a 215/40r18 is the exact same diameter as stock. For 19" wheels, a 215/35r18 is the exact same diameter as stock. See what I did there?

"Wheel protection" is a subjective term that should only be associated with the end-user and their driving abilities. An 18" wheel is just as prone to bend as any other 19" wheel, it's really only dependent on the driver and their driving habits. If you're a putz and hit potholes all the time, then get 17's because you're a moron. If you take good care of your car and are a good driver who pays attention to obstructions and imperfections in the road, get 19's!

If I were in your shoes, I would get 18x8+32's with 225/40r18 tires all around. The IS was never made for staggering wheels, and actually handles slightly better with non-staggered wheels/tires. Plus, since price is an issue in your original statement, I would keep the cost down as much as possible and get the greatest amount of life out of your tires as possible. IE rotations, etc.