Hey @Sasnuke ,

I have a '17 IS350 awd and was wondering if I can get away with the following setup on stock suspension:

Front: 19x 8.5 +35, 235/35/19
Rear: 19x 9.5 +35, 275/35/19

Thanks in advance!

 

Welcome to the forum!

For the front specs, no problem.
For the rear specs, absolutely not. Firstly, did you mean 275/30/19? If not, then the AWD system is not going to like a tire four sizes larger on the rear.
If you did mean 275/30/19 then chances are on big bumps the tire would hit the fender.
A 19x9.5 +35 is hit or miss fitment already, but add a 275 tire and you're asking for trouble.
If you tried a 265/30/19 in a narrow fitting tire, then you should be ok with the stock suspension. I wouldn't go putting adults in the back seat though.

 

Thanks for the quick reply!

For the rear, I did intentionally write 275/35/19 as that is a popular tire setup on the Fitment Industries website. Correct me if I'm wrong, but the aspect ratio is simply a circumferential type measurement. I guess what I'm asking here is, how does the adjustment from 30 to 35 (aspect ratio) affect the rear setup in the context of the AWD system? Additionally, would spacers allow me to work in the 275's, assuming the fender in question with the 275/30 is the inside-middle fender? Thanks in advance!

 

The fender in question is the outer fender, so spacers would just make the problem worse.
If you have a link to the Fitment Industries info please post it...I'd love to see what they have online...never have I ever seen a 3IS with 275/35/19...I've seen 265/35/18 and 275/30/19...even 285/30/19, but never 275/35/19.

The AWD system works on the premise that when two wheels are spinning faster (i.e. the rear) than the other two (i.e. the front), this is perceived as a loss of traction. The system will then divert power to the other wheels (i.e. the front) to restore proper traction to all wheels.
Consider this just a very simple explanation of one operation of the AWD system.
For AWD systems to function properly the wheels need to be the same circumference...key word being 'circumference'.
Stock 3IS staggered tires are 225/40/18 and 255/35/18...however the circumference of both size tires is approx. 25 inches...the is achieved by controlling the Aspect Ratio of the tire.

The Aspect ratio (30 vs 35) is a percentage of the width of the tire. So a 235/35/19 means the sidewall is 35% the measurement of 235mm (approx. 82.25mm).
A 275/35/19 means the sidewall is 35% of 275mm (approx. 96.25mm).
Circumference of 235/35/19 is 25.5 inches and 275/35/19 is 26.6 inches...approx.
Right away the rear tires are larger, so the AWD system will think the smaller wheels are always spinning faster, i.e. a loss of traction scenario, and will try to divert power accordingly.
Basically the AWD system will be in constant operation until something burns out or grenades. The system was never designed to engage the AWD at all times (this ain't a Subaru)...it's meant to engage only as needed.

I've seen members get "Check AWD system" messages on the dash for simply putting a tire that is one size larger on the rear...yours is going to be 4 sizes larger (235-245-255-265-275).

 

Thanks for the explanation! That all really makes sense now.

 

Need help guys.Does somebody know where can I find this rim?

 

Did you google ‘lexus 74395’?
Seems to be lots of sources out there.