Hi guys. I'm new to the Is F sport family. I recently bought a 2017 IS 200t blue. It's an amazing machine. I wanted to know if I can change the rear tires, from 255/35/18 to 255/40/18 to match the thickness of the fronts? Just finding info before my next tire purchase. Thanks guys!!

Can it be done without causing any odometer warning signs ect ect?

Sonic the hedgehog

 

I am curious what you mean by match. The aspect ratio is exactly that, a ratio (tire width to sidewall height). The front and rear tires are as close to the same size as they can be. The rear is a smaller ratio, but of a larger width.

Mathematically, there is less than 0.060" difference in diameter from front to rear (although that can vary by tire). Going to a 255/40-18 will make the overall diameter near an inch difference.

Side note, love that color!

 

You can do that, most likely won't have an effect on the speedo, as tungstn said, it's 0.060 bigger which isn't a big deal. If you ever lower the car on what people normally lower it on (Down springs), you will most likely rub so keep that in mind

Congrats on the car, beautiful color and spec

 

Congrats on the new ride! Love the blue too.

With regards to the rear tires, since your suggestion is to change the aspect ratio (second number in the tire size), then I'm assuming by "thickness" you mean the height of the sidewall.
Currently the front sidewall is 90mm and the rear is 89.25mm...the difference of 0.75mm that the rear is smaller. If you increase the rear to 255/40, then the sidewall is 102mm...12mm bigger than the front...or about half an inch. Overall the tire is 1 inch in diameter larger as Tungstn indicated.
Realistically if you want them to match, you're there already with the stock tires.

Can you do it? maybe. The VSC and TRAC systems may have objections to it when they see different wheel speeds between the front and rear though.
Keep in mind it will also raise the rear of the vehicle by half an inch and the speedo will read about 2-3 miles faster than you're going around 60mph.
Pretty sure you would be the first to run this setup.

 

Hey, thanks again for your help. I just want to match the fronts 40 thickness on rear. The tears are 255/35/18. I would like rears with 40 instead of 35.

 

Oh ok, thanks also for your help. I guess I'll leave it as is.lol I did this on my last car 2000 GS 300 with the stock F sport rims.

 

Ok great help bro. Thanks. I'll see what I'll do. Just want a bit more meat on rears to have bit more comfort..lol