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Will 225/40-18 snow tires be ok to run on rear wheels as well? I have IS250 F Sport AWD.
Since our cars were designed to run staggered wheels & tires, I'm not sure if this will work. However, I've seen others who have purchased snow tires & wheels sets that aren't staggered (225/40-18 all around). I would definitely check with a tire expert (Tire Rack or a reputable tire shop) and ask for their advice.
The staggered setup on your vehicle is a 225/40R18F and 255/35R18R. On average, those tires are 25.1" and 25.0" in overall diameter. Those two sizes are so close that the rotational speed is nearly identical. The traction control, ABS, etc. are all directed by the wheel speed sensors, which measure how quickly your tires are rotating. With such a small difference in OD, the stock staggered setup is rotating at the same speed as if you had a square setup. Running a square setup for winter use will not cause any problems. I actually recommend it because you'll have better grip on the rear end of the vehicle if the rear tires are following in the path cut by the front tires instead of trying to plow their own.
The staggered setup on your vehicle is a 225/40R18F and 255/35R18R. On average, those tires are 25.1" and 25.0" in overall diameter. Those two sizes are so close that the rotational speed is nearly identical. The traction control, ABS, etc. are all directed by the wheel speed sensors, which measure how quickly your tires are rotating. With such a small difference in OD, the stock staggered setup is rotating at the same speed as if you had a square setup. Running a square setup for winter use will not cause any problems. I actually recommend it because you'll have better grip on the rear end of the vehicle if the rear tires are following in the path cut by the front tires instead of trying to plow their own.
just to clarify, are you saying that its okay for a 3IS staggered RWD to run a square setup, if using oem specs say 18x8 45et all around or 18x8.5 50et all around?
if i run 18x8 45et all around, wouldn't i also need a 5mm spacer for the rear wheels to account for the 45et vs 50et difference?
I'm running the same all around 225/40/18. You don't need spacers because 5mm difference is there only because the rims are wider, this way the larger tires can go further toward the shock, so the load is still centered on the hub.
I hope this makes sense. Bottom line, 8" +45 is ok in rear and your wheel will be in the same position with respect to your fender. You can also save money and do 225/45/17 no problem. Putting 8x8.5" +50 in the front is definitely a NO though
I've scuffed my 18s in winter quite a bit and wish I went smaller.
Yes you can run square set up on an AWD IS.
I ran 245/40R18 all around on my IS350 AWD before.
You will have better traction in snow with narrower tires.
As many others have said, 225/40R18 will be fine for a square setup. My dealer threw in snow tires for free when I purchased the IS and used the same configuration. I had the same concern with going square when the manufacturer's setup was staggered, but after some checks, the rolling diameters are so similar that it makes very little difference. The difference is well within the +/- 2% rule of thumb.
As many others have said, 225/40R18 will be fine for a square setup. My dealer threw in snow tires for free when I purchased the IS and used the same configuration. I had the same concern with going square when the manufacturer's setup was staggered, but after some checks, the rolling diameters are so similar that it makes very little difference. The difference is well within the +/- 2% rule of thumb.
I have 225/45R17 front and back snow tires and they work well except some visual compromise . I also had concern about going square but when realizing the standard configuration for IS (IS250 & IS350) in some countries is actually square setup with 17" (225/45R17), it relieved my concern.
