Actually the stock sedan tires are 245/265 f/r. The coupe are 255/285 f/r.

The largest tires to go on the stock sedan wheels which are 8 1/2 front and 9 1/2 rear are 255 front and 285 rear if you are interested in the correct fitment and not just what size you can get on without rubbing.

Sorry for hijacking this thread, but have the same question.

I have the same stock wheels as well and planning to buy PS4S tires, and also up the sizes a little

They are currently:
Front: 245/35R/19
Rear: 265/35R/19

So I can go 285/35R/19 rear and 255/35R/19 front without any problems and correct fitment?

Would 275/35R/19 rear with same 245/35R/19 front maybe be better setup?

Yes, as per the many threads confirming this.

I already changed the fronts to this size.

I will change the rear's as well once they're more worn.

Got it, thanks! Just seems like such a big jump, 255 to 285 without any issues on the same wheel width. Will surely help on better grip though

I went with PS4S with 255 F and 275 R to keep the ratio the same as stock. More grip ,quieter and rides better.

I would not go to a 30 aspect ratio as it does not fill the wheel well as much unless your going to lower the car and then you could go either way. But remember the suspension is stiff already and a 30 would make that worse.

I plan on going 295/30 on the rear when the 265's are gone. The difference in radius between 265/35 and 295/30 is roughly 1/8 inch which will not provide very much of anything visually, except from the back.where they are 1.5" wider each. Since I don't autocross anymore and have no plans on power sliding corners on the street I don't see an issue having the rims 1/2" width under standard recommendation. Several have advised the PS4S fits at that size without rubbing.

The 35/30 numbers are the aspect ratio that describe the sidewall height of the tires. The number represents a percentage of the tire's width, not a measured length. So a 305/35-19 tire will have a larger sidewall than a 245/35-19 tire even though the aspect ratio is the same (35% of 305 as opposed to 35% of 245). If you want to keep the sidewall height the same, as you go significantly wider you eventually have to lower the aspect ratio.

With the sizes you are talking about, 35 is the way to go.

I agree.
With a 9 1/2 inch rim the widest Acceptable tire is a 285 and the preferred is a 275.
Just rubbing is not the whole reason to choose a size. The shoulder of the tire is not supported enough if you go wider and the face of the tire is not in full contact. The latest Corvette just added a 1/2 in wider rim to its tire with the same size tire as they say it did not support the shoulder enough. Also the 30 aspect tire is smaller and won't fill the wheel well . It was said it is not much smaller but if you go larger with a 35 it is larger than the stock. a 295 /30 is 26.0 inches and a 285/35 is 26.9 so you get a better ride and .9 in. larger tire to fill well.The ride is some what better and I think it is too firm now and I would not want worse.