Tire setup recommendation

[QLITV]

So I decided to go with the Hancook’s RS4 and my next question is should I go with a 275/40 profile tire upfront and 285/35 rear or can I just do 35 and 35 front and rear.
The difference I see is that the 40 profile tire has a Higher load index of 1700 plus is 1” taller, the 275/35 load index is 1500 for the fronts and also the 275/35 and 285/35 have almost identical overall tire diameter... better balance set up? Should i not worry about the load index?
My car is a 370z roughly 3200lb and new wheels are front 18x9.5 and rear 18x10.5.
Im trying to reduce understeer!
Im currently running front 245/40/19, rears 285/35/19 on stock wheels.
What do you guys think?

Thanks,

-Jorge

[SlowMiataDrew]

Might be nit picking here but how are you able to fit 245/40/19s and 285/35/19s on an 18" wheel

[SlowMiataDrew]

Also, what tires were you running before?

[QLITV]

Been running on 245/40/19 and 285/35/19 indy 500 on stock 19 wheels.
I bought a 18x9.5 18x10.5 set of wheels just trying to fit appropriate size for autocross.

[Loren]

Reducing the difference in width between the front and the rear tires will help reduce understeer. But, just changing from "average" tires to "kick-ass" tires will also have a great effect.

I'd start with the tire change mostly. Don't go nuts with the tires sizes. If you're running 245/285 now, try something like 255/285... just a slight difference. You want to figure out what kind of difference just a better tire is going to make.

From there, there's also a little bit of "driver tuning" involved. You can learn to drive around a little bit of understeer. A high-powered rear wheel car typically SHOULD be set up to slightly understeer so that you can put power down earlier/harder coming out of a turn without kicking the tail out so easily.

Tires first. Try to keep the overall diameter of the tires within about 1/2" of stock if possible.

You also didn't mention the offset of your new wheels. That's something you need to be considering. Moving the offset in or out AND fitting a wider tire can cause clearance problems.

[QLITV]

Thanks Loren, base on what you say and what Hankook offer for tires the 275/35, 285/35 are closer to stock diameters so I ordered those. Ready for more driver tuning!