Because the car gets imbalanced towards oversteer. The extra power to the rear wheels creates a need for extra rear grip. If you look at higher power cars- like the 270 HP Genesis Coupe I used to have, are 225 up front, 245 in the rear.

But those cars, like some exotics, your mentioned genesis coupe, or familiar to me MR2 with from factory staggered setup also have rest of suspension built around it.
Ours - isn't.
Installing forced-induction doesn't meant that i'll press accel sooner in curve. I'll balance in same way as when NA mid-curve. Thus i'll prefer same grip bias as when NA/as when on narrower tires. Thus - back again to square setup, just wider, instead of making it understeery one that NEEDS power oversteer, much more mass transfer with braking, or much more throwing around for inertia flick, or fix back that grip bias with other suspension changes to get properly rear rotated all the time .. when one simply may not do that mistake of staggered setup in first place to not have to fix it.

It can be easier to break traction, thus causing oversteer, but staggering to "fix" a driver problem just makes handling worse everyehere. Though given the average driver, I do see why this might not be a bad thing... It doesn't change optimum setup, which happens to be square on this car.

cjd: average driver .. i guess has stock alignment (already more on understeerish side).

As many on track prefer less understeer balance then this stock setup, i guess making it even worse then stock makes even less sense. Or leaves less of adjustment range to enhance alignment, when lot of it is 'spent' on 'countering staggered setup'.

I've run a ton of different staggered setups on the S2k (225/225 to 205/245) and FD (255/265 to 235/275) and for me, handling balance at the track was not tremendously affected.

Also, tales of increased tire wear for staggered setup are bunk. Average tire wear is pretty much the same. The difference being that you might wear the rears out sooner than fronts depending on alignment and usage, but in that case the fronts are lasting longer than they would have if rotated to the back.

In my experience, a well-balanced FR car with a decent alignment (in particular, not too much toe-in) should wear tires fairly evenly anyway. And if the rears wear out first, replace them first, no biggie.

If you wanna do it, IMO there's no big downside. But then again there's probably no good reason to unless you're making significantly more rwhp...

Actually, the hot setup for S2000's is non-staggered. However, you need to tune the rest of the suspension to restore balance. When I first went to a square setup on my last S2000 (17x9 wheels w/ 255's), it was evil handling. I had to crank my Gendron sway bar to the stiffest setting to restore handling balance.

Total tire wear may not be any different square vs. staggered, but do you really want to hit the track, or wet streets w/ nearly worn rears and relatively fresh front tires? I see being able to rotate tires as a HUGE benefit to balancing wear (and thus handling balance) throughout the tires' lives.

If you're wearing front and rear tires fairly evenly on a rwd car, you're not pushing the car hard at all, so go ahead and pick your setup based on your styling preferences. :D

Positives:
- More grip in the rear and more tendency toward understeer. Understeer is usually a negative but this combo is better for drag racing if that's your thing. Given the car, I'm gonna guess probably not.
- Most will say it subjectively looks cooler.


Negatives:
- Changing the front/rear grip bias on the vehicle without adjusting the rest of the suspension means you are moving in the opposite direction from an optimal setup.
- More expensive, and all of your money is going into making the vehicle worse.
- Most sport compounds are directional so you already can't rotate side to side. Introduce a staggered setup and now you can't rotate them at all.


Really there is hardly any reason to do it and a lot of reasons not to. Anything that you gain can also be realized to almost the same extent with a better tire compound and proper throttle control.

Yardjass: i'd strike out positive "most will say it subjectively looks cooler", or at least "most" bit. If my own view can be of any representative - 1) i don't have tendency to look under cars to see tire widths be those parked or driving in front of me, so i guess most won't notice it at all 2) if i'll actually notice or find out that fact, i'd think that owner is lame poser that doesn't care about handling. To spare his feelings i'd keep quiet about it though :)

People that may decide that it's cooler i guess guide by three reasons, all wrong from practicality & handling points - "it's setup seen on some expensive exotic sportscars and/or some race cars, it should make mine as cool and better performing as those", and "wheel well/fender/suspension clearance allows to fit wider wheels in rear, so if i want to get absolutely widest i can, i should go staggered", and "i'll install turbo/sc, this is RWD car, i must have more traction rear".
All these reasons can be explained, why they are wrong .. but it's their car, their money, their hard beliefs of what should be better .. so they are free to pay to make car worse. And i'm free to laugh about them and think it's lame, not cool. Or advise/reason against for those that can be reasoned.

There is no one "hot setup". For sure 245F/275R Hoosiers or R1S will outhandle the hell out of 255 whatever square which everyone thinks is *the* S2k "hot setup"...

Replace tires when they need replacing, whether square or staggered. Worn rears? Replace them.

I've been streeting and tracking non-staggered on the S2k and FD for 10 years. ~200k street miles and upwards of 100 track days. I haven't had any issues managing tires.

The idea that not wearing rears more rapidly than fronts implies that one is "not driving hard enough" is just dumb. Anyway for most of those who are wearing rears at a fantastic rate in the S2000 it's down to running a stupid amount of rear toe-in, not because they're driving so awesomely hard...
I don't push it on the street much, certainly nowhere near 10/10ths. At the track, I do, and with nearly 500rwhp in the FD I do go through rears more rapidly than fronts. It's not a big deal... When I did run a stupid amount of rear toe-in on the S2000, yeah, I wore the rears WAY more quickly on the street and at the track. With a reasonable amount of rear toe, it's a lot more even wearing front/rear.

Long/short: Stories about going to a mildly staggered setup ruining the handling and giving terminal understeer are B.S. There's no good reason to go, say, 225/245 on a 54F/46R 200hp twin, but it's certainly not going to kill the handling balance and tire life if one decided to do so.