Well my 18x10+34 (Forgestar) fit fine (if very slightly wide at stock camber) in the front, and use a 10mm spacer in the rear (but that's just cosmetics, you could go anywhere from 0 -> 20 on the rear spacer there and be fine). So I would think you could go 18x10+38 with a ~15mm spacer in the rear and be fine. They're just 4mm further to the inside than mine.

One of the bonuses of the cheap Forgstars is that they're made-to-order and you can spec whatever offset you like.

I'm running the same setup (forgestar 18z10 +34). This is one of the cheaper square setups and not a bad wheel. No spacers needed to run them all around. As with any aftermarket wheel on this car though you will need extended studs (or bolt on spacers with longer studs) to get adequate thread engagement with aftermarket wheels. see below.

http://www.the370z.com/wheels-tires/...ud-length.html

I was under the car today looking if this would work. A couple of issues Posche calipers are on the back side (rear) of the disc. You maybe could fabricate some CF for the 370 but, I think the effectiveness is downgraded with the more twist and turns. You would also need to contend with our sway bar endlinks. Bottomline is the Porsche has a straight shot onto the rotor center where we do not. The idea might work but, I think we would need to come from the back side of the lower control arm to make it work.

over steer with stock tire setup
 

Will the square setup help with oversteer?

The front turns in nicely but rear seems to come round pretty fast.
Not really interested in spinning out in traffic. So have been careful.

is front 18*10 +45, rear 18*10 +15 with 275/35/18 all around still a square setup?

Since our cars have staggered tires (larger in the rear) in stock form, going to a square setup reduces your rear tire width, which if anything is a move in the direction of more oversteer, not less. However, keep in mind how gravity and contact-patch interact. In some ways it's not as much a change as you'd think, and in others it's a very big change in the feel of the car. The hardest part for me to get comfortable with on switching was that the rear end was looser under trail-braking, requiring more careful brake modulation and slight steering corrections at times to prevent an oversteer spin under trail-braking. Once I got used to it, I really liked it though. That little bit of extra looseness makes it easier to get the car rotated just right while trailing.

I don't know if there's an official definition. One of the nice benefits you'd be missing out on, though, is the ability to rotate wheels all over without remounting tires (and only needing spare wheels in one size/offset).

If your saying it comes around fast on corner exit under power than just meter the throttle better or you have some setup issue. 370Zs do not oversteer at the limit from the factory, not even close. Though not nearly as badly as 90% of vehicles on the road probably.
If its on corner entry, might need to look at the way your managing weight transfer with the brake and throttle input.
Yep.

Square refers to running the same wheel width front and rear and kind of assumes your running the same diameter. Offset is just the distance from the actual centerline of the rim to the mounting face in millimeters. Running different offsets will likely prevent your from swapping wheels front to rear easily.

*Didn't know you had replied when I wrote this Wstar, oh well lol.

corner exit
 

Hello,

It seems that at mid corner the back travels faster and into a
decreasing radias half circle cicrle(that is what it feels like). Even though the back is not coming loose.
It feels like what you would think a paper diagram of over steer is. When the rear starts to whip around when the corner pushed to hard and you spin out.

Problem being I am taking slight hot corners on the street not the track.
And it is wanting to fall right into that curl of oversteer. I guess I know the feeling of it happeneing but a bit reserved to push the car to an unwanted spin. But most tight hard corners have a different feeling for the front verses the rear. Front holds firm but rear feels like it will flick out deeper in corner. Most cars I have driven before would tend to loose front grip and slide there first. Not have the back end feel like you when you hammer the throttle out of a corner to fishtail the car.

Guess probably my setup(ride height, preload on coils, etc) I am trying to get better. As to why I also asked about going square next year.

Most rear-wheel-drive cars tend to be over-steery, and most drivers prefer them that way. Most front-wheel-drive cars tend to be under-steery. Lately, some newer rear-wheel-drive cars are tuned at the factory for slight understeer in many cases because it's safer for a novice driver (controlling/recovering from understeer is more instinctual without training and practice). Our Z's are in this category: they are a rear-wheel-drive car, but they have some gentle understeer tendencies unless you really stomp it at the wrong time (at which point VDC will probably kick in, slow you down, and make a mess of everything). With VDC off you can still push yourself into oversteer in a low-speed corner with the throttle pretty easy though.

All of those nuances aside though: unless the car's setup is way out of whack, it's really up to the driver to manage the rest. You might want to make setup changes to change the nature of the car and make it feel more natural to you, but the bottom line is it's on you to control the rear end of the car with throttle and steering inputs. It takes a lot of practice. Personally, I wouldn't go after switching to a square wheel setup just to try to address this issue (which it wouldn't do anyways I don't think) - I'd focus on training yourself instead. Learn to predict better, react better, use smooth-but-fast precise inputs to the throttle and steering, etc. If you get good enough at that stuff, any actual setup problem in the car will just be an annoyance, but not a dangerous hinderance.

TL;DR - Sign up for a DE or Auto-X event near you ASAP :p Experimenting with a car you can't control on the street is dangerous.

Brian and I ran 18x12 wheels with 320 width Hoosier slicks square at Laguna Seca. The car felt incredibly balanced. The car didnt oversteer much at all. had a slightest hint of understeer in some turns but not bad.

tech article on going square from long acre racing
 

As a newbie I found this pretty informative.

http://www.longacreracing.com/articl...t/Squaring.pdf

the suspension has to be tuned around a square tire setup to be able to use the grip to on both ends to its potential

That goes way past any kind of tuning or setup I've ever done on my car :) All I mean by "square setup" is the front and rear wheels are identical.

I switched to square(per clint and some companies recommendation) and it does balance the OEM setup a lot better. Knowing a bit more now I can see Clint's point on tuning with a square setup.

With a good corner balance and correct spring rates, for someone that knows what they are doing, a wider track, especially upfront on a car with an engine that stands up tall is an advantage.

Wider track up front helps with our high CG (v6). Without a square wheel base the car is going to inherently always "push". It's basic geometry and physics. Pushing is fixable via sway bars, but if you don't have to deal with a geometry problem, why should you?

Don't want to be negative, but this is exactly why I don't like a lot of the Z Specs in the "racing" world. They aren't good specs for our car.

What are the pluses and minuses of going square vs. staggered? I've ran staggered since I got the car in 2009 and have tweaked everything to the way I like it. But now, I'm going from 19 to 18" wheels and found out that NT05's don't come in 245 45 18 fro the fronts, so I was considering going square, but that would mean I need to change my camber, toe, sway bar settings, etc. to fine tune everything again (which I don't mind doing if there's more advantages to going square).

Originally, I was going to go 18x9 fronts and 18x10 rears on the Forgestar F14's and 245 45 fronts, 275 40 rears, which would keep the overall diameter same as stock. But since NT05's don't come in 45 sidewall for the 245 fronts, I'll need to either go to a 40 sidewall front and 35 sidewall rear, which would decrease the overall diameter by about 1", which I don't want to do b/c I need to drive this car daily also - and even as is, I'm having a hard time on driveways already. 1" lower would really be a pain to drive on the street.

If I ran square, it'd be 275 40 18's all around on 18x10 wheels. What offsets would you recommend if I wanted close to flush front and rear? Or keep the same offset front and rear and use a spacer? In either case, please recommend what offsets and what spacer size I'll need. So hard to decide! Your inputs would help a lot. Thanks.

I run Enkei PF01's, 18x9.5 +35 front, 18x10.5 +15 rear which sits pretty flush with no spacers necessary over the sport brakes. Right now I have Toyo R888 275/40r18 on them which have felt great. After they're done I'm going to try a staggered tire though, Nitto NT01 275/40r18 front 305/35r18 rear. We'll see how it handles then.

Did you start with 19" wheels stock? If so, going down to 18" wheels and staying with the 40 size sidewalls on the tires, did you notice a difference in overall diameter? By the numbers, going from 245 40 19 (front) to 245 40 18 should decrease the overall diameter by about 1", which I'm tyring to avoid.

Did you notice a difference? Should I even worry about that?

Do you happen to have pics of your car on this setup?

Why go through all the expense of switching diameters and your setup if you are running NT05? They are your biggest limitation and nothing you do is going to make you much faster with them.
Now if you are going to the NT01 then that is a whole other discussion.

I have a set of hankook RS3's 275/35r19 on my stock Rays which I do like. I purchased the Enkeis which were 18" and went with a 275/40 to keep the same height because the car is lowered already and a smaller sidewall would make it an additional inch lower and I'd scrape everywhere.

One downside is that it will make your speedo read about 3% high. Possible upside and downside: effectively lowers the gearing on the car slightly.

Would be nice if more track tires were made in 275/40R18. Seems like 285/35R18 is pretty much the only option.

The difference in diameter between a 285/35R18 and a 275/35R19 is only .7" so ride height change should be only about .35"

yes, that's exactly what I was concerned about also. I didn't want an inch lower b/c of the lower sidewall. thanks for the info.

I'm not going from 19" to 18" to go faster (necessarily). I wanted to save some weight, and save some money and just wanted to experiment and see. My main concern was having something that will work on both street and track (which I don't go to that much anymore).

If I can go faster, that'll be a bonus, but that's not the main reason why I'm doing this. In fact, I don't track nearly as much as I used to, so I'm not that obsessed about time anymore.

Didn't mean to really say an inch lower overall, but even the .4 inches would be brutal to me right now at my ride height. I need me a new driveway lol

Yeah, I realize that it would only be half the calculated 1" difference since the wheel is mounted in the center. But even half an inch is way too much for me. In fact, I called Eibach today to ask if it's common for their springs to sag. When I first put them on 5 years ago, I was able to make it in and out of my driveway just fine. Now the front of the car scrapes, even if I'm very careful. And it looks lower also.

But I'm surprised that you went for 305 35 19 to 285 35 18 and you saw almost no difference in overall diameter/ height?? or did you mean 285 35 19 and 305 35 18, which would make more sense b/c the added width would add to the sidewall height a little and negate some of the change to a smaller wheel.

For my fronts, should I go with a 255 40 18 or a 245 45 18? (rears will be 275 40 18). The general rule of thumb is that when you go up or down 1" in wheel diameter, you compensate for that by adding or subtracting 5 to the sidewall number. But the width would affect the overall diameter also, so I was thinking I can stick with the 40 sidewall if I increase the width to 255 instead of the stock 245? And this will give me almost the same overall diameter?

So I have been running Enkei PF01 in 18 x 9.5 ET35 (Subaru fitment) with 25mm spacer at the rear and 12mm spacer at the front fitted with integral hub-centric locating rings to suit the Enkei bore-size of 75mm.

I have progressively reduced the rear bar stiffness from Whiteline to full soft and am now about to go back to a std rear bar and may even try without a rear bar sometime in the near future.

I have run 265/35R18 Yokohama A048 R-Specs (Nitto NT01 in 275/35R18 earlier but could not get replacements until very recently) and most recently ran the A048 with a 4:08:1 rear diff ratio and the car simply keeps getting quicker.

I am now carrying nearly 4 degrees of (negative) camber on the front and the car continues to point and take a set with power without darting or over-steering on throttle application BUT I do have to be very smooth on turn-in and going to WOT - too abrupt and you need to have your game-face on to catch the rear.

The more I stiffen the front and soften the rear with bars on the A048, the better it turns, the more mid-corner it carries and the quicker the car gets.

I am running a lot more rear rebound and front bump than in the past so weight transfer onto the front under brakes is slowed down a bit or the rear brakes can get a bit chirpy (I am still running OEM ABS but have disabled the yaw sensor to avoid the ABS controller getting its knickers in a twist and trying to pitch me off the circuit).

I'm running Kw V3 dampers and when I have recovered from purchasing my sequential box (was a 5-figure investment that I've still not shared with SWMBO) will invest in Penske shocks (I bought a pair for the front of my historic race car and they are a superb piece of kit) as the next upgrade. I already have a selection of 2.25" ID springs from 400lb/in to 1200 lb/in in 100lb increments so I don;t think I'll need more springs .. if so, they can be had locally from our motorsport spring winder (King Springs).

Whilst I can appreciate that some of the hi-power cars on the forum can exploit a lot of tyre, I'm still pretty happy with my (relatively) narrow width as I certainly don;t mind drifting the car at high-speed - the only thing I demand is balance and predictability at the limit.

My last dyno run netted 208Kwatw which is a lot less than some reported figures for NA cars here, but I am happy that all the killer-wasps are under the load pedal and can be called up when needed.

In terms of ride height, I run little tyres to gain a CoG benefit without extreme suspension arm angles of lowering the car on the coil-over. I get to keep near standard amounts of bump and droop which means I can avoid the camber gain in bump that comes from being 50mm lower on the coil-overs - it also gave me a gearing benefit and I find that with the 645mm diameter 265/35R18 tyre, my 4.08:1 FD, that I get to use 6th a lot more than I used to (previously I'd hold 5th to Vmax at the faster circuits we use) although last year at our quickest track, I was running out of rev's in 5th because the setup was getting me onto the straight faster and I had to use 6th. With the 4:08:1 FD, I'm now pulling 6500-6600rpm into T1 at PI GP circuit and need 6th uphill at the back straight at Sandown and this is as much about the setup getting me onto straights faster as well as the gearing benefits of little tyres and low FD ratio.

My bottom line is that square has been very good for me on the track, but I continue to make changes and have never gone back to my initial setup (because the OEM shocks are long gone).

The key is having 2 sets of wheels, but since you are not tracking, maybe not important.

I run 245/45R18 on the front on 8.5 x 18 and 275/40R18 on the rear on 9.5 x 18 RAYS Gram Lights for DD duty

Picking 245/45R18 or 255/40R18 is simple - I would not go 255/40 because the OD is ~661mm and the OD on the 275/40R18 is 677mm which is near as dammit the same as 245/45R18. The difference is 15mm and that might just about be enough to confuse the ABS calibration - others might offer e definitive response but I have always stayed with 5mm OD for my tyres.

I realise you're not tracking so much, so take my comments with a grain of salt, but I see your choices being driven as much my how low the car is as much as anything else.

245/45R18 on an 8.5 wide wheel with 275/40R18 rear on a 9.5 wide tyre is a match but 255/40R18 is not a good match unless you so the same front and rear.

You get that tranny installed yet? :yum::yum::yum:

Is going into the race car first. Dog-Box with straight cut gears in a daily driver can be a PITA.

2015 is about acquiring HR head conversion bits and Grand-Am spec rods and 14.5:1 pistons and then building a hi-comp Grand Am spec motor for E85. When the engine is built and goes into the car, so will the trans (I have an H-pattern Holinger available to go back into the race car). For the Z34, I'll need to go Motec or Haltech to run the engine and that means the car comes off the road, loses 350kg, gets a cage and I go Modern Sports Car racing with the Z34 instead of historic racing.