As intuitive as having as much rubber on the road might seem, is there a point that is overkill for the Z? Seems that some are running 245s all around, but I was thinking of going wider (once I get my track wheels). Toyo offers RA1s in 245/40 and 275/35, and there's the Kuhmo V700s at 265/35 and 285/30. I could get a set of hte Nismo wheels for a reasonable price, and the RA1s would fit well. The Kuhmos would require a 9" and 10" wheel respectively. Would having that much tire benefit the Z or slow it down?

Pros and cons of each set: Nismo wheels are affordable, but RA1s are about $1000 for the set. A set of wheels for the Kumhos would be several hundred more for the set, but the Kumhos are $40 cheaper per tire. And of course there's the option of getting an extra set of OEM Track wheels and throwing some 245 rubber on it all around.

I don't have much problem rotating, and my rear tires tend to wear about 40-50% quicker than my fronts.

Thoughts?

 

Personally I'm going to go with the 245 all around set up just so I can rotate them for max life. I think if you run the staggered set up you will always replace the drivers front quickly. Especially if you ever go to CMP. If you have 4 the same you can swap around and rotate. Maybe if you had a higher HP Z it would matter more. Similar to a Vette's set up.

 

I used to wear the front left tire with the OEM suspension, but since I installed the FLT-A2s last summer, the front tires wear equally (even with the -1.7 degrees camber). In fact, it's scary how evenly the fronts wear. At Mid-Ohio, James pretty much worn his front left tire bald, while mine has plenty of tread left. What I can't figure out is why my rears wear faster than the fronts since I don't drag race the car, nor do I indulge in parking lot donuts. I have since lowered my tire pressure in the rear to see if they'll wear a little slower...

 

What the pressure did you use before? You sure you don't need to increase it?

 

I've been running anywhere from 32 to 34 cold, normally the same front and rear. Unfortunately, the center of the tire in the rear wears prematurely, normally an indication that the tire is over-inflated. When hot, the fronts are normally ~40psi and the rears are ~42. I've had the tire pressure at ~45, but once the tire heats up, it gets greasy really fast (or the fact that it gets greasy and has too little of a contact patch at that pressure).

 

On the track, I have been using front 255/40-17 Kuhmos Victorracers and rear 255/45-17 Hoosier RS303's. The car behaves great, and feels well planted. I've done 1 day at Road Atl, and 2 at VIR on the current set of tires, and when I started with them, the kuhmo's were half worn from auto-x, the Hoosiers were bought used with very little wear. They still have one or two track days left on them.

I ran 275/40-17s at Little Talladega, and it felt phenominal, but I boiled the power steering fluid with the stock cooler.

Now I run the 275s for auto-x, where I can really use the extra grip. May even go larger next time.

 

It seems you've done your homework. Not many people out there have. Check my other posts. I have a like new - perfect - set of Black Racing N1 Pro's 8.0 and 9.0 in Rims shod with new Kuhmo VictoRacers 245/45/17 and 275/40/17. I have run in the Porsche Club for 7 years and have a good idea of how to tire a car. My dad bought a Z, and let me tell you, with those tires it is amazing. Would be a great SCCA autoX car. I am really impressed with the Z's performance. Right from the factory with the right tires this car can kick but (provided you have the right driver.) Do not listen to anyone that suggest the same size front and rear. You will have oversteer - it may look fast but it wont be. Also make sure the overal diameter is close. The Z's traction controll will get screwy if you don't maintain similiar ratios. I'm in Baltimore - Come up to a Chesapeake PCA event - www.pcachs.org and I trial fit the tires and rims for you. We're running at Cumberland Airport this weekend. Come on out!

Dive it like you stole it!

Racerjsz
White 996 GT3

 

Interesting approach racerjsz... I'm referring to your admonition not to listen to those running same size fronts and rears.

John - I'm a big proponent of no-stagger. I don't like understeer and I certainly don't get too much oversteer with my 245/40-18 Hoosier R3S03s all around. But to answer your real question, I don't think there's anything wrong with going wider (say 265 all around instead of 245 all around) as long as your wheels are appropriately sized and you aren't running into clearance problems.

But there's more to it than contact patch. Tire compound is a big factor too, and I'm pretty sure that a set of 245 Hoosiers will give you as much or more lateral stick (with proper camber) than a set of 265 Victoracers for example. And the narrower Hoosiers will have lower rolling resistance, rotational mass and unsprung weight. So there are a lot of factors in play.

I'm quite happy with the grip and balance that I get with my 245 Hoosiers but if I had wider wheels I probably would have gone with 255s all around.

Racerjsz's setup isn't necessarily bad, but my setup is certainly a little bit faster. But it's all advice... At least I'm not trying to sell anything

 

I guess I could be off base. You seem to know what your talking about and there is a guy running 275's all around at a nat'l level. I can't figure out how they fit. All my experience is with Porsches which need a wider rear. We test fit a 255 on the front of the Z and it seemed too close for comfort on hard turns at full lock. I agree with the Hoosier comment - I run A3S304's on my car (actually run the R's on the rear!) Hoosiers are the best if you can afford almost twice the price of Kuhmos. All I know is with this combo the Z was fantastic. Bring that Z or the Turbo down to Ripken Stadium - we have NY guys show up and run.

 

racerhszL Thanks for your input. The Z has lots of room in the wheel well, enough to accomodate a 275 front and a 305 rear, but it's a tricky fit. I think there are several Zs in autox that run 275s all around, but autox is different than driving a larger road course, and I don't feel comfortable cramming a 275 tire on an 8" wheel (that's what they're doing).

Jason: I was waiting for you to chime it. I guess what I was trying to say earlier is that since I'm wearing the rear tires down so much faster, I figured that a wider tire might help the balance wear fore / aft. With my suspension setup, I feel the car is pretty neutral. Now, I'm in no way a professional road racer that loves serious rotation where the rear end is definitely getting worked (not full on power-steering), I'm simply not at that driving level. Do you have any comments as to why my rears would be wearing so fast?

Ah, this is definitely a tough decision...

 

John - I hadn't gotten that part of your question (maybe I need to read more carefully). It's actually a good question and one where the solution is not immediately obvious. But here are some thoughts:
- First of all, you're wearing the rears symetrically (within the tread) so that implies that you don't have a camber problem. But it sounds like you need to lower pressure a little bit to promote even wear.
- That being said, you will gain a little bit of durability by going to a wider rear tire so it may be worth it. However, if you do this, you'll probably need to stiffen up your rear bar (or soften front bar) to maintain neutral balance. It's an option and probably would work, but I wouldn't expect a huge improvement in rear life because you wouldn't be addressing the real cause of the wear.
- Which brings me to my last point. I would first suggest playing around with your bars. You may just have too much rear bar stiffness which is causing more rear load transfer than is optimal. The problem with that is that you will end up introducing some understeer (and I don't know what settings you're running the bars at now). But my suggestion would be to try that first and see if there is an improvement. It will also improve the even-ness of your wear across the tread (lower load on the tires keeps them more rounded). If you get too much understeer that way, perhaps it's time to add negative camber in the front. But either way, I don't think you'd get worse balance from doing this than you would by going with a significant stagger.

Anyway, those are my thoughts. I think it's always a good idea to first experiment with the things that you can change for free rather than invest more money.

racerjsz - you're right that the P cars are a little different than the Zs. The Z is front-heavy at a 53/47 split versus the ~40/60 split of the 911s so the stagger that makes a lot of sense on a 911 can be a hindrance on the Z. Also, John and I are talking road courses where the corners are less tight than autocrosses and you just don't get the big, lurid power-on oversteer that you can get dodging cones (I have some great videos of completely sideways fun runs in my car so I know what you mean). How do you like the GT3? That is a fun car...

 

Right now I am planning for 265/35/18 Front and 285/30/18 Rear Advan A048 for track on 18x9.5 wheels all around. I will let you guys know how it works out!

 

There is no way I would ever use traction control or VDC on an auto-x course! (in the Z)

 

Exactly. The only thing that would be affected in autox as I see it MIGHT be the ABS setup.

Actually, maybe on a rainy day you might want to play with VDC, but I haven't run in rain so I don't know.

 

If you have ABS, on the autoX, use it. There's no way to beat it. I don't know if the Z has the same self preservation mode as the P cars or BMW's, which kick in if the car gets way out, which it most likely will in an autoX if you have to rotate the car in a tight corner. If when you turn it off, it stays off no matter what then it is a non-issue. John, note my statement about the hoosiers. I run "A" compound fronta and "R" on the rears for reasons similiar to your question. We're only 1.5 hours north of DC - come on up!

 

The VDC (stability control) along with traction control can and should be cut off. They are way too intrusive to be used in competitive autox.

ABS you can't cut off with a switch. What I was saying was that equal diameters may mess with the ABS computers, but I doubt it will significantly affect autox performance.

 

ABS is too "binary" in it's action to be significantly affected by using the same size tire.

VDC definitely needs to be off for AutoX, but maybe on at the big tracks depending on your level of confidence.

I'm running AutoX 265/35-18 (Kumho Ecsta V700) all around on stock size rims (Enkei RPO2-J) and find the car better balanced but still not as well balanced as I'd like. It is still almost impossible to induce oversteer by lifting the throttle, which makes decreasing radius corners a real problem. However, in a constant radius or increasing radius corner the car does very well.

I like my setup quite a bit, and it was $2000 out the door for the four wheels and tires.

With the Z's size and weight, the wider tires definitely help, but I've also noticed that the power steering will get laggy in quick turns when I have the racing tires on (doesn't happen as much with the street tires). You may want to stay on the 245's just to help reduce any power steering issues.

-D'oh!

 

I finally got my new set-up. 255/45 Kumho MX on 17 x 9 MB Motorsport Competition wheels.

I wouldn't go with a tire larger than this on a 9" rim. Chose same size all around for the same reasons that SCC did.

Also got my rear Brembos installed, along with my replacement front Stoptech SS brake lines, routed behind the upright.

A pic:

 

Good to see you got your new rear brakes and wheel/tires. On a 9" rim, 265s fit fine (well within manufacturers recommendations). How heavy is each wheel / tire?

 

I would stick with same size tire front and rear. Wider rear tires will just cause it to understeer more in corners. Unless you are making big HP and need the extra traction in the rear, then stick with same size. For a Z with stock or close to stock motor, a 245 to 255 should be more than enough. I am running 245/40-17 on my T2 car.

Alex Long

SCCA NorPac Division T2 Champion 1998/1999/2000/2002