Alright, I have now seen more companies coming out with 18" DOTs. What has anyone tried for road racing. I want the RA-1s, but they don't quite fit. How much can we stretch it without negatively effecting handling, or ABS? RA-1 now has a 245/40/18 which is perfect for the front, but rear they only have 305/35/18 or 285/35/18. Keep in mind I have 8.5 front wheels & 9.5 rears (TE37). HELP!

 

you can go with the 285's in the rear with no problem. i was running 265's on the stock rear rim. and with the lower ratio (35) vs 40 you would have the same setup as i do now. i only notice the abs acting up when i am traveling less than 35 mph. at the track it will not affect it at all. by the way where did you find the 245-40-18's and how much ( thats exactly what size i am running all around right now ).

 

Eh? Last time I checked Toyo's website, they had 225's and 275's in 18's.

 

check into Kumho V700, Michelin Pilot Sport Cup or Pirelli PZero Corsa... www.tirerack.com carries them all abd they all have 18", but I don't remember what widths


hope that helps,

PeteH

 

I called toyo, and they said that Speed Challenge, cars are now running RA1s so they came out with new sizes in 18.

 

Ah, very nice.

 

You can also check into the Hoosier R3S03 in size 245/40/ZR18 for the front and 275/35/ZR18 for the rear. The rim for that combo is 8.5 front and 9.5 rear. They both run full wheel and tire diameter of 25.3 inches, with a circumference of about 79.5 to 79.6 inches.

 

I have 275/35/18 RA1 in the garage waitin for summer.

theyll be paired to 245/40/18. yes the backs are smaller, but it will increase acceleration. not bad for racing with the VDC off. and the difference shouldnt be a problem for normal driving.

 

I'm running Kuhmo V700's

265/35-18 all around
18" x 8" x 35mm Enkei RPO-2J all around.

-D'oh!

 

Another question: To shave and heat cycle or not to shave and heat cycle? I want max longevity out of these.

 

Please correct me if I'm wrong, it looks like the V700s have a pretty bad reputation compared to Victoracers or Ra1s. They are cheaper, but with a car as heavy as the Z I want a comp tire that isn't prone to chunk. Of course the Hoosiers are nice, but a set will run ~$1k.

 

there's a lot of debate on heat cycling... you can pay Tirerack $30 (or whatever they charge) per tire to do it, or you can go out and drive down the highway at 60 mph for about 30 minutes and get the same results. I've been using r-compound tires for four years and have never heat cycled any of them. And, I typically get 5 weekends out of a set.

Shaving is a different story. Some tires you have to shave. The Kumho Victoracer almost always has to be shaved. But, it is not available in 18". Kumho recommends shaving the V700, which is available in 18". I have almost always used Yokohama AO32R and I've never shaved them.

One of the logest lasting r-compounds I have seen is the TOYO RA-1. I have friends who track Audi S4s and they use these tires... one set will easily last 5 weekends, but remember, they run the same size all around and they rotate front/back and they rotate the tire on the wheel to get more life out of them.

My one experience with Kumho Victoracers was not good. I had slightly user rears and brand new fronts. The fronts flat-spotted after one boneheaded mistake early on Saturday and were ruined by the end of the day. I will never buy another Kumho product for my Z, race or street compound... but that's just my opinion. And, I've never used the V700.

My current set of Yokohama AO32R hard compound (275/40-17 all around) have been to one track event, about 400 track miles plus another 160 miles driving to and from the track. The still look brand new. I suspect I will get another four weekends out of them. They were not cheap... a little over $1000 for the set.

You are looking for 18" track tires, so be ready to pay $1k or more for a set. Unless you go with Kumho... they may be cheaper, but they won't last as long, so you will actually end up spending more.

Hope that helps,

PeteH

 

You could always use 245/40-18s all around and get rid of that understeer. You're not using most of that extra grip on the rear anyway (unless you have done suspension changes) so a 245 all around is pretty much as fast (and more entertaining) than running some sick-wide rears.

Your call. I'm running 245/40-18 Hoosier R3SO3s on the Rays Track wheels. Pretty good combo - and the 4 mounted wheels still fit in the car (with some room for tools and junk).

Jason

 

The understeer is already completely gone with the 350evo bars. What do you think about 245/40 front and 275/35 rears?

 

Since the 350evo bars are adjustable, I think you could do it. The thing is that ultimately, you're tweaking handling balance by removing rear end grip to match front end grip with that big of a stagger on this car.

You see, the Z doesn't have great weight distribution (53% front is not horrible, but it isn't great) and it doesn't have a ton of power either to break those meaty 275s loose if you're driving it properly (smooth inputs). So, I think you can do it - but you're not really gaining from it. You'll have to run a lot of rear bar, which will allow the car to be neutral but may affect other aspects of handling (particularly in transitions since you'll have much more rear roll stiffness than the rest of the suspension is designed for).

So ultimately, you can do it and I don't think it is necessarily bad, but it isn't really necessary. The reason you see big staggers on 911s for example is that they have 60% of the weight on the rear axle. Z06s run big stagger because they have 400+ hp and can easily use up the rear grip through cornering + acceleration.

But having some natural understeer is a good thing anyway in a street car. Unless there's prize money that you're going for, there is nothing wrong with having some understeer in your car - as long as it isn't too much, you'll still have a blast at the track and with your setup, the car will still be very fast.

Jason