stevensa

Hello All,

I am going to be needing a new set of tires this spring for my 02 z06 with stock 17x9.5 and 18x10.5 wheels.

Here is my situation, I plan on running the Redline Time Attack series sometime in the near future, which has a maximum tire width in the street class of 285.

Now I have read various threads stating that a minimum difference in tire diameter is required for the TC, AH, and ABS to work, however I am looking for some first hand experience in this thread.

Now I have read various times that running a 275/40/17 up front is a nice tire size, and I would be forced to run a 285/35/18 in the rear.

Now the stock front tire diam is 25.34 and the rear is 26.12 for a .78 difference. The 275/40/17 is 25.66 and the 285/35/18 is 25.85 for a .19 difference.

My main questions are,

1. Has anyone ran this tire size combination?

2. Does this seem like a decent setup as far as being neutral and good handling? I figure it is close to being square and should be fairly decent.

3. How will the ABS handle the close tire diameters? I dont use the TC or AH when on track so all I really need is the ABS acting correctly.

4. I have found these tire sizes in the Nitto NT-05 and Kumho Ecsta MX, any preferences or experience?

Thanks in advance, I appreciate and am open to all input.

-Andy

Greywolfe

I ran the NT05s for a few track days and they had really good grip for a street tire. I ran 275/295.

mcomte

i autocross with hoosier 315/35/17 a6 all around and have no issues with abs activation or problems.

stevensa

Good info here! Just out of curiosity, how does the tc/ah act with the same size all around?

TedDBere

I ran a 275/285 on my coupe for years but never on my Z06. You'll have to turn the AH/TC off but that won't effect the ABS.

If you can only run the 285 in the rears I'd be tempted to run 285s all around. That's not much rubber in the back of a Z06 though and the Porsches had some issues with the 285s coming off the rims in the rear due to the low profile and lots of power and weight on them.

Why a maximum of 285?

stevensa

Yeah I am not a big fan of the 285 rears. The car has some basic bolt-ons, cam, and 4.10's so even now with the 295's it can be a handful coming out of turns.

The 285 is just a maximum tire size rule that the organizers setup, I dont know why they chose it.

How did your car handle with the 275/285 setup?

rustyguns

turn it off. it slows down the engine

what type street tire are you limited too?

stevensa

Haha, like I said I dont run with it on, just curious!

140 is the lowest wear, 285 max

sperkins

ABS will work fine with a square 285 set up.
What type of track/course will you be competing on? If it's a tight course you may want to consider a smaller front tire to help the car turn in, but if it's a longer road race style track, you'll be better off with 285's on all corners. Plus, you can rotate them to any position to maximize tire wear. I've heard good things about a Dunlop street tire, but I forget exactly which one.

rustyguns

for 140's get these:

http://www.tirerack.com/tires/Spec.j...irePageLocQty=

you will win!

stevensa

All of the events are held on larger road courses.

Are you talking about the Direzza Star Spec? If so I looked into those but they dont carry the size I need.

When running the square setup, I assume you mean picking up a second set of 10.5 rears?

stevensa

Which sizes in particular? I dont see any in what I need.

rustyguns

its a long list. you cant see them?

what sizes are you limited too?

stevensa

Either the 275/40/17 with the 285/35/18 or a 285 square setup which has been discussed thus far. Unless I am missing something I dont see either?

autoxer6

Grassroot motorsports did some Extreme tire testing in June '09 issue. Tires were tested in 15 inch sizes on a honda civic.

Here is a summary of times from worst to first.

6th - Falken RT 615 Mean time: 35.302 Sec Quick time 35.125 Sec.
5th - Dunlop Direzza Sport Z1 Star Spec Mean time: 35.209 sec. Quick time 35.061
4th -Toyo Proxes R1R Mean time: 34.522 sec Quick Time 34.452 sec
3rd- Bridgestone RE-01R Mean time: 34.478 sec Quick Time 34.430 sec.
2nd- Bridgestone Potenza RE-11 Mean time: 34.266 Quick time 34.238 sec.
1st - Kumho ECSTA XS Mean time :34.170 Quick Time 34.030 sec.

All tires were shaved to 3/32 and and test performed on an Autocross set up. Locally (Milwaukee) we have a very competitive street tire class. The Kumho has been the tire of choice for Z06 sizes.

You'll have to make a call on size to meet you local rules.
http://www.tirerack.com/tires/Spec.j...irePageLocQty=

stevensa

I have heard great things about the XS, unfortunately the only size they have that is decent for the rear is the 315/30/18, which is too big for the class.

I use the mx now in the rear in stock size, and they do pretty well.

What do you run, I may consider a 275/40/17 front with 315/30/18 rear for a non-RTA tire setup.

autoxer6

Whats wrong with the 275/35R18 XS? I know it 10mm less than you would like but I think most people will agree that compound is more important than 10mm width.

Size isn't everything

stevensa

I gotcha, but now we are down to a 275 from the 295 which is on there now. The 295's get squirrely now as is with the cam, gear, and Kumho MX's , I just feel like a street tire 275 would severally limit the car.

stevensa

Now my next question is this. I will not always be trying to compete in the RTA series, and will just want to run an optimum street tire set for a while.

Would the Kumho XS in 285/40/17 and 315/30/18 work pretty well when RR?

avizandum

According to your OP you're rake will be way off with a front tire 1/2" taller than the rear. You should adjust the heights (lower front and/or raise rear) to accomodate and you'll be fine.

I faced a similar situation with my C6 and with a little dialing-in got to a very nice balance. Start by getting as close to factory rake as you can.