NeoTuri

iTrader: (2)

I've been autocrossing some old 275/40 V700's on 17x9.5" wheels (43 offset). These were used as rain tires by a national competitor. The setup was to test fitment for a wheel/tire combo.

So far so good. I will have to roll the fenders a little if I want to maintain a ride height near 25" though.

I dialy drive my Rx8 on the OE 225 tires, and auto-x a few times. The last time I took it out, I put the 275 wheels on the car and gave it a try. Right away, I noticed that the front wheels would feel like they are binding up at turn in and gave a sense of understeer. The car still drove great (and for other reasons I am probably faster in a stock Rx8 with heavy wheels than my modded Rx7 O_o ).

Anyway, I read that 245's are faster on it (in B-Stock) than 275/285's which brings me to my dilemma:

I will be updating my gear to V710's for next year, and I had some questions about handling and steering response for some tire combinations:

Setup 1) 275 on all four corners
This is what I'm used to. I have the suspension set to be neutral, and it feels balanced to me. My lines have to be straighter than if I was running on all 235's, but I like the extra lateral grip. I imagine I will drop some extra time by moving into a fresh, more competitive set of R-compounds.

Setup 2) 275 front/315 rear (if 315s will fit on a 9.5" rim).
My concern with this configuration is that I will get understeer. I know I'm not supposed to correct this by setting up the car to be loose in the back, so that's where I am stuck. I also worry about being able to heat up 315's in a car that weighs close to 2700 lbs.

Setup 3) 245 front/275 rear
Concerned about understeer

I'm looking for some advice before I commit to a tire combo and start making the necessary changes.

tia.

2MCHPWR

iTrader: (2)

what spring rates do you use?
i'm in similar boat.
i used v700's last yeat but this coming season i'm gonna switch to v710's.
i have 8.5's up front and 9.5's in the back. 245 up front, 275's rear.
but i have two sets so i thought about running the 275's all around. wheels are ssr's 9.5 with +42mm and i didn't like how they fit up front. what do you think?

http://www.ponycars.net/images/rx7/275s/index.htm

i think the bottom of the fender is about 26 inches high.
you are 43mm and i'm 42mm. did it hit your inner fender or fender liner? whats your ride height?

the 245/275 was very neutral on my car (3.90 gears, 400 hp, 410 tq at very low rpm, 5kg/mm springs front, 4 rear) but the the v700's weren't fresh.

i would never put 315's on 9.5's for ax. they need like 11's ideally. for draggin...maybe 9.5's if you wanna be cheap, but i wouldn't do that for ax.

NeoTuri

iTrader: (2)

Heh, not only do mine fit like that, I am also at a 26" ride height.

Springs:

700 front, 500 rear

When I first installed my coilovers for the Koni's, I may have put them in wrong because it allowed the shock shaft too much play and caused my right front tire to "unroll" my fender.

The left side does no such thing eventhough it has the most load.

Sandro

iTrader: (1)

According to Kumho specs http://www.tirerack.com/tires/Spec.j...irePageLocQty=
with 17/9.5" you should only use 275/45
However, all the 17" tires seem to have too high diameter, compared to stock. Unless you change your final drive, your acceleration will suffer.

Sandro

iTrader: (1)

Sorry, I hit the send button too early..there was another sentence I wanted to add

The Hosiers have 245/40/17 with 24.5" diameter. Those should give you a much better gearing. You can have similar diameters with the V710 but only in 18"

2MCHPWR

iTrader: (2)

so i guess i should give it a shot if yours fit like that too. still a little concerned since you have much stiffer front springs than me. wonder if my front will compress more. also what neg camber do you run? i think i'm only like -1.5 but i wanna try for -2 during winter hiatus. i heard that helps tucking it in under compression.

and sandro's concern is pretty true if you just have 287 hp. lower center of gravity is another benefit of the smaller size he mentioned.

NeoTuri

iTrader: (2)

I am working on the hp figure over the next two months. The goal is something closer to 330-350 whp with a new IC (it's still stock) and airpump (it's wasn't working when I put the car on the dyno).

I have considered trying Hoosiers but I don't like the peer reviews about the performance dropoff after you starting running said tires.

I need to add that my camber settings are still stock. Something that may change AFTER I am more acquainted with my tire setup.

It's like there's no winner combination:

V710's are too tall. Hoosiers are probably not my cup of tea (and expensive).

Should I trade gearing advantage and lower stance for lateral grip, or vice versa?

NeoTuri

iTrader: (2)

By the way, I do have a set of SSR Integral A2 (17x8) for my street wheels.

If I go with 245-265, my wheels will simply switch roles.

Sandro

iTrader: (1)

245/45 and 275/40 both give you the same 25.4" diameter
The 245 on the 8" rim will weight less but the 275 give you more rubber
I would tend to agree with your concern that too much rubber may not get warm enough. I personally don't have enouch experience to give a personal opinion on this since I have been using stock rims. Consensus seems to be though that you want to have more rubber unless there is a significant weight penalty.
And the V710 work pretty well at relatively low temperatures.
Also, since you are targeting heigher power, you may need the 275 anyhow.
Finally, I don't see any advantage in using staggered sizes front and rear, and tire management is obviously better with four equal wheels.

DamonB

I'd go 275 at all corners. The V710 heat very quickly; you won't have trouble heating them as long as you drive it hard. If the temperature outside is hot most of us have to soak our V710 between runs to keep them from getting too hot. A two driver car on V710 in warm weather can actually be a problem at times because it becomes so hard to keep the tires cool.

As for speed if the V710 you're running now are old new tires are going to be faster regardless of size. The V710 sidewall is softer and the steering response is slower than the V700 or any Hoosier. This makes the steering feel numb and slow until you get used to it. Persevere. The stick is there but they require some adjustment to the driver to get the most out of them.

Chadwick

iTrader: (12)

Go with 275's all the way around. The 710 is a great tire and you will be happy with the grip compared to what you were running.

NeoTuri

iTrader: (2)

How does the Hoosier A6 compare?

I've searched high and low and can't find a definitive comparison between the two on the same car.

The reason I ask is that I see a 295/35, and it has about the same diameter as the 275/40.

Mahjik

iTrader: (1)

Hoosiers generally wear MUCH quicker. While not the A6, you can see some comparisons with a few other tires:

http://grassrootsmotorsports.com/ima...5_tiretest.pdf

NeoTuri

iTrader: (2)

Yeah, I read that last year. I used to run A032Rs.

Just curious about the Hoosiers.

Now, I need to figure out what to do about my fenders...

2MCHPWR

iTrader: (2)

275-40-17's on 17x9.5 +42mm

i just drove with above setup but the screws that hold the fender liner were making marks on the tires during bumps. no way i can race like that so i guess i'm sticking with 245's front and 275 rear this year.

NeoTuri

iTrader: (2)

My tires clear the screws on the sides of the fender by 2 to 3 mm. It's pretty damned close.

A fellow autocrosser recommended milling down the screw heads or replacing them with ones that do not stick out.

2MCHPWR

iTrader: (2)

neo - how about mid-season status update?
i've been loving the v710 245-45-17 front/ 275 rears. -2 neg camber up front keeps outside and inside at near equal temps. can't find a fault in the tires. i haven't been out of the top 5 (of 100-125 cars) all season. My suspension allows tons of front/rear weight transfer though; you should see the vids on my site. But thats for another thread.

NeoTuri

iTrader: (2)

Thanks for asking,

I went with 275 on all four corners. They don't rub anymore (a tad bit shorter than V700s apparently). Though, I will need to replace some trim pieces damaged by my previous attempts at tire fitment and your typical auto-x wear and tear.

Earlier this year, I used some traction treatment on the V700's to buy me a little time. The stuff really works, and gave the old tires some kick before I finally corded them.

V710s + Some mildly aggressive mods (i.e. weight reduction & bigger IC) = Great improvement!

I picked up on average 3 seconds (relative to SM2). I currently lead the class in points, but my new goal this year is to get a little closer to the PAX class (typically dominated by stock and ST cars). Out of 180-250 drivers, I can place somewhere in top 20 raw times. Atlanta has allot of fast drivers, so if I could somehow make it into the top 30 (overall PAX), I'd be happy until I could do some other things to the FD.

The alignment is still not exactly where I need it, so that is on my to-do list. Some more neg camber should hopefully improve some cornering grip. With the car performing well, it's really up to me to make up some time.

At the last event, I watched some video and noticed my driving is much smoother than last year, but I am not on the throttle enough. I think my braking is okay, I just have to find a way to keep my foot on the gas longer (left-foot braking scares me).

ULLLOSE

iTrader: (1)

The 245-35-18 works well on the BS RX8 because of the 8" wide wheel limit. The BSP ones I have driven on 18"X9.5" with 285-30-18s are much quicker. If you have the money I would try the 18 setup, shorter and wider than the 17s.

If not go with #1. Back in the day when the Tri-point RX7tt was the top dog in ASP they were on 275s front and rear, I think they were on 17X10s.

NeoTuri

iTrader: (2)

I may be looking at 18x10 when I begin my search for lightweight wheels.

2MCHPWR

iTrader: (2)

can v710's be "flipped"?

reza

Yes you can flip them. Performance is a bit off since the tire is not level for the first few runs. And after that its normal again.