StrokerAce

I suppose you have proof like in stopwatch times for autocross or track?

bse50

we don't autocross here in italy and yes i did test the different compounds with a chrono.

mwood

Generalizing is always dangerous and will always lead to holes in your hypothesis...

"235 or 245 wide tires on a 9" wheel will provide best results"? No, I don't think so. Wider is better, as long as the rim width properly supports the tire...generally, so why not 275 on a 10" rim? or 295 on a 11" rim? On most every road race course you might encounter, you'll go faster...generally.

bse50

You're right, i was wrong generalizing but i am preparing a couple of hard exams so i'm always in a hurry

What i forgot to add was: given our power outputs on NA cars.
Go too narrow and you won't have enough traction, go too wide and the added weight\increased rolling resistance will produce some negative effects.

Does this sound better? I am just a car enthusiast, not a pro driver so that's merely my opinion and i would like to understand more.
For sure going too wide with the stock rim width is not ideal for track purposes while it may be ok for autoX.

visitor

I run 295's on 9.5" rims :D Depending on the course, I'm anywhere from 8-10 seconds off a B Stock 8 :D

tmak26b

Sorry for the late reply, been busy all week. Anyway the peak time difference between the two tires were three seconds exactly. BUT, the best times were done at different times of the day (for some reason the RX-8 is very sensitive to heat, the power dropped substantially as the temperature rose). For comparison sake, I chose a lap from another session with similar track condition. The difference ended up being 1.9 seconds slower per lap. This is with basically the same car and driver over a 3.2 miles course.

http://img170.imageshack.us/i/rx8r888z1.pdf/

As for driving feel, the R888 just feels like a much gripper tire. I was pleasantly surprised to see the time difference to be so small. If I recall correctly, the car seem to roll a lot more with the Z1. I had a tough time going through fast corners with it because the car felt like it was going to understeer straight into the grass. (this is why a huge speed difference in the uphill esses and west bend). As far as longevity, the Z1 can't match the R888. After 20 minutes of hotlapping, the Z1 had a nice blue streak to it while the R888 remained the same. Of course that is expected as the Z1 is more of a street tire while the R888 is a true race rubber.

As for the tire/wheel issue, I think 8" is perfect for the 245. The tire wore perfectly along the edge with a relatively mild alignment, I felt and looked like I was able to get the most out of the car and tires. As for the 265" on the 8" rims, I wasn't too happy with it. For one, I thought the tires were too much for a stock power/suspension RX-8. Also the 8" limited what I was able to use from my 265". You can see a noticeable different in wear pattern on the 265 than the 245s. If I were to do over on the stock rims, I would do 245/35/18.

Stretching a tire for autox is fine, but it's completely useless for the track. I did it because I had these tires left over from my other car, I wouldn't have done it otherwise.

Also as a sidenote, the bloody RX-8 is slow on the track. It is 2.5+ sec slower than an EVO, 5 sec than a 350z and 10+ on a C6 Corvette with less grippy Toyo tires.

bse50

you need some driver mod
Also the fact that your car loses power while hot is not normal.

tmak26b

It's the same driver, so not sure what you can do.

Car is definitely losing power under the high temp, god knows if it is the ECU pulling timing or what

G-ReX

I ran in June in what I think were similar conditions to yours (mid 80's & muggy) and the car got progressively hotter, but lost no power. My last runs were my fastest each day, but I'm also fairly new to this. My speed at the end of the front straight was similar to yours - about 117, but my runs nowhere near as consistent as yours.

OOC, am I reading the graphs right, are you single apexing Oak Tree?

tmak26b

I was doing 120 to 121mph, but I brake at the 1 marker. another board member that went with me that dayy said his car made noticeable more power, he was also a second or two quicker. he was faster down the straights and turns, yikes!

fastlaneracing

Interesting to hear, so I and bse50 aren't alone with the theory of wider rims after all?

Yes RX-8 are quite affected by temperature.

I don't agree about stretching, I think its ok for tracking but not so important for autox because of lower speeds, but hey you can't agree on everyting.

Thanks for your report! =)

tmak26b

autox has a lot more qquick transitioñ, it would benefit more from stretching the tire than on track. 245 wore perfect on the stock 8" rim.

fastlaneracing

Quicker transition yes but still lower speeds, it's the load burden (thats get higher with speeds) that makes sidewalls to flex.

tmak26b

The wider tire has a bigger contact patch, it becomes very useful in quick transitions like slolam. But you can't get good even wear when you stretch a tire like that, forget about even wear across the tire...

fastlaneracing

I think we are saying the same thing now?

G-ReX

tmak, what pressures did you run on the Star Specs? I'm at the track fiddling, but the tires seem to want much lower pressures than my old 050A's.

tmak26b

34psi f 34.5 in rear. nice blue mark on the tread edge

Razz1

I wouldn't run a 275x10 at the track.

The RX8 doesn't have the power to use it.

the extra weight is horrible compared to a 245x8.5 or 255x9

G-ReX

Big thanks to you - that worked much better. I started at 38 like my old B-stones and they felt like crap.

tmak26b

The idea of bumping the tires 5-10psi is history for high performance tires. You shouldn't have to go more than a few psi more than recommended tire pressure. You can probably go up slightly if you decide to go more than 15 minutes on them to prevent too much heat from building up. Honestly I didn't feel much chance as I build laps, the car only dropped off slightly near the end of the session.

The exception to this is the R888, they seem to like 40psi+