Guess what is faster, R888 (R comps) vs Dunlop Z1 street tires
 

I finally decided to pull the memory card out of the RX-8 and started digesting the data from my last track day at VIR. Here are something interesting I found between the R888 vs Z1.

The R888 I have are shaved, on stock 8" rims in 265/35/18
The Dunlop Star Spec Z1 are like new (<500 miles on it) on stock 8" rims with 245/40/18

Guess what is faster and by how much? This is at VIR, I think a 3.4 miles track. The weather condition was roughly the same, maybe the Dunlop was in slightly hotter weather. The track was about 1 sec faster when I did my lap with the R888, so I will keep this in mind.

I'd say the Dunlops were faster, strictly because you stuffed a 265 R compound on a 8" rims. The Dunlops you used are more within the spec for that size rim.

???????????

Seems like kinda a skewed comparison giving the size differences between the two...

I'll go with the Star Specs. I have them on my Elise and they feel better than the R888s we run on the Spec Miata. :P

I'm curious as to what you thought of the Dunlops at VIR. I'm hitting VIR this coming weekend - first time on the Dunlops, same size as yours.

If you guys want more of a HPDE tire ya should have gone with the NT05's. The Star Specs are the top AutoX tire, but heat up a bit too much after about 10-15 minutes and start to chunk. I know that both of you guys AutoX frequently, but just throwing some information out there. I'm currently on NT05's for my track wheels, and going to be getting Star Specs next season for my autox wheels.

265 on 8" wide rims must be a terrible experience, Im personally going for 9" wide rim for 235 R888

Why "must" it be? Do you have any experience? Are you with the tire cops?

The R888's are too wide. This increases the rolling resistance and weight. That is why the Dunlop tires were faster.

you would get your butt kicked trying to compete with that stretched Euro-mentality setup

the fastest SCCA B Stock drivers run 285/30-18 on 8" wheels (the rules require OE diameter and width wheels within +/- 6.8mm offset)

the general word I hear is that the newest street tires are very surface/setup dependent, so even if they were the same size you might get a different result at a different venue, your driving style likely influences the results too

Is it so? Before you guys starting with "euro mentality stuff" you can maybe check with Toyos engineers before?

Ignorance is a bliss ehh?

265/25,4 = ~10" I saved some time for you, thats what Toyo recommend.

StrokerAce: yes I am currently running on R888, are you?

You must be feeling pretty blissful then .... your calculation method above is basically useless for this purpose

You'll get your clock cleaned here in the US running those skinny tires on such wide wheels. I'm talking from direct racing results/experience, not theory or recommendations. I mounted up and ran almost every reasonable race tire size on 8" wheels this year; 225/40-18, 245/35-18, 255/35-18, 285/30-18, and 295/30-18.

You guys talking about autocross or track use? There's a significant difference, in terms of optimizing rim/section width...

Putting a 265 on a 8" rim will degrade it's performance, at least when compared to mounting the same tire on a 9" or 10" rim, I'm sure we will all agree.

And, if the 245 has a slightly better compound, that, in combination with the degradation of the 265 on an 8" rim, might make the 245 faster on a particular surface.

Also, Toyos as a rule have soft sidewalls (do the R888s?) and that would make the effect of mounting on a too-narrow rim even worse.

I heard a rumor once, and this is only a rumor, that the R888s and the R1-Rs use the same compound, with the treadwear difference being made up by the R1-Rs having a greater tread depth. If this is true, and you believe Jason's testing of the Star Spec vs. R1-R in Sports Car, then I could see the 245 SS outperforming the 265 R888, at least with the R888 mounted on a too-narrow rim.

As somebody above pointed out, this stuff is very context sensitive.

I don't agree and I ran 265's on both 9" and 10.5" widths.

Even if it does degrade performance, all else being equal among the top street tires a 235 won't be faster than a 265 on a 9" rim. There's simply not enough grip level with a street tire for the response of the 235 to offset the overall higher grip of the 265. If it was, you better believe all the STX/U racers would be on the smaller tire. The only reason any of them run a smaller tires is either fitment or availability for a given diameter.

The 265 will fit on the BMW chassis and was run succesfully in STU by Mike Simanyi, etc.. It's a tight fit and requires the exact offset and max allowable fender clearancing modifications, which most people don't do because of the cost and trouble. Once the STX-BMW owners start getting whipped and are serious about winning they'll make the jump or else.

Fine - you found that 9" is an more optimum rim fitment for a 265 than a 10.5. I suspect you would have found the same for an 8" fitment - it would have been slower than the 9" for the 265.

But, anyway, you misinterpret what I am saying, which is that a narrower tire with a superior compound could be faster than a wider tire with an inferior coumpound, particularly if the rim choice favors the narower tire. I'm not saying it is true as a rule, but I could see it happening.

You are stating that for STX, the 265 will be the fastest setup, all other things being equal (i.e., rim width & compound) and that is likely correct.

I didn't say 9" was optimum, the difference was there, but not to the degree that is being suggested

as one example, consider the weight difference between the two wheel widths all else being equal

there are other impacting factors too

I would have gladly chosen a 285 or 305 width tire on the wider wheel had the rules permitted such

I guess you guys missed the part when the OP said "track", not "autocross". Going with a wider section tire than the rim width will support (in terms of sidewall profile) is a completely different ballgame on a track car, compared to Solo. The turn in characteristics can be compromised to a degree that not only will the driver lose confidence, the tread squirm can also set up some strange oscillation of the tire's surface, physically unsettling the car. Heat management also becomes a bigger problem, as that same tread squirm can lead to greater temps. And the wider tire with the bulging sidewall will also have a big negative effect on terminal speeds on straights.

Yeah, for autocrossing the '8, a 285 section A6 is about as good as it gets, but for track use, my guess is I'd prefer a 245.

Good point.


No doubt.

Yes, you are correct - this thread was about track performance. Got nats on the mind, I guess.

except that you're guessing

I suppose you missed the part that most of the road race classes that specify DOT tires also specify sizes close to OE, not to mention the longer, higher speed sweepers and minimal transitioning as compared to autocross, and a wider tire will heat up less than a narrow one for a given weight loading, ad nauseum

you don't think the Koni Challenge teams would run a wider tire if allowed by the rules?

take another guess .... ;)

I'm only guessing in regards to the RX8, but I have real experience with other cars (including FV/FF). You reach a point where sidewall control trumps section width in a road racing application...which will also include heat and distribution of heat in the tread surface and tire carcass (that movement of the tire over the rim causes some notsogood heat localization probs), besides the tread squirm/movement over the rim issue. (edit, I forgot the next point before) And we haven't even determined what has happened to the contact patch, as the tire is being squished....the contact patch gets wider, but "shorter", so lateral grip may go up, but longitudinal contact patch is compromised (like, braking, which is much more important in road racing). Loss of top speed is also something to consider. We lost nearly 4mph on the vintage FV car when going from Goodyear FV slicks to Dunlops that were only .5" wider...of course, that was with 65hp to play with and that was also an open wheel car, of course...

I think the Koni Challenge teams might run a wider tire if allowed, up to a point and within reason, but you're guessing there, too. There's no way they'd run the type of section width to rim width that we run in Solo, I'd be willing to bet you. How can we find out?

Well Toyo only have couple of 100.000 test hours but you probably know better... ;)

Can you please stop with your "ass kicked, clock cleaning" it dosent help arguing your cause.

I respect your point of view even if I dont agree with you and that without denigrate you.

I do have hands on experience myself, you do know that there are a world outside your bubble?

235 or 245 wide tires on a 9" wheel will provide the best restults. You could say our "stretched" mentality sucks but what about your "bigger is better" one? ;)
265 wide semislicks with a close to stock car and stock rims is not an option to consider if the location is a track. While tracking the car sidewall flex and excessive resistance are a complete waste of time.

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

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

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.

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.

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

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.

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

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

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?

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!

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! =)

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.

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

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...

I think we are saying the same thing now?

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.

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

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

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

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+