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 "*** 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.