This is perhaps not an issue for most track/auto-x type situations where you can get any/all compounds in the size you require.

However in my specific application (200tw or greater, unlimited width) is a bit different.

The wheels for this exercise are square 18x10.5 Z06 wheels

From the current crop of tires the Pilot Sport, Falken RT615k and the BFG Rival can be had in a 315/30/18

while the RS3 only goes up to a 285/35/18

and at an even shorter option the Star Spec Z2 only goes up to a 285/30/18 which is a tiny 24.8" tall tire.

Given that the RS3 is generally considered to be faster than the Rival would you still choose it when you have the choice of stepping up the width that drastically? Tirerack lists the rs3 at 10.1" of tread width vs 12" for the Rival. Is that enough extra width to overcome the compound difference?

 

Based on the selections you have listed. I would go for the larger size. The RS3 is not that much better to give up 30mm of tread width.

 

The 285 is WAY wider than the Tire Rack specs. Unless you want to test back to back, there is really no way to know. I think the 285 would fit well on that rim. I think a 315 might be a little much. I know people do it, but I'm more of a fan of proper tires/wheel sizing versus most.

If you plan to do STU in SCCA, you have to go 285. If there are other forms of racing you want to do that dictate one size over another, I'd go with that. If you're on a budget, I'd make that the deciding factor.

 

While, some would disagree with the claim the the R-S3 is faster than the Rival, nobody would disagree that the 315 Rival would offer significantly more grip than the 285 Hankook. It would not be even close

 

Has anyone tried Rivals out back, RS3s up front? Tire mullet

 

Well the first two mentioned just aren't fast enough for what you do Brad. So really this is between the Rival and the RS3.

Further we are back to thing that's in the other thread about width of tire vs. width of rim and all things are not equal. I'd personally be on Hankooks due to compound differences. That might well change next year, but as of now that's what I'd do.

 

I might disagree with that. Yes the BFG is wider but it's shown 12" of tread is measured on an 11" wheel and he has 10.5's. The Hankook's 10.1" of tread is measured on a 10" wheel. Figure that when the BFG is squeeze is crowns some and when the Hankook is on a wider wheel it plants better. And we know that the each tire likes each of those things respectively.

Like usual Lane and I are on a similar page. You don't know unless you try. I just know that the Rival is what it is and what it was said to be when it debuted (I was there too), which is not the fastest tire, but one that can make hero's out of zero's and is tolerant of mistakes. It is that to a point. But it depends on the car and the surface. Fact is the RS3 works better than the *current* Rival compound on more surfaces and on more cars.

Rivals are great on nose heavy, limited camber things. I suspect the ZII SS will be pretty fast as it had stiff construction but a bit of a compound issue for stiffer cars with power. Now that it's still stiff and has a softer compound, well that's more like an R-comp we know and might prove to be a good thing, *if* they aren't too stiff when on the 10.5" wheel. But again it's one to think about testing. Softer compound, shorter tire (helps gearing and lowers the Cg for free).

If I was running Optima stuff in my C5, I think it'd be on the list to try for sure, but more likely it would come down to the rims I ran which I'd try first. Being I have a FRC with stock wheels 8.5/9.5 I'd likely try Dunlop first in 255/285. I'd try the same size in the RS3 on Z06 wheels first though as the wheels are wider and the Hankooks need that more and respond to it better than Dunlops which are much stiffer.

 

Not yet mentioned, but you should also factor in the difference in the weight, and rotating mass, of the tires being compared.

If the larger size is five pounds heavier, the nominal rotating mass would be approximately 4 times, or 20 pounds per corner. Eighty pounds is nothing to take lightly.

As mentioned above, back to back testing would be the best way to compare.

 

This is all great discussion so far guys! to a point it is somewhat proving what I had suspected, the wheel width is more of the limiting factor than the stamping on the side of a tire.
Lane whether this makes a difference to your remarks or not my z06 isn't STU legal so I'm not bound by sticking to a 285 width. My primary focus is the USCA events which have no tread width limit. my 2nd focus would be local TT events which happen to have a 285 width restriction for street class so the RS3 allows me to double dip there. my 3rd focus is local auto-x events in CAM which again have no width restrictions.

I was afraid that I may have to buy a 2nd set of wheels and test tires back to back for myself, of course with the suspected new tires/tread compounds that are supposed to come out this winter that "could" render most of this discussion useless if a new challenger appears.

lastly thats a good point about the rotational mass and lighter weight of the Z2* and one I haven't forgotten about, my Z06 is under 3,000lbs due to careful part selection and the extra mass I could save in the tire department certainly is appealing.

 

So the answer is: It depends.

 

Wish the Z06 had a place in ST. I believe the only thing that can't be changed on a base C5 to equal a Z06 in ST is the gearing (and of lesser significance power), which apparently is enough advantage to keep it out.

 

And the engine. Between the two that's not insignificant.

 

Being stuck with no options other than stock and full-on SSP/SSM is terrible though.

If I could go back in time and buy a base C5 or even an LT1/LT4 C4 instead of a Z06 I would do it.

AFAIK no one has a class for a lightly modded C5Z whatsoever in any autox or road course time trial competition.

 

um. Well you have SSR or A-street both. That's a lot of options really. Car can win in any of 3 or 4 classes (tougher in SSM but clearly in SSR, AS or SSP). How many classes do ya need?

The normal car is less competitive in as many places. Can win BS (and has). No R-comp stock class anymore. Also goes to SSP and SSM with the Z06 so why? And we think will do very well in STU. That's two, vs. 3 maybe 4 on a good day.

Anyway, way off track now....

 

If you put in a seat that fits a 140 lb driver you only have SSP or higher. A base car can just run STU with light mods, a Z06 cannot.

In NASA any C5 gets put into TT3 or higher which is unlimited modifications. The best Corvette to compete in both road course and autox with limited mods is apparently a C4.

To answer the specific question in this thread, though:

You want to run what Danny Popp ran at the Ultima stuff. 315/335 Rivals. Maybe even 335's up front too if you change up your front aero to accommodate them. (This is pending any new compounds being released in 2015)

 

yep, that's the way it works. No guarantee that a car can be competitive everywhere, that's how you end up with 1000 classes, and part of the issue now.

As for the Rivals. Be careful. There are certain reasons that some folks run what some folks run.

 

I know, I'm just bitter that my plan A was taken away by NASA and then plan B was taken away by SCCA (CAM class). Now I just lose no matter where I go... oh well, it's not like it's pro racing anyway.

I just remembered that this discussion is somewhat pointless: The 315/30/18 BFG Rival doesn't really exist anymore for sale and AFAIK is out of production. The only way to get a set would be to find a NOS set laying around in someone's basement/warehouse.

With the 10.5" wheels the best in-stock choice is the 285 RS3's, but expect to be beaten by people with 12" wheels and 335 Rivals.

 

You mean a C6Z or GS? Um, that's a stretch. Remember the cars aren't as well balanced in slow stuff due to the rim disparity, and have other small issues. I'll tell you right now if all I cared about was pure speed on as many courses as possible I'd not have a C6 I'd have a C5Z. It's smaller, shorter and just a touch better all around. However, I love my C6Z and am willing to live with the shortcomings. But having sold my GS to a guy who went to A-street with it on 335/18 Rivals, and having driven it since.... I'd much rather be in a C5Z on Hankooks at this point for A-street.

 

not to derail the thread any further but a lightly modded C5Z on 285's could run in the global time attack series in the lowest class. I'm unsure about your area but locally we have a time attack series that mimics the GTA series and mildly modified Z06's do quite well there also.

 

He's not running SCCA, he said unlimited width plus 200UTQG on a C5Z - that doesn't exist in SCCA.

I was assuming an Optima-style ruleset, so a decent amount of weight toward high speed performance and the ability to build the rest of the car around the giant tires. (and the competition is doing exactly that)