Since OP is chiming in, I feel less bad about derail

SSP would be fine if they had a version that didn't involve large r-comp tires. As it stands, I can't do much to the car unless I also want to spend tons of money on tires. Recurring costs of running SSP are too expensive for me.

 

Thats the consensus I hear from many people right up until they get beat by a c5z on the "wrong" 275/295 rival setup. I have beaten several of the 335 square shod cars at both auto-x and road course, and I expect to beat more of them later on down the road with more upgrades to the overall car/driver package.

While there are certainly drivers/situations where the huge by wide setups with 315/335's are faster, I'm convinced there are also situations where the narrower overall car on 285's is faster.

With that being said the corvette is one of the easier cars to stuff huge by wide rubber UNDER the car but nobody in the USCA type events is persuing that route yet that I've seen.

Except Hobaugh. that gorgeous monster tucks all its tire quite nicely

 

295 Rival vs 285 RS3 is a wash IMO, toss a coin in that case or look at contingencies/pricing/availability. 335 Rival vs 285 RS3, on the other hand, is a big difference but like you said you need the car/driver package to support it. I've "beaten" people on Hoosiers while I was on street tires, but I'm not about to claim that it was because I had better tires.

Also thanks for the info on global time attack series, I like their "enthusiast" class rules so far. Don't know if anything like that exists in the Northeast but I'll look around.

 

If you have a choice between compound and width, go for the sticky compound. I've been testing seriously since 1988. And that means real testing with data sheets to record every variation and then back to back runs with a baseline tire to try to factor out learning and change of track conditions. We used to test for three and four days at a time with people who do this for a living at the major auto companies.

I've tested every thing up to the A6 and found that once you have "enough" width for the weight of the car, adding more rubber didn't make much if any difference. Sometimes the really wide tires (like up to 315's all around on a C4) made the car feel rubbery, but it wasn't an faster and the clock doesn't lie.

One year at Nationals a DSP BMW 325 was just as fast as the winning BSP Corvette, (and that was no slouch car either, driven by Guy Ankney). The BMW was on 225 Hoosiers and the Corvette was on 315's. I watched the Bimmer and he was absolutely hooked. So a BMW on 225's can beat a BSP C4 that was built to the max, it all depends on how much tire you need and how it gets used.

What I'm trying to say is that compound determines the final friction coefficient, or the amount of grip. Putting on a bigger set of tires that don't have as good a friction coefficient won't normally get you there in my experience.

All that said, you need to have "enough" tire to get the job done, and every tire is different. Some tires have a lot of crown and you might need more of that tire to get "enough". Other tires roll over more and you might need the right rim width to get them to work. Some tire and rim combinations let you run lower pressures and improve the footprint, while others can cause you to have to increase pressures, and while that makes the car sharper, it can result in less grip than other combinations.

In addition, even though one tire in one size works really well, the same tire in a different size may not work worth a crap. Way back when the Yokohama A001R was developed for an RX-7 showroom stock series in Japan in a 13 inch version. That tire and it was always better than the same tire in a 14 inch size. BFG developed their "Salina" compound tire on Roger Johnson's 16 inch wheeled Corvette. It took years before the 17 inch cars had as good a tire from BFG.

The only way to know for sure is to test and try. And you have to try the range of sizes, pressures, and setups that optimize the car for that tire or you are wasting your time. If you can't do that or won't, then look at what works for other people and copy that.

The introduction of the 200 tw tires changes the game and the baseline, but as always, some folks will, sooner or later figure it out and in time you'll see people really hauling the mail on 200 tw tires and they are the ones who did the work spent the time and money, and got the jacket to show for it.

JMHO and qualified as such.

 

That's a very well written explanation. +1

 

While I don't have much autocross experience I would think that too much tire would be a detriment since given the limited amount of time run, a wider tire will never get to its optimum operating temperature.

 

I agree, up to a point. With the BMW, I am sure there were more variables than just tire width.

If we are comparing apples to apples here, a 285 R888 on a 3100lbs C5 will not be as fast as a 315 R888 on the same 3100lbs C5 setup (unless its a fast track where top speed is critical).

Comparing tire sizes or compound is one thing, but throw in different tire compounds at different sizes into the equation and its a pointless argument. You want the best compound and the most rubber. (within a reasonable balance of scrub radius)

 

I'm sure there was more to that bimmer than just the tires, but my point was that there's a lot more to it than adding wider tires. My point was that the Bimmer was just as heavy, not as wide, didn't have as good a front end geometry, didn't have as good acceleration, and it was still just as fast. My point is if you are really hooked up you'll fly and when you find that sweet spot in the setup it's pretty amazing.

We tested back to back V710's on the front of my Z06, and the 275's were just as fast as the 295's. The 275's were a bit sharper, but the clocks couldn't find and difference between the two tires. 275's were big enough. Once you have "enough" tire you just don't gain much going wider. You would think that the 295's, being almost an inch wider would be faster, but they weren't. There wasn't any more grip, and we couldn't add any more front roll stiffness, even with the wider tire it just wouldn't hold it.

I don't know about the R888's since I haven't tested them. These cars like more tire on the back and could well be faster with some more width back there and that may indeed help. Since the Z's used 295's as the OE size going down to 285's may well result in the back end being "under tire'd". That's why you have to test. Generally you don't want to go lower than the OE size since that often results in not having enough tire to do the job.

But the question from the OP is would the car be faster on a narrower tire with a better compound or a wider tire less sticky compound. Since the stickiest tire in 200 treadwear class aren't available in the necessary sizes for a C5Z, he's trying to figure out what is likely to be faster, a slightly narrower tire with a better compound, or a wider tire that isn't quite as sticky. It isn't pointless at all. He wants to go as fast as he can within the rules and the tires that he can buy. His choice is a bit less tire in a stickier compound, or a wider tire that isn't as sticky. Neither is the optimum, but the optimum doesn't exist so he's trying to figure out what will be the best choice. And the answer is he probably needs to test both and find out. I'm just saying that if you can get enough tire then the sticky tire wins. If you don't have enough, the wider tire wins.

Also I'm prefacing my comments for autocross since that what the OP was asking about. Track sessions and races are different altogether since overheating and the tire going off is an issue that isn't often present in autocross. It's generally wise to upsize a bit from the optimum tire for tack duty since tires going off by the end of a session or race can ruin your fun.

 

With Midwestern Council You can run a C5-6-7 in Super Street . Almost unlimited rules ,but a 140 tread wear tire .The C5 can also go in the X classes .

 

That is interesting. From all of the data my buddy and I have collected, the wider tires always post faster lap times, even when steering scrub radius is effected. The only time we have seen a wider setup negatively effect lap times is when it effects bump scrub radius on rough tracks (Sebring). Even then, it becomes more of an issue with driver confidence than car capability. The only thing we noticed was the driver swore the car was slower due to the way it responded to driver input and approached the limit, but the times showed otherwise.

Not to mention the cost benefit of running larger tires due to a reduction in tire wear.

Granted, as you stated, I think I am commenting in the wrong thread, as it is based around autocross. The data I have is on much longer tracks, higher temps, and longer stints.

 

You hit the nail square on the head thats exactly what I'm asking!
also thank you for stating that your comments were about auto-x which is my primary focus.

This is good info as well and not at all pointless, it's been somewhat eluded to but one of my main goals for this exercise is to compete in the Optima Ultimate Street Car events which have both an auto-x and a road course portion. They also have a speed stop which in my mind is more similar to the auto-x than the road course. So with 2 of the 3 timed portions being autocross esque I'm trying to optimize the setup to be as effective as possible there, while still having the flexibility to adjust for track duty.

In addition to that a local group has setup a time attack series which I'd love to participate in to help hone my road course driving. The street tire class has a 285 width restriction which would suit the RS3's perfectly.

I'm going to try to source a 2nd set of wheels over the winter so that I can try to do some back to back testing with my current BFG setup compared to the RS3's.

Thanks for all the comments so far guys!

 

what a great thread. I'm somewhat in the same boat as well, debating between 285 RS3 vs 295 Rival. I ran SCCA A-street with Rival this year and wanting to try RS3 in 2015.
I really appreciate all of the opinion and inputs in this thread.

So, why do I keep hearing *CURRENT* compound of BFG Rival? Are there any talk of revising compound for Rival in 2015?

 

I know smaller tire cars (spec miata, chumpcar) are having problems with delamination, so I wouldn't be surprised if they are doing compound revisions.

I am running 315/30/18 square and have had no heat related issues.

 

More than talk, pretty much a certainty.

 

All else being equal, more rubber down is typically better. However, all else is NOT equal.

Depends on which tires you ran. How wide "wider" is. There is a difference between say a 275 to a 295 vs. a 295 to a 315 (just making up sizes here as a for instance) on a 9.5" wheel.