X25

I think I could get to 1:48s, yesterday, if this excessive vibration issue did not happen. I will definitely try my chance again, next time.

As you also alluded to, I'm not fully acclimated with this car, yet. That said, I can easily say that all those reviews that said Z06 is too tail happy, or has too much power for the chassis, etc. are all false. Both with R888Rs and R7s (the only two tires I tried this car with at the track, so far), I had no trouble putting the power down, and never got scared about where the car is heading : )

Re: R888R vs. R7, I think there's more to it than just the difference in traction. I have come to learn with my Z51 that you really need to match the traction/tires with your suspension, or else the car will not feel right at the track, which rubs your confidence. Something new that I'm learning these days is the difference in how the behavior of tires change as they start overheating, etc. With R888R, you can still make similar lap times later in the day when temps climb higher, but the major difference seems to be at how it behaves at the limit. It provides great feedback in the first few laps or when it's cold out, but at some point, it becomes greasy at the limit, even though overall traction is impacted less. This also means, the tire likely makes it easier to wreck the car as it overheats. I notice this behavior in most tires, especially street tires, but R888Rs had it more than I'm used to among the track oriented tires. Considering all these, barring the noise issue, I think R888Rs are excellent street tires for me, and that's where I want to use them. In fact, I'd like to say that MPSS ZPs were very disappointing at the street (and Seattle is likely not warm enough for them to work half the year).

Re:GS build, if you drop in a 600 whp built engine in there, switch to Z06 gearing, I'm not sure if it's any lesser version now, both in terms of cost, and power : ) If you keep investing, I'm sure you can hit your targets at some point, but you'll likely have something that will sell for much less than your investment, which begs your question.

Indeed, sidewalls add to the wheel spring rate, so we need to be careful! Track tires typically come with stiff sidewalls, which reduce their impact, but it's still significant. I wonder how Pirelli's sidewalls are (stiff vs. soft).

Back when I had the Z51, switching from 275 NT01s at front to 315 NT01s was a massive change. In fact, it had so much more traction that it overwhelmed the stock springs/suspension, and forced me to switch to coilovers, which itself transformed the car. After experiencing all that, I can't see myself using anything less than 315s (or 305 slicks) up front on any C7.

I tried 315/30/18 335/30/18 R888Rs on the Z06 at the street, and they worked well. Later, I sold the wheels/tires to my friend, and he made great lap times with it at Ridge Motorsports Park with these tires. Keep in mind, though, the overall gear ratios will be reduced (shorter) and the speedometer will show a bit higher speeds than actual (~%3) : )
His video using the 315/335 18" R888Rs..

lobsterroboto

Just gonna throw this out there... .5 second difference between R888R and a Pilot super sports tells me less about the tires than it does about the driver.

BrunoTheMellow

Have you driven a z51 with the super sports ZPs from 1 track day to the next to the R888R? Of the same width? Probably not. I have. I can assure you in a stock suspension z51. The r888r was not much faster than the super sport. On a best lap comparison. Now a full session, yeah the mpss starts going away. But the mpss zp has to be a different compound than the mpss normal. It is a very good tire for what it is.

Hell, my friend just drove a z06 to a 2:24 today on supersports with 3 rivers going through the track. That was his time ever driving a c7 corvette. Granted he knows the track and has hit a 2:23 on his Zl1 1le (good conditions). MSR cresson that is.

X25

My 2 cents: That's actually the issue with the stock suspension. When you put on anything with higher traction, it starts excessively leaning, limiting what you can do with the better tire. In this case, I'd blame the suspension tune : )

lobsterroboto

I drove exclusively on the PSSZP for a year and a half before ever using any R comps on my car.

I've driven on PSSZP and NT01s on the same day very similar widths but not exact and I've driven on different days the R888R
Also, Pirelli slicks, Hoosier R7's, Proxes RR etc.

I'm not sure why this is even up for debate. PSSZP is just not as fast as an R888R period. a .5 variance between the two is certainly down to the driver not taking advantage of the R888R.



FWIW A stock cayman GT4 goes 2:19 around the same circuit. Hell a GTS2 prepped mini cooper will do it in 2:22

BrunoTheMellow

I don't think many people have gone from the pss zp to any r compound on the same sizes. That's the thing. Usually people jump up sizes and do other mods in conjunction.

I also tried hankook rs3s (which are supposed to be somewhat good) in the same size and lost 1.5 seconds to the zps. This is on the 1.7 which I got some 800 laps on.

maybe I didn't push them to the limit and still didnt trust the extra grip but any time someone talks bad about the c7 super sports it's because they are overheating them or expecting them to last a full session with no cool down.

lobsterroboto

PSSZP is a phenomenal tire imo and the very best in its class. I can totally see losing time on the RS3 ez. You're also damn right that they turn to **** if you push them for the entire session.

Poor-sha

My reason for going with the GS was to save weight and therefore consumable costs. I haven't reached my Z06 times yet but I'm also on essentially the same suspension and brakes but with less aero, worse gearing, and 200 less HP. I guess we'll see how my experiment pans out but my goal is to have a car with competitive performance to the ZR1 but about 400 lbs lighter. Cost wise it'll probably be a wash and yes resale will be very tough so I'm in this car for the long haul.

X25

Well, I did that, too, and invested in my '13 Mazda Miata way beyond I can ever dream of recouping. I'm definitely in that car for the long haul. It'll be ready, soon, and I'll see if I can beat my Z06 lap times with 2600 lbs, 300 whp, and 285/30/18 R7s all around.

It's currently at the body shop, getting wider fenders:



Good luck and have fun with your project!

fatsport

I think you’re build goes way beyond costs - this is the ultimate C7 track car. When I’ve run with NASA I’ve seen a lot of great C6Z builds with the same attributes- big N/A motor, lightweight, efficient aero, close ratio gears.
People have said GM went to the ME because the front engine platform was maxed out. I completely disagree that it was maxed out, ZR1 is way too nose heavy. This is maxing it out👍

Be awesome to see the ultimate Miata build duke it out with the GS-R. I think the chassis’ would be close but the Miata would need a few more ponies to run with 700 hp. Would be a great race.

X25

Checked out how much the tires spinned on the wheels. My finger indicates where the valve stem used to be by. I used a green marker, which doesn't show up on pics, so I pointed myself.


LF


RF


RR


LR - massive move!


A pic from the weekend; it was fun, and there were only 6 cars at the track.

BrunoTheMellow

Are you seeing any fender spat wear on this car?

daleong

Just as information, I talked to one of the Corvette Michelin tire engineers and the PSSZP was made with much of the same technology used in the Sport Cup 2's - but with more tread depth for longer life and hydroplaning resistance. Also it has a specific tread compound designed/mixed for the Z51.

fatsport

I think a big part of the success of the ZPs is the awesome footprint GM and Michelin designed into them. They used the runflat stiffness to increase the contact patch, creating a far larger one then sized. As an example here’s a 285 Cup 2 on a 10” wide wheel compared to a 305 Pirelli slick on an 11”. Just about the same contact patch.

X25

I see a little bit of rub at driver side, but none on the passenger side. To be honest, it's very minor, and I am pretty happy to see no clearance issues with these big/wide tires. If anything, I wish we could try 335 front tires like people do on C6; it would be nice to see what happens, but apparently C7 fenders are much more limiting.

BrunoTheMellow

Well if it helps. I ran a 295/30r18 on a 10.5 inch wheel with +65 and rubbed only fender liners. So you should be able to interpolate that to a Z06 offset. I don't think your 315 tires tuck into the fender under compression. Would be nice to verify without a spring. Or some other method. I think you just don't rub due to the vertical tire to spat gap. So the only limiting factor on a 335 would be the 5% extra height it seems.

X25

The spat also comes down in height as it ends. It currently only rubs (slightly) right by where the spat meets with the fender. 335 would likely touch the end of the spat, which is also lower in height, and so, lower clearance.

The Z07 comes pretty tall from the factory. Here's hoping it doesn't mess with performance too much; I've been very much enjoying low rubbing both in wheel wells, and also on the road surfaces.

X25

By the way, did I ever post the SAE corrected dyno numbers? Below is the chart from same dyno run, but with SAE correction, 3rd and 4th gear pulls. Stock + BMS filter:

tiborrules

I just had my first track day on 285/35/19 and 325/30/20 R88R's with my Z06/Z07. My car has the LG drop spindles front and rear which dropped the ride height approximately 1.3". Under hard track driving the passenger side tire rubbed through the plastic fender lip for about a 4" area. My car has 711 whp and I was driving it hard. I seriously doubt that it would have rubbed with stock suspension heights. I will be using these tires for street use as they get better traction than the sport cups. Surprisingly the rears hook pretty good considering the 711 whp. I am going to buy a second set of wheels and tires for dedicated track use.

BrunoTheMellow

285/35r19 is 1" taller than stock 285/30r19. That's the biggest reason why you're rubbing so much. You're running 1" taller front and rear tires..