The Official C8 Corvette Thread...

[MX793]

I'm not sure if the PS4S is actually any stickier than the PSS tires. I recently had the PSS on the G37 and just replaced them with PS4S as they are discontinuing the PSS in the G37's size, and the PSS was probably stickier and more aggressive at the limit, but the PS4S supposedly wears better and has better everyday manners (feels very similar around town). 

In addition I wouldn't be surprised if Chevy toned down the aggressiveness of the GM specific tire compounds for the new PS4s compared to the PSS for the C7s, as people experienced tire cracking in the PSS tires when moving C7s around at cold temperatures.  It is somewhat tolerated for Cup 2s for the Z06 and ZR1, but less okay for the supposedly street PSS tires for daily driver C7s.  It would explain the lower lateral G's achieved by the C8 compared to the C7.

That said, off the self, non GM OEM PSS like the one on my C5 Z06 and the G37 never experienced any cracking even down to very low temps (temps in the teens) in my experience.

I think part of the big complaints of the Z06 ZR1 C7s was their tail happy nature and inability to put their power down, while the C7 grand sport was the sweet spot in the C7 line-up.  I think GM this time shifted to optimize the chassis for the higher HP cars rather than the base cars.  Supposedly this new C8 structure feels extremely solid and stiff, and it can definitely put the power down.  Expect to see some ridiculous performance numbers with the higher HP versions.

My understanding when I was looking into the PSS vs newer PS4S is that the dry performance is essentially the same, but the 4S has noticeably improved wet performance and longer wear/life.

[565]

Don't forget about the different tires

https://www.motortrend.com/cars/bmw/m2/2017/2017-bmw-m2-review-long-term-update-4/

Different days for those lap times so they are not comparable.  the PSS times were in 95+ degree weather so the M2 probably was way down on power that day.

https://www.motortrend.com/cars/bmw/m2/2017/2017-bmw-m2-review-long-term-update-2/

The PS4S test was posted in Dec so temps were probably more reasonable.

The numbers don't lie. The PSS pulled the same .99Gs and the PSS was just barely faster in the figure 8 than the PS4S.  The PS4s aren't any better in the dry than the PSS. 
As someone that had PSS and PS4s on the same car, I can tell you the PS4s are no better than the PSS for dry performance.

[r0tor]

Ps4s isn't better laterally - they are much better longitudinally (ie braking/acceleration) which is suspiciously where C&D notes the biggest C8 advantages

[MX793]

Ps4s isn't better laterally - they are much better longitudinally (ie braking/acceleration) which is suspiciously where C&D notes the biggest C8 advantages

Except braking was worse than the C7 as recorded by both C&D and MT.  Might have been brake system calibration (ABS, and the C8 is brake-by-wire) rather than tire limited, though.

[Galaxy]

https://www.caranddriver.com/reviews/a29462701/2020-chevy-corvette-by-the-numbers/

Bravo GM

"But normal driving also is where the C8 gets tripped up by elevated expectations. More than a few of us were hoping for more character, more drama, and more personality when we weren't hammering it. Ferraris and Lamborghinis snarl at you like caged tigers even when you're just moseying through downtown. "

Actually, I would rate that as a positive that it does not pretend to be flying down the straight at Le mans if in stop and go traffic in LA.

[12,000 RPM]

If you're going to track it occasionally it is.  Why get a GT350 otherwise.

You can enjoy RPMs on the street

[giant_mtb]

Corvettes have always been pretty tame at normal road speeds.  Those big American V8s don't have to work their asses off like the Ferraris and Lambos do to drive normally. 

[FoMoJo]

You can enjoy RPMs on the street

Yes you can, but by the time you're in second you're over most speed limits.

[Eye of the Tiger]

Yes you can, but by the time you're in second you're over most speed limits.

Unless you're driving a 4 cylinder Dakota

[FoMoJo]

Unless you're driving a 4 cylinder Dakota

Yes, I should've qualified that...if you're driving a GT350.

[CaminoRacer]

Yes you can, but by the time you're in second you're over most speed limits.

The El Camino is that way too.

[Xer0]

Less then a second doesn't seem that impressive considering it has the newer chassis, about 40 extra hp, better tires, and presumably a better transmission.  We'll see what the higher spec cars look like.

[Laconian]

That 0-60 time is insane. I guess going midengine was the only way to keep the Camaro from cannibalizing Corvette sales.

[MX793]

Less then a second doesn't seem that impressive considering it has the newer chassis, about 40 extra hp, better tires, and presumably a better transmission.  We'll see what the higher spec cars look like.

Except it doesn't have better tires (unless the track is wet).  It's also heavier, which offset most of that power increase.  Power to weight ratio is only 1.9% higher for the new car.  And while I'm sure the DSG is "better", the 8AT (which is what C&D's C7 was fitted with) was no slouch.

The brakes are also reportedly weaker.  Might be a calibration issue with the ABS sensitivity.

[Eye of the Tiger]

Performance, smurformance. So it's fast. But the interior is ugly as hell.

[Xer0]

Except it doesn't have better tires (unless the track is wet).  It's also heavier, which offset most of that power increase.  Power to weight ratio is only 1.9% higher for the new car.  And while I'm sure the DSG is "better", the 8AT (which is what C&D's C7 was fitted with) was no slouch.

The brakes are also reportedly weaker.  Might be a calibration issue with the ABS sensitivity.

Nothing I've read says the PS4S is a worse tire than the PSS.  Plus, the C8 is running more tire at 305s vs 285s in the rear.  That the 8A is no slouch doesn't mean the DCT isn't better and worth precious time.

I kinda was expecting more.  We'll see what happens at LL2020.

[Payman]

 M/T:

"Severe understeer will help prevent the overeager owners from pulling a Mustang exit at their local cars and coffee."

[MX793]

Nothing I've read says the PS4S is a worse tire than the PSS.  Plus, the C8 is running more tire at 305s vs 285s in the rear.  That the 8A is no slouch doesn't mean the DCT isn't better and worth precious time.

I kinda was expecting more.  We'll see what happens at LL2020.

P4S isn't worse, but it doesn't provide more dry grip either.  PSS vs P4S on dry pavement is a wash.  And more tire on the rear doesn't necessarily mean more corner grip.  The fronts are the same width.  Too much tire at the rear can lend to an understeery setup, hurting balance.

The difference between shift times in a DCT and an MT are huge, which is where a lot of the performance gains come from.  An MT typically takes about 500 ms to shift.  A DSG will be closer to 100-150 ms (some as quick as 60, but most are between 100 and 150).  A good AT can be as quick as a DSG, and the 8AT in the C7 was benchmarked against Porsche's PDK and actually shift more quickly.  So shift times probably aren't meaningfully different between the two gearboxes.  There may, in fact, be no difference in shift time, and therefore no measurable performance advantage.

[12,000 RPM]

Less then a second doesn't seem that impressive considering it has the newer chassis, about 40 extra hp, better tires, and presumably a better transmission.  We'll see what the higher spec cars look like.

You are looking at the change the wrong way. It's 25% faster to 60, which is a shitload given the minimal changes made.  It's like if a truck goes from 12MPG to 18MPG. "Thats only 6MPG, what's the big deal"... bro that's a 50% improvement, that's huge. And in the context of performance cars, it's a rocket.

[r0tor]

P4S isn't worse, but it doesn't provide more dry grip either.  PSS vs P4S on dry pavement is a wash.  And more tire on the rear doesn't necessarily mean more corner grip.  The fronts are the same width.  Too much tire at the rear can lend to an understeery setup, hurting balance.

Every comparison I have seen points to the Ps4s putting up better stopping and acceleration numbers.  Lateral grip is about the same but longitudinal is significantly improved.

[MrH]

I just hope this kicks off a new era of mid engine cars.  Bring back the MR2!  Next gen S2000, make it midengine!

[Xer0]

You are looking at the change the wrong way. It's 25% faster to 60, which is a shitload given the minimal changes made.  It's like if a truck goes from 12MPG to 18MPG. "Thats only 6MPG, what's the big deal"... bro that's a 50% improvement, that's huge. And in the context of performance cars, it's a rocket.

Its 25% faster to 60 but only 1% faster on track?  This isn't helping your argument.

P4S isn't worse, but it doesn't provide more dry grip either.  PSS vs P4S on dry pavement is a wash.  And more tire on the rear doesn't necessarily mean more corner grip.  The fronts are the same width.  Too much tire at the rear can lend to an understeery setup, hurting balance.

The difference between shift times in a DCT and an MT are huge, which is where a lot of the performance gains come from.  An MT typically takes about 500 ms to shift.  A DSG will be closer to 100-150 ms (some as quick as 60, but most are between 100 and 150).  A good AT can be as quick as a DSG, and the 8AT in the C7 was benchmarked against Porsche's PDK and actually shift more quickly.  So shift times probably aren't meaningfully different between the two gearboxes.  There may, in fact, be no difference in shift time, and therefore no measurable performance advantage.

This is a car that's heavier, more powerful, and has more weight on the rear in general.  I doubt GM would put more rubber on there to dull the car and 305s is what Porsche is running in its 911s so while more rubber can make your car a bit of mess this isn't the same as a kid putting 245s on the front of his base Civic.  Also, the track article mentioned how the car was secure and planted, going so far as to say its boring (car reviewers are never happy man) while the C7 was twitchy.  Maybe the C7 needed more tire in the rear to keep it in check 

As for the DCT vs 8A, even assuming the 8A is a decent transmission, the DCT would presumably be better since its a newer design and there would be no point in it if it didn't provide some improvement.  Its worth time on a track and all of these add up.

The C8 accelerated faster, hit faster top speeds, and braked later into turns but it couldn't really shake the C7.  Z51 to Z51 just doesn't seem like that big of an improvement from a pure performance standpoint, and this was a track that looked to favor higher hp cars anyway.  We'll see when they take it to Lightning Lap next year how it does and how it compares, but right now the big performance improvement of this new chassis might just be at the higher spec Z06/ZR1 cars.

[MX793]

Its 25% faster to 60 but only 1% faster on track?  This isn't helping your argument.

This is a car that's heavier, more powerful, and has more weight on the rear in general.  I doubt GM would put more rubber on there to dull the car and 305s is what Porsche is running in its 911s so while more rubber can make your car a bit of mess this isn't the same as a kid putting 245s on the front of his base Civic.  Also, the track article mentioned how the car was secure and planted, going so far as to say its boring (car reviewers are never happy man) while the C7 was twitchy.  Maybe the C7 needed more tire in the rear to keep it in check 

As for the DCT vs 8A, even assuming the 8A is a decent transmission, the DCT would presumably be better since its a newer design and there would be no point in it if it didn't provide some improvement.  Its worth time on a track and all of these add up.

The C8 accelerated faster, hit faster top speeds, and braked later into turns but it couldn't really shake the C7.  Z51 to Z51 just doesn't seem like that big of an improvement from a pure performance standpoint, and this was a track that looked to favor higher hp cars anyway.  We'll see when they take it to Lightning Lap next year how it does and how it compares, but right now the big performance improvement of this new chassis might just be at the higher spec Z06/ZR1 cars.

MT noted that the car understeers heavily at the limit.  I'm sure the father rear tires contribute and that trait was intentional since mid-engine cars tend to be prone to snap oversteer otherwise.

As to DCT vs 8AT, the advantage of a DCT vs a fast shifting AT is not quantifiable in singular lap times or drag strip runs.  The advantage is in sustained performance.
One big advantage of a DCT is heat.  ATs generate more heat, which can be a problem in sustained lapping because the trans can overheat unless you carry a bunch of extra coolers.  The advantage of the DCT is much the same as oversized brake rotors.  If you have enough brake power to lock the tires, a bigger rotor won't help you stop any faster.  It will, however, handle harder sustained use before overheating.  Hence why many performance packs include bigger rotors as an upgrade.

[CaminoRacer]

I think the fact that the base C8 isn't much faster than the C7 is more of a testament to how well they engineered the FR C7, not that they screwed up with the MR C8.

[r0tor]

https://www.motortrend.com/cars/chevrolet/corvette/2020/2020-chevrolet-corvette-c8-vs-2020-porsche-911-comparison-test-review/

I think it's telling that the Vette is new and has room for a bit more improvement in future years/models.

[r0tor]

I think the fact that the base C8 isn't much faster than the C7 is more of a testament to how well they engineered the FR C7, not that they screwed up with the MR C8.

This... It's a maxed out platform vs one that's still in development

[12,000 RPM]

Its 25% faster to 60 but only 1% faster on track?  This isn't helping your argument.

I thought you were talking about 0-60 times. But yea 1 second over a ~90s lap is still pretty big considering how evenly matched the cars are in spec.

[565]

Nothing I've read says the PS4S is a worse tire than the PSS.

Actually people have noted the PS4S is a worse track tire than the OEM PSS in C7 Vettes.

https://www.youtube.com/watch?v=X18tjycJoqI

This guy went from OEM PSS to PS4S on his C7 and had significantly worse performance.

Its a discussion that comes up in the Vette forums.

https://www.corvetteforum.com/forums/c7-general-discussion/4200073-pilot-super-sport-vs-pilot-sport-4s.html

https://www.corvetteforum.com/forums/c7-general-discussion/4018012-michelin-pilot-sport-4s-4.html

"It's actually a downgrade, and no ZP. Multiple folks have reported slower track times on the PS4S. I know there are tire site reviews out there saying PS4S is an improvement over the PSS, but those are reviews pertaining to many different types of vehicles and are not usually performance-oriented. It just so happens that the special version of the PSS ZP Michelin and GM engineered for the C7 works better in terms of handling and grip."

"I think others are seeing the opposite, AKA an advantage of the PSS ZP on race tracks. There was a detailed account here within the last couple of months where someone w/ significant track experience was reporting worse laps times on the PS4S."

"Any one else seeing less grip from the MP4S on the street compared to the stock MPSS's? Granted I only have about 300 miles on them since the install on my 14 Z51 but I'm getting the TC system kicking on around corners that really worn stock MPSS's had no problem with. Does it take about 1k miles for the tires to get broken in?"



The reason is that the C7 runs vette specific PSS compounds, that allows it to achieve 1.11gs while non Vette specific PSS tires don't achieve the same grip.  The trade off is that the same Vette specific PSS tires will crack at low temps while the regular PSS tires do not crack at these low temps.

GM often specifies special more aggressive compounds for their OEM tires, and this puts this prone to cracking.  There is a service bulletin for it, and you are not supposed to even move these cars under 20F.

https://static.nhtsa.gov/odi/tsbs/2016/SB-10082862-5448.pdf

I'm not sure if the C8 also runs special aggressive compounds as well on the PS4s, however I would not be surprised if they decreased the compound aggressiveness to closer to a stock PS4S tire given the number of complaints that people had with the OEM PSS runflats cracking in the winter.

That, and the purposeful understeer would explain the reduced lateral G's pulled by the C8 compared to the C7.

[r0tor]

Umm "ZP" in Michelin land isn't some super secret compound - it's a "zero pressure" run flat

[giant_mtb]

Umm "ZP" in Michelin land isn't some super secret compound - it's a "zero pressure" run flat

What's your point?  A run-flat is going to have some sort of different construction than a non-RF, presumably affecting performance in some way.