Taller in the front and shorter in the rear, are you concerned about issues? LG said the computer didn’t like when they changed sizes with 265/35 up front and 305/30 in the rear I believe.

 

It’s 4/10 taller in rear ,

 

i think what matters to the computer is the ratio of front to rear diameter. Your setup has a difference of 2.4%. I have always heard that if under 3% you are a OK, but no guarantee. The systems are getting more sophisticated, so it’s possible the tolerances are smaller.

 

Right, but stock is a 1.4” difference. I think the tolerance limit is based on fully worn front or rears vs brand new front or rears, which is 19/32 though maybe I’m wrong.

 

Someone has to be guinea pig 🐽, I’m guessing square would work but having my rears 4/10th taller should work , I will know within a few days and I will post finding

 

Why are you guys replacing the stock tires before trying them? The PS4S were designed for the car, by people that might know a little. Spring rates were set to match them, shocks, lsd, abs, brake pads, everything designed together.
Did you look at G Speed’s thread? They were faster on the stock tires than the track tires they tried. Had 2 awesome drivers try them too.

 

yes the c8 is very good right out of the box 📦 (But) 245’s up front are a joke and honestly the R71R’s are as close to a Hoosier as you can get and it’s 200tw to stay in stock SCCA classes, the 275 I’m putting up front with all the negative camber I can get will easily knock off 1 1/2 seconds on 60 autocrossing . I’m also waiting for hawk to make a dusty/ noisy ( not kidding) autocross pad like their plus’s . If like the c7 base/z51 cars the rotors can’t handle the track pads I will be looking for DBA rotors ( best bang for the buck) , as I said stock C8 is good I’m going to make it great !

 

Cool, didn’t know you’re doing autocross, I’m a track guy. Let us know how you do

 

Looking forward to your results as I like to autocross and run time trials. Hoping the C8 isn’t as sensitive as the C7, though imagine they’re not going backwards as the computer systems get more complex.

 

Fatsport being a track guy Learning I autocross you now know I’m not replacing stock tires I’m just adding another setup for car , my 2nd set of wheels are in the oven as I type getting powder coated.

I like these c7 centers better because chrome around edges - c8 cap edges are black yuk

 

My favorite feature that no one seems to talk about (and I didn’t know about until today) is tire temperature. Every car should have this and we should all feel fortunate to have it on the c8. I don’t know if any other car that has this feature.

 

I ran my own experiment. I was 2 seconds faster on cup 2s than sport 4s. The 4s are really good tires but they don’t heat as fast, they don’t give as good feedback as the cup 2s and I was able to get 2.8 60s with the cup 2s consistently and haven’t done better than a 3.0 with the sports yet. Although to be fair conditions where less ideal for my 60 tests on the sports.


I am very impressed with the sport 4s. They are better tires than I thought they would be. But the cups2s are simply a better tire for the car hands down. They should be an option and likely will be standard on the zo6. A little more road noise but who cares. Your pretty much all out with them on anyway so you can’t hear it over the engine noise anyway.

 

Any videos, track and lap times? That's interesting. 2 seconds is a lot but believable.

 

I know you said you can’t share everything at the moment, but how long was the track? Were the cup 2s more confident inspiring because of more grip and allowed you to be faster everywhere? What alignment specs did you run if you don’t mind sharing?

 

Let’s not forget the cup 2’s are 180tw and the sport 4’s are 300tw that means a lot ! Especially when it’s the same tire company. I didn’t need to see any testing to know cup 2’s are better than sport 4’s - the tire I’m going with we destroy both theses tires easily. R71R’s are 200tw but definitely are ringers ! Remember 200tw is the lowest Tw and stay in SCCA stock classes. The easiest way to find out what tires preform best just look up SCCA Nationals results and look at tires on the Podium.

 

Re71Rs won't destroy cup 2s. They are "200 TW" tires. They are much stickier than hankook rs3s which are also 200 tw. Pirelli pzero corsas are like 80 tw, but they aren't faster than cup 2s. Maybe the same speed. But they are garbage for track days, 1 lap heroes.

Ignore that treadwear number. Just listen to lap times.

​​​​if you want the best street legal tire, go with a Hoosier. If you don't want to buy new tires every track day, go with the cup 2s. If you dont want to spend a ton of money, go with nt01 or r888r.
​​​​​​

 

275's up front...

 

I will post videos after the track reopens. I don't want to get anyone in trouble. I have PDR footage on both tires. If I give the track size, everyone will know the track so for now, let's say that the 2 seconds was a good improvement but not insane based on the number and size of the turns in the track. If a track had more straights, the improvement would likely be less. The cup2s boost confidence because you can simply feel the track better through the car. I'm not trashing the 4s. They were very good...better than I thought they would be but they tend to wander inconsistently in the very same part of the track. I guess I would say that I was never totally sure where their limit was. It seemed to change both in braking and in the turns.

To be fair some of it could be psychological and some of it could be that I learned the track and conditions that day. I started on the 4s and put in 24 laps in total with 3 breaks. 6, 8, and 10. I started at 10am 62 degrees and the track conditions and temp stayed very consistent all day. It reached 64 degrees a 2pm.

I tried the cup2's next and put 30 laps on them. So I had 24 laps down before I tried the cup2. I also went in thinking the cup2 were going to be better, so I got in the car with more confidence (which was already foolishly high because I felt I knew the track with this car much better than I did 2 hours earlier). With the cup2s, they warmed up fast and once they did you could figure out where their limit was quickly and it stayed really consistent.

With that consistency, the cup2s made the car easier to drive fast. I was able to brake later and carry more speed in the turns.

I followed GM's recommendation on alignment and lowered front and rear as far as it would go.
Front - Cast +8, Cam - 3, toe .1
Rear - Cam -2.5, toe .1

 

I will concede track days the cup 2’s May beat R71R’s but I mostly autocross and cup 2’s do take a little longer to warm up for autocross and the fact the cup2 is 180tw it puts you into prepared/ modified classes where the R71R’s keep you in street class . Cup2’s put you in same classes as A7 Hoosiers ( not a fair fight)

 

Totally agreed... Once I can get wheels that fit for the A7s, I'm getting them. It won't be a fair fight against the cup2s...but until then I'm happy with my decision on the cup2s.