Z/28: Let's Talk Tires!

[Chumlee]

On my 3rd set about to move on with 6k miles.

2 sets of Trofeo R and 1 set of Hankook RS-3. 6 track days and 12 autocrosses total.

I can report that the RS-3 is about as close to an R-comp tire as I have been with a street tire. Not to mention, you can stay within the street tire (200tw) category at various competitions.

It turns on a bit quicker than the Trofeo-R but I felt like it offers significantly less grip. But the gap isn't as big as you expect. Besides the aforementioned, they are dirt cheap in comparison. I would recommend for those of us in a warm climate seeking an "all season" street tire (southwest with little snow or rain.)

I won't write about the Trofeos as I expect most owners are plenty familiar with their antics by now. I'll just say they're the best R-comp tire I've experienced yet, far ahead of the 888's on my old GTR. They'll grip as well if not better than a set of NT-01's without sacrificing longevity.

I have a set of A6 Hoosiers sitting around for an event in December, but for the time being I'm sticking with the Pirelli Trofeo-R. Looking forward to measuring the gap between the Pirelli's and the Hoosier's at Buttonwillow in December.

[lostwon]

JST wait. It's not for nothin' fresh A6s are called "Purple crack". 'Course they be gone in 60 laps, too. They are real hero makers while they last.

Enjoy.

[Doubleblank]

Had a track day today at Grandsport. Health issues (bad feet) kept me from getting the Finspeed wheels/Trofeos reinstalled. So I drove on the Michellin PSS' s. Guess what? I didn't crash or even go off track. Imagine that!

[X25]

Originally Posted by Doubleblank

Had a track day today at Grandsport. Health issues (bad feet) kept me from getting the Finspeed wheels/Trofeos reinstalled. So I drove on the Michellin PSS' s. Guess what? I didn't crash or even go off track. Imagine that!

Makes sense. PSS tires must have kept you at safer speeds :p

[L99CAMA2011]

Originally Posted by Chumlee

On my 3rd set about to move on with 6k miles.

2 sets of Trofeo R and 1 set of Hankook RS-3. 6 track days and 12 autocrosses total.

I can report that the RS-3 is about as close to an R-comp tire as I have been with a street tire. Not to mention, you can stay within the street tire (200tw) category at various competitions.

It turns on a bit quicker than the Trofeo-R but I felt like it offers significantly less grip. But the gap isn't as big as you expect. Besides the aforementioned, they are dirt cheap in comparison. I would recommend for those of us in a warm climate seeking an "all season" street tire (southwest with little snow or rain.)

I won't write about the Trofeos as I expect most owners are plenty familiar with their antics by now. I'll just say they're the best R-comp tire I've experienced yet, far ahead of the 888's on my old GTR. They'll grip as well if not better than a set of NT-01's without sacrificing longevity.

I have a set of A6 Hoosiers sitting around for an event in December, but for the time being I'm sticking with the Pirelli Trofeo-R. Looking forward to measuring the gap between the Pirelli's and the Hoosier's at Buttonwillow in December.

Chumlee. How do you like the Z28 vs the GTR. I would love to drive a GTR just to see how it is for a car.

[brt3]

Originally Posted by brt3

I just installed a set of Yokohama AD08-Rs on my OEM wheels. I've only driven them for a few (mostly freeway) miles so far and they're not broken in yet, but at first glance they seem to be a good middle-ground between Trofeos and the S-04 on the street.

1. There is NO tramlining on irregular surfaces, and I drove over quite a variety of not-smooth pavement during my ride home from the shop. In this regard it's as good as the S-04 for street use and very well-behaved.

2. They feel very responsive on the street, and are far better in this regard than the S-04. However, this was a 20-mile drive, and I didn't have a chance to push the tires at all. No high-speed cornering was attempted.

3. They are firmer -- with a slightly harsher ride -- and noisier than the S-04. However, they're nowhere near as harsh and noisy as the Trofeo.

I will report back after trying them under more aggressive cornering conditions, as I think the stickier/more aggressive nature of this tire, compared to the PSS, may make it the ideal street/high performance tire for the Z/28...

Just spent a day driving at COTA in the wet. IMHO the AD08-R is a great tire for specialized track use -- namely, cold and/or damp conditions.

I still haven't worked out the optimal tire pressure, but they were probably around 37 warmed up. TPMS failure prevented real-time data, but I'd guess that's about right.

Nice initial turn-in and quite responsive to changes in direction. They coped well with the wet track. Most importantly of all, they are completely linear in response and very predictable. I had a nice little tail-out ballet going...

[brt3]

Day Two in the wet at COTA. The AD08-R does not have the mega-grip of the Trofeo-R -- but it's a damn good tire that is, IMHO, the best street performance/light track usage tire available for the Z/28. Drove the car on a wet track with TC set to Level 4, and it was a blast. It's very easy to tell when the tire is losing grip, and it's very easy to adjust what happens to the tail of the car by changing steering angle or adding/removing throttle or brake. A hooligan would have had a blast, but I was trying to optimize my lap time...

[andig]

Originally Posted by brt3

Day Two in the wet at COTA. The AD08-R does not have the mega-grip of the Trofeo-R -- but it's a damn good tire that is, IMHO, the best street performance/light track usage tire available for the Z/28. Drove the car on a wet track with TC set to Level 4, and it was a blast. It's very easy to tell when the tire is losing grip, and it's very easy to adjust what happens to the tail of the car by changing steering angle or adding/removing throttle or brake. A hooligan would have had a blast, but I was trying to optimize my lap time...

Good intel brt3 - thanks.
My Trofeos won't last too much longer and I want to replace them with a tire that won't be a complete dog on the track but also won't try and kill me on the street when the road is cold, damp or both.
From what you have written above, it looks like the ADO8-R could be a great compromise.
How do you think the ADO8-R's will hold up in the Texan heat when it finally arrives again?
Andy

[brt3]

Originally Posted by andig

Good intel brt3 - thanks.
My Trofeos won't last too much longer and I want to replace them with a tire that won't be a complete dog on the track but also won't try and kill me on the street when the road is cold, damp or both.
From what you have written above, it looks like the ADO8-R could be a great compromise.
How do you think the ADO8-R's will hold up in the Texan heat when it finally arrives again?
Andy

I wish I knew, but I only know that they have a 180 treadwear rating -- and I think they might also be available in a 200 version. Also depends on how you'd be using them -- heavy track usage, at COTA (for example), vs. AutoX...

[johnr265]

Originally Posted by brt3

When I'm on-track I'm alternating between oil temp & pressure and TPMS. The Trofeo Rs have a fairly narrow window, regarding optimal pressure, and running in high temperatures makes it very hard to get this just right. The "do not exceed" pressure is 34, and optimal is 32. So, yes -- I often have the TPMS screen up when I'm on the track...

I'm not sure I agree with those pressures. Just came back from the track. NJMP. I had a lot of sidewall rollover with those pressures. Alignment was -2.1F/-0.8 rear (all we could get in the rear). I gradually crept the pressures up and ended at 38 hot all around and the car felt pretty good. Track temps were cold (mid 30's to mid 40's) so not ideal but I assume tire rollover would only be worse at higher temps. Doesn't make sense to have tire pressures around 32 on such a heavy car. Anyone else find otherwise?

[X25]

Originally Posted by johnr265

I'm not sure I agree with those pressures. Just came back from the track. NJMP. I had a lot of sidewall rollover with those pressures. Alignment was -2.1F/-0.8 rear (all we could get in the rear). I gradually crept the pressures up and ended at 38 hot all around and the car felt pretty good. Track temps were cold (mid 30's to mid 40's) so not ideal but I assume tire rollover would only be worse at higher temps. Doesn't make sense to have tire pressures around 32 on such a heavy car. Anyone else find otherwise?

Pirelli's own page states the optimal hot temp is 2 bars (29 PSI?). GM states one should never drive this car at the track at below 26 PSI, possibly due to saftey concerns. I'd imagine 23-24 PSI cold will be the most optimal based on these numbers, but it seems it would not be possible to do so without safety concerns. When I try my Trofeo Rs at the track, I intend to set them 26 PSI cold and probably leave it at that, since it will be the closest to optimal without going outside GM recommendations.

Regarding sidewall, I have not yet tried Trofeo Rs, but most if not all R compounds all have pretty stiff sidewalls; could it be something else contributing to what you felt? You're using them on wide wheels (like OEM Z/28), right?

[brt3]

Originally Posted by johnr265

I'm not sure I agree with those pressures...

I do run higher pressures at colder temps; otherwise the tires never get up to pressure during a session. Mid-30s is damned cold, for the Trofeo R, without a doubt.

For reference, in normal weather (70 and above) I usually run 28 PSI cold, which usually gets me to 34 PSI hot. Once the tires get to 35 PSI in warm weather, I can feel the car getting a little greasy. That's the upper limit of what I want to see during a session.

However, these numbers were not just by the seat of my pants. Guy Gamba from OnEdge Performance attends HOD track events. Guy has forgotten more about tires than most people will ever know. I always get off the track quickly and stop by his booth, where his crew goes over tire pressures and measures the temperatures across the tread. Over the course of four days and two different events, we determined these were the optimal tire pressures for me and my driving style in this car.

The main point being, we are different people with different driving techniques. Your mileage may vary...

[brt3]

Originally Posted by X25

Pirelli's own page states the optimal hot temp is 2 bars (29 PSI?). GM states one should never drive this car at the track at below 26 PSI, possibly due to saftey concerns. I'd imagine 23-24 PSI cold will be the most optimal based on these numbers, but it seems it would not be possible to do so without safety concerns. When I try my Trofeo Rs at the track, I intend to set them 26 PSI cold and probably leave it at that, since it will be the closest to optimal without going outside GM recommendations.

Regarding sidewall, I have not yet tried Trofeo Rs, but most if not all R compounds all have pretty stiff sidewalls; could it be something else contributing to what you felt? You're using them on wide wheels (like OEM Z/28), right?

Your are 100% correct about Pirelli's recommended pressures. However, the Z/28 is an outlier amongst the other cars that use these tires. It's far heavier but also capable of massive G-loads under braking and cornering. Those loads plus the weight of the car mean that the pressures need to be just a bit higher with the Z/28. That's been my experience, but what works for me may not work for you.

I would caution you, though, that the pressures you're considering may not be safe with this car. I'd recommend you start high and slowly bring the pressures down -- and I'd be surprised if you don't feel the car getting worse when you get to 32 PSI and below...

[MARKSTI]

I tried as low as 24 cold and as high as 29 cold and played with pressures in between as a starting point.
With my style of driving the car liked 31 psi rear hot/32.5 psi hot in the front.

The lower pressures felt like the tires were almost rolling over.

Dang car understeers still even with a lot of front camber and caster..needs a stiffer rear bar or another upgrade but that's another tread.

I think nto1s for me next time.