Oh4GTO

Finally did my first track day this year on my new wheel and tire setup. Wheels are 18x11 and 19x12. I got a set of Pirelli DH scrubs from GT Tires, a reupatable source. Sizes are 305/660/18 and 315/705/19 (no the rears dont rub). The front has amazing grip, zero push. The rear however is a little disappointing. Tail end would get happy about mid turn, something that my NT01s never did. I should note when I ran 325 NT01s out back, I only had 275s up front. The car pushed but the rear was planted.

I'm having two thoughts here. The taller rear tire added some rake to the car so I can lower the rear end or raise the front some. The front and rear tires were hitting 30psi hot. I can try lowering the rear pressures as well.

What's everyone thought on my next steps?

BrunoTheMellow

I run same pressure all around. 29-30 hot. No problems being tail happy. Maybe you just got unlucky with this batch of tires. It happens in the world of used tires. Hard to diagnose. Alignment ok? Check lca bolts for slip.

Oh4GTO

I did check them. They are all marked. Also the car does this in left and right turns so at least its consistent. I'm gonna try lowering the rear a little. I have WGI next month and hope that these will run better on the higher speed and banked turns.

Racingswh

Disregard. I thought you were on 18's.

If you're running with RTR at WG you're more than welcome to try these sizes I have using the 18" wheels. They will work fine on your car.

Poor-sha

What track? Which corners? You said mid-corner but are you on the brakes, gas, coasting? Is your GS a Z07? Is it stock suspension?

For reference I am running 305/645-18 and 315/680-18 so a 35mm diameter difference and you have a 45mm difference so it's not that much different.

It could just be the construction of that size tire as they do design them for specific vehicles. For example, the 325/660-18 DH was horrible on the rear of my C7 because it was designed as a Viper front tire.

I would try raising the front some. I tear up the rear wheel liners with a 680 rear tire so if you're not rubbing now it's just a matter of time - check the bracket and hex bolt on the rear inside of the rear wheel liner, mine was literally skinning the tire until I removed the screw and bent the bracket back.

Racingswh

I like the 325/680/18's in the rear. They work well. I am not a fan of the 19's and the tire height choices on Corvettes.

BrunoTheMellow

You need to check your ride height with your street wheels and track wheels. Your rear slicks are 1 inch taller than stock. That means you raised the rear least 1/2" so the front splitter is lowered by maybe 3/4" to 1".

You probably have the rake a bit too extreme. Remember. 30-45 mm front to rear difference.

Oh4GTO

The rear is definitely higher because I have more room to get my aluminum pucks on the QuickJack. I'll compare the two and see what it comes out to be.

Oh4GTO

NJMP Thunderbolt
Happens on longer sustained turns. Off the brakes and not powering out yet. Flat surface and no camber. Seems to handle high speed turns better. 50-60 mph turns get loose. Non Z07 and stock suspension. A little lighter with a race seat and passenger seat removed.

The 315/705-19 is used on the rear at Ferrari Challenge so I dont think it's the compound. PSI would hit 31 right at the end of the session. Maybe 1 or 2 laps but the behaviour doesnt change.

Maybe I'm expecting more out of them than they can provide? However they communicate quite well. I was sceptical at first but I can sense and see the yaw quite early and can easily make the proper correction. Not the snap monster I though they would be.

I dont rub anywhere. I went around and tested it on various roads. There was one area where the liner poked out a bit but I used a zip tie and pulled it inwards. Haven't heard a single thing since. I'm sure offset makes a difference and the fact that it's a 315, which calls for a 19x12 rim according to Pirelli so that part is good.

X25

If it's not rubbing at all, I wonder if your rear caster is wrong? I run 0.8 degrees positive caster at the rear, which bring s the tire closer to the front side of the liner.

Oh4GTO

I have it at +.7. It has been this way for almost two years. I have it checked every few track days. There was one spot it rubbed where the liner had a bump in it that I pulled back with a zip tie. No more rubbing.

RX82Z06

Go back to new NT01s.
Unless you have first hand knowledge of heat-cycles & storage conditions scrubs are a crap-shoot.
FWIW, my last set of scrubs, over 3 years ago from GT Tires, were junk and I tossed them after 1 event. I’ve only run new tires since then.

Racingswh

Aren't NT01's expensive? I haven't ever bought a new set of slicks myself. I used to buy new Hoosiers but once I started using scrub slicks I stopped. I just don't have the budget for new tires.

For the money I don't think you can beat the Pirellis from Todd. They are so cheap and for track days who cares when lap times aren't very important? I am not fast by any stretch but they are fine at least for me. 1:59's at Watkins Glen and 1:25's at NJMP Thunderbolt for reference on Pirelli scrubs from Todd.

X25

NT01s are entry level R compound tires; they're certainly not race tires.

Scrubs are certainly good alternatives. They're not always consistently good depending on how they're used, but you can't beat the price!

I personally started leaning on RRs for practice/shake down, and R7s for doing my best laps. RRs are very consistent, so I can concentrate on my driving and not be confused by variability in tires. I still have~20 scrub tires remaining, but hopefully won't replenish them when I'm out of them : )

BrunoTheMellow

I'm on like my 6th set of scrubs. And they have all been fine for at least 3 track days. Or fine enough to have fun by the end of the 3rd day. I'm paying 50-80$ a tire locally. Even with a failed set I'd still save an absurd amount of money not buying new tires

Oh4GTO

Cant beat that price. For me 4 tires plus shipping is 750. So after two sets of scrubs I could have new NT01s or Toyo RRs. After these are done I will go to NT01s. They are very consistent and predictable and last a long time.

BrunoTheMellow

Search fb marketplace local. Find local race shops. Ask around.

If you're not in a local hpde group on fb, Join one. The texas one, for example, is massive.

Level8Drummer

First check alignment. Second are your rear toe links factory oe? Third it could be the tires, sometimes you get less heat cycled fronts and more heat cycled rears. They likely didn't come off the same car with the same track time. I had mixed experience with Todd. He stood behind his tires ok, you just never know what you will get.

If you are buying new dor r tires go proxies rr.

L8d

Citation

Bought a set today, you might want to call Mike at John Berget Tire 262-215-2291. Pirelli 305/60-18 and 325/680-18. $120/each plus $100 shipping for the set = $580 total. Not as cheap as what Bruno paid but Berget will ship anywhere. Guaranteed only 2 heat cycles.

This will be my first time on a slick. Any advice beyond taking it easy? Previously mostly on RE71r (smaller wheels).

Level8Drummer

I may use them in the future. Expect no warning when the slicks break traction. Just silence and a loss of grip. Up until that point however, they will cover up every mistake you make and grip like crazy.