Shortcutsleeping

You're totally in our heads....we CERTAINLY want to run COTA, we almost consider that our home track over MSRC honestly.

As to ECR, yes to that too, but the times won't mean much because there is not an established pecking order like MSRC or COTA. For instance, running the 1:21.2 at Cresson full of gas and a miata pass on exit...we know the car is 1:20 capable on stock runflats with an alignment and that is up there with a stock C7z on stock tires...and Slick is a base Z51 only car. As a driver I want to run ECR (ran 1:48s in Scratcher during w2w) just for the sheer fun of a new smooth track, but it is hard to justify time/money burn when we could be at Cresson still developing the parts that are coming off the drawing board now. I don't know what we'll run at COTA, Louis is a much better guesser than me....I just wanna Send It and see what happens and where we stack up.

Edge Addicts is there mid May. Hmmmmmmmmmmm

Costas
cars and such...

VetteDrmr

I wish I could just "Like" darn near every post in this thread; one of the best I've enjoyed reading in a LONG time. GSpeed and Costas, thanks so much for your posts!

Have a good one,
Mike

PeteC7

MOAR!.....please.

Shortcutsleeping

UG....
While most of Texas is back to business, AUSTIN is not....and the Edge Addicts event this weekend at COTA has been CANCELLED.

But....I think we'll still be testing this weekend (everyone do your "no-rain-dance" starting now) and we should have a surprise or two for the thread.

Costas
cars and such...

lobsterroboto

weather is looking more promising for NOLA this weekend... just sayin.

Lempaweong

I must missed your reply big time!
I don't have the fancy temp camera either, but I used probe and pdr data to set a base line. And reading the tire wear definitely helps too. I was running 295/325 r888r, giving that stock is 285/335, I was surprised the car became understeering and unpredictable at corner entry (same corner, same speed, and trail braking). But at high speed corner, the rear is very stable and the break away is smooth and predictable. And with most my buddies running r888r that year, including few m3/4 and s2000. M3/4 all sufferd the same understeering and unpredictable feeling like my car, while the s2000 simply couldn't get the tires up to temps. So we came to the conclusion that r888r was most suitable for middle weight car (3000-3300ish? and that's probably why c5/6 run them with no issues), and prefer a square setup, so the front won't overheat (hopfully).
Comparing r888r with cup2, they both have the r-comp tire characterastic, small slip angle and relatively small window of grip. Only small difference I noticed it's that r888r is better at accerlation outta corner, but it's pointless since cup2 is faster at corner anyway.
Even cup2 (new and heat cycled) is faster and more consistent, I still think r888r is a good tire. It's cheap, wear is low and has good cold grip, a solid option for a chill open track day. I will try it agian in the near future with wider 18/18 or 19/19 setup and see how it goes.

Shortcutsleeping

Well shoot....rain.
We had some things to test but sadly they stayed in the shop and Slick and I got to go play on a wet track. A few times the rain really slowed waaay down and the wind was strong and we almost kinda sorta got a skootch of a nearly dry line in a few spots and then the rains came back.

BUT, we got more experience behind the wheel and to play with various settings AND give quite a few folks rides in the glorious orange sound machine.

As always, turn the volume up!


More neat stuff soon....stay tuned!

Costas
cars and such...

smitty2919

Odds of adding a x pipe to get rid of the farm truck straight piped sound at any RPM other than WOT??

Dooo ittttttt

GSpeed

Slick 4: The Grip Awakening

By: Paul Costas



Test day done, folks. Did it all go smooth? No. Did we get to test our new sway bars? No. Did the GoPro work just fine? No. Did we prep for the new brake pads? No. Did Costas keep it on track as always? No.



Was it a good test day? ABSOLUTELY.







We learned a TON and made a LOT of progress and, just like no battle plan survives first contact, we made changes on the fly, relied on our network and still came out of the day with our heads held very high.



First off, we’re back testing at our home track here in Cresson. Just like our wet-test a few weeks ago, we are running with The List HPDE group. Having starting my ‘playing on track’ obsession back in the late 80s, you’d be hard pressed to find a group in Texas I’ve not run/instructed with and I must say how impressed I’ve been with this new group. They are great communicators and do an exceptional job at setting expectations. We run Slick in the advanced group and while (of course) novices should hold the line and point the passing driver around, when you get to the quicker folks a lot of them (and I do this too) will go off line so the passing driver can keep the momentum up and get that data/sector time/lap time that they are chasing. The groups are smaller, it feels very ‘family’ and everyone I’ve encountered has been great to work/drive with. If you’re chasing track time in Texas, head on over to TheListHPDE.com and they are on the socials as well.



First order of business was to re-baseline the car. Like most tracks in Texas, Cresson is very dependent on rubber buildup (yes, it rained recently) as well as track and air temp. What seems to be similar conditions can easily have a full second or more difference and times on the same day from a cloudy 65* morning will easily add 2 seconds in the late afternoon 90* sunshiny day. Track loses grip, motors make less power. In my coaching I always caution folks to not read too much into lap times that are not in the exact same conditions. Its easy to get down in the mouth when you’re not as fast as you were last time, but if the track has slowed down a full second and you’re only .5 off your personal best, then in reality you are ahead of the game.



I do a quick session on the factory wheels and tires to get our baseline. Now, the car only has about 2000 miles on it, but 1500 of those are on the track. The tires have some meat left but I was several seconds off our quick time in the same configuration. Checking with a few racers on track, they were a touch slower than their ‘quick times’, but not 2 seconds. Grabbing the durometer we find the Michelin are now on the backside of their life. To put this in perspective, the hot Michelins gave the same reading as my buddy Mike’s 5000 mile old commuter tires on his Mazda6 beater that he had just pulled up in. DOH! Comparing against the R888s on the shelf, the Michelins are now a full 10 points harder whereas when we got the Toyos they were within a point or so. Yikes.



The Michelins are not ‘dead’, but they are certainly a ‘step down’ from their prime. As a person who has tracked durometer ratings for an exceptionally wide range of tires, the Michelins are exhibiting normal behavior. They’ve got a LOT of laps and the edges have been hot-cold-slid enough times that the initial softness is gone. They’ll likely stay in this ‘decent’ state for a lot of heat cycles, and if they are equivalent to other Michelins we’ve run (street stuff, not race) then they’ll finally go ‘dead’ (durometer reading adds another 10 points) until you wear the little bit of rubber off the carcass and expose cords. This is my guess, but I’ve done this a few times.



Pads: When I arrived early, Chase was wrapping up the brake pad swap. We had run out of factory pad and Cobalt had sent us several sets to test. We did this as a ‘pad slap’ and sent it. As we all know, there will be pad material left on the rotor and TYPICALLY Cobalt pads can be pad-slapped with zero issues. Of course….we had issues.







The Michelin warm up was a few laps to get everything warm and bed in the pads a bit but by the time I came in, a light braking application resulted in a good vibration. Pushing through this vibration reduced it a ton, but being a big trail-braker I was hoping this would work itself out soon. <Foreshadowing> <Would the brake vibration only cause one problem? No…no it would not> <sigh>



We have a quick chat and decide to pull the Michelins and go to the Finspeed/Hoosier setup. A passenger slides in and off we scoot for two laps to get rid of the mold release and get some pressure built up. Back in the hot pits, the crew ensures nothing is rubbing, re-torques the brand new wheels and away we go. The brake vibration is inconsistent but still only really noticeable on light brake application. When I really get into the brakes the vibration is greatly reduced and the brakes feel great.



So….you see this coming right?



We go back out, and I warm the tires more and setup for a “pretty quick” lap. I go through rattlesnake (largest waste of track in Texas, I’ll fight you if you disagree) and head down the hill, making a nice two-apexer and scoot up the hill toward Ricochet. I’m carrying too much speed so I lift and ease into the brakes to bleed off some MPHs and the vibration is very faint. I get to the turn in point and my left foot is barely breathing on the brakes and as I rotate the car in, the car USUALLY slows down a bit more. The big heavy Michelins and the big heavy factory wheels get impacted by the slip angle the Michelins operate at and we slide a bit and that slide creates friction and allows me to lose that last 1-2 mph so my apex speed is perfect.







Usually. However, the Hoosiers operate at a much lower slip angle. Especially when I’m not asking for full grip, I’m just asking for a twitch. The Finspeeds are light and stiff and are not impacted and so my speed stays up. No big deal, I’ll just give it JUST A BIT MORE BRAKE PEDAL on my way to the apex. Easy peasy.







It was, in fact, not easy peasy. The vibration got a bit worse, the back end started to step out and I’m quickly presented with two options. A) Try and catch it and slide it down, then correct and go. If this works I’m a hero, and if the rear bites in, I’ll experience snap oversteer the other way and we’ll go backwards off the track at 80 mph. Consequence of action: Low chance of success, high chance of Louis not happy. Or, we can do B) Straighten up, slow down as much as I can, go straight off in a controlled fashion, drive AROUND the pothole at the end of the rumbles and come back on track. Consequence of action: I end up taking Slick off road, but it’s dry and low chance of not happy Louis.



Option B it is and you can hear my passenger laughing as we go off.



Pulled back into the pits. Chase: “that grass was way too long over there, good job”. I love my crew.



With that we get the Hoosier’s up to speed and while the brakes are beginning to cohabitate better, they’re not the usual Cobalt-perfect, but honestly it is not their fault. We should have pulled the rotors and did a light cut on them or put on fresh rotors. I’ve worked hard and spend a ton of time/money/testing to find out what allows me to pad slap from street to track pads with no cutting, but that’s a story for another time.



After a few sessions we get everything we can out of the Hoosiers. It is lunchtime and we sit and do a deeper debrief. The car is not balanced. It is kinda close, but we’ve got a low speed push (not horrible) and we’ve got high speed oversteer. We are losing exit speed in ricochet, complex and big bend due to the high speed push. At medium speed and high speed we have great turn-in. At low speed the oversteer is manageable. (reminder: I’m in track mode with all nannies off. We’ve tested the race modes and PTM stuff…I prefer it all off. On the fastest mode one time I was exiting Big Bend at the turning limit over 100mph and some nannie played with the brakes and I almost went agricultural. Not cool.)







Time for the network. As I’ve preached, GSpeed is SO WELL CONNECTED. Thanks to Paul Simmons and Neil Roberts we’ve got the car mapped and the suspension analyzed and so we conference call Neil (one of the best race engineers in the business) and lay our cards on the table. It is decided to abandon the sway bar changes for the afternoon and concentrate on getting the car balanced as it sits and THEN do bars.







So we do that. We lower the rear. Then again. Then fill in the rear spoiler with more surface area and add a 1” wicker, and then lower more, and then add some 5” tall wickers on each side. Lots of cardboard, alum plate and gaff tape and lots of sessions to figure all this out (plus other tweaks). Sometimes in HPDEs it is tough to get a full timed lap, but we just need a few corners and I come right back in. TheListHPDE is so great to work and Louis quickly analyzes data and correlates it to my feedback and we keep making changes and keep making laps.







By the end of the day we are EASILY running in the 18s with a passenger seat still installed and a passenger in that seat (so +225-250lbs on the right side....on a left-turn track!). In the heat of the day when the SM guys are fully 2 seconds off their normal fast times.







So….the brakes bit me again when I went to setup a fast lap and I went down into Big Bend. I had slowed on the straight and again turned in a bit too fast knowing the scub would pull out a bit more speed. As I got close to the apex, I was slowly pulling in the left lever to downshift and I was barely easing onto the brake and as I pulled the lever the car hopped a bit and I double tapped. I quickly up-tapped (no biggie, no overrev) but I hate mistakes like this. Argh.



HUGELY fantastic day. GSpeed also fixed at least half a dozen cars that were at the track with various maladies and I did some coaching/driving of a GSpeed customer car and then also did a shakedown on another GSpeed build as Slick was getting turned around for another session (thanks Chase!!!).



As usually, the car was solid, always started and ran with the temperatures under control. The brake pads required a bit more pedal and I had to relearn the muscle-memory spot where I was pushing for the stock pads and that took a bit. We did a TON of tweaks and for the most part we always went faster and I got more confidence in the car. Having a car get loose at Ricochet or Big Bend exit is certainly not optimal and I’m really proud of the team for throwing away our plan to focus on a different path and getting it done.



HUGE THANKS to the GSpeed crew, especially Chase who had to babysit me the most today. Thanks to Neil for the top notch meeting of the minds, and to all our extended network folks (Simmons, Hester, etc) who always pitch in and keep our collective effort producing solid results. #Network



Next up will be more wheel rate by sway bars. I can ‘crash’ the front dampers in the lower speed stuff now that I have the grip/leverage the Hoosier/Finspeed’s provide and I think we’re getting out of their comfort zone in the medium speed stuff. I think they are still good in the high-speed (mph, not shock) stuff though. Or do we press the ‘ZFG’ button and go straight to Penske’s?







And yes…we already have a big carbon splitter and I saw some wing mount patterns that said “SLICK” on them over in the fab shop so who knows what we’ll be testing in a few weeks…



Stay tuned!!!

PRE-Z06

18s with a passenger in the afternoon heat is smokin! Great detailed write-up, can’t believe you included the part about mowing the grass lol...have even more respect for you with the transparency though, looking forward to the next session! I second your comment about TheList putting on great events, TMS infield under the lights has been my favorite.

Shortcutsleeping

LOL, thank you for the kind words. One of the great things about working with Louis and the GSpeed crew is while we might not always share ALL the bits of the secret winning sauce recipes publicly, we typically do share the mistakes. I'm blessed I don't have many "offs", but I've been doing this long enough that my ego isn't dictating what I share. Meh, it happens. In the next day or so I'll post up another play vid and include the off...the grass pattern behind the car is hilarity! Well, that and my passenger laughing.

Some video of an afternoon 18 with an off-line pass and a passenger and me driving just a kiss conservative.



Costas
cars and such...

jrhoades

What size wheels and Hoosiers? Sounds like the car was generally loose before the changes? Can you share alignment or tire wear experience?

VetteDrmr

Paul,

Thanks for the great writeup and videos! Can't/don't get to the track but once a year or so (retired income, 7 hours away, blah blah blah), but Cresson is my home track and I love your stories!

Have a good one,
Mike

Shortcutsleeping

C'mon Jason, I put the tire sizes in the video!!!
LOLOL

275f/345r. Not disclosing wheel sizes at this point. That's between Louis and the Finspeed folks. Stay tuned.

Alignment is close to what we ended with last time (I don't have my notes with me) and tire wear on the Michelins wasn't horrible. Sadly a few folks have driven (I should say OVERdriven) the car and they didn't stop turning the wheel when the car stopped turning so the edges are pretty hammered. We will likely get real-time-temp sensors on the car soon to get a better feel if we've got pressure really dialed in. At 30 hot the A7s felt pretty good.

The car was a handful on the Michelins. The problem is they were "off" and/or "going off" and we all know that trying to chase your tail and chassis tune a car on worn tires is a fool's errand.

So we baselined the car on Hoosier's and at low speed it was a bit pushy on entry and a kiss oversteer on exit, while at high speed it turned in great and due to CoP migration it had a lot of oversteer at high speed.

And by the end of the day we had reduced the low speed push (it is certainly still there, but it's manageable and so I alter approach speeds and driving style to mitigate it as much as possible) and we took a ton of the oversteer out on high speeds. We likely won't fine tune this setup further, but there is likely a few more small gains to be had. Instead we will go splitter/wing and balance from there.

Costas
cars and such...

Shortcutsleeping

Mike,
So glad you enjoy the writeups and vids...that's what it is all about. Let us know when you'll be at Cresson again and please stop in and say "hello!"

Costas
cars and such...

jrhoades

Sorry, hadn't seen the video yet

No worries on sharing, I have 10.5s and 12s on mine based on pre-arrival offset guesses, interested if you fit more, especially in the rear. 345s work great on 13s.

Are the remaining balance issues steady-state, or transient. i.e. addressed with springs/bars/alignment, or with shocks? Car has the mag shocks right?

I'm not super familiar with how the PS4Ss behave very late in their life, but even when new, they are generally only good for one hot lap before their performance starts to fall off.

A7s would probably get past their peak after a couple laps too on something as heavy as the C8. You may find R7s more consistent over the session.

Shortcutsleeping

OMG GO WATCH THE VIDEO.... LOL....heh....it's nothing great, but a fun listen and watch.

The remaining issues AS WE FINISHED LAST SATURDAY:
--Low speed transient response. At low speeds on A7s I can 'crash' the dampers since they don't react fast enough. They are costing us a chunk there. Medium speed corners I *feel* like we're leaving a bit on the table but honestly can't swear to it, and at high speed when you just 'bend it in', the dampers feel fully integrated and caught up. Yes, car is a 2LT z51 and has magride and front lift. So we can currently adjust the rear, and soon will be able to adjust front.
--We've made big strides in getting the rear to behave, but honestly it could behave a tick better....but it is CLOSE....Louis and I (and team) have a 'next steps' call and it'll get decided if we are going to chase tenths/half-seconds on the current setup, --OR-- is it time to push the 'aero' button?
--Interestingly we did not get an e-diff error on A7s, which we really thought we would get. Both Louis and I know folks in unique "C8 applicable" positions in GM who are doing development as well and we're sharing data behind the scenes, and that coupled with our network has taught us quite a bit. For example we've had the suspension completely mapped and analyzed to see what first order changes are and what second order changes are. We're playing with both.
--Before aero we may try an XX% increase in wheel rate with Louis' new sway bars. Would that slow down the damper speed enough to get the mag-ride happy again? Personally I don't think so, but several things we've tested have surprised us and all our tricks don't work like they used to.
--Aero...I've already built a biglip carbon splitter that looks like it'll work fine and some rear wing mounts are not far off. Clearly the aero isn't going to help our low speed pushiness, but should make mid to high speed stuff better.

Most stuff we can do to further reduce low speed push will bite us in other factors. Go from 275 to 285? Sure....but then high speed balance is worse for exit oversteer and that is typically worth more lap time. We've got the front end what I'd label as 'entirely manageable', and so honestly I just deal with it. We've reduced it a ton and it isn't a big impact.

Steady-state the car is nice. It is easy to move weight fore/aft with light throttle/breathe on brakes....and that can tighten or loosen up the exit trajectory in a very predictable way. The car is just SUPER easy to drive fast now...I was taking passengers and running damn respectable times with no drama.

I'm not that familiar iwth the PS4S either, but they seem to act like you indicate. You need to be quick one of the first few laps and then they drop a bit. Now, however, I can't even seem to get a fast lap out of them and the durometer tells the story....they are 10 points off of where they were the first 1200 track miles (LOL!).

Agreed on A7s typically, but setup well and driven tidy they can surprise you. At NASA NATS at MidOhio we were the only car in the field on As and not Rs and it was a 45 minute race in the 85+ heat. I set our fastest lap (and set track record, and set fastest race lap by over 1 full second) on the second to last lap and lots of folks were amazed the tires stayed under us. Louis has good setups and I drive on the front side of the grip curve and not the back side, so we both work to minimize excess heat and it seems to work. You're right...this is a heavy car, but a 345 is a good sized tire. We'll keep testing and when it comes to long runs I can see us going to a Pirelli DH maybe.

How's your car coming along?

Costas
cars and such...
--

BaylorCorvette

Very true. On a local track a few years ago on my C7 Z51 I was running 2:00:xx times on Nitto NT01's that were an inch smaller in diameter both front and rear and also wider front and rear. However on the stock MPSS runflats I was running 1:57:xx times. So three seconds faster! The car felt much more planted on corner exit. I was surprised.

OuchIAteMyself

I'm stock everything on mine still. I noticed the same thing w/ the PS4S tires. Lots of tread left, but the compound is cycled out.
The search is on for tires and/or wheels now.

Also, on COTA I started to experience some pretty drastic pulsating from the brake pedal as well. Any idea how to improve the situation?
I'm about to swap out the pads w/ G-loc , but perhaps the stock rotor is warping. Not sure...

RapidC84B

@KNSBrakes has some nice 2-part floating stock replacements from Girodisc.