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…