Hmm, certainly more control and for me more edgy (very reactive). Alas I have MSS adjustable sport springs and afe front sway bar. In fact it's so reactive , I only use "track" steering for street driving to make emergency swerves safe (otherwise too boosted and over-active). If just doing just Z06 bushings I suspect the change would be much milder.

 

Z06 control arms are much stiffer than Stingray's per GM engineers' interviews, but are still simple rubber. You can install them and would probably not even notice any difference at the street (but don't count on my word :-) ). The main benefit will be less 'alignment deviation' at the track where bushings usually stretch/yield, reducing the effective camber, etc. that is applied on tires at the track. For Z51, I thought this would be a great compromise.

I used to run Delrin bushings, which are much closer to spherical bushings on the support they provide, but would still soak up some of the vibrations. To this day, I am yet to see any manufacturer come up with a kit. I reached out to one of them (Borg) and made an offer (that I would pay him the full price for delrin kit, but he would need to buy a set of control arms to develop the kit without my car being out of service, and I would then test them on my car), but I was rejected : )

 

Made some good progress today! I exclusively used my about-to-cord R7s today to do a bit of suspension tuning before mounting the newer set. I started increasing HSR by one before every session, and kept dropping laptime, finally hitting 2:14.7. I did not improve my time during the next (and last) session after that (with +1 HSR at rear only), but I realized my fronts were corded, and rears were likely due.

Lap time progress:
For perspective, my best time with these same tires was only at 2:17s just last week, and my overall best time with this car was around 2:15 before that, so I'm happy with the progress. That said, my best time with my former car (C7 Z06) was 2:12, and that was also when I knew less about this track, so there is ROOM. I'm hoping to improve it tomorrow with the fresh tires.

Note on alignment:
As a reminder, my alignment is -3 / 8.2 / 0 Front, -2.6 / 0 / 0.05 Rear (Camber/Caster/Toe).

• The tires corded from the outside shoulders, not inside shoulders. Perhaps the new bushings indeed help with retaining the camber : )
• As such, it looks like -2.6 rear camber was not too much (or else it could eat up inner shoulders first).
• The car's balance was also good, and the rear was easy to control. I did not have any incidents, but when the rear slid a few times when I overdid it, it was always easy to recover.
• Rear toe:
  • A few folks asked me about increasing the rear toe since it's common on other platforms. I kept it at 0.05 toe in per side at the rear as GM recommended. The car feels pretty stable to me, despite running with both TC and ESC off all the time.
  • My logic is that GM's track alignment recommendations are already biased on the safe, conservative side, and if they needed more toe to keep it safe, they definitely would have. They must have relized the toe curve of the rear suspension in compression provides ample safety.
  • I should also note increased toe means more heat, more wear, and lower speeds, so it doesn't come 'free' : )
  • My recommendation would be adding more of it only if you feel your car is not stable at the rear.

I do have a pyrometer to really test these out, but well, I'm lazy and don't have a pit crew to check it out in hot-paddock area.

Note on tires:
Speaking of tires, The leftover R7s from last season lasted remarkably well until they corded today. They had a torturous life...
R7 295/30/18, 345/35/18
Mounted: 9/1/2025
# of laps: 173
# of heat cycles: 22

Pagid RSL1E pads:
Speaking of hot, the pads have been holding up excellent. I don't see any premature wear, and I think this will be my winner pad for a long time (taking the crown from ST47s).

Here's the best lap from today:

And this is the PDR version. I think I like my custom overlays more : )

From default coilover settings:
+2 HSR all around
+3 LSR all around

HSC - 24 clicks, HSR - 12 clicks
LSC - 30 clicks, LSR - 30 clicks
Default settings:

• FRONT LEFT
  • HSC+10, HSR+8
  • LSC-8, LSR-7
• FRONT RIGHT
  • HSC+9, HSR+8
  • LSC-8, LSR-8
• REAR LEFT
  • HSC+6, HSR+7
  • LSC-10, LSR-8
• REAR RIGHT
  • HSC+6, HSR+7
  • LSC-10, LSR-8

Area27's driving school, Academy27, has switched to mostly C8 Corvettes and a few Cadillacs. They have mostly Stingrays, and a few Z06, eRay, etc. My car is far behind them on the trailer : P


High speed rebound is the nut BELOW the top adjuster (of the low speed rebound), which was not accessible by the regular tools that came with the coilovers.


I found this in the local auto parts store. 5/64" square fits loose, but I was able to stick it into the holes to turn the ****. JJ will be sending me adjusters similar to the top adjuster to have an easier time from now on. Ironically, he said he didn't put those on since that **** is hard to turn..


I kept improving the lap time within every added HSR, until the last session (where I only added +1 HSR to rears). The car was feeling good at the rear, though, and realized I was losing time due to front tires, both of which were corded.


The rears are not yet corded, but you can see that a line is beginning to 'appear'.


Today, I also decided to try a new app, "Telemetry Overlay", to see if it's better than RaceRender. The answer is a RESOUNDING NO. This app does not let me customize gauges on data. It has a few premade dials and data available (like GPS speed and coorindates, G values, altitude, engine speed, throttle, etc.). However, I cannot add any custom data (e.g. Engine oil temp that I really care about, or FIXING the OBD-based speedometer data to correct for tire diameters, etc.).

On the top of that, it costs a whopping $199. I'm glad I just installed the trial version : ) The reason I wanted to test it out is since RaceRender's H265 input support is broken after Microsoft's update to its HEVC codecs suite, and converting inputs back into H264 takes a lot of time. My current workaround is using Handbrake app with hardware-accelerated H264 codec (NVENC), which processes the 1080P 30P video input in about 1/3 of its runtime on my laptop.

 

Today, during one of the earlier sessions, the car displayed something along the lines of "Acceleration reduced. Drive with care" inside a tight turn where it was trying to shift as I was banking hard left. I checked for error codes, and found this:

I am guessing P287C within my context (probably not a learning issue like suggested by the code) means the transmission unexpectedly struggled to shift (i.e. solenoid couldn't shift), and it cut power to protect it. It never repeated again, but it was enough to distract me from lap times.

Here is when it happened:

Anyway, still dropped the time a wee bit more today to 2:13.9. I also played with two video feeds and created this:

Once I have a bit of time, I plan to change the transmission filter and the fluid, in case that issue was caused by contamination in the fluid.

 

With regard to rear toe settings, I think with stiffer suspensions/sway bars, and less suspension travel in bump/rebound, the lower rear toe values are probably less of an issue. Stiffer front springs also help reduce dive under heavy braking.
Stock suspension, where suspension travel is greater, is where the potential for the rear to toe-out. When I was on stock suspension is when I noticed it most.
Also, when you run more front tire, you also need less help getting the car to rotate, so on 305/355 the car has more front axle grip. When I go back to stock 275/345 in 20" track tires, I will probably reduce the rear back to .1/side to just help the front axle a bit more.

This is exactly the same phenomenon/setup we see with 981/718 GT4 cars that are also mid-engine, with similar rear bump-steer issues. Once you stiffen up the car, you can run alot less than factory spec (.16 deg/side), which I typically run about .08/side.
The other issue is most shops who align this car also don't check the rear bump-steer, and don't set the caster to help keep it more consistent. If you do this, you can also run a lower static toe-in, because you can literally see what your toe deviates to throughout its range.

All that said, .05 to 1.5 is not a massive change that is going to wear tires faster, tons of cars run .1 to .2 rear toe-in factory specs without any issue with tire wear.
I saw no adverse wear issues from .05 to .1 to .15....and my mph was always the same as well.
What I did notice is that the car is a bit easier to drive sideways, when it does slide/rotate., and you can drive it into corners a little harder.

Your car looks great on track and seems to be handling well!

 

Thanks for your insights! Indeed there is a lot to consider (e.g. suspension stiffness over OEM, tire sizes, ride height, rake, etc.). In some cases, I'm sure higher (rear) toe would be a good tool to use.

Regarding lap times, I think they are starting to get close to my personal optimals, but I'm also about 1 click away from the stiffest high speed rebound settings. Looks like I will need to send it back again at some point, so we can 'center' these settings, and I would have more room to play and explore. Even though the feedback on rear-end has vastly improved, I am also wondering if I can get sharper response from the fronts, but on that, it might never feel perfect in presence of an electric power steering filtering the feedback (i.e. no suspension setting would ever make it perfect). Speaking of which, these valving targets might become a good starting point for others also looking into using this platform with similar tires. The main point is, they are way different than what Z51 needed, despite both cars sharing similar weight and identical suspension geometry. It's been an 'adventure'..

My next event will likely be in early May, and I plan to replace engine and transmission oils before that. Here's hoping that little transmission 'hiccup' never happens again : )

 

Nice to see your lap times getting closer to your all-time PB's.

Yes, it's interesting how seemingly different these cars are with such a wider track width and how it affects the usable spring rates and shock adjustments. I've experimented with going to the stiffer end of my adjustment range on the TTX, and found the car continues to respond nicely when on sticky tires.
Now that the platform is even stiffer with the new sway bars, I've noticed that rear tire pressures and camber play even more a role than before. On the stickier Kuhmo, when running almost -2.6 rear, and once the pressures hit about 33-34psi+ rear, the car feels like it basically tips over in the rear as the whole rear rolls over based on the tire having higher pressure.

It feels like the car is riding on the center of the tire, and when you have a slight bend when driving straight, the whole rear of the car sort of teeters over onto the cambered tire, and off the center of the tire. It doesn't do that with the softer side-wall Conti ECS02 though, but I do have more inside wear on both tires though with -2.55 rear camber tho, so I need to back that down again to about -2.3 ish. Those tires aren't quite sticky enough to run that much camber, and will help add more straight line stability for the Kuhmos.

Funny enough, once I go back to the 275/345 setup with the Nankang CRS tires, I'm sure I'll have to change things again to optimize, lol. But I have a feeling the car will be faster than ever with those tires, so I'm really looking forward to it. It's a never-ending chase, but that's part of the fun.

 

Hmm I run into that 'greasy' rear-end issue as well all the time, especially in longer sessions. Besides a bit of crowning effect with high pressures, I think it has a lot to do with the tires overheating, losing their grip. I usually start with tires around 22-23 PSI, and by the time I hit 31+ PSI, the tire is about 120+ degrees F hotter than where it started, and that's INSIDE chamber temp. The tread might be hitting even higher temps, especially in full sunny days with tarmac hotter than anywhere else, especially in the afternoon.

Actually, you can test it out. Just start at much higher cold pressures, like 30+ PSI, and I bet it will not get greasy at 33-34 PSI : )
Contis you use are 355mm rear, right? That would also help mitigae this issue. I bet they'd hit the same issue a few PSI over that, if you could overheat them to that level.

For this reason, and since it's not the ideal conditions I'm shooting to tune for, I usually try to keep it to 4-5 laps max when tuning the suspension (and then take a 2-lap cooldown to restart). This is sometimes very hard when there's someone at the track teaching their kid how to drive fast in their Porsche Cayenne or a hypercar owner driving their precious car at "7-tenths", and you lap them every few laps with your clunker.


In other news, I got my adjusters for the hard-to-reach HSR settings on the fronts.. I will need another track day or two to try all the settings (1-2 clicks to go until full stiff), and looking forward to seeing if I hit a point of dimishing returns along with these settings. Alas, there're no good events available right away, and it'll have to wait a few weeks...

These will definitely "help" with the settings. That said, since I'm getting very close to the max settings, I will likely need to send the coilovers back one more time, so that the current settings can be 're-centered' in the adjustment range...

 

The crowning effect is exactly what I'm experiencing specifically with the Kuhmos, but not with the Conti ECS02 (which I don't really care about as they are just slow, non-sticky tires for non-ideal weather or drive to-and-from lapping). My tires aren't getting overly temp hot or greasy, as I usually don't start that low. I typically start about 25 front, 27 rear, and then bleed down after a shorter first session. I honestly think I just need to run even lower hot pressures now with the Kuhmos, maybe like 27-29 front, and 30-31 rear hot. The crowning feeling/chassis roll doesn't happen at the beginning when the tires are low pressures and more contact patch is on the pavement, it's only once the pressures get to about 31-32 psi or so. It's a combination of very stiff suspension, a bit too much rear camber, and maybe this specific tire.

I'll be interested to see how the Vitour and Nankang CRS do in the next couple months once I finally get those, but given they are similar fast 200TW, I have to assume it's a possibility with those as well. But once you achieve the type of platform stiffness the both of us are running, we are putting a ton of load into the tires and asking alot of them, which is fine, we just need to figure out how to make the tires work optimally for the setup.

None of these 200TW tires seem sticky enough to justify me running -2.6, so will back it down as my Kuhmos wore really even with about -2.2. Other than that, the car feels great, is very fast, and just a real joy to drive at the limit.

 

Has anyone tried reverse rake? I was at an Optima event 2 weeks ago and all of the c8 guys stingray, E-Ray, Z06 were swaring by reverse rake. It was actually even rake but i didn't name it.

 

Yes… rear of car low makes it work better. Way different than C5/6/7.

 

Yeah this topic keeps coming up.. The head instructor of a local race track also suggested this. He said when he was racing with the Audi R8 GT3 (or something) race car, that's what they did to make the best lap times. He said they softened rear, too. I'm yet to try it myself to be honest. Since it's such a departure from OEM settings, I always chickened out (XACO)..

 

How would you achieve reverse rake? Lower the rear and increase the front shock lengths or something? I assume you need coil overs to be able to really do it?

 

Well this cars comes with coilovers even from the factory? Stock suspension rake was 26mm per my calculations (not taking tires into account). Even the OEM shocks provide enough adjustment range to flatten or reverse that I think.

Suspension rake per my measurements:
Z06 Stock: 358 mm F, 385 / 383 mm R. 26 mm rake.
Z51 Stock: 365 mm front, 388 mm rear. 23 mm rake.

With OEM tires, I think total rake hits ~43 mm for Z06. If anyone has more precise numbers, please chime in.

 

Where do you take the front and rear measurements? I am curious to go measure mine.

 

I used a frame bolt on both sides, something that is going to remain constant; you are just looking for the distance since all cars are different.

 

My suspension measurements are from hub center to the start of fender. I actually measure from the wheel's lip to the fender, and add an offset (half of total wheel lip to wheel lip length) to make it easier to measure.

 

I attended the second half of a track day at Ridge Motorsports Park, today. I continued from where I left at Area27 (Canada), and learned a few things.

I only attended 4 sessions, and it got pretty hot in last session (82 degrees F) compared to the first (68 degrees F?)

• First session: Last Canada settings, and first shakedown lap: 1:49s (heavy traffic)
• Second session: Noticed rear end is very heavily compressed in turns 2, 3, 4. Added +4 Rear LSC to stabilize: 1:47s
• Third session: +1 Rear HSR: Even though a wee bit faster best lap, the rear felt greasy times. It was very easy to recover, but it felt like I was suffering from too much rebound: 1:46.7
• Last session: Decided to undo all HSR since best lap in Canada, and stabilize the rear with even more LSC. +4 LSC, -2 HSR Rear, -1 HSR Front: 1:45.46 despite heat.

Well, that was it. Here is a quick video:

Next steps: This whole suspension tuning has been a learning experience! I bet it would be cheaper to just give it to a professional driverto dial it in for me, but I digress. There are a few options to try for the next time.

1. Alignment: The tech did -2.6 camber on my rears by mistake last time, even though I wanted -2.5. I am thinking about getting reduced back to -2.4, and also make the toe +0.1 per rear corner to see check if what you've guys have been talking about makes a difference. An additional 0.05 toe is so small, and I can't see it doing much harm anyway, to be honest.
2. Rear sway bar: More rear support keeps helping me. I did it with HSR first, and hit other issues. LSC can help as well, but too much LSC will reduce traction when it comes to straight line and corner exit acceleration. Sway bars only activate when loaded up in the corner, so it might be a better solution.
   • Ordered Eibach rear sway bars, and will try them at some point.
   • OEM Z51 rear sway spring rate is 300 lb/in. Eibach rear sway bar is +40%, and +70%. (422 and 510 lb/in). FYI, Z06 rear bar is 203 lb/in.
3. Droping rear height (by 0.25" or so): Some folks swear by it, and so does our chief instructor at Area27 who raced Audi R8s professinally. I will eventually try it,but considering OEM Z07 can do amazing lap times with its humongous rake, it makes me wonder..

Anyway, I'm thinking about doing (1) first, and see what I can do with it. If or when I do (2), I should definitely take back some of the LSC to see the impact (possibly better corner exit acceleration).

A lot to test and the test data is unfortunately only as good as the driver's interpretation, so I have a feeling that this will take a while : ))


HSC - 24 clicks, HSR - 12 clicks
LSC - 30 clicks, LSR - 30 clicks
Default settings:
FRONT LEFTFRONT RIGHTREAR LEFTREAR RIGHT-------------------------------------------

Current settings:
FRONT LEFTFRONT RIGHTREAR LEFTREAR RIGHT
Eiback bars come with regular mounts that allow the sway bar to clock itself back to neutral, unlike OEM mounts which don't let the bar really turn neutrally, unless the mounts are loosened. This would make it easier to hit real neutral with adjustable links.

 

What gear equipment were you using to record this? In other words, camera, software and hardware. NOT transmission gear.

Thanks.

 

Get those hands down.