Given all of the discussion regarding the C8's supposed tendency towards understeer, I found the following bit of information to be very interesting:

"The wheels of the race car (i.e. C8.R) are four inches wider at the front and two inches wider at the rear when compared to the standard car."

This obviously indicates that the race car is using relatively wider front tires than the stock car to help reduce understeer!

 

good to know

 

Yeah . I mean. It's common knowledge c6s and c7s perform better closer to square. 315/335 for example.

 

Just for some ballpark speculation, and if the OP's source is accurate, and if the tread width grows proportional to the rim growth, I calculated that the front tread width grows from 8.6" to 12.6", or a 46% increase. And the rear tread width grows from 11.2" to 13.2", or an 18% increase. Then, 46% / 18% = 2.55. This means the front tread width increase is approximately 2.55 times greater than the rear width thread width relative to the OE tires' width. So then following this sizing theory, if you'd increase the rear OE 11.2" tread width by .6", you'd be increasing it by 5.5%. Therefore you'd want to increase the front OE 8.6" tread width by 13.75% or 1.18", totaling 9.78".

So if all of the above holds true, C8 owners desiring more neutral handling can find it with a tire change to Hankook slicks as follows:
Hankook Ventus F200 C5 (medium compound), see: https://hankookmotorsports.com/wp-co...Guide-2020.pdf

Front:
250/650R 19" x 9.5" (fits 8.5" - 10") Section width 10.4", tread width 9.8", diameter 25.59" vs. stock:
245/35ZR 19' x 8.5" (fits 8.0" - 9.5") Section width 9.8", tread width 8.6", diameter 25.8"

Rear:
300/680R 19" x 11.5" (fits 11" -12.25") Section width 12.6", tread width 11.8", diameter 26.77" vs. stock:
305/30ZR 20" x 11" (fits 10.5" - 11.5") Section width 12.3", tread width 11.2", diameter 27.2"

 

It's a bit simpler than that. Fit the widest tire you can.

Likely a 295/315 combo. Maybe 285/315

 

Good info!!!

I will be going with:

Front wheels and tires: 19x10 wheels with 275/30ZR19 Michelin PS4s (approx. 1" larger tread with the same diameter as stock).
Rear wheels and tires: 20x12 wheels with 305/30ZR20 Michelin PS4s (the Porsche version with approx. .4" larger tread with the same diameter as stock - I would prefer a larger 25 aspect ratio tire but nothing suitable is currently available).

and also:

Lowering the front 1" (one can only do this if the front lift option is NOT selected), lowering the rear .75". This change will increase down force and reduce understeer.

Seting the front camber to -2.5 degrees, front caster to ~ 8.0 degrees and front toe in to 0.0.
Seting the rear camber to -2.0 degrees, rear caster to ~ 0.0 degrees and rear toe in to 0.0.

If initial testing results in too much oversteer, mounting an adjustable rear anti-roll bar which is centered on the stock anti-roll bar. Then decrease rear roll resistance until neutral handling is achieved.
If initial testing results in too much understeer, mounting an adjustable front anti-roll bar which is centered on the stock anti-roll bar. Then decrease front roll resistance until neutral handling is achieved.

Adjusting tire pressures as required to fine tune handling.

 

Weird. Wider tires help it handle better?


Also, the C8R might as well be a 458R. Other than looking similar, it has virtually nothing in common with a C8.
heres a video of the c7R. What makes you think "OEM C7" about that?
https://www.youtube.com/watch?v=B_4p...ature=youtu.be

 

Why dont you drive the car first? Also... Those wheel selections are terrible for tracking. 25 aspect ratio? On what? A 305? That's like a rubberband tire.
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lol this is going to end with a C8 in a wall.

 

There are LOTS of ways to diddle with the oversteer/understeer relationship. {
Anti-Roll bars
Tread Widths
Track widths
Roll centers
Roll axis inclination
Springs
Shocks
Ride Heights
Camber
Toe
and even air pressure
} to name a few.

The race car has probably alters all of the above, so blindingly following what the C8.R has done is going to lead in an unprofitable direction, unless you change all of them.

Besides, one should wait to drive the car to see what it needs to be completely satisfying.

 

The C8R has nothing in common with the C8Z51. Again, you might as well base your decisions on the 458 or something. It's probably more similar to a 458 than a C8R, to be honest.

 

Yes, wider front tires with the same width rear tires will reduce understeer when everything else is equal.

30 aspect ratio. This exact setup has been used on a McLaren 720 for competing in the One Lap of America race. Besides, I want a setup that works both on the track and the road. Furthermore, these tires are the same diameter as stock so the cars electronic systems will be happy!

When driving at ten tenths, I'll be driving on a track.

If you actually read my post, you might notice that I will be modifying many of the items on your list.

Actually, the C8.R has a great deal in common with the stock C8 since it uses the same chassis. Obviously, unnecessary items have been removed to save weight and, among other changes, the suspension has been tuned to eliminate the excessive understeer.

 

outstanding advice

 

Huh, turns out a picture is worth a thousand words....

 

I don't mean to be rude but you sound like you've never been on track. ever.

Do you Know how aspect ratios work?
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This is a quote from GM media:"The C8.R utilizes a production 2020 Stingray chassis structure produced in the Bowling Green Assembly plant. The chassis is then modified to meet race series requirements.".

Yes, I have both motorcycle and car track experience. I am switching from motorcycles to cars because I am older and going down on a motorcycle at the track hurts!

And, yes I know how aspect ratios work. As I mentioned in a previous post this tire setup has been used to win track races in the One Lap of America which is basically a 3,500 mile race.

For the record, F1 will be switching to low profile tires in 2021.

I don't know how much you know about aspect ratios, but with proper suspension design, low aspect ratio tires work fine.

And, finally, yes, you are being rude!

Also, for the record, the changes that I am suggesting are not for racing. Instead, this setup is meant to promote a neutral handling road car that can be effectively used for track days. I would guess that the Z06 version suspension and tires will be somewhat similar.

 

You guys need to read this (especially the first paragraph). The Toyota Supra is tuned to be "neutral", handling wise. "Neutral" is a 2 edged sword.

https://www.caranddriver.com/feature...lightning-lap/

 

I will be ordering the over steer option this is based on quantum mechanics
1 larger steering wheel
2 smaller rear tires
3 louder horn
4 chrome rims

 

I think you're missing the really thick sarcasm.


It has the same frame rails. That's about it. No part of the suspension/suspension geometry is similar. It's all custom fabbed stuff. I'm not sure I'd refer to "thrown in the trash and designed ground up" as merely "tuned."

 

Sorry for being dense. I did think that anyone that was tracking a bike would know about the effect of wider tires!

Where does "thrown in the trash and designed ground up" come from?

I assumed that the A-arm attachment points remained the same but that longer, steel A-arms are used in place of the stock aluminum ones. Regardless, I find it encouraging that the stock chassis is used.