Hello - I have noted the lack of availability for reasonable track tires over the past long while now, and just took delivery of my C8 which I'm setting up for road course work. So I think that I've settled on just using OEM wheels to then have access to GY 3R's (when they're available) and Sport Cup 2's. For the Sport Cup 2's I was thinking about 265/35/19 and 325/30/20 - and will lower my car some (just like the looks of a tight wheel gap).

So does anyone have on track experience with these tire sizes? Thoughts appreciated.

 

I don't know much about C8 wheels or how much space is available in the wheel wells. Will 18 inch wheels fit the car? C7 owners use 18 inch wheels with the C7 Carbon Ceramic Brake Cars that have 15 inch rotors.

If you can fit 18 inch wheels then you could purchase used Pirelli Slicks for far less money and run just as fast. It looks like your stock tire diameters should be 25.8 inches in the front and 27.2 inches in the rear. If the tires would fit you could run 265/660/18 on an 18 x 9.5 wheel with an overall diameter of 26 inches. In the rear, you could run 325/705/18 on an 18 x 12.5 wheel with an overall diameter of 27.7.

The stock tire diameters establish a ratio of 1.054 (rear/front) while the Pirelli's give you a 1.065 ratio. As long as you stay within 0.04 of the stock ratio the C8 electronics shouldn't have a problem with them. The Pirelli's will give you more track days than the Cup2s, will have equivalent performance to the Cup2s, and will definitely provide better wear than the Cup2 for about half the cost of the Cup2s. As for wheel cost Apex wheels seem to be a good example of lower cost with great durability.

Bill

 

Agree with the above if youre going to be tracking all the time. These will be worth the money and save you money in the long haul as you can use takeoff r compounds


https://cicioperformance.com/product...noblock-wheel/


If you're just going to be messing around pick up a set of oem 5 spokes for 300 bucks and have fun. Ive got three sets i paid a few hundred for and have a street set, rain set, and dry set

 

Thanks Bill and bhvrdr, I've given some thought to Pirelli take offs but haven't been able to get there. So I bought a set of OEM's and am hoping that 265/35/19 and 325/30/20's work and will just use Sport Cup 2 for now. Hoping that those sizes work once I dial in some track alignment settings but I think I've seen enough to think that they should work. Appreciate the info.

 

I ran Falken RT660 on Aerolarri forged 265/35/18x8.5 and 305/30/19x11 for the first time today. No issues, aside from needing more negative camber (still on factory alignment). Massive wheel gap though, since overall diameter is -1.9% and -3.7%. Speedo was reading fast as expected by approx 4-5%. If 315s weren't backordered, I would have bought those. I wanted a little extra meat up front to counter understeer, but 325s should fit without issue.

I went 18/19 for tire selection and weight. My fronts are 20mm wider but still 1.1lb lighter per wheel/tire vs stock. Same width rears are 10.4lbs lighter per side!!

I just posted some info and pics here, post #538: https://www.corvetteforum.com/forums...post1605252599

 

I run 18s exclusively on my car and have been pleased for the most part with tire availability. If you are setting your car up for road work use do yourself a favor and address the brakes and the suspension, the car is woefully undersprung from the factory.

Have fun!

 

Hello, whosurdaddy! In my opinion I've been very happy on track running Cup 2s on OE sized wheels. I use 255/35 front (26" dia.) and stock 305/30 rear (27.2' dia.). The 255 front is 10mm wider than the OE 245 as this eliminates the remaining understeer that the track alignment doesn't correct.

Also, I question if 265 Cup 2s up front would be compatible with your wheel width. Some 265 Cup 2s call for 9"-10.5" width. Other 265 Cup 2s call for 9.5"-10.5". The OE front wheels are 8.5." And there's no advantage to increase the rears as you'll just exacerbate the understeer. Also, the track alignment in the owner's manual is good with the exception of the fronts. The stickier Cup2s need at least 3.25 negative camber, and possibly negative 3.5.

If you are determined to try the 265s up front, you should then try 315s in the rear, no wider to keep the understeer away.

 

Thanks for that - I've heard that I should expect some understeer. When does this present itself? Corner entry/mid-corner/exit/all of the above? And does changing the way you enter (slower on the steering angle) and how much you trail brake help? Advice here would help me come up to speed faster, so interested in your thoughts. I already know that I'll also have to deal with weird braking with that brake by wire stuff.

 

Understeer is designed in the chassis design to provide a safer car at the limit. It tends to be safer for a driver that is getting in over his head to experience understeer which inspires getting out of the throttle rather than driving off the road. Ideally, once coming off the throttle the weight returns to the front axle and the push from the rear axle is reduced hence understeer is resolved. Also, as you said, trail braking and a slower rate of turn-in can eliminate understeer. So while it is possible to drive around the understeering characteristic, and in fact every track driver stops an understeering moment every now and then, it's faster for the car to be naturally more balanced front to rear.

And while there are many elements that impact a cars F to R balance including but not limited to physical weight distribution, spring rates, anti-roll bar setting, front tires' air pressure vs rear tires' air pressure, and more, the tires' contact patch size will have an decisive effect if all other elements remain constant. So, if you keep your rear at the OE 305 and increase the front to 255 you have slightly improved the F to R balance closer to neutral. Then with a more neutral handling car with all things equal, you'll be able to enter the corner faster. Of course go fast enough and understeer will be there again and you can trail brake, turn in more slowly or go for even larger front tires (and wider wheels). It can be a vicious circle. From my experience if you are staying with OE wheel sizes, fronts at 255 is the way to go with the OE 305 rears, with at least negative 3.25 front camber. I'm trying a negative 3.5 degrees with my next alignment. Lastly, I would personally be reluctant to install 265s on an 8.5" rim because an overly wide tire for a specific rim size results in a crowning tire hence actually a smaller contact patch, and if you lower the pressure to eliminate the crowing, you'll roll-over on the shoulders, the tire will overheat, and etc.

 

Nice explanation by @copjsd . I'll add a couple cents...

I just finished Ron Fellows Level 1 at Spring Mountain in May. Their cars are on stock Michelin PS4S but with track alignment. The car still has understeer bias at the limit. The two biggest takeaways I had from the school were to trail brake a lot and use throttle steer, both skills help keep weight on the front axle. Depending on the corner, we would even trail brake past the apex at times. Longer corners, throttle balancing the car mid corner, we often used lift off throttle steer to get the nose down and better rotation towards the apex. There are several Spring Mountain C8 PDR videos (since they give you an SD card to keep) on YouTube, many with instructor comments or instructor driven hot laps. My instructor demo lap was excellent, with really good explanation along the way. I plan on uploading some of the school videos when I get a chance.

As far as 265s on 8.5" rim... Although 255 is max recommended for 8.5", autocrossers have been going up to 265, even 275. It's true, squeeze too much tire on and you end up with less contact patch. If you go wider than recommended, you need to use tires with stiff sidewalls and/or dial in negative camber to allow lower pressures. My Falken 265s on 8.5" show much better wear characteristics after a track day versus the stock 245 MPS4S. YMMV

 

Thank you @copjsd and @c0bra C8 ! Knowing what to expect when I get to the track is helpful and will also help me make some decisions. Love seeing comments about using all of these inputs to generate different corner dependent results. I have been doing this a long time, and I don't think that I'm the only driver that would say its been a long time (since my C5) since I've really felt comfortable behind the wheel in a Corvette. I just felt like my C6 and C7 Z06's were uncertain throughout the whole corner after initial turn in (turn in speeds were massive on those cars). I've spent a lot of time behind the wheel on Porsche GT cars also where I felt like adjustments were easy to deal with and didn't love the terror I felt behind in my later model Corvettes. Super happy to hear all of this feedback about being able to free myself up a little bit in the C8. Realize that this may not be everyone's experience and that suspension mods could have gone a long way.

 

Most Mid-engined cars have a critical cornering <something: maybe threshold>-- once you are cornering at this G-force-speed relationship:
a) if you remove-throttle, the rear end will glide out
b) if you add-throttle, the rear end will glide out
This is how you find the natural speed the car will carry through the turns.
A skilled driver can go through such a corner slightly faster by judicial timing of adding throttle and adjusting steering. Thurn 9 into 10 at (now demolished) TWS had this characteristic.

{NOTE WELL: removing throttle is like backing off the pedal by 1-2mm, adding throttle is like pushing the pedal down 1-2mm--NOT flooring it or backing off entirely}

 

Wonder if we could get to a more neutral balance by dialing out camber at the rear vs track specs (instead of reducing rubber at the rear)? So -2* vs -2.5*. If you look at F1 cars the seem to have much more negative camber up from vs rear.

 

IMO, reducing the rear contact patch rather than increasing the front may work to get the F to R balance more neutral however the net result will most likely be slower cornering speeds. Ideally you want every corner to provide the maximum grip while attaining a near neutral balance. However, if you set the rear camber at a negative 2 degrees you will likely wear out the outer shoulders prematurely.

 

Negative camber sets up a benign side thrust (inward) as long as it is not too aggressive..
This side thrust desensitizes the car to bump loads at the contact patch and can be used to increase temperature in the tire and move it towards the inside.
When too much heat is generated, excess wear occurs.

 

Thanks for this advice. I ordered a set of the new Forgedlite MC5s in OE sizing, and some Cup 2s based on your recommendation. Looking forward to trying that setup and the alignment recommendation, for spirited driving. Not sure if I can track my HTC because I could not wear a helmet in it without dropping the top. (way too tall)

 

This is an older thread from when I was setting up when car was new - spring 2022. As a follow up I stuck with blah heavy used OE rims as track wheels (just couldn’t make up my mind and they’re cheap) with Sport Cups 265/35 and 325/30 on per manual alignment settings for now.

After 5 days at VIR and 2 days at Summit Point I find the whole set up stupid heavy but I’m living with it - though the whole car feels ponderous on track. Applying a different driving style vs C7 platform with a slightly slower more patient corner entry and much earlier/fuller throttle in exactly the same way I drive GT3’s.

I’ve gotten some minor rubbing on the top inside of that mudflappything at the trailing edge of each front wheel well. Good track car, needs more power and to be more stiffly sprung.

 

Have you tried Supercar 3R's? I found them to be faster on-track than Cup 2's (in stock sizes) and the turn-in is more precise. I was surprised that the C8 doesn't seem to like the Cup2's as much as my C7Z did.

 

I haven’t, this is my first season with this car. Liked them on my C7 Z06.