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Wheel size question - C7 GS

 
Old 03-01-2019, 09:56 AM
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GoatHead
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Default Wheel size question - C7 GS

What are the advantages of running 18" other than tires cost/availability?

I am getting nervous about stock wheels cracking/bending and ruining a track weekend, and I am considering forged or spin-forged wheels. However, I have small garage and smaller budget, and I am considering one set of wheels in stock sizes for both street and HPDE.

Another question: Which brands are considered strong, dependable, track worthy, and not braking the bank? I know it is a tall order, but I am sure not every HPDE enthusiast has a deep pocket for Forgeline. I am not racing and I am not a club member.

Thanks,
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Old 03-01-2019, 11:07 AM
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Originally Posted by GoatHead View Post
What are the advantages of running 18" other than tires cost/availability?

I am getting nervous about stock wheels cracking/bending and ruining a track weekend, and I am considering forged or spin-forged wheels. However, I have small garage and smaller budget, and I am considering one set of wheels in stock sizes for both street and HPDE.

Another question: Which brands are considered strong, dependable, track worthy, and not braking the bank? I know it is a tall order, but I am sure not every HPDE enthusiast has a deep pocket for Forgeline. I am not racing and I am not a club member.

Thanks,
Pretty much it's all about tire availability and cost. I can run used slicks for a fraction of the price of new tires. That and weight, Going from stock wheels with runflat tires to slicks and 18" Forgelines dropped 55 lbs from the car. However, the car was designed around the run flat tires.
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Old 03-01-2019, 11:33 AM
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Originally Posted by Poor-sha View Post
Pretty much it's all about tire availability and cost. I can run used slicks for a fraction of the price of new tires. That and weight, Going from stock wheels with runflat tires to slicks and 18" Forgelines dropped 55 lbs from the car. However, the car was designed around the run flat tires.
Thanks for the response.
I drive to and from the track, so slicks are not an option for me. Also, I am still Green, so performance and lap time is not priority either. I have 3 sets of MSS ZP - one on the car and the other two I bought off other cars in like-new condition. So, I have plenty of rubber to last me until the end of the year at least.
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Old 03-01-2019, 03:09 PM
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Getting a non-OEM set of wheels makes running a 315 tire on the front a possibility. I've really liked how it's changed the balance of the car on the track (no more understeer, unless I've really overcooked the corner entry).

18x11 on the front and 18x12.5 on the rear, but to get the fronts to fit without rubbing I think you'd need a wheel available with the correct offset... and that might not be available from an off-the-shelf wheel.

So far I've only used with BF Goodrich Rival-S (315/30-18 front and 335/30-18 rear) but they've done well on the street and the track. I wouldn't hesitate to use these as my only wheels/tires if needed, but I do like having the stock wheels/tires around to swap to between track days.

Weight difference between OEM and my Forgelines...

Stock Grand Sport wheels and tires:
Front with 295/30-19 MPSS = 52.6lbs
Rear with 335/25-20 MPSS = 60.4lbs

Forgeline GS1R Open Lug w/Cap:
Front (18x11) with 315/30-18 Rival-S = 51.6lbs
Rear (18x12.5) with 335/30-18 Rival-S = 53.2lbs

On the front increased the wheel/tire width and still lost at least 1lb each... the rears are over 7lbs each. Both sets have TMPS, so that should be the same.
The stock tires are near end of life (front is down to the cords) and the Rival-S are fairly new and have a bit of pick-up from a track day... so difference might be a tad larger if they were both new/clean.
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Old 03-01-2019, 05:50 PM
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That's a lot to answer.

Forgelines are great, I own a set of them (my third over the years), but they do cost. For my C7GS I ahve 2 sets of Forgestars too. And I've had a lot of those over the years and they are certainly more cost effective and stronger than a cast wheel or a replica. And not heavy either.

BTW am a dealer for both, which is partially why I own some of each, mine are all in 19" more on that later.

As for tires. First the front brakes are an issue particularly for 18" though it's not terrible with steel. It's a bit pain with carbon though. Still not impossible but options are very very limited. Things liek the BFG Rival S... you can track them but they do get hot and greasy in a few laps and slow down. The wear isn't like a true street tire, and they suck in any kind of standing water. I mean *suck* but are fast in the damp because of the compound.

Another option is to go 19" all around. Again this depends on your tire choice a lot but there are a lot of more true street tires out there that will work well on a track than you might think, and 19" rears cost less than 20's.

I do tires as well as wheels and I have another wheel option in 19" square that are sub $1200 for a set, and are flow formed like the Forgestars but aren't forgestars. And are much quicker for me to deliver. And we can talk about tire options that best suit you, if you like since the wheels and the tires need to fit each other... but also you have to watch sizing to keep the Electronics gods happy. And there is a new batch of pretty darn good dual purpose tires on the way. Not official yet, so until it is I can't say a lot more, not a big secret and the tire already exists for other GM cars, just not pricing and final sizing information out yet.
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Old 03-01-2019, 05:58 PM
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This is my current car on CF5's in 19" all around (on my fall/winter tires). I have another set for other tires.






This was my previous C7 GS on my Forgeline VX1R's. Also 19" all around
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Old 03-01-2019, 10:04 PM
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Signature wheels... lower price, custom (perfect) offsets, forged
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Old 03-01-2019, 11:10 PM
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Well there's retail price, and then there's actual sale price. I will admit when I went over there to take a look I was expecting to see a number quite a bit less. But that's not exactly a different kind of price range from forgeline.

In fact I did a set of Porsche wheels using the big center-lock design which tend to be more expensive and out the door deliver to the guy they were quite a bit under six grand. Don't get me wrong I realize that is not chump change, which is why we offer the flow formed wheels. I'm just saying that a lot of those wheels have a retail price of 4500 to $5,500 a set from signature, and there's a little bit of room to work.
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Old 03-01-2019, 11:53 PM
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I too have a C7 GS. I just purchased a set if C6 GS wheels and NT01s. All seasons are going on a 19/20 set of wheels for daily driving. I will be towing my track wheels in a trailer. There are many tire options in the 18/19 C6 setup that are dual purpose and much cheaper. I would recommend Super Sports which are non zp in that size. A lot of sales going on right now especially on the rears. Check TireRack, SimpleTire, and Tirebuyer. This way you have a kind of dedicated track setup that will allow you to drive to the track and be cost effective.
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Old 03-02-2019, 02:19 PM
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My signature wheels (SV502) for my C7 Z06 were $3600 (18x11, 18x12.5), and the offsets are perfect.
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Old 03-02-2019, 04:29 PM
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Originally Posted by NTMD8R View Post
My signature wheels (SV502) for my C7 Z06 were $3600 (18x11, 18x12.5), and the offsets are perfect.
So about the same as a set of CCW TS12s.

Bill
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Old 03-03-2019, 05:19 PM
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What size/brand tires do you run with the 19s? I run 19x10.5 19x12.5, but I am new to HPDE and just picked tires that were closest to the oem radius. 295/30/19 (I had a set on hand or I would have used 285s) and 325/30/19

Originally Posted by [email protected] View Post
That's a lot to answer.
or
Forgelines are great, I own a set of them (my third over the years), but they do cost. For my C7GS I ahve 2 sets of Forgestars too. And I've had a lot of those over the years and they are certainly more cost effective and stronger than a cast wheel or a replica. And not heavy either.

BTW am a dealer for both, which is partially why I own some of each, mine are all in 19" more on that later.

As for tires. First the front brakes are an issue particularly for 18" though it's not terrible with steel. It's a bit pain with carbon though. Still not impossible but options are very very limited. Things liek the BFG Rival S... you can track them but they do get hot and greasy in a few laps and slow down. The wear isn't like a true street tire, and they suck in any kind of standing water. I mean *suck* but are fast in the damp because of the compound.

Another option is to go 19" all around. Again this depends on your tire choice a lot but there are a lot of more true street tires out there that will work well on a track than you might think, and 19" rears cost less than 20's.

I do tires as well as wheels and I have another wheel option in 19" square that are sub $1200 for a set, and are flow formed like the Forgestars but aren't forgestars. And are much quicker for me to deliver. And we can talk about tire options that best suit you, if you like since the wheels and the tires need to fit each other... but also you have to watch sizing to keep the Electronics gods happy. And there is a new batch of pretty darn good dual purpose tires on the way. Not official yet, so until it is I can't say a lot more, not a big secret and the tire already exists for other GM cars, just not pricing and final sizing information out yet.
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Old 03-03-2019, 06:40 PM
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I was told that the slightly taller tire profile when using 18" rears provides better bite on corner exit. But that could be tire brand specific (Hoosiers?). And I don't have personal experience with that - to get the front-rear stagger right with the tires I wanted to use at the time, I ended up having to use 19" rears for my track wheels.
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Old 03-03-2019, 08:33 PM
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Originally Posted by bill.c6z06 View Post
I was told that the slightly taller tire profile when using 18" rears provides better bite on corner exit. But that could be tire brand specific (Hoosiers?). And I don't have personal experience with that - to get the front-rear stagger right with the tires I wanted to use at the time, I ended up having to use 19" rears for my track wheels.
I think technically that is correct and it's why you tend to see larger diameter rear tires on purpose built racecars. The issue is simply will it fit without tearing up the car. I ran 680 diameter tires on track and it still tore up the rear fender lined and I had to bend back one of the support brackets that was grinding on the tire. You may get a 705 to fit but if you are really hammering the car it's going to tear stuff up.
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Old 03-04-2019, 12:19 AM
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$3600 for wheels isn't really cheap, and all I can really say is that folks might want get a quote on some before deciding.

As for the 18" and putting power down. It's mostly a myth. A race tire is pretty stiff no matter what, and 18" gives up some contact patch length to 19". And unless you are running the really call 345 18, then you aren't gaining much "softness" in the construction. i have not run 18" rears on my C7, but i did run tests on my C6 18 to 19" and found on tangible difference in power down capabilities. I did so on both BFG Rival S and Hoosier A7.
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Old 03-04-2019, 12:40 AM
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Originally Posted by Viking0728 View Post
What size/brand tires do you run with the 19s? I run 19x10.5 19x12.5, but I am new to HPDE and just picked tires that were closest to the oem radius. 295/30/19 (I had a set on hand or I would have used 285s) and 325/30/19
The size and brand has a lot to do with what you want/expect from the tire. Some buy based on cost, some base on ultimate speed, some on wear, etc. You do not need to stay with OEM radius but it does help to make sure you are not going too far off of it.

So, are you after the fastest tire? A tire that you can drive to the track, maybe in the rain, and not die? Will you change tires, or have a rain set? Do you run someplace where it's super hot, or super abrasive?

You could run a Hoosier A7, or R7, or the Pilot Sport Cup 2's or Pilot Sport 4S, or Continental Extreme Contact Sport and on and on. Each has pro's going for it (and there are others as well). in 19" the "fast" 200 TW stuff like Rival S and RE71R don't really have a suitable front or rear size and those get pretty greasy quickly on the track. Most that run them seriously in time trial situations only do a few laps and pit because the fastest laps are already done by then.

Happy to help, but some context in what you are seeking would be helpful. I do not like to just make recommendations in a blanket manor, but more specifically.
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Old 03-04-2019, 06:45 AM
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Originally Posted by [email protected] View Post
The size and brand has a lot to do with what you want/expect from the tire. Some buy based on cost, some base on ultimate speed, some on wear, etc. You do not need to stay with OEM radius but it does help to make sure you are not going too far off of it.

So, are you after the fastest tire? A tire that you can drive to the track, maybe in the rain, and not die? Will you change tires, or have a rain set? Do you run someplace where it's super hot, or super abrasive?

You could run a Hoosier A7, or R7, or the Pilot Sport Cup 2's or Pilot Sport 4S, or Continental Extreme Contact Sport and on and on. Each has pro's going for it (and there are others as well). in 19" the "fast" 200 TW stuff like Rival S and RE71R don't really have a suitable front or rear size and those get pretty greasy quickly on the track. Most that run them seriously in time trial situations only do a few laps and pit because the fastest laps are already done by then.

Happy to help, but some context in what you are seeking would be helpful. I do not like to just make recommendations in a blanket manor, but more specifically.
I will drive to the track. I'm in Florida, so the cold weather isn't that much of a concern, all my track days will be local to Florida or the Southeast. I have a set of daily tires (OEM wheels with MPSS), I will change to my 19s for the track, drive there, then drive back and switch to my daily tires.

I'm looking for a balance between affordability/durability/performance. I don't want to spend money on track days and then wish I had better tires, I also don't want to buy tires that are more than I need and will wear out quickly which means I have less money for track days.

Thanks for the quick reply.
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Old 03-04-2019, 08:48 AM
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As I mentioned, get a set of C6 GS/Z06 OEM wheels off of someone on the forums. NT01s will easily last you 15-20 days depending on skill. Also they will wear out before they heat cycle out. You can run them down to the chords. Your looking at 2K at most for this setup. Shop around for tires. Some places have cheaper fronts and others rear.

To keep costs down further, buy lightly used OEM pads. $150 for a set with little miles is common.

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Old 03-04-2019, 01:02 PM
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NT01 is an option, but the biggest rear is a 325/30 which they only spec up to a 12" wide rear. And the 305 is what you'd want on the front as it fits a 10.5, but is also shorter than the 285/35 which helps keep all the nannies happy.

That said, I'd look at R888R. And I say this because they come in a LOT more size option in 19". 275/35, 285/35, 295/30, 305/30, 325/30 and 345/30. If you need help on those, I deal with them as well. And I hear tell Goodyear is coming with a new version of something in a lot more sizes too.
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Old 03-04-2019, 02:07 PM
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For 18" wheels... Rival-S, NT01, R888R, and Hoosiers (R7 and A7) are all available in 315/30-18 (front) and 335/30-18 (rear). There are also some non-DOT slick options if one decides to transition to towing their car to/from the track.

I drive to/from the track on Rival-S and will eventually do the same with NT01 or R888R (with a second set of wheels/tires for daily driving). One of the main reason I went with 18" wheels is the huge number of options available when it comes to tires... both in brands and performance levels. I'm starting with the Rival-S (a street tire), then will likely move to the NT01 (R-Comp), and eventually maybe even to slicks (but that's a long ways away).

When I was looking at tire sizes, diameters, etc. I too had concern about the traction control/PTM and how it would react to non-OEM tire sizes. From what I could gather, and I'm far from an official on the subject, my goal was to keep the rear tires slightly larger than the fronts (MPSS rears are 103.10% the diameter of the fronts). Here's a table of what I was looking at:


Another question to ask when it comes to choosing tires... what brake pads are you using? If you're swapping pads, then it's not really an issue. If you're looking to keep the same pads for street/track... I don't think you'll be happy getting a wheel setup that can only run an R-Comp tire (NT01/R888R) or DOT slick (Hoosiers). I did quite a few track days on the OEM pads and the Rival-S without issues (having proper brake fluid is a must, and I understood that I'd need to be gentle on the brakes compared to a more track-focused pad). That said, I've since started swapping rotors/pads before track days and have noticed a big difference in the braking potential.
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