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The only advantage to cast is cost.

You NEVER see a true preformance car sporting cast wheels.

Then of course the reciprocating (it's late....you meant rotating/rotational?) mass reasons why forged is better...
Considering that the average SS owner has a fairly high likelihood of curbing at least one wheel relatively soon after purchase, I'd say that cast might actually be "better" when it comes to replacing a wheel--but I understand your point, if using the car to it's ultimate performance capability is the primary consideration, as far as what it means to use light(er) wheels. With a 4000# vehicle, this COULD become an issue.

In reality, from an outright safety standpoint, it would probably be better to use Caprice PPV 18x8 HD steel wheels for track events, even though they weigh more and leave a bit to be desired in the looks department. They are confirmed to clear Brembo calipers, but I am not sure about the use of D1474 front pads (with dampers)--non-damper pads can be substituted, if there's a clearance issue. If more wheel bead width is needed to support a fatter tire, just have them widened.

It's not clear if the cost difference is reflected at the parts counter....that gets into production volume to impact cost per part, knowing that these are for a relatively low production application--at least by GM standards.

Buying the forged SS wheel, it arrives in a box that says "Made in Australia", yet it's clearly marked on the part as produced in the USA. Is every SS wheel purchased by Holden first shipped to Australia, re-packaged, and then shipped back to the US into GM SPO (as spares)? Someone at GM doesn't care or realize that the 14-15 SS wheel could easily be moved directly into the NA parts system without taking a Tour of the Pacific, if that's in fact what is happening--and it has to impact the wheel cost here.

2014/2015 SS wheels: $795 each list + $50 core
Front
Rear

2016 SS wheels: 92281327 & 92283925 do not price--will check at dealer
?
?

Viewing the offerings from WheelKing (in Australia) certainly brings some confusion about OE wheel costs, but it has little bearing on buying OE wheels here. Their pricing is not relevant, really, as it represents take-off inventory, and as the 2016 SS type wheel is newest, it is also least available in the aftermarket, so the demand vs availability makes them cost more for the time being.

Forged (Alcoa) 14/15 SS
front - $2430 AUD (set of 4)
rear -
$1746 AUD (set of 4)

Cast 16 SS (WheelKing calls them forged!)
front - $3160 AUD (set of 4) black
rear - $1980 AUD (set of 4) black
 

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Absolutely fascinating!


1. Helloooo .. they are made in china indochina !

2. Price? I said cost of MAKING THEM.
Casting aluminum is far cheaper than forging aluminum,
made in china indochina is far cheaper than made in the US,
and that includes shipping and greasing the skids.
Cost is why GM dropped ALCOA! How much, that I don't know.

And forged is much more durable than cast, not just rims, any product.
Cast is not friendly to flexing, forged is.
Cast cannot take too much abuse, forged can.
Cast cracks easily, forged not.

I'm done. This could get insane and I don't know why.
The cast vs. forged is pretty clear.

.
Sometimes I need to listen to myself!

No chrome on the 2014-2015 wheels - polished and clear coated. Won't bore with the advantages of FORGED by Alcoa over the Asia sourced castings on the 2016.
From another thread, but applicable.


China makes excellent products just as they also make c**p junk. You just have to specify what you want and demand compliance. Don
We can probably buy the same cast rims at Walmart.
I simply gravitate to "Made in USA" stuff where at least I know there is minimal slave labor or child labor.
One must wonder how much of the so called '17 SS may be made in china indochina.


In the trivia department, for "GMC Trucks":


On thing I have not seen addressed yet: Which type of wheels look best when coated with brake dust, cast or forged?
LOL ... Nice sense of humor! Needed that !


Not picking on you Bill...

The only advantage to cast is cost.

1) You NEVER see a true performance car sporting cast wheels.

You also have to realize the metallurgy differences between the aluminum in casting vs forging. It's a given that forged metal must "flow" under pressure into the desired shape (hint bend or break). 3) Cast metals by comparison are brittle and prone to cracks and fractures.

Note that I am not saying the OEM '16 cast wheels are weak and will fall apart. They are made to handle the vehicles weight and expected load rating and forces. However, 2) when Bubba hits a pot hole, the forged wheels have a better chance of survival, and better chance of repair (through heat and beat methods).

Then of course the reciprocating mass reasons why forged is better...
1. Almost almost correct. There is this '16 SS; However you did say "true performance".
This change in production (dropping USA Alcoa) was ill-conceived; bean-counter decision for sure.

2. Agree

3. Agree


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I live in Michigan, used to drive around 100 miles a day (some days I've done that and more depending on what I need to do and where I need to be)

Potholes are everywhere, can't always avoid them.

It happens when you drive a lot, and the roads suck. I have select routes on purpose but sometimes you can't win haha.

FYI / neat info - As far as GMC...it was really Rapid anyway out of Pontiac. That's why they are "allowed" in the Pontiac Oakland Club. I pass Rapids old power station regularly...
 

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While it is true that many cast metals are brittle (e.g. Iron), cast or forged aluminum is NOT brittle at all.

Unlike steel, aluminium cannot be successfully designed to flex at all in a wheel application, so they will NOT suffer from fatigue if they are designed correctly.

It's true that a forging gives a more uniform material, but as I noted earlier, more importantly, a stronger alloy (40%+) is normally used when forging Al wheels. So the increased strength MOSTLY comes from the better alloy.

In the case of cast wheels the designer will increase the amount of metal in the wheel to compensate for the weaker alloy and the less uniform grain structure.

At the end of the day, in a car like the SS, the only REAL difference is the weight, you can pretty much bet that they perform almost identically in service. (Pot holes and all).

i.e. I bet the engineering performance specs are identical. (Weight excluded)

Not picking on you Bill...
Cast metals by comparison are brittle and prone to cracks and fractures.

Note that I am not saying the OEM '16 cast wheels are weak and will fall apart. They are made to handle the vehicles weight and expected load rating and forces. However, when Bubba hits a pot hole, the forged wheels have a better chance of survival, and better chance of repair (through heat and beat methods).

Then of course the rotating mass reasons why forged is better...
 

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But you can't narrow it down like that. If you notice in my reply about going down to 245, you also note I mention about increasing to aspect ratio to 40.

But let's say you kept the 35 aspect ratio on a 245. You'd go down from a 96.25mm sidewall (OEM SS) to an 85.75mm which is a 10.5% change. To gain back the load rating and heat tolerance, you need an even thicker and heavier sidewall.

Like I said, yes drag slicks are wider than 275. But look at the wheel diameter and sidewall aspect ratio. Again, watch in slow mo. Understand drag cars don't have to turn corners.
I agree, but that doesn't really answer or clarify what I asked.

I'm not arguing aspect ratios (which we both know are just a percent of tire width) and I mentioned keeping sidewall height the same (which we both agree would require a higher aspect ratio).

This is simply a question of "is wider better," more specifically for street tires (as that's what most of us run). So let's even just leave drag slicks out of it. As I mentioned before, I'm well aware of what drag slicks do, how the walls wrinkle and have seen the videos.


I'll give my personal example again. I went from 225/60/15 rear tires to 275/35/18 on my classic Mustang. The significantly stiffer and smaller sidewall should be worse for traction, the overall height is very similar, but I noticed a HUGE improvement in traction.
 

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I agree, but that doesn't really answer or clarify what I asked.

I'm not arguing aspect ratios (which we both know are just a percent of tire width) and I mentioned keeping sidewall height the same (which we both agree would require a higher aspect ratio).

This is simply a question of "is wider better," more specifically for street tires (as that's what most of us run). So let's even just leave drag slicks out of it. As I mentioned before, I'm well aware of what drag slicks do, how the walls wrinkle and have seen the videos.


I'll give my personal example again. I went from 225/60/15 rear tires to 275/35/18 on my classic Mustang. The significantly stiffer and smaller sidewall should be worse for traction, the overall height is very similar, but I noticed a HUGE improvement in traction.
And the rubber compound was also very different too.
 

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this is a really good point...

As when you are off-roading on sand for example, "airing-down" the tires changes the contact patch by making it LONGER. the same principle applies in drag racing where a wider tire will have minimal effect on reduced 0-60 times whereas a taller-tire (higher sidewall) with reduced pressure will make a larger difference to launch.

Note its important that you keep the overall diameter the same or less than stock as you don't want to be losing mechanical-advantage (application of torque to the tarmac)

peace!

Boz
So we're still all agreeing on lower pressure and taller sidewalls being better for traction.

I'm just still trying to focus on the 1 statement no one else is backing up:

When he responded to someone who went from 275 to 245 tires, he suggested that would INCREASE traction for acceleration.

Everyone else seems to be saying there should either be: 1. No difference, or 2. The 275 should be marginally better.


Other than some random online discussions from people who "learned something different in engineering class," I can't find much.


I'd love so see some real world testing. Has no car magazine done a simple tire swap and compared skidpad, 0-60, etc with the same brand tires? I'll keep digging.
 

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Fascinating. https://youtu.be/gI-aqzscRAM

I've was always in the wider is better camp because bigger contact patch. Apparently wider is better because it allows you to use gripper rubber. TIL.
That video is overly simplistic, and it begins with the incorrect assumption that a wider gives you a larger contact patch, which according to my research is not the case.
 

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Bleh.... still can't find what I'm looking for.

Here's a test with results that DON'T surprise me, but aren't really helpful.

C&D tested a very slow VW Golf with the base engine (non-turbo).
Not surprisingly taller wheels and wider tires helped with cornering, but the added weight slightly hurt acceleration.

Why it's not helpful? That car isn't traction limited at all.

Effects of Upsized Wheels and Tires Tested - Tech Dept. - Car and Driver


Then there's Hotrod magazine.
How to Select a Tire - High Performance Pontiac Magazine

"Lubbers also noted that for bracket racing, you want the biggest tire possible. The term “wider is better” applies here. Drag Racing School professor Frank Hawley said it well here a couple of years ago: “Stuff the biggest, stupidest tire you can fit under the fender wells.” What you give up in speed can be gained back in consistency."

This definitely suggests increased traction (60 foot times) are better with wider tires, even though the added weight hurts you in the top end.

Why it's not helpful? They're talking drag slicks. So we can't necessarily assume the same will be true for street tires.


For drag radials, there's this article:
http://www.stangtv.com/tech-stories...101-what-you-need-to-know-about-drag-radials/

Only conclusion about width is that with wider tires you can run lower tire pressure and increase the contact patch.


Why it's not helpful? I'm not airing down my street tires on the street. Aye aye aye

At the very least I think I've concluded that wider tires don't have the impact on the street I thought they did.
 

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I will throw my hat into the ring now. The first cast wheels for Corvettes were plagued with problems that delayed them for a year. That being said they still had problem with porosity owners were having tires leak down thru the rims. That was a nite mare for warranty work the 63 Corvette knock offs had this problem and delayed coming on line the aluminum head introduced in or about 1960 were withdrawn from production. In 1986 I ordered a new Corvette with aluminum heads car did not come with aluminum heads so I backed out of the deal my 1985 was the same engine so forget it.
Just wanted you guys to know all the problems GM had with Aluminum parts.
Now back to your regular program.
z51vett
Doug
 

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True, but it's just because GM and their suppliers were not used to working with Aluminum. (Totally different properties to cast iron)

Despite all the uproar with recalls, etc, automotive parts (and cars in general) are built to a such a high technical standard that engineers in the 1960's would not believe it possible at the price we see.

I will throw my hat into the ring now. The first cast wheels for Corvettes were plagued with problems that delayed them for a year. That being said they still had problem with porosity owners were having tires leak down thru the rims. That was a nite mare for warranty work the 63 Corvette knock offs had this problem and delayed coming on line the aluminum head introduced in or about 1960 were withdrawn from production. In 1986 I ordered a new Corvette with aluminum heads car did not come with aluminum heads so I backed out of the deal my 1985 was the same engine so forget it.
Just wanted you guys to know all the problems GM had with Aluminum parts.
Now back to your regular program.
z51vett
Doug
 

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While it is true that many cast metals are brittle (e.g. Iron), cast or forged aluminum is NOT brittle at all.

Unlike steel, aluminum cannot be successfully designed to flex at all in a wheel application, so they will NOT suffer from fatigue if they are designed correctly.

It's true that a forging gives a more uniform material, but as I noted earlier, more importantly, a stronger alloy (40%+) is normally used when forging Al wheels. So the increased strength MOSTLY comes from the better alloy.

In the case of cast wheels the designer will increase the amount of metal in the wheel to compensate for the weaker alloy and the less uniform grain structure.

At the end of the day, in a car like the SS, the only REAL difference is the weight, you can pretty much bet that they perform almost identically in service. (Pot holes and all).

i.e. I bet the engineering performance specs are identical. (Weight excluded)

I believe this whole discussion is about semantics. In my profession, we R&R parts based on cycles or events.

Structural metals such as aluminum, do not have a distinct limit and will eventually fail even from small stress amplitudes.
In these cases, a number of cycles is chosen to represent the fatigue life.
Adding a stress point, such as oxide or metallic impacts with a curve or a pothole, significantly affect the life of the item.
The tire is the "bodyguard" - it is designed to take the hit so the metal does not suffer. Proper inflation is critical.

As you stated, grain structure and alloy variations heavily weight on such cycles.
So does the process, hot or cold, the aging, the exposure, the hardening.
Fatigue limits are and have been controversial since men created forged swords.
To a great extent, some personal preference comes into play.

However, controversy put side, at the end of the day, pound per pound, forgings rule the day - its science.
Maybe we should move the discussion to pistons or rods?






.
 

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On the OEM wheel, I'm yet to see a discussion of the only thing that matters - wheel's moment of inertia. The weight itself doesn't matter much, but how the weight is distributed in the wheel will determine how much of the engine's power will go to accelerating the wheel itself. Someone should measure that ;)

On the contact patch size,wheel width etc:
Wider tires do not increase contact patch size, only change the shape of the patch. The shape determines how you grip. Contact patch size is determined by weight of the car and pressure in the tires.
That's only true of bicycle tires with no sidewall. Car's tire is a lot more complex than that high-school level physics analogy. In automotive street-legal tires with load-bearing sidewall, wider=larger contact patch. Every time.
Here's my favorite contact patch calculator. Play with it.
BND TechSource - Tire Data Calculator (needs Java to work).

That doesn't mean that straight line acceleration will be better in a wider tire though. Longitudal grip depends on the contact patch size, but also on how evenly pressure is distributed with in. More even distribution = more grip. If the contact patch is short, the distortions near the edges will be large, and the area with no slip will be small, and the grip will be lowered compared to the tire of the same circumference and higher sidewall (=narrower).

In practical terms, I think that may only come into play with winter tires, which have sidewalls soft enough for the overall size of the contact patch to change less for the wider tire. For summer tires 275/35/19 will have more grip in any direction than 245/40/19, since the increase in the contact patch will be large.
 

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I will throw my hat into the ring now. The first cast wheels for Corvettes were plagued with problems that delayed them for a year. That being said they still had problem with porosity owners were having tires leak down thru the rims. That was a nite mare for warranty work the 63 Corvette knock offs had this problem and delayed coming on line the aluminum head introduced in or about 1960 were withdrawn from production. In 1986 I ordered a new Corvette with aluminum heads car did not come with aluminum heads so I backed out of the deal my 1985 was the same engine so forget it.
Just wanted you guys to know all the problems GM had with Aluminum parts.
Now back to your regular program.
z51vett
Doug

Add to that the porosity and cracking problems with the aluminum Northstar engines, 1992+
Aluminum may well be the most abundant metal on the planet, but it is simply more difficult to work with.

.
 

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That's my point, Aluminium wheels HAVE to be designed not to flex at all or they will fail after a period.

Thus, strength is the major factor in Aluminium wheel design and in the case of the SS, my guess is that the 14/15's and the 16's are equal in that department.

Are the forged ones better? Yes, in the fact that they do the SAME job with less weight.

I believe this whole discussion is about semantics. In my profession, we R&R parts based on cycles or events.

Structural metals such as aluminum, do not have a distinct limit and will eventually fail even from small stress amplitudes.
In these cases, a number of cycles is chosen to represent the fatigue life.
Adding a stress point, such as oxide or metallic impacts with a curve or a pothole, significantly affect the life of the item.
The tire is the "bodyguard" - it is designed to take the hit so the metal does not suffer. Proper inflation is critical.

As you stated, grain structure and alloy variations heavily weight on such cycles.
So does the process, hot or cold, the aging, the exposure, the hardening.
Fatigue limits are and have been controversial since men created forged swords.
To a great extent, some personal preference comes into play.

However, controversy put side, at the end of the day, pound per pound, forgings rule the day - its science.
Maybe we should move the discussion to pistons or rods?
 
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