New Cor 4-piece Wheels ***WARNING***

[The Stig]

Aluminum 6061-T6; 6061-T651

Subcategory: 6000 Series Aluminum Alloy; Aluminum Alloy; Metal; Nonferrous Metal

Composition Notes: Aluminum content reported is calculated as remainder. Composition information provided by the Aluminum Association and is not for design.


This first picture doesn't really mean much, it's more of just the chemical breakdown of Aluminum 6061. Aluminum 6061 is the Aluminum that Cor uses to make ALL of their wheels.

All black screenshots were taken from this LINK




Now, let's take a look at Ultimate Tensile Strength, you'll see that Al 6061 is rated at 45,000 PSI. That means it takes 45,000 pound-pressure per square inch of material before the material will bend, stretch, weaken, break, etc. So, assuming that the wheel broke not because of a manufacturing defect (or something similar) then that wheel was experiencing 45,000 psi and that's why it broke. I'm a volunteer firefighter and the pumps on our trucks only go up to about 300 psi. So that should give you an idea of how much force that is.

Adressing the idea that the "track" use damaged/weakened the wheels, again - not so much. Please direct your attention to Fatigue Strength, which is also known as Fatigue Limit. This is the point in which a material begins to weaken the material. In Al 6061 the fatigue limit is 14,000 PSI. Again, compare that to a fire hose.



This picture is more for information/reference than anything else. But now we're going to rule out the possibility of the "powder coating" causing the wheel breaking. Powder coating is usually done at ~400 Fahrenheit for let's say 30 minutes.

Aluminum 6061 (again what Cor uses in ALL of their wheels) has the following metallurgic properties:


This screenshot was taken from this LINK

Meaning, that in order for the Aluminum alloy to be weakened it must be heated to least 650 degrees Fahrenheit, and kept at that temperature for 2-3 hours before being cooled. Now I will admit, if this is the process that your powder coater uses then if/when your wheels break it's all on you.


I'm done for now, I might add more links later.

[The Stig]

Originally Posted by Tay

Please tell me more!

Originally Posted by Tay

These are supposed to be fully forged.

see my above posts

[CamaroFTW]

Sorry I just dont get buying all these mesh wheels for track use. They just seemed destined to fail. Great for street and car shows though.

[usmcjlp]

I have COR wheels purchased from Nineball. So far no problems and they bent over backwards to get the exact finish that I wanted. I agree that it sucks to have this happen and to receive a letter from an attorney. But let's give the company a chance to respond before we run them into the ground.

I wish nineball would weigh in here because he does a lot of business with COR. I know there are several other members that own these wheels as well. I haven't seen any other complaints from camaro5 members. Let's not rush to judgement here.

[dangjohnny]

There goes one wheel manufacturer to scratch of the list.

[midnighter]

That sucks.

[Fish-man]

How can COR wheels be worse (or better) than any other wheel? Truth is that compared to OE wheels, there is little known about which tests, or how many tests were run on anyones aftermarket wheels. Even if you knew that, how would you know what was good, without indepth knowledge about wheel engineering? Anyone with a CNC big enough (or mold equipment) can build a wheel (scary)

If COR markets as if it were for aggressive (track) use... then they should stand behind their product.

[Tay]

Originally Posted by The Stig

Aluminum 6061-T6; 6061-T651

Subcategory: 6000 Series Aluminum Alloy; Aluminum Alloy; Metal; Nonferrous Metal

Composition Notes: Aluminum content reported is calculated as remainder. Composition information provided by the Aluminum Association and is not for design.


This first picture doesn't really mean much, it's more of just the chemical breakdown of Aluminum 6061. Aluminum 6061 is the Aluminum that Cor uses to make ALL of their wheels.

All black screenshots were taken from this LINK
Attachment 435557


Attachment 435558
Now, let's take a look at Ultimate Tensile Strength, you'll see that Al 6061 is rated at 45,000 PSI. That means it takes 45,000 pound-pressure per square inch of material before the material will bend, stretch, weaken, break, etc. So, assuming that the wheel broke not because of a manufacturing defect (or something similar) then that wheel was experiencing 45,000 psi and that's why it broke. I'm a volunteer firefighter and the pumps on our trucks only go up to about 300 psi. So that should give you an idea of how much force that is.

Adressing the idea that the "track" use damaged/weakened the wheels, again - not so much. Please direct your attention to Fatigue Strength
, which is also known as Fatigue Limit. This is the point in which a material begins to weaken the material. In Al 6061 the fatigue limit is 14,000 PSI. Again, compare that to a fire hose.


Attachment 435559
This picture is more for information/reference than anything else. But now we're going to rule out the possibility of the "powder coating" causing the wheel breaking. Powder coating is usually done at ~400 Fahrenheit for let's say 30 minutes.

Aluminum 6061 (again what Cor uses in ALL of their wheels) has the following metallurgic properties:

Attachment 435565
This screenshot was taken from this LINK

Meaning, that in order for the Aluminum alloy to be weakened it must be heated to least 650 degrees Fahrenheit, and kept at that temperature for 2-3 hours before being cooled. Now I will admit, if this is the process that your powder coater uses then if/when your wheels break it's all on you.


I'm done for now, I might add more links later.

Wow. Thank you Stig. This is great. Ok dinner it is.

Just to clear things up. The wheels were painted and not powdercoated. Thanks again Stig.

[SS 376]

It's a shame because Cor and these other me-too forged wheel makers like 360, Vossen, DPE, etc. are making piles of money selling these wheels. I guess all that money is going to website design and not engineering.

OP, you're lucky this happened on a closed circuit and not on the road. You could've been killed. I've seen the story on jalopnik but make sure other auto websites like autoblog, etc. learn about this.

[The Stig]

Originally Posted by Tay

Wow. Thank you Stig. This is great. Ok dinner it is.

Just to clear things up. The wheels were painted and not powdercoated. Thanks again Stig.

I was kidding about the dinner thing, just let us know how it turns out.

[Nine Ball]

OP, sorry to see your Mustang get damaged like that. I agree that Cor would likely have avoided this mess, had they just taken the time to do the material analysis and report the actual findings, before denying your warranty claim. Just for your own information, most wheel companies will void any warranty if wheels are refinished or repaired outside their facility. While I don't necessarily agree with that, it does make it clean and simple to define what is allowed in terms of warranty. I did see they edited their website to include "track use", which does paint a negative picture on Cor.

This is the first time I've seen any Cor products fail in this manner. They use the same industry standard 6061-T6 aluminum forgings that every company uses. Cor manufactures wheels for numerous brand labels, including being the original manufacturers of 360 Forged - when they were in their prime. I've not seen any 360 Forged wheels fail like this, either. This makes for an unusual case, for sure.

I suppose the lawyers are involved, and will ultimately decide on what is right. Only the lawyers will win in a case like this, unfortunately.

Good luck, and if I can assist you with questions, feel free to email me at Tony@DV8motoring.com

[Pentatonic]

Originally Posted by The Stig

...

You got some things correct, but some things incorrect. 300 psi is not a force, it's a pressure (or stress) depending on the situation. It's force per unit area. You can take a 300 lbs force over 1 square inch and generate 300 psi. 300 lbs over 0.1 square inches (much smaller area) makes 3,000 psi. You can generate an incredible amount of stress with a modest force if your area is small enough. This is how sharp knives or sharp needles work. Materials are measured by how much stress they can handle.

Also, ultimate tensile strength does not come in to play here. When cornering, those wheel spokes are in shear, not tensile. Shear strength for aluminum is about 0.65 * ultimate tensile strength.
http://en.wikipedia.org/wiki/Shear_strength

In a really tight corner, a car can corner with about 1 G of acceleration or more. Any good engineer designs to a conservative model (since dynamic loading can be very hard to predict). So let's assume that the 1 G of acceleration is imparted onto one wheel. Let's also assume that the one wheel uses only 1 spoke to handle the load. So 1 G in a 3,800 lbs car is 3,800 lbs imparted into one spoke in shear. By the looks of the picture, the cross section area looks to be about 1 inch by 1 inch, or 1 square inch. so we've got about 3,800 psi of shear stress in a conservative estimate. There's also the weight of the car, which I'm going to ignore since this post is getting too long already.

Another aspect to take into account is the stress concentration factor or stress riser. Anytime you have a sharp radius or a transition from a small cross section to a large cross section, there is a stress concentration factor. The stress concentration factor can double the stress or more depending on the situation.
http://www.chegg.com/homework-help/q...-let--q1467387

The wheel failed right where I'd expect it based on the stress concentration factor. Casting defects or porosity from a sub-par manufacturing process also produces stress risers. Let's say the stress concentration factor is 2. So then you've got 7,200 psi of shear stress.

Shear strength for 6061-T6 aluminum is about 29,000 psi. Aluminum doesn't have a fatigue limit, so fatigue strength in shear will drop continually depending on how many cycles it's subject to. Typically for this instance, an engineer will assume a million cycles. At this cycle amount, you can drop the strength by 50% or so; rough estimate, so you've got 14,500 psi as the material strength.

If you've got about 7,200 psi of stress from your loading cycle and 14,500 psi of material strength, the design safety factor would be 2, based on a conservative model but ignoring stress from the weight of the car.

Again, I ignored the weight of the car, and my wife is yelling at me to go to the store with her, but you get the idea....

[The Stig]

Originally Posted by Pentatonic

You got some things correct, but some things incorrect. 300 psi is not a force, it's a pressure (or stress) depending on the situation. It's force per unit area. You can take a 300 lbs force over 1 square inch and generate 300 psi. 300 lbs over 0.1 square inches (much smaller area) makes 3,000 psi. You can generate an incredible amount of stress with a modest force if your area is small enough. This is how sharp knives or sharp needles work. Materials are measured by how much stress they can handle.

I know. If you're referring to when I said "to give you an idea of how much force that is," which was referring to the PSI inside a fire hose as a reference point. Had I said, "you can imagine how much the 'pressure' of being hit by a hire hose would be" it would have just sounded awkward.



And in reference to the rest of your post - I have NO idea what it means. I'm in medical school, and have never taken an engineering course in my life. What I posted was just what I gathered after a little bit of internet research.

Edit: Shear strength for Al 6061-T6 is 30,000 and the fatigue cycle is 50 million - info is in the attachments I posted. But again, your explanation goes over my head.

[UF4LIFE102SS]

I also bought COR wheels from Nineball. No problem so far. I went to COR'S facility in Doral and there r alot of brands that go thru there that u wouldn't think do. From what i heard the face of the wheels are done in CALI. So he's right there, that is where most are made.