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

[Pentatonic]

Originally Posted by The Stig

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.

Depends on what text book you use; 29 ksi, 30 ksi...why do you think us engineers like to use safety factors?

Also, there is no set fatigue cycle. 50 million is a safe estimate if you use the working load and you may see that in reference books, but I used peak load in which case 50 million cycles would be overkill and would be over-designed and hence also overweight.

In either case, to properly analyze the strength of the wheel, you'd have to look at a variety of load cases; braking, cornering, vertical impacts and analyze the stress state in each against the material spec.

If I had a spare 30 minutes, some motivation and the dimensions of the wheel, I could figure it out, but I have none of that at the moment.

[usmcjlp]

This is another example of how the internet can go wrong. A story gets posted and everyone rushes to judgement. I assume that a lot of the folks posting on the company don't own the wheels. There are dozens of Camaro5 members that own the wheels without issue.

I'm not trying to bash anyone, but this wouldn't be the first time a company got run into the dirt online.

[So Cal Camaro]

I haven't liked COR Forged since they made a post vouching for the PTS dude who ripped off a few members on here. http://www.camaro5.com/forums/showth...=206380&page=3 They would have been far better to have handled this wheel issue for the OP on the other thread. Listening to Nineball, this is the only wheel he knows of that had a failure...I trust him on that.

But if COR wanted to avoid this negative publicity, wouldn't them replacing the guys set of wheels been a class thing to do? The few thousand bucks they might have eaten would have been much cheaper than the damage their reputation will take amongst the folks reading about it here and all the other forums I am sure this is being posted on....not to mention attorney fees...

I get you bought a set of their wheels, and if it were me, I would be more concerned about whether my wheels would break under stress after seeing that picture of the broken wheel rather than defending the company that made them.

[LC]

I'm very happy with my COR wheels.. so...

[Falundir]

I'm days away from buying a set and was going to go with the Cor F1 Encor for street and track. Kinda scares me now...

[CamaroFTW]

Originally Posted by Falundir

I'm days away from buying a set and was going to go with the Cor F1 Encor for street and track. Kinda scares me now...

OMG CANCEL!!! Life is too important!

[Falundir]

[CamaroFTW]

"COR" Italian translation: "RIP"

[So Cal Camaro]

I'm thinking I would look elsewhere...thinking Forgeline or HRE....

[Tysen]

Thank God you weren't hurt...and that only a Mustang was damaged.

I'm buying new wheels soon, and Cor will not by on my comparison list.

[Nine Ball]

We carry a lot of brands, but if someone were primarily interested in performance or track use, I'd only suggest a few brands for that. Brands with proven track experience, who supply wheels for pro racing teams. From my brands list, that would only be Forgeline, Fikse, or HRE. The vast majority of wheels out there were only intended for street use, including about 99.9% of the cast aluminum wheel market.

Tony

[malave7567]

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.

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....

great post, I was about to look at that myself, since I had a few extra minutes after lunch and SolidWorks open, lol. I deal with a lot of tooling made from cast or machined aluminum 6061 or 2024, so I understood what you meant

[fastkevman]

Statement From COR Wheels
October 24, 2012 by COR Staff
Due to some unfortunate circumstances regarding a set of COR forged wheels, we feel that it is necessary to publicly address the situation and reiterate our company’s commitment to quality and customer service that has helped us build a strong reputation within the industry.
We are sure that many of you feel this response is long overdue, but given the sensitive nature and legalities involved, we had no alternative but to proceed with care, so as not to inflame an already volatile situation. Until this time, we have had nothing but excellent feedback and reviews from our clients concerning our products and service. In relation to the number of wheels that we have produced, our warranty adjustments have been less than one tenth of one-percent, which is a superb standard for any manufactured product. This is due in no small part to our commitment to building long lasting relationships with our distributors and returning customer base whose support is well recognized and very much appreciated.
The isolated incident that occurred with one of our clients was very unfortunate and unforeseeable, and we are thankful that there were no injuries. The product involved was designed, developed and third-party tested to ensure its integrity, strength, and reliability. The safety of our customers is extremely important to us, and is not a matter taken lightly by any member of our organization.
It is customary–and our preference–to service our customers directly. The client elected to bypass our resolution process by communicating with us through third parties (specifically an attorney). We sincerely hope that those following this series of events can appreciate that we had no other option than to turn this matter over to our product liability carrier, which exists specifically to address situations such as this. To be clear, the claim for warranty denied on the published letter was a response to the client’s attorney’s demand letter, and not COR Wheels refusing to stand behind its product. Prior to the involvement of legal counsel, the client was offered a full refund, regardless of any specific warranty considerations. We would like to clarify that the revisions made to our warranty were a direct result of the client’s attorney’s assertion that our terminology was vague. This does not speak of the safety and appropriateness of the product, which we feel is 100-percent safe for use on or off the track, but rather to the applicability of our warranty. With this revision, our warranty policy is more in-line with industry norms, which even at the OEM level precludes the use in a track environment.
As a final thought, we at COR wheels want to reiterate our commitment to the performance aftermarket and help further everyone’s understanding of the process and technology behind automotive wheels. We have a standing invitation for any interested party or any member of the media to visit our headquarters in Florida, tour our facilities, and meet the individuals responsible for designing, creating, and manufacturing the products that we are so very proud to offer. We sincerely hope that you will avail yourselves of this offer so that you may observe first-hand, our manufacturing and quality control process and the effort that goes into each and every product that leaves our facility.
Sincerely,
Christopher Robles & Robert Herrera
Founders & Owners
COR International, LLC
2799 NW 82nd Avenue
Miami, Florida 33122
Phone: 305.477.5850
Fax: 786.427.1324

[Obzen]

Originally Posted by fastkevman

Statement From COR Wheels
October 24, 2012 by COR Staff
Due to some unfortunate circumstances regarding a set of COR forged wheels, we feel that it is necessary to publicly address the situation and reiterate our company’s commitment to quality and customer service that has helped us build a strong reputation within the industry.
We are sure that many of you feel this response is long overdue, but given the sensitive nature and legalities involved, we had no alternative but to proceed with care, so as not to inflame an already volatile situation. Until this time, we have had nothing but excellent feedback and reviews from our clients concerning our products and service. In relation to the number of wheels that we have produced, our warranty adjustments have been less than one tenth of one-percent, which is a superb standard for any manufactured product. This is due in no small part to our commitment to building long lasting relationships with our distributors and returning customer base whose support is well recognized and very much appreciated.
The isolated incident that occurred with one of our clients was very unfortunate and unforeseeable, and we are thankful that there were no injuries. The product involved was designed, developed and third-party tested to ensure its integrity, strength, and reliability. The safety of our customers is extremely important to us, and is not a matter taken lightly by any member of our organization.
It is customary–and our preference–to service our customers directly. The client elected to bypass our resolution process by communicating with us through third parties (specifically an attorney). We sincerely hope that those following this series of events can appreciate that we had no other option than to turn this matter over to our product liability carrier, which exists specifically to address situations such as this. To be clear, the claim for warranty denied on the published letter was a response to the client’s attorney’s demand letter, and not COR Wheels refusing to stand behind its product. Prior to the involvement of legal counsel, the client was offered a full refund, regardless of any specific warranty considerations. We would like to clarify that the revisions made to our warranty were a direct result of the client’s attorney’s assertion that our terminology was vague. This does not speak of the safety and appropriateness of the product, which we feel is 100-percent safe for use on or off the track, but rather to the applicability of our warranty. With this revision, our warranty policy is more in-line with industry norms, which even at the OEM level precludes the use in a track environment.
As a final thought, we at COR wheels want to reiterate our commitment to the performance aftermarket and help further everyone’s understanding of the process and technology behind automotive wheels. We have a standing invitation for any interested party or any member of the media to visit our headquarters in Florida, tour our facilities, and meet the individuals responsible for designing, creating, and manufacturing the products that we are so very proud to offer. We sincerely hope that you will avail yourselves of this offer so that you may observe first-hand, our manufacturing and quality control process and the effort that goes into each and every product that leaves our facility.
Sincerely,
Christopher Robles & Robert Herrera
Founders & Owners
COR International, LLC
2799 NW 82nd Avenue
Miami, Florida 33122
Phone: 305.477.5850
Fax: 786.427.1324

hmmm the plot thickens.....

So was it a matter of the fact that they were willing to refund the wheels but not pay for the damages to the car?