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Bent, cracked rims discussion......No personal attacks!

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Bent, cracked rims discussion......No personal attacks!

 
Old 05-16-2019, 02:40 PM
  #41  
Road machine
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Originally Posted by GeoGS View Post
Like most of all us that have a Grand Sport or Z06 I also have thought long and hard about the wheel problems. While changing out my brake pads to less dusty ones, and looking over my rims. Every thing still ok. But this is only with 750 miles on my 19 GS. I noticed a dimple on the edge of one of rims. I should have taken a picture. Now this looked like they did a Rockwell test on this wheel/rim to me. Rockwell is hardness test. They used to do this kind of test where I used to work. It would leave a dimple in the metal. Too hard the metal cracks, too soft it bends. Not sure what scale GM uses. Not sure what range they have either or how much the hardness varies around the wheel/rim.

Would be interesting to see how thick the OEM Flow forged rims are in respect to third party Flow forged rims. Would there be a difference where all third party are thicker?
Would be interesting to see how long they apply pressure (and how much) when flow forming in respect party flow formed wheels. Is it just once around like a can opener, or is many times with pressure reduced each time? When Ford had a problem with the Firestone tires it was found that they were rushing the process of heating and curing the tires, to get more tires out the door. With the shorter curing time it created a weaker tire. With less pressure and less spinning times more rims out the door with maybe a weaker rim ? Not an engineer, but still think about the rim problem.

Wheels that bend would seem to be softer then the ones that crack which would seem to be be more (brittle) hard. Wonder if GM does any testing on the ones that are bad? That would be to see if they were too hard or soft. Or even if the hardness (rockwell number) is uniform around the wheel or hot spots on the wheel?

With leverage theory and it always cracking/bending on the inner barrel seems right. The question that comes up why the third party Flow forged wheels not cracking or bending like the OEMs both have cast faces? If they were I would think we would have/had some members on here talking about. Now I seen a few pictures of third party wheels cracked, but it did not say how or if there was an accident or damage at a track. Granted there are less of them than OEM ones. But I think not hearing of one on here says something.

With the leverage theory it also must take into account the unsprung weight. Not sure what every OEM weighs and comparison to the wheels problems. You would think the ones that weigh more would be the ones that had the most cracks and bends. Are third party Flow forged that much lighter? Now the Full Forged ones are. If weight a big factor in all of this. Then the ones that have ceramic fiber rotors should not have much of a problem with bending or cracking the rotors. As they are about 6 lbs lighter of unsprung weight.

Maybe this all has to do with the thickness of the outer edge of the wheel. As this is where the crack starts. Or even the shape of the outer edge. Not an engineer, just throwing this out there.
The Dimple you noticed is the high spot of the wheel. No wheel is perfectly true, so manufacturers mark the high spot of the wheel. No tire is perfectly round either so they put a dot at the low spot. when mounting the tire to the wheel the mechanic is supposed to put the dot from the tire in line with the mark on the wheel for the truest possible assembly.

As for rockewell hardness, that is not used for aluminum alloys as aluminum is not hardenable in the way steel alloys are. Aluminum is age hardened or annealed (tempered) , and the state is noted as either T0 for annealed T4 for natural aging at room temp or T6 for artificial aging (100-200 deg C for X anount of time) and some alloys can be brought to T8 temper. Other alloys (mostly sheet metal) use an "H" with a number behind it to show the temper state. The actual hardness is shown on either the Brinell scale or the Vickers scale. Rockwell is also a scale but aluminum would not even register on that scale.

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Old 05-16-2019, 02:48 PM
  #42  
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Originally Posted by golfbone View Post
This cast vs forged issue has been asked and discussed many times in the past.....it is my understanding that the Z06 wheels are Cast aluminum.

https://www.corvetteforum.com/forums...or-forged.html

Not sure if the Z51 wheels are the same but pretty sure that we have on the Z06/GS is cast. Whatever it is it ain't working!

See post 34.....that is the accurate answer to how the wheels are made.

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Last edited by Road machine; 05-16-2019 at 02:49 PM.
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