Well then, I stand corrected. haha
I was under the impression that it was a combination of width and offset, with the width factoring in the most. I was mostly going by my wheel manufacturer's website because they categorized "concave" wheels based on width and not offsets.
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I agree that most of the time which the lower offset with wider width will equal to deeper concave, but take a look of our fitment page, we don't categorized concave wheels "fully" based on width and offset but actually wheel that's been built. I personally think it is not appropriate for manufacturer to provide the wheel concavity without the specific spec.
Shelby GT350's fitment F19x11 ET25 R 19x11.5 ET55 has less concavity than 19x10 ET40 for the 987 Boxter. Even the Ferrari F12 got Mild face for the 12.5J crazy wide wheel. The reason is the GT350 and the F12 run a much bigger brake plus the distance between hub to fender are limited.
At the end, there isn't right or wrong since concavity is subjective, but as we build or advertise our wheel, we compare the similar size wheel side by side to determine the amount of concave we think it belongs to whether is mild, medium or deep etc...
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