Does someone have a loose D-90 6X16 or 8X16 52 offset where they can take a photo of ALL of the markings on the back of the wheels. The magnesium and aluminum wheels use the same part numbers, I have what appears to be the magnesium version with the "Mg" markings, I want to see what the other wheels out there look like.

 

Will do.

 

Here ya go. All marks between spokes. Mine show "Mg" also, so while I'm not positive, I think it's safe to assume they are magnesium.

Sorry for the nasty condition of the outside face, but I ran through some mud just before I took them off.

 

Well based on that the C4 lightweight does not have a special wheel all D90s appear to be magnesium. The C4 weight parts manual shows the standard part number wheel that matched the number that is on this C4 lightweight that I looked at which also matches the photos and the PET for a standard wheel part number. I thought at first maybe is the same part number but built from magnesium. The wheels on the car have the same "Mg" markings. So I guess all the D90 wheels are magnesium, is that right?

 

That is what I thought as well, but I seen several listings that show aluminum. Maybe someone can clarify this for us.

 

AlSi7Mg is the alloy the wheels are made out of. Al is aluminum, which is mostly what the material consists of. The material also has a small amount of silicon (Si) and magnesium (Mg).

Here is some more info: http://www.matbase.com/material/non-...ixo/properties
I think the 7 in AlSi7Mg means that there is 7% by weight of silicon in the alloy, and according to the above there is 0.3% magnesium.

 

I did some more reading and research. Based all all the factory data, Jurgen Barth's book, part #'s in the factory C4 lightweight parts manual (yes I have one) inspections of several C4 lightweights, and stampings on the wheels being the exact same on C4 lightweights and regular road cars, the old wives tale that the C4 lightweight had magnesium D90 wheels is simply not true. Some of the early authors must have been confused with the 964RS and thought the 964 C4RS too had magnesium. Nearly every author since has copied the incorrect early writings. The parts manual actually list a 6 and 8 inch version as standard with regular part numbers or an optional 7 and 9 inch package, again with a normal 964 and 928 part number. Solved, all D90 wheels have some magnesium but not a high % as found in the 964RS.

 

Yessss!
Thank you Jeff, for confirming what I thought all along.