the main difference between OEM and aftermarket is in how the alloy is mixed......
lets see on one end of the spectrum, say 10, you have pure %100 steel non alloys on the other end of the spectrum, say at 1, you'll have %100 alloy with various percentages of alumninum and other weaker, cheaper metals mixed in-at this end of the spectrum steel may be less than 30% of the total mixture...which results in a weaker but not necessarily cheaper (I'll tell you why in a minute) rim.
so at 10 to 8
we have 95%-99% Steel wheels/non alloys. These are usually the stock wheels on earlier BMWs and cheap american cars with less than 16 inch diameter tires and hubcaps. Usually cheap to moderate price range, but the strongest wheels you can put on your ride. They also tend to bend when damaged and can be hammered and be repaired. My spare tire is a 15inch steel wheel for this reason. 7 to 4
in the spectrum you have OEM rims which combines a rich mixture of steel and strong alloy alumnimun...on OEM the materials may not deviate from greatly aftermarket rims in this range but the biggest difference between low quality aftermaket and OEM is probably design, balance and wheel symmetry.
This is where you're spending money for quality. The rims are sensitive to cracking
and bending slightly when damaged. 3 to 1
has almost minimal steel, you'll find cheap chrome replicas here, wheels that tend to not last as long and may not support heavy trucks or rough roads, the main benifits are you'll have a lighter wheel most suitible for track races and speeding. Here the emphasis is more on the type or the grade of the alloy ingredients....Here is also where you are going to spend the most money, more than OEM in some cases for special order chrome reps and ultra-light, ultra-cool racing wheels. At this end of the spectrum you are paying alot of money for bling, style and size. The most expensive rims are found in this end of the spectrum. But they'll also be the most weakest and sensitive rims for damaging. These rims tend to shatter (like plastic) and crack extensivetly when damaged.
So we can conclude that with aftermarket and replicas the pricing does not always reflect the quality of alloy ingredients
as so much it reflects consumer demand and style.
WIth OEM you are always paying for quality and (somewhat) for style. But style is standard-no bling and stock (yawn) for OEM and quality is what you'll be really rewarded with.
But when you buy aftermarket reps more than likely you'll be paying for bling bling style and popular demand (ex. Sprewells) and not OEM quality regardless of what they are advertising.
My bias is for OEMs especially when buying a BMW or similar luxury vehicle. These cars already have an extensive line of OEM style and sized rims and should not give the consumer any reason to wonder into Sears or Pep Boys to buy aftermarket rims.
Also they are good aftermarket brand rims like BBS, Borbet, ALPINA, etc...that make OEM and better quality rims...so you can mix it up to your liking....
go to TIRERACK.COM for more information. Also in my experiences
this website www.thewheelexchange.com
(google it, or check ebay) was the best for top quality BMW replicas.