It's very difficult to build a strong gravity cast wheel (that is wider than 10") without compromising the long term durability. This is the nature of CAST wheels in general, and gravity cast wheels in particular. Even if someone wanted to build a 10.5" or 11" gravity cast (or even low pressure cast) rear wheel, it would weigh 32-35 lbs. Who's going to buy that?
The porosity of these wheels will limit what size you can build. The larger you go, the more likely you are to incur structural integrity issues.
On the other hand, Forgestar uses Flow-Form casting method, which results in a much tighter grain structure, that has fewer inclusions. (metallurgical imperfections) The metal grain flows in the same direction, which improves the mechanical properties of the wheel. The strength of a flow-formed cast wheel is
more uniform throughout the entire wheel surface, and thus the wheel is less likely to bend or crack upon impact with a curb or pothole. It's not as strong as a forged wheel of course, but it's the best technology available in cast wheel manufacturing.
Now that advantage also drives up the price of the wheels as a result. Aftermarket wheels that are made utilizing the flow-form casting method increases the tooling and manufacturing costs. (compared to gravity and low pressure casting methods)
By using flow-form casting, Forgestar can build a cast wheel that is very wide without the same fears that gravity and low pressure cast competitors will face. That doesn't mean they are bulletproof, but they will resist bending and cracking much better than the other two options. (assuming the same wheel design)
Also...
Regardless of which casting method is used, it will be difficult to get a lightweight cast wheel that is also very strong. That's because the strength of the cast wheels is tied very closely to the total mass used in the final product. This is also true of high-tonnage forged wheels (8000T), but the margin for error is much wider. In other words, you have greater latitude in shaving off metal without sacrificing the overall strength of the wheel.
With cast wheels, these margins are much, much smaller. As you whittle away metal (to achieve a lighter weight), you can also reduce the overall yield strength of the wheel if you cross the line. (bypassing the minimum mass threshold required for that design) It's a delicate balancing act, and you cannot go too far. If you do, it will defeat the entire point of building a stronger (more expensive to manufacture) flow-formed wheel product. You can literally
create a structural weak point where none existed before. FEA stress simulations, building an actual test wheel prototype, and applying real world impact, cornering load, and fatigue durability testing (at a certified wheel testing facility), is essential to avoiding this worst case scenario. This will reveal where the boundaries are. (limits)
FYI: It's important to note, that no aftermarket wheel is immune to bending or cracking with enough impact force. (no matter how much it costs) Overall quality is not always directly tied to the price you pay. Don't make the mistake of assuming otherwise.
All that being said, I would strongly recommend the following cast wheels in the under 3k price range:
BBS (of course)
OZ Racing
ENKEI
Two companies that I'm currently on the fence with:
Forgestar
Alufelgen
Not enough solid info in my research database to recommend either of these brands yet. Contacted both a while back, but I am very disappointed with the some of the decisions made by each brand to this point. Hopefully things will improve in the very near future. They both seem to have some promise, but I have seen my fair share of promising company's go under by not making the right decisions at the right time.
Timing, preparation, applying proven marketing strategies, and solid business management skills are crucial. Customer service issues, and a poor product supply stream (to meet the demand), will hurt you in the ultra-competitive aftermarket wheel business.
