Not sure, I know they are strong as I did my first track session on them and was all over the curbs and driving them on some pretty rough roads where I live. Again I have the Konig Feathers but these are the same quality.
For those that can go to 15's the best way to go, if rules allow, 4x100 change, and these roll formed, 15x7, +35mm,10 lbs, $128, Konig made Avanti Racing Storm. I prefer this style over the Konig Dial in I have in 15x9 but had to make sure to clear my 11.75" BBK up front.
They have several 15x8 there but not sure any are made in +35, most are +25mm in that size which sucks for our cars.
This is a new Konig, made in 15x7 and 15x9, +35,4x100 sizes, I will likely switch to these for the track when they are in stock in a month or so.
Unfortunately one of the few, maybe only 15x8 +35mm they have on that site is the Enkie PF01, 12.8 lbs, roll formed, $247 per wheel
The RPF1 in 16x8,+38mm would work, $229 each but probably not over my BBKs and the new 16x8 coming out is less money and would fit.
DAMN, edited now...quoting myself....
"I just got off the phone and am excited to know in just a few months some killer 16x8 and probably 16x9 roll formed well priced wheels will be coming out and there will be more roll formed but a longer lead time in 17x8 and probably 9" wide as well
"
I just called the manufacturer directly and got the real answer, at least a year away on 17x8 and 9 but not even in the planning stages on 16's due to the lack of tires most buyers would want the wheels for, racers but they might make them sometime......but might not........
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Still the best way to get good wheels is a 4x100 conversion but if you are faced with a set of rules that do not allow a bolt pattern change I suggest putting in the effort to get it changed because you can get superb wheels for great prices. There is no need at all to have to spend a bundle on really expensive wheels when you can do a bolt patten change and get 2.5-3 sets of wheels that are more than good enough for any kind of racing, very low weight, for the price of one set of custom wheels or designer brand wheels