Buttercup

Only an expert like you can answer this:

Does the durability of a wheel change as the size gets bigger? For example, wouldn't a lightweight 15 inch aftermarket rim be designed for a 2300 lb miata whereas an 18 inch wheel probably won't fit a miata but instead for a 3600 lb Lexus?

I see how many people would want to have big rims fit onto their cars, but I'm not a big fan of big wheels. I'm thinking of getting 16 inch wheels from tirerack in the range of 13-17 lbs per rim for my sc300. I know that the rims are going to be cast aluminum one piece. I looked at the Kosei K1 16x7.5/15x7 racing wheels and they are rated at 15.5/13.5 lbs (http://www.wheelweights.net/). These wheels are extremely light when compared to any other cast aluminum wheel. I did read on tirerack.com about the different casting processes, but for the price of the wheel it does not seem that "SPUN-RIM, FLOW-FORMING OR RIM ROLLING TECHNOLOGY" is used. Tirerack.com also displays a spec miata carrying the K1 racer design.

So I'm wondering how long I would expect a set of K1 racing 16x7.5 wheels to last on my 3600 pound car compared to using 15x7 wheels? How about when compared to 18 inch O.Z. Superleggera rims?

Brandon@TR

Wheels have load ratings like tires do. We are very conscious of this and would never offer anything that wasn't correctly loaded. Usually a wheel that has more material in general will resist pot hole damage better. The advantage of forging vs. casting is that it can produce a wheel with less material (lighter) and actually have more strength. I hope this helps.

Buttercup

Thanks for the info.

What I'm mainly concerned with is the lug nuts (or the 5 bolts on the hub) that might crack the rim in pieces.

Where can I find the specifications on wheel load ratings?

By the way, what's the offset on the Kosei K-1 racing 16x7.5 for the SC300?

SoCalSC4

Wow, I would say that would be a very unusual failure... typically, the rims will bend or the spokes will crack before this type of failure will occur. The center area of the wheel is pretty strong, due to the pure mass of the aluminum in this region and the relatively low bending moment due to it's proximity (radius) to the hub, or mounting surface.

We test all of our new wheel designs, and if you test them to the point of failure, it will always be a spoke that fails first. This is a fatigue failure, however, and is different from an impact failure. Also, our wheels are forged, so the aluminum has different strength characteristics from a cast wheel.

An impact failure will typically result in a bent or cracked rim. A bent rim will manifest itself in a shudder while the car is driven- a crack will usually result in sudden and total loss of air pressure (not a good thing).

You can tell quite a bit about the wheel load rating by looking at what fitments are offered for a specific wheel. For example, a wheel weight-optimized for a Miata or Civic is typically only offered in a 4x100 bolt pattern. As soon as you hit 5-lug territory, chances are they are load-rated for the "worst-case scenario," perhaps an LS430 or an S-Class Benz.. This rating is usually 1580 lbs. per wheel.

Keep in mind, a lightweight wheel is a compromise between weight reduction and strength. Race wheels aren't meant to have an indefinite life span- you use them for a seaon or two and replace them. Street wheels are expected to last the life of a vehicle, and must therefore be more tolerant of fatigue stresses- this can only be accomplished by adding mass, and, thus, weight.

Most racing wheels make very poor street wheels- particularly Magnesium wheels (due to their brittleness). If you are planing to track the SC, by all means, get a set of track-oriented wheels. This is not a light car, so if you are driving it through the streets of New York, I would recommend a wheel that is a bit more stout.

Also, if you are ever going to upgrade the brakes, keep in mind that 16 (or even17") wheels won't accommodate most big brakes. It's funny to see how, originally, the big wheel craze was looks-driven. Now, it is driven by the fact that the newer and heavier cars demand more braking power to make them stop. Soon, even the Ferrari F360 and Porsche 996 Turbos will be factory-available with 19" wheels.

We have come full-circle!

Regards,

Bob Hale
Technical Specialist
HRE Performance Wheels

Buttercup

Excellent info SoCalSC4. I wouldn't want to get the supra tt brake rotors cuz they are expensive and
?heavy? and I won't need it once I lighten the car enough.