During a track day at Laguna Seca this Acura Integra with Spoon SW388 wheels broke under the stresses of racing.
There seems to be a misconception in the wheel community that says fake and cheaper wheels like Rota Slipstreams are more prone to breaking than real wheels. In fact, some wheel enthusiasts seem to think that real wheels don’t break. Well, I hate to burst your bubble. According to @AllMotorDan on Instagram from his adventures on the track earlier this month (Sept. 2, 2018) not only did his real-deal genuine wheels break under the stresses of racing, but they’re also irreparable and good as trash.
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I have been getting a lot of questions about my wheel. The wheel did not fail me. I have failed the wheel. I believe the wheel was cracked on turn 6 after hitting the rumble strip / curb. Then after the stress of the Corkscrew and Rainey Curve the spoke separated. No other damage has been caused to the car as far as I know. Luckily all of this happened during the last lap of the last session at Laguna. #physics #sendit #trackthatshit #tonyjacksonmademedoit
Now, don’t get me wrong, Spoon Sports SW388 wheels are some of the strongest aftermarket import wheels on the market. Using a special forged aluminum, the engineering in this wheel is exceptional and are race tested by Spoon Sports Japan throughout the decades this wheel has been in existence.
In comparison, Rota Wheels and most other knockoff wheels use a cheaper casting process although aluminum alloy is also used. What results is a strong and affordable wheel. But as you can already guess, not as strong as forged aluminum. Forged aluminum has a tighter grain pattern at a microscopic level, an inherent property of high pressure and heat.
But how much stronger are forged versus cast aluminum wheels? A cursory refresher on materials science brings up yield and tensile strength, the former being how much force a material can take before changing shape and the latter being the absolute breaking point of a material. I’m not going to pretend that I know what a Megapascal of unit is exactly but generally, the higher the number, the better.
As per this chart the yield strength of forged steel, something generally agreed upon as something very strong, has a yield strength of 556 mPa. Yield strength of a cast aluminum alloy is much less at 232 mPa but aluminum is an overall lighter material. Consider the aluminum alloy AZ80,an aluminum alloy commonly used in Russia (which is where Spoon Sports SW388 wheels were made by the way) to make wheels. After forging, its yield strength is 275 mPa , stronger than cast aluminum alloy but not by much. Both cast or forged, if either meets big enough force, will fracture.
You’ll be glad to know that Spoon is bringing back the SW388 commonly known as the S-Dub. And like all things Spoon Sports, they’ll cost you. An 18 inch wheel will retail around $1,000 a piece. The equivalent cast wheel from Rota? A quarter of the price around $250 a piece. Sure, you’re buying a slightly weaker wheel but is it four times better? Probably not.
All wheels break given enough stress, even real wheels like Spoon Sports SW388 wheels.