You could try calling them?
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Those tires look to be 5", here's another page showing weights for their 5-6" wheels:
https://robart.com/products/aluminum...-tire-1-4-axle
So if they're 5", I'm going to guess they weigh close to 9.4oz. And I'm assuming that's wheel and tire weight, not just wheel. Let us know what you find.