.. When you mix different materials you can dramatically change their original properties. ( try making a cake without raising agent !) So, you are correct Paul when you say the thermal properties of the base element will be different to the complex alloys used in manufacturing. However, adding a high thermal conductor like copper to a low conductor like Magnesium, may not have the effect you might think ! If you take the trouble to look up the properties, you will find that Magnesium alloys (AM60 is a typical alloy used for wheels) hasa thermal conductivity dramatically lower ( it conducts less heat) than pure Mg. Whilst a similar reduction is noticed with Aluminium alloys, they still conduct heat approx 3 times faster than Mg alloys. Mechanical properties are also lower with Mg alloys by a similar factor. IE:- Mg alloys exhibit less than half the tensile, yield, & compressive strength of comparable Al alloys. The only valid reason for choosing a Mg component over Al on a kart , is to reduce the weight ( static weight that is, since rotational inertia is another karting "furfy" as pointed out by others ..and proven in testing by Karting mag a few years back) Mg alloys offer a 33% weight reduction for similar sized components ( but remember they are only 50% as strong !
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