I own a towing co. It's the rims not anything to do with the valves. I change tires regularly I have a Hoffman rim clamp tire machine and all the tools I need to do any repair short of retread. I never looked into where in the wheel it leaks but I would imagine around the spokes and as far as Speedmaster goes. It is common knowlege among mechanics that alloy wheels are often pourous enough to allow air to actually pass through the rim. Also there is the question of temp. cold = less pressure hot = more. Low quality tubes will seep air through the rubber too many don't know that or about the alloy wheels.

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