When I read the California Energy Commssion had tested over 300 tires but didn't publish their results, I began to suspect something else was going on. Then when the 'Governator' was killing programs in his budget, I suspected he'd turned out their lights and the results would never be known. Fortunately, they did and here is the URL:
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The full workshop data is available here:
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The Prius is especially able to exploit low rolling resistance tires. It has one of the lowest air drags and superior drive train so reducing rolling drag from the tires pays at the pump.
Bob Wilson