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Old 03-10-2010, 01:43 AM   #76 (permalink)
roflwaffle
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Join Date: Dec 2007
Location: Southern California
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Camryaro - '92 Toyota Camry LE V6
90 day: 31.12 mpg (US)

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Quote:
Originally Posted by Big Dave View Post
I've talked to literally hundreds of truck guys. Bigger diameter tires actually reduce MPG.

The reason is increased rotational moment of inertia. RMOI goes up with the square of the radius. Big tires are OK if you go long distances at a constant speed, never slowing down or speeding up.

I don't drive that way.
Even w/ large tires RMOI is quite small for most vehicles, something like 10Wh/mile assuming a 0-60-0 every mile. Odds are it's an increase Crr/CdA associated w/ the larger tires.
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