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big tires = bad mpg....why?

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Old 08-01-2009, 07:25 PM
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Default big tires = bad mpg....why?

title says it all. why is it that if you get bigger tires the gas mileage goes down? if you look at simple physics the bigger something is the easier it rolls and the faster it goes. if you had smaller tires they would have to roll more to cover the same amount of distance as a bigger tire. so if you just drove normally the big tires will spin faster than the small tires. so in theory you should get better mpg. but why do you get worse?
 
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Old 08-01-2009, 07:33 PM
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whats easier to lift a book or a bookshelf?? bigger tire are heavier there for taking more energy(gas) to get going and once you get them going your engine still has to work harder to keep those big heavy tires rolling. another thing that factors in is the tread pattern, most people who get bigger tires go for an aggresive tread pattern and that in itself will cause your mpg's to go down.
 
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Old 08-01-2009, 08:10 PM
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The wider and more aggressive a tire is, the more rolling resistance it will have. Going to lower gears will help the vehicle pull the tires along better but only to an extent.
Believe it or not but our Blazers would actually get better mpg with a V-8 rather than a V-6 when running larger off road tires. The V-6 has to work a little harder, where as the V-8 can just loaf along... once again, to an extent. Ever notice that full size Tahoes and Suburbans get just as good, if not better, mileage than our beloved S10's running large aggressive tires?
 

Last edited by bandidolenny; 08-02-2009 at 11:29 AM.
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Old 08-01-2009, 08:42 PM
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ahh i forgot about the whole aggressive tread part... do you guys think a 305 or a 350 would fit in the engine bay with out too much alterations?
 
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Old 08-01-2009, 08:53 PM
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it helps to know what youre driving. i would also suggest using the search function, the v8 swap question has been asked countless times.
 
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Old 08-01-2009, 09:45 PM
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You are correct.In theory the circumference of a larger tire would get you further with each revolution.

30" tire circumference = 94.2"
33" tire circumference = 103.62"

1mile = 5280ft = 63360"


With 30" tires, it would take 672 revolutions to go one mile
With 33" tires, the same 672 revolutions would get you 69632", or 5802ft.

The larger tires will get you 522ft further than 30's with the same number of revolutions. (wheel revolutions, not crankshaft revolutions)

Part of the problem is with the weight of the tires. Four of the ever-popular BFG All terrain tires in 30x9.5x15 weighs 152lbs. Four of the same tire in 33x12.5x15 weighs 208lbs. Like Mike said, more power is needed to get going. The wider tire and aggressive tread pattern will also slow you down faster when coasting causing you to hold the gas down a little longer than you normally would.
 
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