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Ian
Dodge Dakota
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6/12/2002
13:13:07
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 Subject: wheel/tire swap effect on gear ratio?
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I'm gonna swap out the factory 265/65/16's for some 255/55/18's resulting in a little more than an inch increase in overall diameter. I was hoping the increase would yield slightly better highway mpg as I have the 3.92 gears, this is on the assumption that with taller wheels my truck will be more like a stock dak with 16's and the 3.55's. Is this a correct assumption? An increase in mpg (however slight) is just a great way for me to justify some 18's.
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routesixtysixer
Dodge Dakota
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6/13/2002
15:57:21
| RE: wheel/tire swap effect on gear ratio?
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Calculations of the diameter based on your sizes show the new 18-inch to be a bit SMALLER in diameter. 16-inchers calculate to 29.56 inch diameter (265/25.4 x 2 x .65 + 16) and the 18-inchers (255/25.4 x 2 x .55 + 18) calculate to 29.04 inches. This would be less than 2% change in size... probably not really noticeable. Same thing as change from 3.92 to 3.99 gear.
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Waltherone
Dodge Dakota
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6/13/2002
23:51:45
| RE: wheel/tire swap effect on gear ratio?
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Just out of curiosity, what about if you changed from the stock 16 to the RT's and got the same tires as the stock RT's have (I think they are a bit taller than I would get BUT I drive a lot of hwy and that diameter would be nice) with the 3.92's, how would THAT setup compare with the stock wheels on 3.55 gears?
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Hersbird
Dodge Dakota
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6/14/2002
22:19:34
| RE: wheel/tire swap effect on gear ratio?
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The stock 16" tires on the 2wd Dakotas are 29" tall and the stock 17" wheels on the R/T are a shorter 28" tall. The R/T with the 3.92's effectively has the lowest overall gear ratio besides a non-tire & handling package truck with 3.92's and 215/75/15 tires which ends up being about a 28" tall tire as well. www.tirerack.com has the factory tire specs for most tires out there, just search for a size, click a brand, and then click the 'specs'. It brings up a table for the specific tire with the measurements from the factory for all the sizes that tire is made in. The you can use the caculators at www.ring-pinion.com to figure out how the tire size effects RPM or MPH for a specific gear ratio.
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Waltherone
Dodge Dakota
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6/15/2002
01:29:46
| RE: wheel/tire swap effect on gear ratio?
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Excellent....well, I was hopin the bigger wheels would help my hwy mileage a bit but its all good, thanks :)
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