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Ian
Dodge Dakota
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6/12/2002
16:24:01
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 Subject: 18's affect on gear ratio
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Message:
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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Marks DQC
GenIII
 
6/12/2002
19:44:14
| RE: 18's affect on gear ratio
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Message:
You are actually going the other way the 18's will be smaller. 265/65/16 is 29.6" tall. 255/55/18 is 29.0" tall. Circumference of your 18's will be 2% smaller. (If your speedo is dead on now it will read that much too high also.)
Your mileage will probably not change noticably, depends on rolling resistance, etc.
2001 Dakota Quad Cab SLT , 4.7L, Auto, 3.55, Garnet Red over Slate
Zaino, Tint, Vent Guard, Gaylords Lid, Hotchkis, Bilstein, Wet Okole Covers, Painted Grill Shell w/ Ram inserts, S/S Bumper/Valence Cover, Billet Antenna, Precision Roll Pan, APC Clear Corners, Airaid, Gibson
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BigRedDak
Dodge Dakota
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6/13/2002
02:43:19
| RE: 18's affect on gear ratio
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Message:
I think your mpg would improve if you went and got some 135/65/18's :)
ps. how do you calculate total tire diameter?? I tried 3 different ways and came up with weird answers.
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Marks DQC
GenIII
6/13/2002
06:44:21
| RE: 18's affect on gear ratio
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Message:
Tires are spec'd out in width/aspect ratio/wheel size. Therefore a 255/55/18 is 255 millimeters (10" wide), the sidewall is 0.55 times the width (5.5" tall), and it fits a 18" rim.
The tire diameter then is 2 x 5.5 + 18 = 29" tall
2001 Dakota Quad Cab SLT , 4.7L, Auto, 3.55, Garnet Red over Slate
Zaino, Tint, Vent Guard, Gaylords Lid, Hotchkis, Bilstein, Wet Okole Covers, Painted Grill Shell w/ Ram inserts, S/S Bumper/Valence Cover, Billet Antenna, Precision Roll Pan, APC Clear Corners, Airaid, Gibson
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BigRedDak
Dodge Dakota
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6/13/2002
09:41:03
| RE: 18's affect on gear ratio
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Message:
well son of a gun, that's clever of them. Thanks for explaining that Mark.
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BB2DAK
Dodge Dakota
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6/13/2002
11:53:48
|  RE: 18's affect on gear ratio
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Message:
Check out this site.
They have calculators to calculate tire height,
and gear ratios, among other things.
http://www.ring-pinion.com/calculators.shtml
2001 Quad Cab SLT+ 4.7L, 5-Spd, 3.55 Lsd
ARE Cap, ArmaCoat Bed-liner, Pilot PILPL119X Fog Lights
Autolite 3923's, IAT Adjuster, K&N Drop-in w/modified intake
Roadmaster Active Suspension
http://members.aol.com/bsbets/truck/intake4.jpg
http://www.dodgedakota.net/albums/viewer/101.htm
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