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23:08:26 - 04/18/2024
General Dakota Board
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Jetsfan8099
Dodge Dakota
JOIN HERE
9/08/2007
21:05:41
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 Subject: 305/70 vs 285/75
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Message:
Question for anyone that has had both of these tire sizes. I currently have 305/70R16 GY Wrangler MTR's. These are equivelent to 33.1"x12.3". My tread is wearing down and it's time to atleast think about what would I purchase next. My Kota currently works hard to turn these tires (3.55 gears), but I don't want to sacrifice the look. If I went to 285/75 (33"x11.5") would I get some power back from having a slightly lighter tire and less road contact? or is the power loss all attributed to the diameter?
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modain
GenIII
 
9/09/2007
17:49:20
|  RE: 305/70 vs 285/75
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Message:
I don't remember the numbers, or where I can find the article, but (I think) I read that each pound of rotating mass takes .7 HP to roll it.
Weight and diameter factor into a power loss or gain depending on which way you go. Going to a lighter wheel/tire combo will be felt by the butt dyno. I noticed a difference when I upsized my tires on my QC. I got most of it back with the SC tuner and the 91 octane program.
An axle regear will let you keep the tire size you like and make it easier on the engine to spin them.
What's your left foot doing?
==============
2002 Graphite QC SLT Plus, 4.7L, NV3500, Superchips 3715, 3.92 LSD, R/T rear swaybar, no chrome, loads o'fun...
2001 Patriot Blue Durango SLT, 4.7L, 45RFE, Superchips 3715, 3.55 Open (for now)
1999 Forest Green Dakota RC Sport, 2.5L, NV1500, 3.55 Open
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shadetree
Dodge Dakota
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9/11/2007
11:32:17
| RE: 305/70 vs 285/75
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Message:
I personally do not think that changing from a 305 to a 285 is going to help. The problem is that by going to a 33" tire you have essentially gone from a 3.55 gear ratio to around a 3.08 ratio if my math is correct assuming you had a 265 tire to start with. If you want the truck to be close to factory proformance you will need to run a 4.10 ratio and if you want even more torque go with a 4.56 ratio. Its the diameter of the tire that messes with the truck not really the width. Im sure others will chime in with more info but thats what I think is the solution.
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