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14:02:42 - 04/26/2024
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JC
Dodge Dakota
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12/20/2008
18:19:10
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 Subject: Who knows about gearing?
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Message:
I've got a 99 cc 2wd with a 5.2 318 and 3.55 gears. I wanna switch from 30x9.0 tires to 31x10.5. Will the gearing be enough? I don't plan on going any bigger in tire size than that, but I would change gearing to keep acceleration. Would 3.92 be right, or 4.10? I do mostly highway/city driving, no towing, no off roading except a dirt or fire road once in a while just for fun. I also drive cross country a couple times a year. I've got no prob sticking with the 30's if I have to, because I love the acceleration on my truck. It's stock except for intake and exhaust. I live in Cali, so freeway driving here gets up to 90 or so sometimes just to keep up with traffic, so I think 4.10 might be too low? Any gearheads got any advice? Thanks.
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dakota49
Gen I
12/20/2008
19:39:41
|  RE: Who knows about gearing?
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Message:
JC, I just did the math, and the difference in RPM at 65MPH would only be 60RPM less than the 30 inch tires, so I think you would keep most of your acceleration it could however slow some at high speeds. Here's the formula
speed (you would want to cruise) times the high gear ratio (I used .7 Cause I don't know just what the over drive gear is with the auto trans.
speed X high gear ratio X rear gear ratio X tire Rev's Per Mile. then devide that by 60 and that will give you your engine RPM for that speed.
A 31" tire will have a RPM (Rev's Per Mile) of 650.
65(MPH) X .7(OD Ratio) X 3:55(Axle rat.) X 650(tire RPM)= 104991.25 Devide that by 60 = 1749.8541 Engine RPM.
A 30" tire has 672.24 Rev"s Per Mile
If you change to 3.92 you may gain just a tad in acceleration, and your cruise RPM would be just slightly higher.
Hope this helps some,
Good Luck
Dakota49
dakota49
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