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Old 07-06-2009, 08:54 AM
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New Gearing?

I need help deciding which gears I should get for my truck. I have a 10" lift with 40"x15.50" Mud Grapplers. My original gear ratio was 3.73. What should I put in now?
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Old 07-06-2009, 09:11 AM
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4.56
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Old 07-06-2009, 09:15 AM
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minimum of 4.30
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Old 07-06-2009, 10:25 AM
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4.88's ....
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Old 07-06-2009, 10:38 AM
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Here is some data I calculated from a spreadsheet I use to show the different speeds at 2000 rpms in 3rd, 4th and 5th gear.



Looking at this data I agree that you should go with the 4.56 gears.
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Old 07-06-2009, 10:45 AM
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4.88's would work too. They would give you a little more off the line but you would be turning a few more rev's on the highway. Here is the comparison.



So if you do a lot of highway drive you might want to stick with the 4.56's. If you want the acceleration and don't care as much about the fuel bill go with the 4.88's.
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Old 07-06-2009, 11:25 AM
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I do drive on the highway a fair amount so I don't want my gears to low. I was thinking 4.30 or 4.56. I don't tow too much and when I do it is 9000lb toyhauler. As for mpg what affect will the lower gears have on it? I know in my 72 blazer they actually helped. I went from 3.08 to 4.10 because I put a 4" lift and 33" tires.
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Old 07-06-2009, 11:43 AM
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Quote:
Originally Posted by SpecMiataHauler View Post
4.88's would work too. They would give you a little more off the line but you would be turning a few more rev's on the highway. Here is the comparison.



So if you do a lot of highway drive you might want to stick with the 4.56's. If you want the acceleration and don't care as much about the fuel bill go with the 4.88's.
Hey not to hijack the thread but I am in the same boat. Need gears to turn my 37/13.50-20. Currently have 3:73's, was thinking 4:30's, but now that I have a 30 foot 5th wheel weighing in at 8800 pounds I was thinking 4:56's? Would that be to low of a gear or would the 4:30s do? Thanks...
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Old 07-06-2009, 11:46 AM
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i went with 4.56s and only have 37s. I plan on going 40s next time for sure. its too low geared now with 37s. I would recomend no lower than 4.56s man.
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Old 07-06-2009, 11:47 AM
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Well because of where the powerband is you don't want to go too tall or you will be lugging the engine too much especially when towing. The 4:30's would probably be okay for when you weren't towing but you would find that your rig was shifting down to 4th a lot more than it should when towing just because you were running at too low of an RPM to make enough power.

Here is another chart showing the differences in speed in the 1700 - 2300 RPM range of the two gear ratios you are considering.



All around the 4.56's with those size tires will give you a very usable power band. I did a comparison and I am running 245/70 19.5's which have a diameter of 33.4 inches and with the 4.10 ratio it works out almost identical to your truck with 40's and 4.56's.
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