4.0s who have re-geared - Ranger-Forums - The Ultimate Ford Ranger Resource


Drivetrain Tech General discussion of drivetrain for the Ford Ranger.

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  #1  
Old 10-21-2006
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Should I re-gear for mileage

For those who have switched from 3.73 to 4.10, same tires before and after. what was the difference in mpg?

I have 4.10 and 32" tires. at 75 mph i am running just under 3000 rpms, I am getting very poor gas mileage at that speed.

I have been thinking about going to 3.73s (would 3.55 be overkill?) for better gas mileage.

Is re-gearing going to save enough money in gas to justify itself?

The reason I ask is I am going to be doing a lot of commuting soon.

Last edited by RedPowerRanger; 10-25-2006 at 10:31 PM. Reason: Accuracy
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  #2  
Old 10-21-2006
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Hmm..you must have a stick. My Auto @ 75MPH is right @ 2500RPM.

Rick
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Old 10-21-2006
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same with me but I'm more at 2400 or so.....

I also have an auto, 4.0, 4.10 gears, stock tires
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  #4  
Old 10-21-2006
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Did you CHANGE your gears to 4.10 from a factory 3.73 ratio? Or have you always had 4.10's?

The reason I ask is this: when you went to 10% larger tires than stock (approx), your VSS now turns less for the same distance, making your miles traveled seem 10% lower than it is.

If you were factory 4.10, and went to 32's, you should be mutiplying your miles traveled by 1.1 before calculating your miles per gallon. OR, you can just multiply your miles per gallon by 1.1 after you calculate it.

I would point out also, that a factory 4.1 with 32 inch tires is actually traveling at 82 to 83 mph when the speedo reads 75.
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  #5  
Old 10-21-2006
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I bought the truck used with 14k miles, as far as I know the gears have always been 4.10. I am using my GPS device to determine the speed that I'm running, which isn't much different than what the speedometer is reading. I'm pretty sure that I'm not going 80+ mph because most people seem to pass me. The tires are actually a little smaller than 32", 235/85/16.
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  #6  
Old 10-21-2006
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[QUOTE=n3elz]you can just multiply your miles per gallon by 1.1 after you calculate it. QUOTE]
How did you figure 1.1? I came up with 1.05.

I have been playing with one of the RPM and MPH Correlation calulators, and the numbers just don't mesh. Either my GPS is way off on the speed, or I have gears other than 4.10.
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  #7  
Old 10-21-2006
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Okay, well that fits this then actually.

The truck was converted to 4.10's, then you added tires that were bigger and the two cancel out giving you stock calibration (more or less) on your speedo.

If so, then your mileage sucks as bad as you say.

Also verify that the speedo matches the GPS both at 25mph and 75 mph. If it's off by the same percentage, more or less, at each position (or not off) then you're fine.

If it's off by the SAME amount at 25 and 75, you could have an "offset problem" (basically meaning the speedo needle is on wrong, lol).
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  #8  
Old 10-21-2006
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Good Idea. I will verify...

Last edited by RedPowerRanger; 10-22-2006 at 08:08 PM. Reason: New data
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  #9  
Old 10-22-2006
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At lower speeds the speedo and GPS are nearly concurrent. Above 50mph the error noticably increases and seems to max out at 80mph (speedo) to about 3 mph difference.

in 5th gear
2000 rpm ≈ 55 mph
2500 rpm ≈ 67 mph
3000 rpm ≈ 79 mph
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  #10  
Old 10-22-2006
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Quote:
Originally Posted by RedPowerRanger
At lower speeds the speedo and GPS are nearly concurrent. Above 50mph the error noticably increases and seems to max out at 80mph (speedo) to about 3 mph difference.

in 5th gear
2000 rpm ≈ 55 mph
2500 rpm ≈ 67 mph
3000 rpm ≈ 79 mph
Not sure about your GPS, but the Garmin I have is useless above 55mph. Or so that's what the directions tell me.
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  #11  
Old 10-22-2006
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That's really a trivial difference. I'd consider your speedo to be % on" for the most part.
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  #12  
Old 10-22-2006
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i have 32s an 4.56s and at 70mph i am at 3000-3200rpm. my gas milage but i love the power
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  #13  
Old 10-23-2006
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Is there a way to fugure out what gas mileage I would get with different gears?
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  #14  
Old 10-25-2006
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100% sure that I have 4.10s in the rear; just took off the cover to verify. I don't know what is wrong with the calculations. Maybe my Tachometer is off by a large margin.


Anyway, Should I get 3.73s?
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  #15  
Old 10-25-2006
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You will actually lose mileage and create more work on your engine going to 3.73's. they will make the RPM lower sure but you are also making it harder to turn the tire and as load increases, requirement for work increases. You are getting about as good as you will get right now.

And why take the cover off? You can either "a" read the tag on the diff and run the number to see what they are or "b" jack the rear end, index the pinion to the housing and rotate the tire one full turn counting how many times the driveshaft rotates to get your axle ratio. Lot easier than removing the diff cover and then having to refill with lube man.
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  #16  
Old 10-25-2006
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Well, after using the RPM/MPH calculator, the math only worked if I had 4.56 gears. I was pretty sure that I didn't, just wanted to be certain.
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