gearing question

noresttill · Aug 25, 2005

1) I read the sticky.

2) I have a 96 4.0 automatic

3) I am looking at the RE 3.5 and putting 31's on it.

the question:

Iv heard that If you regear with 31s you can acheive better than stock mpg.

Myth??

Thanks, Jesse

MudDawg · Aug 25, 2005

This is well covered in the various gearing threads...but here goes...the stock powertrain is designed to give a good compromise between enonomy and pulling power....if you go to a larger tire...determine the percentage difference between stock and the size you use....lower (increase numerically) the gearing by the same percentage to maintain equal effective ratio.

It's no myth...I went to 33s with 3.73 gears...two major problems....the heep wouldn't pull a greasy string out of a cat's butt....and the MPG went down from 18 to 12. (yes...accurately tracked) I went to 4.88 gears, which put me so close to stock effective ratio that my speedometer was once again accurate. The result...good power and the MPG went back up to 18.

noresttill · Aug 25, 2005

so with 31's and 4.88 gears I would get better than stock? sorry i dont quite grok the idea of gearing yet I guess. would that mean I would have more torque and less top end?? I dont need to drive as fast as a the 4.0 will go

thanks again, Jesse

langer1 · Aug 25, 2005

noresttill said:
so with 31's and 4.88 gears I would get better than stock? sorry i dont quite grok the idea of gearing yet I guess. would that mean I would have more torque and less top end?? I dont need to drive as fast as a the 4.0 will go

thanks again, Jesse

With the proper gear change everything will be the same as it is now.
With 31" you will need 4:10 or something.

SharkXJ · Aug 25, 2005

noresttill said:
so with 31's and 4.88 gears I would get better than stock? sorry i dont quite grok the idea of gearing yet I guess. would that mean I would have more torque and less top end?? I dont need to drive as fast as a the 4.0 will go

thanks again, Jesse

I am not an expert BUT if you went with 4:88's and 31's your gas mileage would drop. Why? Your RPM's will go thru the roof. If you want to re-gear for 31's go to 4:10's.

SharkXJ · Aug 25, 2005

MudDawg said:
This is well covered in the various gearing threads...but here goes...the stock powertrain is designed to give a good compromise between enonomy and pulling power....if you go to a larger tire...determine the percentage difference between stock and the size you use....lower (increase numerically) the gearing by the same percentage to maintain equal effective ratio.

It's no myth...I went to 33s with 3.73 gears...two major problems....the heep wouldn't pull a greasy string out of a cat's butt....and the MPG went down from 18 to 12. (yes...accurately tracked) I went to 4.88 gears, which put me so close to stock effective ratio that my speedometer was once again accurate. The result...good power and the MPG went back up to 18.

Sorry for the hi-jack but I have to ask this. How are you getting 18mpg? Maybe my driving habits are bad but the best I have EVER gotten is 13-14 mpg. I went from Stock gears and 31's to 4:10's and 31's and now I am at 4:10's and 33's. My gas mileage actually got better when I threw on the 33's.

I have a Flow Master but no Air Intake mods done.

langer1 · Aug 25, 2005

19-21 mpgs very common

ks92xj · Aug 25, 2005

4.10's + 32's = 16 MPG city for me

cal · Aug 25, 2005

SharkXJ said:
Sorry for the hi-jack but I have to ask this. How are you getting 18mpg? Maybe my driving habits are bad but the best I have EVER gotten is 13-14 mpg. I went from Stock gears and 31's to 4:10's and 31's and now I am at 4:10's and 33's. My gas mileage actually got better when I threw on the 33's.

I have a Flow Master but no Air Intake mods done.

I have 4.56 with 32's and I get about 17. I'm on a 1987 thats taken HARD abuse. It was getting about 12 when i got it, cleaned the throttle body, replaced the air filter, spark plugs, o2 sensor, and cat.. properly adjusted the cps. Boom. 17. I can get 20 if i drive 55 and dont accelerate hard.

gearing question

noresttill

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MudDawg

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noresttill

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langer1

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SharkXJ

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SharkXJ

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langer1

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ks92xj

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cal

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