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Old 04-05-2012, 03:23 PM   #1
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gear ratio calculator??

Hey guys so I have 2000 Jeep 4.0 Automatic. I got it a few months ago and was planning a gear swap, I have a 3 inch lift with 33's. I did a gear calculator and it says I should be at about 2,000 RPM at 55MPH with 4.10 gears does that sound right to you? The reason I ask is I checked the build sheet and it came with 3.07 gears. I would be happy as S*** if the previous owner put in some 4.10 gears. If he put in 4.10's now i gotta check for superior axles. Thanks for the help guys.

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Old 04-05-2012, 03:25 PM   #2
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If u ready have 4.11s that's awesome but if u don't. Then go 4.56

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Old 04-05-2012, 03:29 PM   #3
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Quote:
Originally Posted by lbailey21 View Post
if u ready have 4.11s that's awesome but if u don't. Then go 4.56
x2!

and that sounds right, ive got 4.11's and at 60mph im right at 2000rpms
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Old 04-05-2012, 04:22 PM   #4
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I used this calculator , and used a tire size of 32.5, since most 33 inch tires are actually smaller, and came up with 47 mph with 4.10s at 2000 rpms. Using 3.73 gear ratio yielded 52 mph at 2000 rpms and 3.07 yielded 63 mph at 2000 rpms.

The question is, "What is your speed now at 2000 rpms?" If you speedometer says around 55 mph, I'd say you probably have 3.73s installed.
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Old 04-05-2012, 04:24 PM   #5
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that is the same calculator I used. at 55 MPH I was at about 2,000 RPMs, Im gonna have to recheck tomorrow. I have been drinking and right now I can't go driving, haha.
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Old 04-05-2012, 05:06 PM   #6
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Make sure your speedo gears are right before u throw out RPMs
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Old 04-05-2012, 10:26 PM   #7
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Quote:
Originally Posted by Border Dave View Post
I used this calculator , and used a tire size of 32.5, since most 33 inch tires are actually smaller, and came up with 47 mph with 4.10s at 2000 rpms. Using 3.73 gear ratio yielded 52 mph at 2000 rpms and 3.07 yielded 63 mph at 2000 rpms.

The question is, "What is your speed now at 2000 rpms?" If you speedometer says around 55 mph, I'd say you probably have 3.73s installed.
didnt see the OP said he had an auto lol, I am at 2000 rpms at 60mph with an AX15
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Old 04-06-2012, 04:56 AM   #8
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I just put 4.10's in my 3 speed auto (on 33's)

Heaps more power - take-off and pick-up much better.
No more constant downshifting in headwinds or steep hills.
Much better offroad - can now tackle steep descents without riding the brakes - it's great to be able to crawl again.

BUT
It's revving its tatas off on the highway.
47mph = 2000RPM
50mph = 2200RPM
60mph = 2700RPM
70mph = 3000RPM
75mph = 3250RPM

With the old stock ratios (3.07's) and 33's, the revs were much lower, but really had to work the accelerator to make progress on the highway. Often had it floored in headwinds or on hills (on the highway) and still struggling to keep up.

Now, with the 4.10's I'm using a LOT less accelerator but revving higher.
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Old 04-06-2012, 11:51 AM   #9
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didnt see the OP said he had an auto lol, I am at 2000 rpms at 60mph with an AX15
Overdrive makes a huge difference.
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Old 04-06-2012, 11:56 AM   #10
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Quote:
Originally Posted by Wesboy View Post
I just put 4.10's in my 3 speed auto (on 33's)

Heaps more power - take-off and pick-up much better.
No more constant downshifting in headwinds or steep hills.
Much better offroad - can now tackle steep descents without riding the brakes - it's great to be able to crawl again.

BUT
It's revving its tatas off on the highway.
47mph = 2000RPM
50mph = 2200RPM
60mph = 2700RPM
70mph = 3000RPM
75mph = 3250RPM

With the old stock ratios (3.07's) and 33's, the revs were much lower, but really had to work the accelerator to make progress on the highway. Often had it floored in headwinds or on hills (on the highway) and still struggling to keep up.

Now, with the 4.10's I'm using a LOT less accelerator but revving higher.
It's definitely a compromise with only three speeds.

I have 33s and 3.73 right now, and while first gear is OK, it's definitely lacking any power from a stop, including reverse. You were right in going with 4.10s, unless all you do is drive on the highway.

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