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gear ratio help

1812 Views 21 Replies 11 Participants Last post by  THE STIG
I have an 05 with a 6 speed manual tranny with 3.73 gear ratio. I have 295-70-17 tires. When Im on high way at 75 mph I am pushing 2500 rpms and I have a top speed of 92 against the limiter. I read the tag in the glove box and my djq is 11.5. I have no clue what djq means. I want to be at about 2000 rpms at 75 mph. What can I do.:confused013:
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Do you have the G56? You can do a gear change to a 3.42 but to do both diffs will cost you over $2000 to have somebody do it.
 

· TECH SPECIALIST
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hold your horses. most of us have lives beside CF, i went steelhead fishing today.

11.5 is the diameter of your diff. ring gear, the AAM rear diff.
strong unit.

consider a Gear Vendors or 3.42 ration differentials front and rear.
Gear Vendors Under/Overdrive, Dodge 4X4 Wheel Drive auxiliary transmissions.
both options expensive but the Gear Vendors gives better pulling takeoff performance.
having one installed now for summer towing travel season
 

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Based on the information that you have provided, it seems like you have a 4.10 axle ratio instead of a 3.73.

If you want to lower your rpms at any given speed, you have two choices: First, you can use a larger diameter tire. Second, you can change your axle ratio to a higher ratio(numerically lower).
 

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Discussion Starter · #6 ·
Based on the information that you have provided, it seems like you have a 4.10 axle ratio instead of a 3.73.

If you want to lower your rpms at any given speed, you have two choices: First, you can use a larger diameter tire. Second, you can change your axle ratio to a higher ratio(numerically lower).
3.73 is what is stated on the tag in the glove box. So that is what im baseing what is in the truck. I allready have larger diameter tires than what comes stock. So with out having to tear my front and rear covers off. How can I find out what is truely in the cases.
 

· Bangin' through the gears
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Dropping from 2500 to 2000 at 75mph is a huge jump. I'm not going to try and figure out the math, but you'd have to go to a BIG tire. Or the 3.42's as was mentioned. What's wrong with 2500 RPM? You getting terrible milage? You could go 285-75-17 which should be closer to 34" instead of the 33" or so that you have now. It's also skinnier so you should have less rolling resistance. But I doubt that tire size change would net you very much RPM drop. Definitely not as much as you'd like.

My suggestion......drive slower Ha Ha.
 

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A 05 with a NV5600 and 3.73 gears and a 295x70-17 tire has the following:

NV5600 6 Speed Manual
Gear 1 2 3 4 5 6
RPM 5.630 3.380 2.040 1.390 1.000 0.730
1000 5 8 13 19 27 36
1100 5 9 14 21 29 40
1200 6 9 16 23 32 44
1300 6 10 17 25 34 47
1400 7 11 18 27 37 51
1500 7 12 20 29 40 55
1600 8 13 21 31 42 58
1700 8 13 22 32 45 62
1800 8 14 23 34 48 65
1900 9 15 25 36 50 69
2000 9 16 26 38 53 73
2100 10 16 27 40 56 76
2200 10 17 29 42 58 80
2300 11 18 30 44 61 84
2400 11 19 31 46 64 87
2500 12 20 33 48 66 91

If you are seeing 2500 RPM's at 75mph I would say you do not have a 3.73. AND I just did the computation with a 4.10 rear which shows 83mph at 2500RPM in a NV5600 truck with the same 295 tire.

GO HERE: http://www.klenger.net/dodge/general-reference/gear-speed-calculator.xls. The top portion of the charts where gear ratio and tire size are can be changed by clicking the box.
 
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if your tires are taller than stock, u are going faster than your speedo says...
 

· Bangin' through the gears
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if your tires are taller than stock, u are going faster than your speedo says...
Good call. I just took it for granted that he would have corrected his speedometer, or taken the speed difference into account.


He could also have a G56 trans.......he hasn't said yet.
 

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Discussion Starter · #14 ·
I just bought the truck so I am not 100% on what all has been done to it. I am not sure what tranny I have. I know that reverse is towards the driver and down. If that helps. I was going to do a road test next to a fairly new car to check for speedo lag. Like i said I just got the truck with 86000 miles and the only visible thing I can see so far is the airaid intake system. Thanks for the link to the sight for figuring ratio's.
 

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Discussion Starter · #16 ·
so how would that affect it. dose the g56 have a lower 6th gear compared to the other one. One more question. If I do have 4.10 and I to go to 3.73. Can I just change the ring and pinion in front and rear or not?
 

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You need to change the pinion BOTH front and rear. Plus let me add something about your tire size. You have a TALLER tire than stock. That means your speedometer reads a lower speed than actual (unless it has been adjusted by a programer or a tech using a StarScan tool). A 295 tire would throw off a stock speedometer approximattely 6%. Meaning if your speedometer reads 70mph you are actually 74-75mph. This difference does not account for the rather large variation you are seeing.
 

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