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3.73s

M1ck3y

By M1ck3y
in Modifications, Wheels & Tires

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KARNUT Senior Enthusiast

KARNUT

Posted
Posted

 I did that often with the cars my wife drove. She would drive mostly in town. The acceleration would pick up and the in town fuel mileage would increase. Later with trucks if they didn’t already come with 373s or 410s I would change them. My trucks early on would carry weight in the bed or pull loads. We would add gear vendors in some. Today with the transmission and final gear combo unless you’re messing with over sized tires. I don’t know if it would be necessary. It much easier to buy the combo to fit your needs. 

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M1ck3y Senior Enthusiast

M1ck3y

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3.23, 33” tires, 4wd. Looking for improvement in acceleration..

Edited by M1ck3y
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garagerog Enthusiast

garagerog

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If you have the 8L90 with 7th and 8th OD ratios, I would be tempted to go with the 4.10 ring and pinion set especially if you occasionally load or tow heavy. The 3.73 will be a huge improvement over 3.23, but with the expense of 2 differentials, you don't want to be left just wanting a tad more. Besides, I see gas prices being stable for the foreseeable future.

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M1ck3y Senior Enthusiast

M1ck3y

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5 hours ago, newdude said:

When you say 33" tires, are they floatation size?  What size are they?  


They’re 285/65r18. Sidewall says 33”, tire Calc will say 32.6”

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M1ck3y Senior Enthusiast

M1ck3y

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7 hours ago, garagerog said:

If you have the 8L90 with 7th and 8th OD ratios, I would be tempted to go with the 4.10 ring and pinion set especially if you occasionally load or tow heavy. The 3.73 will be a huge improvement over 3.23, but with the expense of 2 differentials, you don't want to be left just wanting a tad more. Besides, I see gas prices being stable for the foreseeable future.


Yeah I was thinking 4.10s, maybe even 4.30s max. Problem is 3.73s is the max size for 9.76 and the shop I’m working with won’t do a gear kit that has a spacer (to fit a larger gear).

Edited by M1ck3y
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swathdiver Senior Enthusiast

swathdiver

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Posted
On 9/22/2025 at 7:59 PM, M1ck3y said:


Yeah I was thinking 4.10s, maybe even 4.30s max. Problem is 3.73s is the max size for 9.76 and the shop I’m working with won’t do a gear kit that has a spacer (to fit a larger gear).

You can change the carrier to run a lower gear.  The carrier you have is only good for 3.23 and lower (numerically) and the other one is good for 3.42 and higher.

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swathdiver Senior Enthusiast

swathdiver

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Here are your effective ratios and rpms at speed as configured now:

 

image.thumb.png.11d24cc4df38b6e8db9db8a831a56bba.png

 

3.42s:

image.thumb.png.31b738330419be943ad82d7d184020eb.png

 

3.73s:

image.thumb.png.6a1e8d8673a1cf9bf77699b97f65ebc2.png

 

4.10s:

image.thumb.png.41020df38f9f8733bad3454449016e3f.png

 

4.30s:

image.thumb.png.828977308aa539743031ecaf54d982a3.png

 

https://demandaam.com/expview/976-RearAxle-Salisbury-12Bolt

 

The Ram with the 5.7 Hemi and ZF 8-speed transmission can come with 3.92 gears.  You're equivalent would be 4.10 gears.  So, it's not too much 1st gear as some say.  Those trucks leap off the line at the track like nobody's business.

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M1ck3y Senior Enthusiast

M1ck3y

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8 hours ago, swathdiver said:

You can change the carrier to run a lower gear.  The carrier you have is only good for 3.23 and lower (numerically) and the other one is good for 3.42 and higher.


Any thoughts on how changing gears will affect the driveshafts critical speed? 

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davester Senior Enthusiast

davester

Posted
Posted

The driveshaft's critical speed (in rpm) will not be changed.  What changes is how fast the vehicle is going when the driveshaft is going at that rpm.

 

A lower gear ratio (3.73 for example), you will be going faster for a given driveshaft speed/rpm, vs a higher ratio (say 4.10).

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M1ck3y Senior Enthusiast

M1ck3y

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3 hours ago, davester said:

The driveshaft's critical speed (in rpm) will not be changed.  What changes is how fast the vehicle is going when the driveshaft is going at that rpm.

 

A lower gear ratio (3.73 for example), you will be going faster for a given driveshaft speed/rpm, vs a higher ratio (say 4.10).

 

Right, I’m wondering how much my top speed will drop after changing gears…

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GETGONE Enthusiast

GETGONE

Posted
Posted

Unless you're tuned it won't matter anyways since it's electronically limited to 112mph.

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davester Senior Enthusiast

davester

Posted
Posted

Actually, you would get a different top speed just changing the gear ratio, because most GM trucks have the VSS at the rear of the transmission or transfer case, so the ecm miscalculate the speed the truck is going, and the limit it applies will similarly be off.  Tuning the truck to fix the speedo would then return it to the 112 limit, unless the limit is also changed as part of the tune.

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