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Discussion Starter · #1 · (Edited)
In looking through several threads here, and across the web, I've failed to find a complete calculator that will assist users in taking several factors at once and putting them into a single calculator. So, I made one.

At the top of this calculator, you have a chart to assist you in determining your transmission gear, based upon your transmission, if you have one of the listed transmissions. I've taken the most common transmissions and placed their individual gears into the chart to assist you in getting your final RPM, which appears to be the most important factor when re-gearing. Nobody wants to be cruising down the highway at 3400 Rpms..... that just eats up way too much gas.
Please realize, that an Automatic is also considered a slush box (slang), so you will get some slippage with the Torque-Converter, which may affect your final RPM. However, this calculator is designed to get you close to what you should be expecting.

In this calculator, you can first figure you're tire size accurately, which will be used to determine your overall gear ratio.
As well, once you get your accurate tire diameter, you can enter that number into the provided fields and come up with a RPM based upon your Ring & Pinion, selected transmission gear and the speed your are moving. I didn't pre-populate the tire size field with the calculated tire size, due to some folks running actual 35" tires, or a tire size that is different than what is stated on the tire side wall. We all know that different manufacturers produce different tire sizes, thus, the tire size field is left editable.

I was unable to embed this document, so I've just linked it to a Google spreadsheet.

Please CLICK on the below image to be taken to the document.
This Google Doc gives anybody the ability to edit the fields in RED.



As you all know there are lots of charts out there to guide you in your selection of what gears you should get for your larger tires. And, you all should know these are just guidelines, and it should be noted these calculations are usually based upon a final drive ration of 1:1...... FYI


Hope this can help ya all, and if so, maybe a MOD can make it a sticky...

Because my 2015 Silverado has a 6-speed, I'll be going with 4.56 gears.
 

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Discussion Starter · #5 ·
This thread seemed to have died off really quick.
I've updated my calculator to help others figure out the best gear ratio for their desired tire size.

I had some time to update the Final Drive EFFECTIVE gear calculator. I've added in a calculation that will give you the EFFECTIVE gear that you will have, after installing larger tires without changing your Ring and Pinion. This is helpful in that you can see what gear ratio you are effectively at, and where you want to be at with your larger tires. I've also added a side chart showing the most common gears and tire sizes. This will give you an idea of good gas mileage vs performance for towing. As well, I've added a second input for the desired tire size you'd like to install. You can see percentage change of the overall diameter, giving you an indication of just how much of a percentage change is affecting your gears.

hope you all can use it

Click on the image to go be taken to the Google hosted calculator
 

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So what does it mean by poor performance? is that in regard to towing or in general? Because based on my calculations going up to 33"s should help my MPG a bit lol

Also I feel like adding a little note box to the chart with common stock tranny gear sizes would be cool.
 

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Discussion Starter · #7 ·
aliasbane said:
So what does it mean by poor performance? is that in regard to towing or in general? Because based on my calculations going up to 33"s should help my MPG a bit lol

Also I feel like adding a little note box to the chart with common stock tranny gear sizes would be cool.
I suppose "Poor performance" is a subjective view. some may see great gas mileage as great performance at the cost of not being able to tow much. While others may see being able to tow 10k lbs as great performance, while their gas mileage suffers.....

performance is all subjective....

can you expound on the "note box to the chart with common stock tranny gear sizes...."
 

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Pretty well substantiates the 4.10 diffs with the 6L90 in my 2500 riding on 275/70R18 rubber as being an ideal setup. That is one of the main reasons I bought it, along with payload capacity. I get excellent power performance and only 1-2 mpg average less than my previous 2013 1500 with 5.3 and 3.42 diffs that weighed 1000 lb less.
 

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According to this chart i have 3.73 gears..... Not 3.42 like the build sheet says
 

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Discussion Starter · #10 ·
judsonlimited said:
According to this chart i have 3.73 gears..... Not 3.42 like the build sheet says
how do you figure, I'm curious how you came to that conclusion. I want to be sure the information is accurate...
 

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Check it, i was the last one to use it all my info is in there.
Also this one isn't the only chart to tell me that, a few other online ratio calculators have said the same thing
 

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Discussion Starter · #12 ·
Someone is using it right now....

glad to hear that this chart is confirming what other charts have stated.

Something else I've noticed is that when people are using the chart, you can see the numbers changing, and you'll see some kind of character in the upper right corner of the browser. In this particular case it's an armadillo .....
 

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Yeah i noticed that while i was using it. All of a sudden the numbers changed :lol: :lol: voodoo

But at that speed, that RPM, and tire size, the 3.42 ratio doesn't match up. so i moved up to 3.73 and sure enough it all matches. It had to have been a dealer gear swap or something from the previous owner because i still have the 8.5" 10 bolt rear end
 

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2010 GMC SIerra All Terrain C.C. 4x4 5.3
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Cool spreadsheet Steve. It would be a little easier on the eyes to change the bright yellow to a light grey and the font to black vs the red. Just the header ones.

Capture.PNG
 

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Discussion Starter · #16 ·
For those who may not be familiar with Google online documents, they are shared documents. If you use the above Gear Calculator AND you see that the numbers are changing without your input, you are witnessing Google's share feature. One of the other anonymous users, as indicated by a icon in the upper right section of the calculator, may be editing the document while you are viewing it. You can chat with people while viewing the document if you choose to. Google assigns names such as "Anonymous Rabbit" and "Anonymous Grizzly" to users that are viewing or editing the document at present.

 

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Discussion Starter · #18 ·
Glad you like it.

I hope that folks here can utilize it for their inquiries into the effects of larger tires on their rigs.
I customized the chart to the most common tires and gears for most trucks.
 

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2009 Chevy Z71; sounds fast.
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It was requested that this be stickied. I'll sticky it when you get the results from Monte's or figure out the bug...which may just be Monte.
 
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