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SOONER NATION
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Ok ill admit I did not read all 11 pages, and this very well may have been answered so if its redundant i'm very sorry, I have tried to do the math but I'm really just guessing, so please help a brother out.

I have a 2012 GMC Sierra 1500 SLT Z71 with the 6.2L engine, 6 speed trans, a 7 inch lift and 35x12.5-20 tires, a CAI, and the stock (3.42?) gears, the lift and tires were put on brand new at the dealership before I bought it.

what would be a good gear option for my truck? I want a good all around gear set, this is my DD and I am on the highway prob 60% of the time, but I want to be able to have more power for fun at the light, do some light wheeling/mudding, and be able to tow a boat to the lake this summer.

I also plan on a set of ARH long tubes, Corsa Exhaust, and a custom tune.
thank you in advance.
 

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I have had a lot of ppl tell me recently because I have a 6.2 L engine and a six speed transmission the biggest I should go is 4.10, is there any truth to that?


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Mmm Sandwich
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I have had a lot of ppl tell me recently because I have a 6.2 L engine and a six speed transmission the biggest I should go is 4.10, is there any truth to that?


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Depends more on your tire size. But there is nothing saying that you can't go more. Did they have a reason for their suggestion?
 

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They Just basically said even with 35x12.5s, the 4.56 gears with my 6.2 engine and 6 speed transmission would be too much gear and I would just be roasting the tires off everywhere I went.


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GMFS Enforcer
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Discussion Starter #128
4.10s. Let me start by saying that I take back what I have said about gearing and the 6 speed. You have to consider the whole drivetrain. In short GM figured out that if you strike a balance between pumping losses (throttle position) and engine load, you can good mileage. That is why you get stock trucks with 32 inch tires and 3.42 gears.


OP using the instructions on page one, the math works out to a 3.74. Given the weight of the tires and added wind resistance, it would be wise to go with 4.10s.
 

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thank you all for the help, I am looking on Yukons websight and for my rear GM9.5 14 bolt they only show 4.11, this is fine right? and the front i'm assuming is a GM 8.25 IFS Reverse rotation? again thank you so much.
axist6-I love that quote by Mark Rippetoe
 

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4.56. Honestly at 65mph that comes out to 1,970 rpms and with the heavy tires you'll do better. Plus why waste all the money for just 4.11? It's a 200 rpm difference at 65mph in 4.11 vs 4.56. I'd put money on it you would do better on gas with the 4.56 not to mention the reduced wear on your transmission.
 

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You guys are making this difficult LOL 456 or 411, ready go.
I don't want to spend a thousand dollars for the wrong parts


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Discussion Starter #133
4.56. Honestly at 65mph that comes out to 1,970 rpms and with the heavy tires you'll do better. Plus why waste all the money for just 4.11? It's a 200 rpm difference at 65mph in 4.11 vs 4.56. I'd put money on it you would do better on gas with the 4.56 not to mention the reduced wear on your transmission.
The ideal gear for his combo negating the the tire weight and vehicle height is 3.74. That is why I said 4.10. Remember, the truck had 32 inch tires stock and the purpose of gearing down for larger tires is to restore the performance you had before upgrading.

The old way of thinking that deeper gears = less engine load = better mpg (to a point) works on engines that don't have high compression ratios. The 6.2 has a compression ratio of 10.5:1. While you think that with deeper gears you wont have to have your foot in the gas as much, you are actually losing out a little bit because there are more pumping losses in high vacuum situations on high compression motors. To minimize the pumping losses, you have to have the throttle open more. To accomplish this, you run taller tires, taller gears, or a combo of both along with a transmission that has deeper 1st gears and more gears overall.


OP, 4.56 would be fun, however bear in mind that with 4.10 gears, 35s, 6 speed, and the 6.2, you will still have fun off the line and most likely get better MPG overall with the 4.10s vs. the 4.56. Also bear in mind that with a 9% increase in tire size, the 4.10 gears are a 19% increase over the 3.42s.

Go with 4.10s IMO.
 

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The ideal gear for his combo negating the the tire weight and vehicle height is 3.74. That is why I said 4.10. Remember, the truck had 32 inch tires stock and the purpose of gearing down for larger tires is to restore the performance you had before upgrading.

The old way of thinking that deeper gears = less engine load = better mpg (to a point) works on engines that don't have high compression ratios. The 6.2 has a compression ratio of 10.5:1. While you think that with deeper gears you wont have to have your foot in the gas as much, you are actually losing out a little bit because there are more pumping losses in high vacuum situations on high compression motors. To minimize the pumping losses, you have to have the throttle open more. To accomplish this, you run taller tires, taller gears, or a combo of both along with a transmission that has deeper 1st gears and more gears overall.


OP, 4.56 would be fun, however bear in mind that with 4.10 gears, 35s, 6 speed, and the 6.2, you will still have fun off the line and most likely get better MPG overall with the 4.10s vs. the 4.56. Also bear in mind that with a 9% increase in tire size, the 4.10 gears are a 19% increase over the 3.42s.

Go with 4.10s IMO.


Not to :beatdeadhorse5: AxisT6, but does your opinion on the 4.10 gears with the 6.2 remain the same for us folks with the 5.3 and 6 spd?
 

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Discussion Starter #136
Not to :beatdeadhorse5: AxisT6, but does your opinion on the 4.10 gears with the 6.2 remain the same for us folks with the 5.3 and 6 spd?
What is the Compression ratio of your 5.3? With the way fuel management is these days, it is not as cut and dry. To be safe, I would apply the same rules to the 5.3. The deeper first gear really helps, and as long as you choose a gear that is deeper than your calculated value, you shouldn't have any issue kicking in and out of OD.

This assumes you have factory 3.42 gears also.
 

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What is the Compression ratio of your 5.3? With the way fuel management is these days, it is not as cut and dry. To be safe, I would apply the same rules to the 5.3. The deeper first gear really helps, and as long as you choose a gear that is deeper than your calculated value, you shouldn't have any issue kicking in and out of OD.

This assumes you have factory 3.42 gears also.

Thanks for the input, I do have the 6 spd and 3.42 gears. And also came out calculation wise to I believe 3.74 hence the 4.10 seems to be a logical choice.

What I didn't take into consideration until you mentioned it was the power of the different engines, 6.2, 5.3 ect.....

All said and done, I believe I'm going to go with the 4.10's.......I can report back once I have the work done to perhaps ease others minds.
 

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I got my 4.10s in last week and just completed the 500 mile break in and oil change, I am very pleased with my choice so far, I really think 4.56 would have been too much, and I wouldn't be able to get traction anywhere. Also my MPGS, jumped by almost 5, I am getting a custom tune Wednesday.


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I got my 4.10s in last week and just completed the 500 mile break in and oil change, I am very pleased with my choice so far, I really think 4.56 would have been too much, and I wouldn't be able to get traction anywhere. Also my MPGS, jumped by almost 5, I am getting a custom tune Wednesday.


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What size tires are you running?
 

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35x12.5x20 -44 offset
6.2L engine, 6 speed transmission


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