Axle ratio to tire size input needed

[SilverSurfer5300]

Hello! I'm new to the forum and I just purchased a 2013 Tahoe 4x4. It has the 6L80 6-speed tranny and the GU4 3.08 axle ratio.

I would like to replace the current 275/55/20s (31.9" diameter) with 275/60/20s (33.0" diameter), but all the online axle ratio-to-tire size charts show the current (OE) tire diameter to be too large for the 3.08 axle ratio, already. It seems that the majority of these charts are 20+ years old and were formulated with 3 and 4 speed transmissions in mind and thus, would be very inaccurate for determining ideal axle ratio-to-tire size relationships for 6 speed transmissions.

I am fine with changing gears in the front and rear axles if needed to put me in the ideal torque range. Does anyone have updated axle ratio-to-tire size charts specifically for 6-speed transmissions, or a way to [accurately] figure it out?

 

[Foggy]

Just google 6l80e gear ratios.. 5th and 6th are both OD ratios
You'll want at least 3.42 gears.. But with the 5.3 I'd personally go
with 3.73 . It's kinda pricey doing front and rear.
I have 3.42's with stock height tires.. I'd like a bit deeper like 3.73, but
I don't have experience rebuilding diffs and setting up gears.
My Yukon is used for towing
So You'll have to decide what your actual use is

 

[Marky Dissod]

... just purchased a 2013 Tahoe 4x4 ... 6L80E & 3.08.
I'd like to replace the current 275/55R20 (31.9" tall) with 275/60R20 (33.0" diameter), but all the online axle ratio-to-tire size charts show the current (OE) tire diameter to be too large for 3.08, already.

Because GM is held hostage by CAFE MPG test performance, this is absolutely true.
However, some vehicles are outside of CAFE's aegis.
Those vehicles, that also came with 6L80E, were equipped by GM with 3.42 or 3.73.

... I'm fine with changing front and rear axle gears if needed to put me in the ideal torque range.
Does anyone have updated axle ratio-to-tire size charts specifically for 6L80E, or a way to [accurately] figure it out?

Since GM undergeared your axles from go, instead of a calculator, answer these questions:
1. This is my toy, NOT my daily driver?
Yes, toy = 3.73 ... or ... No, daily driver = 3.42
2. I'm gonna race, or 'play hard' [for money]?
Yes, race = 3.73 ... or ... No = 3.42
3. I'm gonna tow/haul, or 'work hard' [for money]?
Yes, lots of towing / hauling =3.73 ... or ... No =3.42
4. I care more about city MpG, less about highway MpG?
Yes, city = 3.73 ... or ... No, highway = 3.42
5. Many or mostly steep &/or very long hills where I usually drive?
Yes, hilly = 3.73 ... or ... No, flatlands = 3.42

If N is greater than Y, 3.42. However, if N=5, keep your weak@$$ axle gears.
If Y is greater than N, 3.73. However, if Y=5, 4.10.

 

[Charlie207]

Did 3.73 gears come in any 4wd 6L80-equiped SUVs? Or, was that a truck-only thing?

 

[SilverSurfer5300]

answer these questions:
1. This is my toy, NOT my daily driver?
Yes, toy = 3.73 ... or ... No, daily driver = 3.42

No, daily driver. But I do plan on eventually increasing low-to-mid rpm torque ~50-100 lb./ft.

2. I'm gonna race, or 'play hard' [for money]?
Yes, race = 3.73 ... or ... No = 3.42

No.

3. I'm gonna tow/haul, or 'work hard' [for money]?
Yes, lots of towing / hauling =3.73 ... or ... No =3.42

Only occasional towing.

4. I care more about city MpG, less about highway MpG?
Yes, city = 3.73 ... or ... No, highway = 3.42

Yes, I care more about city mpg.

5. Many or mostly steep &/or very long hills where I usually drive?
Yes, hilly = 3.73 ... or ... No, flatlands = 3.42

Yes, hilly.

 

[Marky Dissod]

Did 3.73 come in any 4WD 6L80E-equipped SUVs?
Or, was that a pickup truck only thing?

Specifically, I don't think 3.73 was available for any '1500' GMT900 with 6L80E.
However, 3.73 was available for '2500' and up GMT900 with 6L90E.

Two more questions, by the way:
6. Will I be using taller- / heavier-than OE wheel & tire package?
Yes = 3.73 ... or ... No = 3.42

7. Did GM undergear every V8 vehicle they've ever sold since the late 60s?
YES.

Final decision is yours, of course, but you get the idea.

 

[blondie70]

Why not just run a smaller diameter tire/wheel and do same thing for much much less $$$$ ?

 

[wjburken]

@swathdiver has a pretty handy spreadsheet for this.

I made a calculator with excel that's very precise and even accounts for tread depth. Here's an example of my compact one:

View attachment 402949

This is about what the OP is experiencing now:

View attachment 402953

And this is how his truck would perform with 4.10 gears:

View attachment 402954

So if you compare the before and after, you guys were correct and I was wrong about the 4.56s being more equal, the 4.10s would be more equivalent while running 37s!

That's why I made this! LOL

 

[Charlie207]

Why not just run a smaller diameter tire/wheel and do same thing for much much less $$$$ ?

Because I have 33" wheel/tire combos for summer & winter.

I imagine a 6.0 swap will negate the taller tires.

 

[SilverSurfer5300]

Why not just run a smaller diameter tire/wheel and do same thing for much much less $$$$ ?

Because if I had wanted a minivan, I would have just bought a minivan instead of a Tahoe.


In all fairness, I know that the term "SUV" has evolved into a catchall term for everything that is neither a car nor a pickup, and the majority of current SUVs are basically nothing more than large hatchback cars with slightly taller suspensions than their sedan counterparts. . .

But I want my Tahoe to fit the traditional definition of an SUV: a 4x4 truck with a chassis-length cabin.