Regearing Question

[gmartin1215]

My 4x4 09 Tahoe came stock with the 6L80 transmission, 3.42, and 265/70/17 tire/wheel. I currently run the 285/70/17 tires/wheel on the same gears and transmission. I eventually want to move up to the 315/70/17 tire/wheel. For you all that know gearing, what size gears should I be looking at if I want the best overall performance between fuel economy and power?

 

[OR VietVet]

First, are you sure those tires will clear? Second, if you are trying to keep the same oomph off the line and try to have a decent mpg, then I would recommend a 4.10 gear. I am sure there is a graph someone can post that really narrows it down to what it should actually be. That is a lot of money to spend on the front and rear diffs for the sake of running a tire like that. But hell, who am I to question spending money on a rig.

 

[CaptainAmerica1]

4:10 with a 33” tire sounds about right…

 

[gmartin1215]

First, are you sure those tires will clear? Second, if you are trying to keep the same oomph off the line and try to have a decent mpg, then I would recommend a 4.10 gear. I am sure there is a graph someone can post that really narrows it down to what it should actually be. That is a lot of money to spend on the front and rear diffs for the sake of running a tire like that. But hell, who am I to question spending money on a rig.

I have a lift; the larger tires will clear. My rig goes off-road, so I want more ground clearance.

 

[gmartin1215]

I can see where a 4.10 makes sense for the 4-speed transmission but is the same true for a 6-speed?

 

[gmartin1215]

Doing some simple math after researching, a guide said to divide the New Tire Height (measured in inches or CM) by the Old Tire Height, then Multiply by the Original Gear Ratio.

so with what I have and where I want to go...
3.42(35/31.7) = 3.78, or in what is available, 3.73
I have a 4" lift and a steel after-market bumper that will have a winch, and running a larger tire will add more weight and resistance. I also pull a small trailer occasionally and sometimes heavy load in the rear of the Tahoe. So 4.10 seems like that might be better.

In this case, would it make sense to go to 4.10 from 3.42? If I was going to 3.73 then that seems like I would not gain much and would not be worth the cost to change.

Regearing front and back is going to run $2500-$3000, so I want to make sure the change will make sense.
By going to 4.10 on a 6-speed transmission and upgrading to a 35" tire, will I have a good mix of performance and fuel economy?
I do a mix of highway and off-road driving.
I also want to go with OEM gears. I think AAM provided the gears to GM? If not, where are the OEM gears coming from?

 

[gmartin1215]

@swathdiver what does your fancy calculator say?

 

[Foggy]

No matter what, you will lose MPG with a bigger/heavier tire..
The gear ratio change to 4.10 will just make up for the taller tire

Your performance should be similar to the 3.42 w 31" tire, other than
you are having to spin more weight- lots more
You will still want to "tune" your PCM for the tire height and gear change
or it'll be a real pig (prob like now IF you didn't do the pcm changes for your 33" tire)
You can gain a lot of better behavior by tuning the transmission for your situation

 

[swathdiver]

@swathdiver what does your fancy calculator say?

3.73 Gears will bring you back to essentially stock gearing on stock tires. 4.10s will give you a little more giddy-up and tractive effort in 4LO.

If you ever go back to the stock tire height, the 3.73s will be more friendly for street and highway driving than the 4.10s. Though many don't mind them at all.

 

[gmartin1215]

View attachment 385809
View attachment 385810
View attachment 385811
View attachment 385812
View attachment 385813


3.73 Gears will bring you back to essentially stock gearing on stock tires. 4.10s will give you a little more giddy-up and tractive effort in 4LO.

If you ever go back to the stock tire height, the 3.73s will be more friendly for street and highway driving than the 4.10s. Though many don't mind them at all.

This is awesome!!
Thanks!!!