Gear Ratio Swap. (A questions asked a thousand times)

[KC_Hubbs]

Im considering changing the gear ratio in my truck and this is all new to me.  Heres my details:

 

2013 Silverado z92 

5.3l V8

4WD

crew cab

3.42 current gears. 

35in tires.

 

 

     Im looking into gear swaps, and im looking at either a 4.11 or a 4.56.   Right now with the 3.42 I run about 1375rpm at 60mph.    Usually ill get about 20mpg with this set up.  Not bad for 35in tires. 

 

   However, i dont like that the truck has to run hard to get up small hills.  So, i was thinking about re-gearing.   Im just not too sure how much my rpms would go up with those gears I mentioned earlier. Most of my driving is city, and small roads.  

 

 

   Also, I was looking into buying the gears myself and taking them to a shop and Im a little unsure about all I need to buy.   I know Ill need ring and pinion gears and install kits for both front and back. Not sure of what else though.    

   Upon inspection, I believe my truck has a 8.25IFS front, and a 8.6 rear differential.  When looking at gears, i see some are listed as reverse direction.  Im not sure what to choose.  

 

    Any help would be greatly appreciated. 

[cr250Silverado]

I use this website based calculator. Let’s you see two set ups side by side. Put in your transmission ratios (or select the 4L60 or 6L80), differential ratio, and tire size. It shows what rpm or speed you will be running at. You can even change rpms to see speed, and change RPMs to see speed in the tables at the bottom.

 

do you have the 4 or 6 speed transmission?

 

http://www.grimmjeeper.com/gears.html

[KC_Hubbs]

I have a 6 speed. 

[cr250Silverado]

https://www.intercotire.com/tire_size_change_gear_ratio_calculator

 

Assuming your old tire was a 31”; using this this basic calculator above you would need to go to 3.86 (doesn’t exist, closest is 3.72 or 4.11). 4.11 with 35” seems reasonable, but go with 4.56 if you want more power or if you tow.  Plug the gears into the first link and look at the RPMs (freeway speeds), and see what ratio keeps YOU in a comfortable RPM range. Keep in mind you will want to tune your ECM/transmission for the new gears (and tires if you haven’t already). That first link is great, you can play with the numbers and see how often your truck will be shifting (look out for that really low first gear in the 6spd).

[dard6555]

Just out of curiosity, what do you consider a small hill and how fast are you wanting to climb said hill?

[SierraHD17]

4.56 with that size or even 4.88.  I run a 33.5" tall tire with a 6 speed truck and tach 2100 at 70 mph with 4.56.  You will down around 2000 rpm with a 35 and 4.56.  Don't be afraid of more gear versus less.