done a little research on what i need to get heres the setup i have -

3.73 grears
30" Orginal tires

What the gear calculator comes up with after the 6" lift and different tires

4.72 gears
38" new tires.

now i get why my milage sucks.

i do moderate towing during the summer time. dual axel horse trailer and sometimes bobcat on the back of a deck over.

whats my best option for new gears to not only save my milage but my tranny with the lift.

 

buler buler...anyone anyone?


i looked up some stuff, i guess the lowest the dana 60's can support is 3.54 what will this do for my rpms on highway speeds and towing such? just want to try and make my trans last as long as possible

 

Not sure if I understand your post completely. You're running 38" tires on stock 3.73 gearing, right? I'm confused on how you came up with a 4.72 gear ratio number in there.

If you're running larger tires on the stock gears, and trying to tow heavy loads with it, then you're going to have problems. You do not want to drop to taller (numerically lower) gears, such as 3.55's with your setup. That would make your problem even worse. Rather, you need numerically higher gearing to match your tire size.

My truck also came with stock 3.73 gears. Right now, I'm running 4.30's with 36" tires.

If you are towing often, you'll need either 4.30's or 4.56's. I routinely tow very heavy loads with my truck, grossing over 16K lbs, and it pulls that weight around easily.

Yukon gears are good. I picked up mine from Randy's Ring and Pinion.

 

the 4.72 is the equivilant of what he needs to run to get back to what stock with the 30 inch tall tires with 3.73 gears (38/30x3.73) = 4.72 gear. right now his gearing is like a 30 inch tire with a 2.94 gear (30/38x3.73) i personally would go with a 4.56

 

ahh exactly. so what are my rpms gunna look like when i put those 4.56's in? am i going to see higher rpms at 55 or lower im at about 2000 rpms right now at 55

 

and im not to sure i went online and did the gear calculator here it is.

Gear Calculator


all i did was put in my orginal 30 " tire and my 3.73 gears, then changed the new tire size to 38" becuase thats what im getting. it comes up with 4. something. i though the goal was to get factory gear ratio as much as you can, which means putting 3.54 in it woudl bring it as close as possible.

 

That calculator is what you use to find the gears NEEDED to return the overall gearing back to original when changing tire sizes.

So, to get the truck to run the same as it did with the small tires, you need to install 4.72 gears, which don't exist. The closest commonly available is 4.56, which is close enough.

Also, most SD trucks of that year came with 265/75-16 tires, which are closer to 32 inches tall. Using this in the calculator nets a required 4.43 ratio, which again doesn't exist. You are still good with the 4.56 gears.

 

thanks guys, it was a 2 hour discussion with my dad last night when i was trying to figure this out. knew someone on here would know what i needed. the help is much appreciated.

 

It can get confusing.

For 38's, the sweet spot is between 4.30s and 4.56s. However, since there isn't anything available between those two sizes, you'll have to pick what you want to go with. 4.56's will net you higher RPM's on the highway, so your highway mileage will drop a little (no biggie though, your mileage already dropped with the lift and tires). However, you'll get more "grunt" down low, and it will be better for towing with your larger tires. 4.30's aren't that bad for 38" tires, and still tow quite well.

 

true i mean i do do mostly high way driving to and from school. if you could guess what woudl i be getting at about 55 with the 4.56. i know its a guessing game but im already at 2000 rpms at 55. dont want to go much higher

 

Just remember that if you go with 4.56 ratio gears you going to have to buy huge tires all the time($$$) since your rpm`s will be way up there if you try to go back to smaller tires. Something to think about, not to mention accelerated brake and whl bearing wear.

 

How can you be running 2000 rpm's at 55? I have 3.73 gears in my 02 with the factory 265/75R-16 tires and I hit 2000rpm's at 70 mph. My 97 has 4.56 gears in it and it hits 2000rpms at about 55mph. It has the factory 235/85R-16's on it.

 

CPS - will that be more then what i already have from the 37" tires?


and CampSpringsJohn - I have 37 " tires and 6" lift. makes the rpms higher with the bigger tires.

 

I would think with bigger tires that would work in reverse. The bigger the tires, the lower the rpms it would take to hit the same speed when compared to the smaller tires. Unless you already did a gear swap in the differentials.

 

X2 i agree

i am running 37" tires and 8" lift with 3.73. i run with the over drive off if i am running under 65-70 mph. if i am running 55-60 mph in overdrive my RPM is around 1500-1700.

mic