So I have been kicking tires lol, this is what I came up with. My truck has to have 3.55 gear ratio, at 65 its 1800 or so and sucks as a 1 ton tow rig. This tire comparison is a Firestone LT 235 85 r16   to    LT235 75 r16 
     Tire 1                                             Tire 2                          Diff

Diameter 31.73                                29,88                          -6.19

with 9.25                                           same   
sidewall 7.86                                     6.94                             -13.33
circumference 99.68                        93.86                          - 6.19
Revs/mile 635.65                              675.02                        - 6.19
Speed 10   vs     9.38
             20           18.76
             30           28.14
             40           37.52
             50           46.90
             70           65.66
This is some big diff. Im just not smart enough or able to search to find out if just changing tire size if I can achieve a 3.75 gear change just by down size my tires. Im sure someone has figured this out before. 
Or am I stuck with changing rear end gears?

For your setup to get that inch down...

 

I ran this size on my old 1996 Dodge 1500 (Lil' Red) and ran great and increased the MPG's. Lighter rotational mass and less rolling resistance.

 

Here is the alternate wider size which still fits your dually. This is the size I'm running on Beast now and no issues. Great offroad performance and great traction on the ice.

 

So you coming from a 235/85 R16 tire this would give you the 3.70 ratio. The magic tire size that is listed on EVERYONE door tag but no one wants to even use...

Edited July 10, 20222 yr by Mopar1973Man

1 hour ago, Mopar1973Man said:

The magic tire size that is listed on EVERYONE door tag but no one wants to even use...

 

Hey! Don't say "no one".  I use that tire size!

 

- John

Edited July 10, 20222 yr by Tractorman

1 hour ago, Tractorman said:

Hey! Don't say "no one".  I use that tire size!

 

Yeah using general speak being out here it all 32 to 37 inch tires on 3,55 gears and wondering why there truck has excessive EGT's and low MPG's. More common issue that most think here. Now there is members here like @IBMobile that run the 245/75 R16 on 4.10 gears which is way good for towing placing final ratio at 4.28:1 to the ground. Talk about a towing monster.

So help me figure this, 245 is wider than 235 ?  Wouldnt 235 75 r16 be better?   And putting a 4.10 in would run how much?

 

Edited July 10, 20222 yr by jlwelding

2 minutes ago, jlwelding said:

Wouldnt 235 75 r16 be better?

Non standard tire that will most likely be difficult to get.

 

Here is the math on the 235/75 R16 tires.

 

52 minutes ago, Mopar1973Man said:

Non standard tire that will most likely be difficult to get.

 

Here is the math on the 235/75 R16 tires.

 

I like this chart. I used it when I decided to change my ratio to 3.373. I have 33" tires. Going to the 4.11 would have been cost prohibitive as I would have had to change more parts in the differentials and overkill and make my gas mileage go down.

9 hours ago, jlwelding said:

So help me figure this, 245 is wider than 235 ?  Wouldnt 235 75 r16 be better?   And putting a 4.10 in would run how much?

 

First number is width in MM, second is ‘aspect ratio’ / R rim size

 

example, my 275/65r18 are the same width and diameter as 275/75r16

 

Same calculator says I really should be running 3.73 gears. Although changing down from 275/70r18 made a significant difference. 

I see the truck in question here is a manual, I use 305/70/16 toyo mud terrain tyres which are 32.8" tall which is just outside the ideal for economy

 

BUT

My truck is auto and when towing I just don't use OD doing this puts my rpm at over 2100 at 65mph but here in the uk towing is restricted to 60mph on motorways  so at 55 to 60  I'm perfect rpm and when not towing and using OD my truck choogles on just nice 

EGT's are never high,  trans temp is always low and my mpg is ok

I don't know what the ratios are on manuals but just because there is a pile of gears doesn't mean you have to use them, I just got lucky and got the tyre height just right for here as OD off is also just right for our 30mph urban speed limits as my truck stays in lockup to just around 30 ish

I would agree that your setup serves you well.

 

"Choogles", that's a good word.

 

- John

21 minutes ago, Tractorman said:

I would agree that your setup serves you well.

 

"Choogles", that's a good word.

 

- John

One of my all time favourite groups is Creedence Clearwater Revival    there's a song called choogling written in 69      fits just nice as in OD my truck is laid back, low revs taking it easy 

 

Keep on chooglin'
Keep on chooglin'
Keep on chooglin'
Chooglin'
Chooglin'

Maybe you don't understand it
But if you're a natural man
You got to ball and have a good time
And that's what I call chooglin'

Here comes Mary lookin' for Harry
She gonna choogle tonight
Here comes Louie, works in the sewer, Lord
He gonna choogle tonight

Keep on chooglin'
Keep on chooglin'
Keep on chooglin'
Chooglin'
Chooglin', chooglin', chooglin'

Waaah, nah, nah

Waaah, nah, nah, nah

Waaah, nah, nah, nah, nah, nah, nah

Keep on chooglin'
Keep on chooglin'
Keep on chooglin'
Chooglin'
Chooglin'

If you can choose it, who can refuse it?
Y'all be chooglin' tonight
Go on, take your pick, right from the get go
You gotta choogle tonight

Keep on chooglin'
Keep on chooglin'
Keep on chooglin'
Chooglin'
Chooglin'
Chooglin', chooglin'
Chooglin', chooglin'

Waaah, nah, nah, nah, nah

Waaah, nah, nah, nah, nah

Waaah

Free, nah, nah

Do it, mama

Waaah, nah, nah, nah, nah

 

 

 

 

You forced me to go and find that song on the Internet.  I remember it now, just never realized that was the word being said.  Creedence Clearwater had a lot of good songs.

 

- John

1 hour ago, wil440 said:

Keep on chooglin'

I digress temporarily from tire size. 

 

Choogle definition, (slang) To ball and have a good time.  

To ball, (slang) To engage in sexual intercourse.   The use of the word ball was used in this context in the late 1960's and early 1970's, I was there and heard it and used it this way.  This brings more clarity to the lyrics.

 

"But if you're a natural man
You got to ball and have a good time"

 

"Here comes Mary lookin' for Harry 

She gonna choogle tonight"

 

 

 

 

With an automatic transmission, 4:10 differential, and 245/75-16 tires I pull my trailer and boat at freeway speed in OD.

55-65mph is 1800-2100RPM.  I down shift to 3ed and slow to 55 for long uphill grades.

 

Another good combination!

 

- John

3 hours ago, IBMobile said:

Choogle definition, (slang) To ball and have a good time.  

To ball, (slang) To engage in sexual intercourse.   The use of the word ball was used in this context in the late 1960's and early 1970's, I was there and heard it and used it this way.  This brings more clarity to the lyrics.

 

 

Wasn't choogling used in another CCR song   something like "choogling on down to ####### " could have been New orleans ??? can't remember, oh yeah I can .... Born on the Bayou

10 minutes ago, wil440 said:

Born on the Bayou

Wish I was back on the bayou rollin' with some Cajun Queen.
Wishin' I were a freight train, oh, just a-chooglin' on down to New Orleans.

That chart has me thinking now.  My wife has decided she want's bigger tires on her Jeep wrangler, currently running 33's with 3:21 gears and an auto.  I was gonna have it swapped to 4:10's in August but now I think 4:56 might be better with 35's.  

Consider it carefully on the rear axle gearing and the top gear of the transmission. As you found how it changed your truck getting the gearing correct. 

 

I've got that other member with Allison Transmission and the final gear is pretty tall and running way too low in top gear at 65 MPH.

Edited July 11, 20222 yr by Mopar1973Man