Rear end ratio ?
10-25-2020, (Subject: Rear end ratio ? ) 
Post: #1
Rear end ratio ?
Rear end ratio 13 speed 3.21 rear ends with 11R 24.5 rubber. ISX 2350 500 hp. I usually run in 12th with the cruise set on 65 this puts me right around 1500 rpm. I thought it would be Ok but I don’t really like the tall ratios. What would you guys recommend I go to if I changed the rear ends? 3.42 3.55 3.73 ? I generally operate on two lane roads and a little bit OTR. On flatland in the plains usually about a 350mile radius of Garden City KS. Loaded 80,000 lbs looking to go maybe 90,000 Lbs. Appreciate your advice.
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10-25-2020, (Subject: Rear end ratio ? ) 
Post: #2
RE: Rear end ratio ?
At least 3.90


User's Signature: The missing link
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10-25-2020, (Subject: Rear end ratio ? ) 
Post: #3
RE: Rear end ratio ?
I would go 3:90... The 3:90, I ran a little Volvo with a nine speed with 3:90 gears in the flats, 65 on cruise, 8 mpg all day long, but I was hauling light loads in a step deck van. I miss that truck. And I wish I had a set in my current truck, running through the mountains here in PA, and it is embarrassing.


User's Signature: 2008 ProStar, OEM 600hp CM-871, 18spd, 3:42, in framed in Rawze's driveway. Every day is a fresh new episode of, "The Twilight Zone"... Rod Serling lives rent free in my head. I can smell the Chesterfields.
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10-25-2020, (Subject: Rear end ratio ? ) 
Post: #4
RE: Rear end ratio ?
If you look around on here , rawze has posted a calculator several times that will tell you the rpm at which speed depending on ratio .
Personally I would gear it to run at 1650 at 65 mph if thats what you like to run at .
But thats just me ...
3.90 would be about 1500 rpm at 65 I believe.
I also had 18 speed in all my trucks though , I did have one 15 speed actually.


User's Signature: The missing link
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10-26-2020, (Subject: Rear end ratio ? ) 
Post: #5
RE: Rear end ratio ?
What would RPMs be with same rears, low pro 22s, 65mph in 13th.
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10-26-2020, (Subject: Rear end ratio ? ) 
Post: #6
RE: Rear end ratio ?
Ive got 3.36s behind an 18 hauling up to 100k. When in Louisiana i cruise at 60ish (55 limit) in 17th(12/9 direct) @1450rpm with ease. In Tx i cruise 68ish in 18th (13/9over). The only problem ive ever had in a 13 with same gear ratio and load is the gap between 5 direct and 6 direct. My opinion. If ur rears grenade and u have to replace em go with a 3.55, otherwise ride the 3.2x.
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 Thanks given by: schISM
10-26-2020, (Subject: Rear end ratio ? ) 
Post: #7
RE: Rear end ratio ?
i replaced in my lonestar 3.36s with 3.70s this gave me 65 1500 70 1600 75 1700rpms with 11r 22.5s. cost was 6 grand for brand new center sections.


User's Signature: 2010 Lonestar - CM871 - 13sp - 3.70s, 2016 T680 - cm2350 - 13sp - 3.36s - skateboarder
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10-27-2020, (Subject: Rear end ratio ? ) 
Post: #8
RE: Rear end ratio ?
(10-25-2020 )the missing link Wrote:  If you look around on here , rawze has posted a calculator several times that will tell you the rpm at which speed depending on ratio .
Personally I would gear it to run at 1650 at 65 mph if thats what you like to run at .
But thats just me ...
3.90 would be about 1500 rpm at 65 I believe.
I also had 18 speed in all my trucks though , I did have one 15 speed actually.

I think you were referring to this..
http://rawze.com/forums/showthread.php?t...3#pid17353

btw: forum memeber 'the missing link' is a career super-B, heavy hauler. He knows what he is talking about.


User's Signature: ->: What I post is just my own thoughts and Opinions! --- I AM Full Of S__T!.
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