4:30 vs 3:73
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Logistics Pro
Joined: Dec 2010
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From: Temperance, MI
4:30 vs 3:73
Im running 36'' tires right now and am going to do gears and before next spring Im gonna need new tires so Im gonna go 38s so the gearing will be where it should be again. My questions are will my mileage suffer compared to what it is no because of steping up the or would it go up because the truck will be running where its designed to be operated? I cant make up my mind on if it would be better or worse with 3:73s and 36'' tires Im running at a lower RPM, or the 4:30s and 38s. Ill let you guys decide for me. Would there be a seat of the pants difference in torque? Thanks for the help
Cargo Master
Joined: May 2010
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From: Snohomish, WA
The difference you will see is only one to two hundred rpm for your sizes and ratios you list. Mileage depends on a lot of things. Your rolling resistance goes up, so don't expect an increase from what you have now.
Posting Guru
Joined: Jan 2007
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From: Millersburg, OR
Stick the 38's on there, see how you like it. Then gear accordingly. 4.30's would probably be a good match for 38's... I run 4.30's with my 40's since I don't tow much. I think CSIPSD has 4.30's with 37's but he hates it. Really depends on what you like and what you use your truck for.
Posting Guru
Joined: Jul 2008
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From: Dalton,Ga
John, i am running 4.56 with 37" and love the set-up....4.30 would put it right on stock, i tow with mine so i wanted to be just a little low..@70mph i am turning 2040rpm(with scanguageII)..the truck pulls much better and doesn't work as hard...honestly the economy seems better because its easier to stay under 2000rpm in everyday driving and she dont feel like a snale...
like Layson said..it all depends on how you use your truck
like Layson said..it all depends on how you use your truck
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Logistics Pro
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From: Temperance, MI
Ive brought this topic up a couple of times before with different questions every time so thanks for responding, I just want to make sure I dont blow $2K+ on something I dont need. Simply put I guess... I dont have many uses for a 3/4 ton truck its not often that I use her for what she was met for. I could easly get by with a half ton truck but I cant get one with a diesel!! Ive had a detroit locker sitting in my garage for over 6 months now that Ive been wanting to put in and about 4 months ago I noticed I have slop in the rear gear. Mileage is "almost" most important. More often than not shes my DD empty outside of all my tools. Oh and a bad a$$ weekend warrior!! Weather it be in the mud or playing with imports and my personal favorite mustangs 
Post Fiend
Joined: May 2009
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From: Pea Ridge, AR
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Logistics Pro
Joined: Dec 2010
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From: Temperance, MI
Thats to have a shop order them and put them in, Ive only had one quote though and it was awhile ago, I dont remember the exact price
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Post Fiend
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From: Pea Ridge, AR
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Posting Guru
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From: Dalton,Ga
is your daily driving in town or interstate???if its interstate then i would try the 3.73 first..i know mine would run 80 under 1700 rpm....the weekend warrior really needs gearing....just my 02
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Logistics Pro
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From: Temperance, MI
Mostly interstate I get sent all over the country side, Im a journeyman millwright and get sent everywhere to fix anything. Ill take all your advice because were only talking about a couple hundred RMPs anyways right. Ill just have to chase more HP and TQ to make up the difference
Senior User
Joined: Nov 2005
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From: Houghton, MI
I run 4.10s in my Excursion on 37s. I was at 6600' and thought they were a good balance because I did a lot of highway driving. Now I'm close to sea level and still like the 4.10s, gives me the option to tow with O/D off and still run 60 on the highway...to each their own.
Elder User
Joined: Dec 2002
Posts: 797
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From: UT
Check out this gearing table...
4Lo.com :: Gear Ratio & Tire Size Chart
I used to be under the impression that if you ran bigger tires, lowering your RPM's with the same axle ratio, would convert into better MPG. If you tow at all, its a must if you want stock like shift points. I've heard of guys going to 285's from stock 235's re-gearing to 4.10's and picking up MPG's. It's even a smaller change than what you currently have.
4Lo.com :: Gear Ratio & Tire Size Chart
I used to be under the impression that if you ran bigger tires, lowering your RPM's with the same axle ratio, would convert into better MPG. If you tow at all, its a must if you want stock like shift points. I've heard of guys going to 285's from stock 235's re-gearing to 4.10's and picking up MPG's. It's even a smaller change than what you currently have.
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Logistics Pro
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From: Temperance, MI
I like that gearing table but according to that for best mileage with 38s I should be running 4:56 gears. The chart says that right now I should be at 2263 rpm at 65 with a manual trans and with my transmission Im spinning at about 1700ish RMP in O/D. I just want to be sure I dont loose mileage by not changing the gears
Senior User
Joined: Nov 2005
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From: Houghton, MI
I think your premise is off. IF you want a milage increase than you have the wrong vehicle and you are going in the wrong direction. Your gearing selection should be based on function and use rather than a milage increase / decrease.