I was looking for a little info for my brother,we are headed to the dealer this a.m to pick up a new truck.It is a 1500 quad 4x4 swb hemi auto "thunder road" it shows a 3.92 axle and was wondering how that will play out with fuel milage? He has the exact truck in a 04' with the small wheels and a 3.73I think. the anti spin is a must what do you all think?? Isit the wheel that makes you have to get the 3.92?? any pro con to this setup?thanks in advance

 

3.92 is an excellent gear ratio for standard through slightly larger tires for a balance of performance and fuel economy.
My opinion (and it appears to be shared by the majority on these forums) is that, even though "on paper" the 3.55's would net better fuel economy, this is not the case. They give a feeling of being underpowered in all but possibly 2wd, single cab models, forcing the driver to use more throttle, thus negating any benefits of the gearing. The 3.55's are also a terrible setup for towing applications, often times forcing the tranny to continuously have to shift to find the proper gear, costing in power and fuel economy (not to mention wear & tear on the tranny).
Unless going to larger tires (bigger than 33's), heavy towing applications, or going to the stripto race on weekends(in these cases the use of 4.10 or 4.56 gears would be in order) the 3.92's are the best gear choice he could have.
I agree that the LSD is a must, but chrysler makes a sorry one. So I would not let the fact that this trucj has one or not be a deal breaker. At some point he should consider a much better one, such as the Auburn Gear LSD or the Detroit Trutrac.

 

thanks for the info... I will pass the info to him.The dealer just called and we are on the way down there.Actually he wanted to let me know the truck he quoted us wasn't there.That just cost him more becuase he is gonna give us a more equipped truck same price.Ya gotta love end of month deals.hey sometimes your the bug and sometimes your the windshield [:@]

 

so i have a 2005 dodge ram 1500 rcsb with the 4.7L v8. my truck has a 3.55 posi. Your saying that if i get a auburn gear LSD 3.92, that I should get better gas mileage.

 

Don't confuse the LSD with Gears, even though they live in the same place, they are different components. ALimited Slip Differential won't effect gas mileage. Now the gears are another story.
What I'm saying is the old "rule of thumb" with gears won't necessarily hold true. On paper, 3.55's should get better gas mileage than 3.92's. But on these heavier trucks, it's just not the case. So, people are thinking that while giving up a lot of performance by having 3.55's they are getting better MPG, when in fact, the lack of performance is costing MPG. The 3.92's are giving the betterof both in real world driving conditions.
I've seen 3.55 geared QC 4.7 Dodge's get only single digit fuel economy when towing just moderate (2000lbs.) loads, as you are forced to use much more throttle to accelerate plus the tranny is constantly dropping gears, causing your rpms to soar and use even more fuel. And with anything over stock size tires - you can just forget it.
So, I believe the 3.92's, overall, are a better choice than the 3.55's. Contrary to the belief of many, gears have no effect whatsoever on overall torque or horsepower, they simply generate more RPM at a given speed, giving the feeling of more horsepower to your "butt dyno" as you are getting into the POWERBAND RPM range faster, and are staying in it longer. This is also why your tranny does not work nearly so hard, especially when under a heavy load.

My point about the Chrysler LSD is that it has always been crap, and until I see different, I'm always gonna be of that opinion. Not only do they not lock up as an LSD should, but these units have a history of coming apart and tearing up rear ends!!! So, I think anyone with the stock LSD would be doing themselves a big favor by purchasing a solid aftermarket unit.
Don't get me wrong, I think Dodge makes the best truck on the market, but all brands have their strengths and weaknesses, and the LSD is a definite weakness...

DMAGS: Let us know how everything turns out, and of course, post some pics...

 

I would say yes, and probably more power to boot.

I am of the opinion that the manufacturers engineer a lot of their setups specifically for the EPA results. It's in their best interest that their products get the best fuel economy, and the lowest possible emissions. That being said, that type oftesting is done under very controlled conditions, and probably doesn't reflect true "real world" scenarios.

I am pretty active in the Jeep (read underpowered) community, and by far the most performance enhancing modification available is proper gearing. Even a stock truck can benefitby fine tuning your final gear ratio to meet your driving conditions.

 

as far as the 3.55 goes. i had them in my 05 4.7 dak and liked them. just recently swapped them out for a set of 4.10 gears and it made a big difference, especially around town driving. on the highway i am about 300 rpm more then with the 3.55 and the mileage dropped of about 1.5/2 miles to the gallon. not bad seeing i was getting 18/19 around town and 22/23 on the highway. and with the corporate rear the truck squats and lays down some sweet strips

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I would never go less than 3.92 in the Ram with 20s.

 

dont most rams with the 20s come with 3.92s? bc mine came with 3.55 and the small 17s and i paid some guy 800 dollars for the 20s and included were four new goodyear eagle LS2

How much should it cost me to get 3.92s installed and everything w/ or w/out LSD

 

i would love to find the price for a 3.92 rear end, or 4.10

thanks