True. It is only required if you change gears or tire size (you would be changing the overall gear ratio) and want to know how fast you are going or have an accurate odometer. May invalidate your warranty as well.

 

I have 3.92's and would've preferred 3.55's. Reason being is better gas mileage, I have nothing to tow, and over the truck's lifetime, the total number of engine revolutions would be less.

 

Here’s the RPM calculations for the different tire and axle ratios combinations. TH = Tow Haul which is 4th gear and is .075 overdrive on the 545RFE trans

2011 Ram w/ 3.92

33” 275/60-20 tires = 1739 rpm @ 65 mph TH = 1946 rpm
31.7” 265/70-17 tires = 1809 rpm @ 65 mph TH = 2026 rpm

2011 Ram w/3.55

33” 275/60-20 tires = 1574 rpm @ 65 mph TH = 1762 rpm


Do yourself a BIG favor and order the Serial Code DMH which is the 3.92 gear and Serial Code DSA which is the Anti-Spin Differential Rear Axle. They are separate orders on the truck.

I ordered my Ram Sport last week with all the options that “I” wanted and the 3.92 anti-spin was a priority. The truck comes with the 20” tires/rims and I got the dealer to do a swap for 17” from the SLT and mount new Bridgestone Dueler Revos that I just ordered from the Tire Rack this weekend. They will do the swap, mount/balance new tires and recalibrate the speedo as an even up no charge deal. I wanted the gearing tightened up more than the 20” tires provided and switching to the 17” will be a much better deal for pulling and a daily driver imho.

Most buyers would be hard pressed to find the exact truck they want with the 3.92 on the lot as only the Outdoorsman comes with this axle…. 99% of everything else is 3.55. The 3.92 will not reduce your gas mileage vs the 3.55 because you’re hauling around a 5400+ lb truck. Trucks get the best gas mileage when coasting and going down hill. Otherwise they perty much suck unless you have a diesel. If you’re worried about fuel milage, you’d be better off with a car imho.

 

I have to agree with you on this point.
Mileage is not going to be stupendous regardless of ratio chosen, so you might as well get the one that makes it perform best.
It's hard to beat the mileage of a Honda Civic, but a truck it is not.

 

3.92's on my 10 Sport... Love them and I average 15.2mpg driving half city half highway. That is good mpg in my book!!!

Just my 2 Cense

 

3.92 with this limited slip ( anti-spin as Dodge called it ) was a must have when I was looking for a new truck in 2009. Didn't even look at one's without it. I lucked out and one of the dealers had two blue ones, a quad cab and a crew cab with this setup. I would do it again now if I was looking but for me, there are no updates yet worth trading the 09 for imo. Now if only we get this 8 speed trans !

 

Drive one w 3:55 and one w 3:92 at a dealer and see what you like. I had the same question and the answers on the board convinced me to get the 3.92, I am very glad I did. I love the responsiveness and overall the RPM's are low so it gets good MPG for a
full size truck

 

I have 3:92 and love them. Still only 2,000 rpm at 70MPH. I have had all sorts of gear ratios over the years (from 2.89 to 4:11) in trucks, Corvettes (3), Cobra, etc and currently have 3:55 in Mustang GT (would rather have had 3:73). 3:92 is the best overall gear for that truck in my opinion. And I still get around 19 mpg on the road. However, mine is 4x4 and I do haul lots of stuff and drive in the mountains a lot. Even with the 3:92 I still have to gear down to 3 in Tow/Haul mode to climb lots of 10-12 %grades.

 

Get the 3.92, wish I did.