Don't mean to hijack, but is there a thread that explains the difference in these gear ratios....

Dario

 

3.21 ratios are a highway gear meaning that at 60 mph the motor will be turning around 1400 rpms to help improve fuel economy. The 3.92 gears are more for towing and at 60 mph the motor will be turning about 1850 rpms. the 3.55 gears basically split the difference. that is the quick and dirty explanation.

 

I also have been asking about the axle on my truck. I can't remember where I found it but I found a reference to the axle and it called out a Chrysler 9.25 29 spline for the '09, not 31.

 

Jayman, would this mean that in the city the 392's are more fuel efficient, and have a quicker take off?

thanks!

DArio

 

this is from justanswer.com. question:i buy a 2009 ram 5.7 4x4 the differentiel is 3.55 standard can i upgrade to limited slip with same ratio at the dealer,thank

answer: Yes it can be done at the dealer; it will still be under warrenty, if done at the dealer also.

i think i will go this way for the warranty.

 

392's will never be better on fuel unless you drive like a granny and the guy with the 355 drives like a 18 year old.
Ya in the city you will have a better hole shot with 392 for sure. Go get 411's or 456's if you want to buy new tires every month!

No matter what you wont get great gas mileage but for a HEMI with almos 400 ponies it gets better gas mileage then the exact size motor I have in my 72 chevy pickup that is pretty much stock, it gets 10 miles to the gallon in the city and 15 on the highway.

 

JUST got a 2010 1500 TRX4 Off-Road with 5.7 Hemi, this is my 1st Mopar, so unfamiliar with axle codes, etc. My truck has the 6700lb. payload package, is the 3.92 standard on this package? Specified 3.92 axle, but RPM seems low for a 3.92, what are axle codes for 3.92 and 3.55 respectively? Thanks in advance, sorry for the rookie ??

 

well i have the 3.55 rear end and run 1450rpms at 60 mph and about 1750 rpms at 70mph. If you are running more rpms at those speeds then I am then you have the 3.92 rear end.

 

I have a 09 Hemi with the 3.92 axle ratio and 20 inch wheels, what would the effect be if I switched to 17 inch tires and wheels. I assume it would pull better wouldn't it. I pull a 26 ft camper in the mtns of NC and even with 390 HP I am constantly using 3rd and 4th gear.
JWM

 

17s wont help. Your truck will not stay in 5th gear because it has no power in that gear for towing. You have to be around 2500 rpms to start making enough power for towing up hills. So its not worth spending the money to change to 17s since they will not make a big difference. That is the nature of gas vehicles, they have to be in 4th or 3rd gear for towing, overdrive is only really needed on flat ground.