I have a lifted 09 with 3.55's and am thinking about swapping to the 4's. Wanting to know if anyone else with a lifted one has done this and what changes they noticed if any. Thanks for your input!

 

4.10's? I think thats a lot of money for not much change. I would go with the 4.56 with your 37's anyway. I havent done it myself but i am running 35's and 3.73. My ratio is nice, i'll go with the 4.56 if i go to 37x13.5 or larger

 

what notable difference would I see with 4.56's?

 

In my opinion,4.56 is suited for rock climbing,not highway use,at least not an every day driver.I think it would be to low of a ratio....

 

i have the 4.56's in my truck and its great. but then again i have a little 4.7 and 38x15.5's

 

The 37's result in a 12% taller gearing than the stock sized 33's. Going to a 4.10 over his 3.55's will result in 15% shorter gearing, so it will more than compensate. It will be like having 3.73's with the stock tires.

 

i got a 6" lift and 37's and was told i would need to get 4.86 gears just to bring it back to stock.either way its about $2800.

 

You are failing to consider what his EFFECTIVE RATIO WILL BE. Just because someone installs a 4.56 ring and pinion does not mean that their final ratio will be 4.56. Tire diameter directly effects effective ratio.

Rams base gear ratio on a 32.5" diameter tire so if you have 3.55 gears, your effective ratio with that size tire is 3.55, but go to 35" tires and your effective ratio is 3.29. Installing 37" tires and your gear ratio is a woeful 3.11 and you probably can't get out of your own way.

IMO the best gear ratio for a combination power/performance and fuel economy (everywhere except maybe people who live on the highway and can't keep it under 75) would be a final ratio between 3.90-4.10.

So, given the OPs 37" tires, he would best be suited with 4.56 gears, which will net him an effective ratio of 4.00. While a change to 4.10 gears will net him a 3.6 effective ratio which will at least get him back to his stock acceleration and fuel economy levels.

The other thing that you need to consider here is that the transmissions in these trucks aren't 1970s era three speed automatics either, with a 4th gear ratio of 0.75:1 and a 5th gear of 0.67:1, these are essentially two over-drive gears, so we aren't exactly talking taching 3000 rpm at 70 mph here either, I'm barely over 2000 rpm at 70 mph with 4.56 gears & 35" tires, not even into what is considered the Hemi "powerband" of 2200-2500 rpm yet...

 

all depends on tire size. Anything above 35" you should seriously consider 4.56, even 4.88 for 38". I have yukon 4.56 with 33" tires on an 06 FX4 and it is wayyyyy too much gear for any sustained highway driving. And it is one expensive mod - 2400 bucks, not to get it right.

 

i had the 4.56's even with my 35's originally and it wasnt that bad. you cant just look at the ratios. that gives a good idea but you also need to consider the added weight of the larger tires and wheels.