Hey guys, I know I have another post on here regarding another issue, but this offer just came to me from a buddy.

Hes got a 05 ram, and is offering a axle swap cause he is trading in his dodge for something else. His rear end have a eaton posi, with 4.88 gear ratio. My rear end is stock 3.55 dog leg. For my daily driver, how do you all think the ratio differance will affect my gas mileage, or for that matter CA Smog?

 

city mpg will go up noticeably, highway mpg will go down noticeably, fun factor will increase by a lot, acceleration will be higher, CA smog shouldn't care about your axle.

i'd do it. rememebr to get your speedo calibrated, and you might want to upgrade tires, as 4.88 is on the high side of what you want with 31s or 33s (31-32 if you ahve 17 inch wheel, 33 if you have 20" wheels)

 

Great gear ratio with 35"+ tires. Maybe even 33's, but a bit extreme in my opinion for anything smaller. Your smog factor will go up, only because your rpm's will be up at given speeds.
You should see a bit of a mileage increase in town, and would lose a bit on the interstates.

 

You won't need to calibrate your speedo.

 

brain fart,

good catch frog

 

Yup. only need to recalibrate speedo for tire diameter changes...

 

Ok, just a quick question. Why would I not have to get my speedo recalibrated for the gear change? Its a pretty big differance going from 3.55 to 4.88! I have LT265 70R 17 tires on my truck now. Would it be such a big differance, where I have to change my tires?

 

The speed sensor is not effected by the gear ratio in these trucks. You have a 32" tire now, might be a bit on the small side for a 4.88, but it will accelerate a lot faster. If you go w/ a taller tire, you will have to get the speedo re calibrated.

 

so then you all think its a no go? if I cant afford taller tires?

 

depends on where you drive. if it's all highway, you'll be turning 2k rpm at low 60s, so it'll cost you a little gas, but that might not matter to you.
if it's half highway half city, i'd do it, you'll pick up mpg in the city. if you drive mostly city, do it in a heartbeat.
you have more incentive to do it because the 3.55s are terrible even compared to 3.92s. sure 4.88s are a pretty big jump, but to me its def an improvement over 3.55s.

plus, if you get them, you'll smoke your tires off in no time cuz of the added torque, then you'll HAVE to get new tires