March 20, 2011I am in the process of getting new gears installed and wanted to know if 4.56s would be good with 38.5in tires? What should i expect my rpms to be around 60-70mph and what mpgs should i see?
March 20, 2011Of the gears that are available for our trucks, 4.56 gears will work and will restore some of the lost low end torque. As for mileage, I am pulling 13 mpg with 4.56 gears and 37" tires. But then, I have also been told that I am pulling a really good MPG for the setup. So, plan on getting about 11 MPG. As long as you have the factory speedo gear (aka, VSS Gear), then your speedo will be fairly accurate (will still read a little low, but only by about 4 mph at 70 mph). So, a lot of your shifting issues that you may be having now with the tranny always wanting to downshift will go away.
As for RPMs that you will be turning, you will be right around where a stock truck would be with 3.55 gears. So, at 70 mph (actual), you will be turning right around 2,000 RPM (maybe just a little under). So, you are right about where you want to be when it comes to gearing for 4x4ing while maintaining a decent mileage number.
Chris "Thermo" Coleman, Nukie, the radioactive 97 Ford X, and K`Re Ann the 03 Jag X
March 20, 2011Thats what I am running but I also have a diesel motor, but I am getting 14mpg at about 10300 lbs.So at that weight I am happy
March 20, 2011Thanks Chris and Mo.
I was already getting 11mpg on the highway so i hope i will be getting more than that. I also have true dual exhaust with no mufflers, k&n cai, and a superchip.
March 21, 2011mudryder, when I went to the new gears, I didn`t really see a big shift in the mileage, what I noticed was a difference in how the truck drove. I had more umpf off of the line and the truck didn`t want to shift as much. I also noticed that my mileage didn`t fluctuate as much between in town driving and highway driving. With the gears, I pretty much pull 13 regardless of what I am doing.
Chris "thermo" COleman, Nukie the radioactive 97 Ford X, and K`Re Ann the 03 Jag X
March 21, 2011Ok thanks Chris,this info really helped, now i have a number to shoot for. I will be happy with 13, ill report back once i get it back and run a few tanks of gas through it.
April 17, 2011Ok ive got my truck back now and have run a couple of tanks through her, but i cant count the first one because it wasnt full. The second tank i got 9.4mpg granted it was all city driving below 50mph stop and go, i was kinda disappointed. But what can ya do? anyway Chris you were dead on with the rpms. 60mph - 1750rpm, 65mph - 1850rpm, and 70mph - 2000rpm.
April 17, 2011Mud, what I can tell you is that if you are doing in town driving and you are accelerating as fast as the cars next to you, yes, your mileage is going to suck. To help with the best mileage, what I do is depress the gas pedal such that the RPMs come up to about 2500 and then the truck shifts. Are you going to accelerate slower than cars. Yes you will. But at the same time, what is more important to you, fast acceleration or mileage? Also, when on the highway, keep the RPMs under 2200, but over 1800. 1800-2200 is the sweet spot for the engine. You get outside of those and the mileage is going to suffer for it.
Chris "Thermo" Coleman, Nukie the radioactive 97 Ford X, and K`Re Ann the 03 Jag X
P.S. I guess I should have mentioned that I have also gotten rid of my mechanical fan and went with dual electrics to help with the mileage and I also ported/polished the intake mildly to help with the airflow. So, I do have a slight advantage there.
April 17, 2011Thanks for the tips Chris. Yea i just cant help but goose it i love listening to and showing off my exhaust. But i will try to do what you said and see if i cant improve my mpgs. Im also ready to get on the highway to see what i can get,i havent had to do any hwy driving yet.
PS i sent you a message about another topic.
April 20, 2011I think I have 4.88s with 37s
plenty of power
probably around 13 mpg