I have had my truck for almost a month now and the gearing is taking some getting used to. I have been crusing at 80 on the highway, i was wondering if i got 315's how much should it lower my rpm's from 2,500rpms going 80? also what speeds do you guys cruise at?

 

I run 65 mph unless I am in a big hurry. Truck really needs a 7th gear to run 80. I don't like turning all that RPM. And mine has 3.73 gears and a 6spd.

 

This might not be a direct comparison as I have the Auto but I regularly move out at 75-80 mph on the hwy. At 70, my rpms are 1875, 75=2050 and 80=2175. I have the 3.73 diff and 315/70 tires.

 

shouldn't it be if you have the same gearing as me?

 

The auto has an od ratio of 0.69.

The six has od ratio of 0.75

 

80MPH?!! Where do drive that permits this speed? In my state (Virginia), anything more than the moving traffic or the speed limit + 5MPH will result in feeding the bears. But, to your question, I'll usually drive 60MPH on state highways (55MPH speed limit) or 70MPH on interstate (65MPH speed limit). Fuel economy really drops as the speed goes up. At 70MPH, my truck delivers 21MPG. At 50MPH (county roads), it gets 24-25MPG.

 

Here in AZ the hwy speed limits are 75mph. If you are going 75 or less, you will be creating a hazard as 90% of the population seems to like to drive between 80 and 90 on the hwy. In PHX, where Caughtinmygrill lives, if you simply follow along with traffic, you will be going anywhere from 10-15 over the limit regardless of what type of road it is... i.e. residential, commercial 35 or 45mph roads and freeways too. It's crazy! Any attempts I've made to abide by the speed limit has resulted in near rear-end collisions and/or a huge line of PO'd traffic behind me. You should have seen it when I was doing the 50mph break in while towing for the first 500miles... not something I care to ever do again. By no means am I condoning speeding or breaking any laws... I'm just saying that 'round here, believe it or not, I feel SAFER to travel at the speed of other drivers rather than following the posted limits... cops don't seem to care unless you are blasting by everyone else @ 100mph or driving erratically. Personally, I don't like this system, but unfortunately, the majority rules.

With that being said, I drive at about 80 when empty, 75 with the boat hooked up (relatively light, aerodynamic load). RPM's are the same as Caughtinmygrill's since we have the same setup in regards to tranny, gearing, and tires.

 

Bd, you're probably running closer to 2300 @ 80 than 2500. In any event, you'd drop almost a couple hundred rev's with the bigger tires.

 

Pop-pop,

Biggrigg is correct, 75 mph is the speed limit on highways with 80+ being the normal rate of travel. You also have to remember that Arizona is much lower in population density than Virginia, at least outside of Phoenix. You will drive 40-50 miles in between towns with nothing around but coyotes and the occassional rattlesnake. Even then, the towns are usually well away from the highway.

That said, I did just get pulled over 15 miles outside of Page, AZ (Lake Powell) for doing 77 in a 65. Highway patrolman was coming the opposite way and at least a 1/2 mile away when he tagged me. I got off with a warning because my speedometer hasn't been recalibrated. Probably didn't hurt that my very cute kids were in the truck with me.

 

On Interstates here in Texas and on trips into Lousisiana I drive 5 - 10 miles over the speed limit. 75 - 80 mph. I also use a radar detector/scrambler. If you drive slower than that you are holding up traffic.

 

At 70mph my engine is turning 2200rpm! I have a 2003 2500 4x4 HO diesel 6 speed. Sticker said I have a 3.73 ratio. I've had the covers off to change the oil but never checked the ratio. Any with the same drive train? If so what rpm are they turning at 70mph?

 

same here in ohio
but Ive never got better than 17.8 MPG

 

I agree.. I don't run 80 in my truck unless I have good reason to. Mine is setup just like PapaPerks... 6 spd, 373's. I need a 7th gear before Im comfortable cruising 80 mph on the freeway.
Scott

 

Move to socal.. You drive 70 on our freeways, you'll get run over. In the fed ex truck today, I hit 100 without knowing it, and I was going with the flow of traffic. I of course immediately slowed down, but my point is, that anything below 75-80 on a so cal freeway is asking for murder.
Scott

 

In Phoenix, the freeway that skirts Scottsdale is nicknamed the Autobahn, 'cause all you see on it is Mercedes and BMW's going 100 MPH +. Arizona DPS is now trying to install permanent photo radar cameras on the freeway overpasses. Just wait until the camera flash goes off and blinds someone, sending them skidding across three lanes of traffic. That will be one heck of a lawsuit.