If you don't mind sharing some numbers, i've been poking around at some gear swap prices this afternoon once again. Wondered if anyone could give me some approximate rpm's and speed so I can compair to my 3.55's with 31.5's as well as my buddy's 4.10's with 32's. My rear pinion seal is leaking and honestly, 3.55's never were cutting it to begin with. I'd rather not drop a bunch of money to buy 4.10 because thats what my friend has which is why I was looking at 4.56's. 33's are the next tires I will buy and the max size that will go on the truck. The truck will be used at 65mph and maybe an occasional 70mph when driving back and fourth to college just to keep up with traffic. With that said, there are numerous hills for about an hour of my three hour trip. My truck will not hold a constant speed w/o doing its downshifting temper-tantrum up a hill. Maybe if I did 4.56's, my truck would be able to get in the torque range far enough to not shift out of OD up a hill . I dont mind doing the calculations if someone could post the formula. Thanks in advance!

 

http://www.ringpinion.com/Calc_RPM.aspx

 

I just wanted to give you a gauge on how big these hills are. I took a different route to college last weekend and I was driving up the hill about 60ish with OD off. With my foot into the gas and it in 3rd gear..... My mph dropped so much that I shifted into second just to hold speed. :/ the powerstroke pulling the camper in front of me powered up that hill like a piece of cake........

 

Using the calculator, it says my current setup is as follows

3.55 - 30.5" - 70 MPH = 2811RPM

My buddys stock setup

4.10 - 32" - 70 MPH = 3094RPM

Options for my next setup

4.10 - 33" - 70 MPH = 3000rpm
4.56 - 33" - 70 MPH = 3337rpm

Thanks aim for the calc first of all. 2nd, Just want to double check that we have 7" rims. And finally we are talking 243 rpm's difference between my friends truck and mine all said and done by going with the 4.56's. Is it a safer bet to get the 4.56's since I have a 318 and he has a 360? Im open to all suggestions, thanks guys!

 

Get the 4.56's no question. The most ideal ratio to have is about a 4.15 - 4.25 effective gear ratio for the best balance of performance and fuel economy.

Effective ratio = old tire diameter/new tire diameter x physical gear ratio

So in your case you had 3.55s with a 30.5" tire and are going to a 33" tire. Therefore your effective ratio would be 4.215 with 4.56s. Without a gear change, your effective ratio would be 3.28 after the switch to 33's which would be pretty pathetic. Staying with the stock tire size 4.10s would be ideal, but with the switch to the taller meats, you need the 4.56s...

 

I went 4.10s on a 30.6" tire and really like it. It actually improves mileage in the city traffic. It hurts a little on the Highway, but I've learned to slow down to compensate. You're kind of right in a hole for our trucks with the 33" tires, 4.27 would be the best compromise, but they don't make them for our axles. You'll kind of have to choose between torquey pickup and slow down on the highway to about 60mph (4.56) or less torquey off the line and you can speed on the highway again (4.10). If gas money is a big concern, like it was for me in college, go 4.10. If not, build your beast however you see fit.

Keep in mind that the RPM's you posted are looking a little high. The OD gear is a 0.69:1 ratio not 1:1 or 0.73:q like I've seen posted before, so you're RPM's will drop more. Once I start passing 2200rpms, my gass mileage goes to crap.

 

318, 33s, hills, low highway speed, I say 4.56

 

I thought the looked a little high as well but when I used the calculator, I took the AOD number.

Im looking at 300 + install kit for the rear. and 215 + install kit for the front. Looks like I might be able to handle the gears for now, and that truetrac that i've pretty much obsessed over for... a long time is now nix'd becaue it can't handle 33's. I was planning on dropping in that truetrac this summer and im glad I did not. Instead bought and installed my westin pushbar & lights. I wired that all up to a custom swith mount I made out of sheet metal. I just installed my my 2" level kit (HBS coil hats), My rancho rsx shocks + steering stabilizer just two weeks ago. lol, that $$ adds up aweful quick. Hopefully if im lucky I can shoot an email over to the automotive department now that im back up at college and see if someone over there wont mind looking over my sholder to make sure im doing the gear install right. Alrighty guys, I appreciate you help. Maybe ill steal my roommates camera in a bit and go take pictures so you guys finally see my truck. Maybe even an exhaust clip or 2 haha jk.

 

Shoot! I now know what you mean aim. I should have been using the AOD column instead of the.... Auto column. Wow, that makes my numbers way off. Let me try this again.

My current stock setup
3.55 - 30.5 @ 70mph = 1916rpm
My Friends stock setup
4.10 - 32 @ 70mph = 2109rpm
My new setup
4.56 - 33 @ 70mph = 2275rpm

The consensus seems to be 4.56 is the answer, and after seeing the new rpms, it seems more realistic lol. I ran my truck this afternoon with OD off and at 3grand it hit 70mph. She was definately winding out. I feel a lot better knowing I should expect around 2300 rpms at my max speed in OD. Also, some guys that run 35's run 4.88's so that makes me pretty much equal ratio. Even if i decide to run 32's that puts my rpms at 2346rpm. That still ain't bad. Im gonna quit ramble'n on, ill leave that to led zeppelin.

 

For what it's worth, with 35's and 4.56, my rpm's at 60 are:
1950 in OD
3000 in OD off