I drove that truck for 4 years pulling that trailer most times over 12,000 pounds and this dump trailer usually loaded broken ceramic well over 12,000 pounds far more than it should have ever pulled that's why I bought a diesel this time. I originally had 4 30 in my 6 wheeler but it was totaled that's why this truck came to be As far as engine oil always ran the 5 w 20 full synthetic Mobile 1 never had an issue with the engine just let her screen that's what they do. I also install Eaton true locker what a difference it made can't wait to put one in my new 2016 f 350 6.7 and get rid of the e locker. Don't go lower then 3.40 the gears hit perfect at 35 tires and this ratio. you can drive 70 at only 2100 rpm or around their , i would not want more rpm and ride for hours listing too 2500 rpm lol and as far as the lift whats does that mater ???? i had 2.50 up front and 5 inches in back loved it.

 

Going from stock size tires to 35s, a 4.33 differential would get you back to the effective stock 3.73 ratio.

A 4.88 differential would put you somewhere between an effective ratio of 4.10 and 4.33.

 

4.88 with a 35" tire is closer to 4.39 as @WE3ZS has in his Excursion.

 

I don't have any of the OEM parts to drop the lift (was bought lifted).

 

The calculator I used says 4.88s would give an effective ratio of 4.24, assuming a stock tire diameter of 32 inches.

 

Thanks for the opinions guys.

Yes i really dont want to hear this truck creaming on the highway at 2500 rpm at all radium.

I will measure the true diameter of my 35'' tire today. I also read that you once you get your new ration you go 1 range numerically higher to compensate for the new weight of the tire.

I know i don't want to go over 4.56's for sure it sounds like.

 

That just seems high to me?

I believe stock tire on this truck was a 275/65R20, which is actually a 34.1'' correct? What is a effective ratio?

 

Per Tire Rack, OE sizes would have been 265/70R17, 275/70R18 or 275/60R20. I went with the worst case, the 17 inch tires.

Effective ratio is what you now have compared to stock. If you go from 32s to 35s and have a 3.73 differential, it gives you an effective ratio of 3.24. In other words, changing the tire size is the same as installing a 3.24 ring and pinion.

 

So I go onto 4Lo.com and input:

Old Tire Size: 34.1
New Tire Size: 35
Current Gear Ratio: 3.73

That gives me an effective ratio of 3.63:1

Then it give me Hi Gears: 3.48, New Gears: 3.83 and Lo Gears: 4.17.

Seems crazy to me!

 

It actually states on my door tag 275/65R20. Strange, i cant believe it was a 34.1'' stock...

Ahh, i understand on effective ratio now.

Went on and did some RPM calculators and with my setup its 1755 rpm at 70 mph based on .7 OD (I think my trans is .71 ). if i up the gear to a 4.30 it jumps to 2023 rpm and at 4.56 it jumps to 2145 rpm.

Just for poops i changed the tire size to a 33'' and stock i would be at 1861, with 4:30 it jumps to 2145 rpm and 4.56 it jumps to 2275 rpm.

Seems like the real question is if i really am going to buy 33's next time or stick with 35's.... If i go 33's next time i want 4.30's, if i go 35's again I will want 4.56's. I'm all for cheaper tires too..

 

lol i meant 4.30 it will be fine with that transmission trust me i drove it and used it every day it feels better then it sounds trust me. the truck was great at plowing too lots of low end power. 2100 rpm for an 2 hrs was bad enough trust me i was thinking of going higher if i kept the truck 4.10 to get around 1800-1950 once again i was in the truck not a web app telling final gear numbers ask around and see what other people think take care

ps BFG 305/65/18 wore out quicker , then BFG 325/ 65 /18. don't know why so i stayed with BFG 325/65/18 three sets the old design then new BFG TWO sucked they could not keep them balanced went back to the old BFG after two months of trying

 

4.56 will most likely make you happy.

4.88 would be fine, but since you don't tow and don't want to rev high and gulp gas like crazy you probably wouldn't like it.

I used to have an F150 7700 and it had 4.10 with stock tire size. That was pretty close to your 35s and 4.56s.

If you towed and were more worried about power and less about fuel usage I would say 4.88. But, that doesn't sound like what you want.

 

I've had no issues with the BFG TA KO2s. Balanced the first time, the ride is smooth as silk.

 

I guess I'm not concerned with fuel usage at all, mostly just listening to the engine wingin' at 75 MPH down the interstate for hours on end. This truck frequents many 5 hour trips for work. (6-7 hours is the cutoff and we will fly).

I was looking on Randys ring and pinion and the 4.30 gearset is OEM, so the cost is astronimical at $740 just for the gears. The 4.56's are only $210 per axle which isn't bad.

I think I'm safe to go 4.56's, if i like the power with the 35's i will get another set of 35's, if i don't then i will down it to 33's. Really don't want it much over 2100 rpm at 70 mph.

 

Once you decide which size tire you plan to run in the future that (and your typical usage) should drive your gear choice.
As has been discussed 33"s with 4.30 will serve you very well, 35"s with 4.56 would do the same. If you were towing then 4.88s would make for a great match to 35"s, that's what I run on our tow rig EX. The effective ratio of 4.39 spins the V-10 at 2230 RPMs at 65 MPH while towing our 11,000 lb TT in OD. The sound of the engine at the RPM range isn't a problem for us on long tow days (up to 10 hours) and the change to deeper gears has actually increased our towing MPGs a bit, unloaded the highway MPG had gone down by approx. 1/1.5 MPG.
Good luck, going to the deeper gears was the single biggest performance increase that I've done to our EX.