Re gearing question?

[Jay Smallen]

Hello fellas! Some time in the near future we're re-gearing our 06 f350 PS AT which is currently on 37's and is a big ol heavy rig. But we love him and want to keep him happy and on the road as long as we can.

We live at 5,000' in the mountains near Tahoe. The rig currently weighs 11,400 lbs loaded for long trips with us in it. Stock gearing is 3:73 and the stock tires were 275 18's. We drive a fair amount of high elevation passes and I still use the rig for work occasionally towing 10,000 ish lbs.

All that being said, I'm looking for gearing recommendations from people with experience.

I'm thinking of dropping to a minimum of 4:88's, but considering 5:13's. So I'm curious what some have run with similar weights and elevations?

Thanks in advance for your time and patience.

 

[ptgarcia]

First of all, great looking rig!

Second, 4.88 or 5.13 is really low. After reading about your situation my gut feeling said 4.56, but I don't have first hand experience with that rig. I can't imagine needing 5.13's to move 21,400lbs around, even with 37" tires. My brother had your year and model truck and pulled a 15,000lb 5th wheel with the factory 3.73s and 35" mud tires. It certainly needed to be geared, but his truck probably would have been perfect with 4.10s. Hopefully someone that has done something similar chimes in.

 

[Billiebob]

Gearing is all about use. Taller gears are best if you do lots of highway, interstate between adventures If you rarely need a 75mph cruise go for shorter gears. But at upper elevations a turbo or supercharger might be a better buy first. You don't mention what engine you have.

Go here to see actual data on what different gearing will do.

Gear Ratio Calculator

www.grimmjeeper.com

ps, awesome little camper

 

[MidOH]

4.56 should be plenty for a diesel.

The f550 has 4.56 gears and 29" tires. So it's doable, 37's and 4.88's. But that's a good combo for the gas engines. Diesels can be a shade taller geared.

 

[ptgarcia]

You don't mention what engine you have.

I think the "PS" in the original post refers to the 6.0L Powerstroke Diesel.

 

[MidOH]

I don't think tall gears are good anywhere. You just don't lose much economy on a modern truck. But you take a ton of strain off the drivetrain.

Lock out your overdrive and set your cruise at your expected rpm after your gear mods, to see what it's like. (Kinda)

 

[Uberland]

I'd go with 4.56s as well...I'm only running 4.11s in my '00 Excursion with a 7.3, but that's because I want to keep the fuel mileage as decent as possible (and the speedo in the ballpark). I can't imagine that such a leap to anything above 4.56 is necessary...