F150Jeff

We got 6"BDS, 3"BL, 38x15.5 on 20" Hulks. (2008 f150 4x4 5.4L xlt screw)

Now redoing the gears, and just need confirmation or suggestions.

The rear diff has 12 bolts (for a 9.75)
The front diff has 10 bolts (for 8.8)
The axle code (on the door sticker) is B6 (Which means 3.73 LS gear ratio)

Now using the formula (Tire Size * Current Gear / 30) I end up with 4.72 as my current gear ratio.

What I'm trying to achieve is a better mileage for the highway. (I know we could buy a Prius, but we'll stick with the truck for now).

Am I correct to assume that 4.56 would give me better mileage, and lower rpm??? (and 4.88 would give me more tork, but not necessarily better on hwy)

Thanks,

Throwitup518

Iv been wondering the same thing... Same set up but gonna run 37's. from what iv gained for 37's I'm right on the border where if I want better mpg get 4.56 and if I want more torque get 4.88. Since my truck is 90% on road and the 10% off roading I do is very mild mud I'm siding with 4.56.

Even though I'm pretty set on 4.56 so many people on here are saying 4.88, but I do 60 highway miles every day! So I like the 4.56 for closer to stock rpm's on the highway

Lifted5.4Lariat

For highway mileage and minimal towing I would suggest 4.56. I have 4.56 with 35's and its very torquey with tons of power and I get around 14-16 on the highway going 55-65.

lifted06kingranch

how much trimming was required to fit the 38x15.5?

F150Jeff

Thanks all for the responses,

We'll go with the 4.56, - Will let you all know how its doing afterwards,

---

Lifted06kingranch, - only a little trimming (about 1 1/2") was needed under the front bumper,

lifted06kingranch

Thanks. I also have a 6" suspension and 3" body and my 35x12.5x20 are border lining silly lol

2008f1504x4

I'm not sure if I will go with 4.10's or 4.56's when I go 35's... 4.10's run barely 50 rpms more then 3.73's on stock tires.... Like 100-150 more then 3.55's on stock tires

Sunsetter

i ran 4.56's with 34's for 6,000 miles before i moved to 37's now i wish i had that torque back. i will probably go to 35's next. if regearing wasnt expensive i would regear again to 5.13's

Lifted5.4Lariat

The reason most people go with 4.56 over 4.10 with 35" tires is because of the little to no benefit for the money. With 4.10 you most likely wouldn't even notice a difference. With 4.56 you get all the factory pep back plus a tick more torque.

2008f1504x4

But I imagine doing the speed limit (75mph here) would suck some gas down with 4.56's and 35's.. Like 8-9mpg I bet