PerryB

That's how I read it.
As far as the gearing avaliable, 3.73 is actually decent with the 6 speed because first and second are pretty low. Still a 4.10 option would be nice.

Bohunter

here's a quick way to figure out your tire diameter:

http://www.discounttiredirect.com/di...nfoTireMath.do

WarSurfer

I guess I need to add a caveat...


I made some assumptions in the first post that need qualifying.


When you use a gear calculator, it baselines based on your factory gear. If you started with 4.10s on 35s (which is a pretty standard tire to gear ratio regardless of vehicle) then when you use the calculator, it will determine the appropriate gear for the tire chosen. IE, 4.56 for 37s, 4.88 for 39s, etc... This excludes crawlers for obvious reasons - I don't go anywhere at 2mph.


BUT - if your truck came from the factory with 3.31 gears, then your results will be skewed. All manufacturers sell variants of popular vehicles that have been castrated by gearing in efforts to appeal to more MPG focused customers. This is nothing new but because you are starting with such high gearing the recommended gear (from the calculator) will not be adequate for turning those big tires.


example:


using a ratio calculator


a truck with stock 3.31 gears and 255s would need 4.08 gears for 37s (2.69)
a truck with stock 4.10 gears and 35s would need 4.40 gears for 37s (3.82)


so - two f150s, identical in every way (trans gearing is the same) but two different 'needs' for 37s. Well, that's because the number that matters is in parenthesis (Effective Gear Ratio - EGR). It should be obvious that an EGR of 3.82 will have a much easier time turning 37s than a 2.69.

My point here is that context matters. Knowing that there is a minimum baseline is important when using a tire to gear calculator.


IF the 09-14 6L80E had different gearing for different F150 variants, then each diff ratio would probably be their own baseline - because it would indeed be tailored for that specific variant.


When the F150 gets the 10spd trans, it will again change the baseline for determining final drive ratio. In theory, it should allow for lower diff ratios while still maintaining decent MPGs but we will have to wait and see.

Steelhead 6.2

Well fellas, I recently installed 4" BDS lift with 35x12.5 tires and definitely got a little more slugage and lost MPG's. I'm running a roush charged 6.2l.What gearing would you all recommend for my set up?

PerryB

With the 6 speed auto I think 4.10 would be a good choice. That trans has a pretty low first and second so you don't need to get so aggressive with the rear gears.

Warsurfer makes a good point regarding the gear calculator charts. They simply return you to a mathematical status quo for the OEM configuration of the truck. They don't account for the increased rotational mass or the possibility that the truck was geared too tall to begin with. Some of the gear manufacturers offer a chart based on intended tire diameter and desired cruising RPM, and these are much more useful. They also give you advise with regard to factoring in transmission type (overdrive or not).

Can anyone tell me why some words in my post become links, and how to stop it?
Thanks

WarSurfer

4.10s came on the Raptor with 34.5's. That ratio will be fine.

Steelhead 6.2

Thanks bud! Thats what I was thinking, but hell! I'm a man and had to be sure!! I can't wait now! This is a good thread!

SteveLord

My new 4.11s took my 5.0 up some steep offroad hills with ease. I have 34.25'' tires.

Highway at 70mph, I get 2000rpm. Only 200 more than when I had the 3.55 gears.

kersh04

Has anyone had any experience with motive gears? Good, bad?

Thanks

PerryB

No experience, but they don't review very well. I went with Sierras and have a little narrow range whine in the rear, 46-52 mph.This is actually my second set, the first set did exactly the same thing. I'm thinking about trying a set of Precision Gears.

P.S. Tried Yukons, they howled.
I have the 9.75 axle and U.S made gears are seemingly non-existing. Supposedly the Precision's are a U.S. made gear