Currently I have a set of 35s on my truck, I think it has more than enough power with the 4.10 gears I have, I am going to buy a set of 37s or 38s next.. Because I dont tow I am not to worried about the power, but I am a little worried about my MPG.. I dont drive the truck much, and I plan on keeping it until its dead, and I only have like 67k on it now, so I have a long time!! I am thinking it should last me another 10-15 years, if all goes well, and we are not floating in the air in space buggies by then..

But I am wondering, since I dont tow or haul, will a set or gears really be offset by the increased MPG? For example I really dont want to pay 2k for gears (estimating cost, not sure what it really is) if all I get is a 0.01 increase in MPG..

Also I was thinking, if I SHOULD infact get new gears, maybe I should just get them not before my lift and tires.. I dont plan on getting my new lift or tires until maybe late summer, as my tires still have alot of tread left..

 

Big tires, lifts, and "better mpg" should never be used in the same sentence.

No amount of gearing or other investment will ever compensate for the aerodynamic, weight, and rolling resistance penalties.

If you need to care, don't do it.
If you need to do it, don't care.

(with care referring to fuel economy)

Lastly, I have yet to see objective evidence that gearing changes affect mpg significantly. Maybe 1/2 mpg? Definitely impacts acceleration, but cruise mpg? As long as truck is in that 1500 to 2500 rpm zone at cruise, efficiency remains about the same. That's one of the benefits of closed loop FI compared to old carb'd stufff.

 

Gotcha, would my 4.10 gears create much stress on the motor/tranny/ ect when turning 37's or 38's? I would rather not blow a tranny early, but I guess you gotta pay to play..

If it makes any difference 90% of my driving is city type driving...

 

More stress on drive line? Yes, but not really much to worry about. You have an '05 with 5R110 tranny, and it is a beauty. It will just generate more heat, shift later, and not be in OD as much.

It will require a lot more power to get those monsters to accelerate - meaning more fuel, more stress, etc. But, these trucks are meant to pull hard and have a very beefy drivetrain, so it should not be a "high risk" amount of stress for the drivetrain. Maybe shorten life expectancy from 400K miles to 200K miles?
But you WILL feel the difference in acceleration. 0-60 times will go up at least a couple seconds, if not more. And take close to double the amount of fuel to get there. Big tires are really hard on fuel mileage around town...

Also expect to see significantly shortened lives out of the steering and suspension components (bearings, tie rods ends, ball joints, shocks etc). Oh, and brakes. They need to absorb a lot more energy to slow those puppies. Probably cut pad life in half.

I'm not really trying to talk you out of it, just want to help you make an informed decision. I run the 315/75-16's because I like to do a lot desert and sand dune driving and need the flotation. But even those cost me a couple mpg - a compromise I chose to make. But if this were my daily driver, I would be putting smaller tires on it pronto. Gas is now $4.50 out here....

 

This truck is my daily driver but I only live 2.5 miles away from the office, so I put $20 into the take every week and I am good to go.. I let my truck idle alot ever since I got my remote start so that also helps kill my MPG.. I bought the truck for a daily driver and home renovation projects.. If I ever got a job with a real commute, the truck would park and I would pick up the cheapest new car I could get my hands on (new for the warranty)

Would better gears help reduce the amount of power needed to get my going, keep the tranny cooler, help with shifting, ect...???

I am just trying to decide if gears should be factored into my lift kit or not.. I am not for it or against it, I just want to do it once and do it right.. 2 years from now I dont want to think I wish I got those gears a back when I did the lift, I know I could just do it then but I would just rather do it all at once..

 

If it were me I would go ahead look into new gears. Hey I understand, the lift and tires are a hell of alot funner to look at than gears. Get them sooner/later. A tuner could help with power. More $ though.

 

you best prepare yourself for replacement gears..

if you go to 37-8' you WILL def. notice the difference in lost power..

as far as MPG goes, theres nothing you can do. once you make the jump to that large of a tire you have to be willing to give up any sence of good MPG. esp with a truck as big n heavy as a SD and with a V10...

 

If gears do nothing for mpg, then maybe I need to wait until I get the new tires and then see what I think of the power, like I said right now I have more power than I know what to do with.. I don't mind upgrading at all though if the thing is like a slug.

 

37's rock!!

STRAPT Performance DTX Carli Suspension Ford Super Duty Coil Over - YouTube

 

you can definately tell you're pushin' those 37's, but the V10 rocks. I've got 4:10 in my 09', AIRAID filter, 5Star SCT tuner, 3" catback. I have my tuner set right now on 87 econo, and I'm getting about 220-230 miles per tank when driving around town, something like 7.8- 8.5 -ish. Last time I checked, I saw 11.5 when cruz set on 60mph, about 2k on the rpm's. I'm sure my speed-o is off a bit.... when my truck had stock tires and suspension, with all the mods, I got 340 miles on one tank coming home from Phoenix to Orange County, SoCal doing about 70-80mph (shhh, don't tell!).

 

So what gear ratio would I want for 37s?? Again I currently have 4.10 with my 35s and again its more than enough power for me, but then again, why would I not want more haha..

So if 4.30 is the best gear for stock size tires.. What would a 4.30 be equivalent to with 37" tires?

 

4:88's

that were you should be looking if your gunna go inside the pumpkins.