I have a 2005 F150 with stock 3.73 gears on 35s.
I have 4 inches of suspension lift and a 3 inch body lift.
I want to take some stress off my transmission and hopefully gain some MPGs, but I don't know what gears to get.
I do minimal towing, mostly cruising around 45-50 and around town driving, and occasionally I'm on the freeway. I also occasionally get off the road.
I am currently getting about 11 MPG on a good day, downhill, in neutral...
I also plan to possibly go up to 37s when my 35s wear out.
So what do yall think would be the best gears to go with? 4.10s? 4.56s?
I mainly want to take the stress off my transmission, which has its tongue hanging out.
Gaining some MPGs would also be fantastic.

 

Go with 4.56's, 4.10's won't make much difference. You will also need a programmer to correct the speedo/odo and so the PCM knows how fast you are really going, a SCT device with CUSTOM tunes recommended.

I doubt you will get any gas mileage back though with that much lift and big heavy tires.

 

You'll need 4.56s just to get back to stock rpms for the same speed as stock. You'll need deeper gears if you want any power back. Consider 4.78 gears instead.

 

Would 4.56s run 37s decently also?

 

Before I can answer that - what was the stock tire size? I need it for the calculator.

If you want 37's, your gas mileage is going to go into single digits.

 

4.56s will do just fine. If it will spend the rest of its life on 37s, consider 4.88s.

 

Stock tire size was 30.6" in height

 

labnerd said stock size was 30.6"

 

Okay - stock tires, 3.73's = 1720 rpm in OD at 60 mph
35's, 3.73's = 1500 rpm in OD at 60 mph
35's, 4.56's = 1840 rpm in OD at 60 mph
35's, 4.88's = 1970 rpm in OD at 60 mph
37's, 4.56's = 1740 rpm in OD at 60 mph
37's, 4.88's = 1860 rpm in OD at 60 mph

Based on that, I think 4.56's will cover you with either 35's or 37's, assuming you have a 5.4. With a 4.6, get 4.88's, it needs all the help it can get.

 

Thanks!!! It's got the 5.4, so 4.56's it will be. 37's are just a thought, I'm not sure that I will actually go with those.

 

You are not taking into consideration the massive increase in rotational inertia going to such large sizes and it's effect on performance. Yer putting that additional mass where it does the most 'damage' - at the outer circumference of the rolling stock.

That chart only deals with steady-state rpm values, with no mention of delta V impacts as a function of rotational mass increases.

I believe you'd be happier with the added responsiveness that 4.88's would provide, rather than returning to the 'status quo'. And given yer moderate / urban usage, I reckon the increased rpm's won't be that much of a nuisance.

Additionally - you'd be somewhat "future-proofed" against the possibility (likely the probability, lol) of eventiually going to 37's. ( If yer at all serious aboot this - and want a REAL kick in the pants, go with 5.13's and don't look back, lol ).

Concur that mileage should not be discussed in the same thread

You'll need to factor in the cost of a programmer to correct odo, speedo and shift point errors - and to help recoup some of that lost tq.

Lastly - the other consideration is braking - that is also significantly impacted - simple physics. Need to budget a brake upgrade to correspond to rolling stock size increases. Most don't - but indeed should.

Just my opinion, aight? Good luck

 

Here's some free MPG's for you. Since you changed the tire size without recalibrating the ECU, you are actually traveling farther than your odometer indicates. In your case, your mileage (on a good day) is 11 * 35 / 30.5 = 12.6.