i have a 2005 5.4 super crew cab F150..it has a 6in lift running on 35in tires.. i did the math and i am only getting 8 miles to the gallon. when i got the lift they said the speedometer would be off by 5mph. didnt really think that would matter. but does that effect the odometer to..cuz 8 miles to the gallon is ridiculous....anybody with lifts can you chime in please..

 

well i know that after i put on my 35s before fixing the speedo i was only geting 8 to 11 and after get the edge and repgraming it its 13.5 to 16 and less total miles on the truck

 

If you're concerned about MPGs, two things I'd suggest...

1. Stock tires/wheels

2. Stock suspension

 

thanks for the help but i will not go back down to stock everything..i just dropped 4k on my lift... is there any programming chips or something that will bump it up a little bit. thanks

 

any of the programmers on the market will adjust the tire size in the PCM


Edge is a preferred programmer by most here

 

This has all been addressed before, do the math. $4,000.00 will buy you a lot of gas!

 

3-inch lift and 35's on my truck and normal driving/towing i get about 11-13... highway my best was 15.5...

mark

 

rbelliston: With the big tires, your odometer is reading fewer miles than actually traveled so it seems like your MPG dropped radically. Oh, it's dropped from the lift and tires but not that much. Job one for you is to pony up to a programmer that lets you correct the odometer readings by changing the tire size parameter in the computer. The big tires also effect how your trans is shifting and that could be causing some MPG loss too. I suggest the Edge. Brick simple but with a lot of useful tools (such as MPG readouts!!!), including a correction for tire size or gearing. It will also give you a power boost and often a slight mpg boost... giving you back some of what the tires have cost. It did for me, anyway.

Speaking of gears, what gears are you running? For best performance and MPG your gearing needs to be a match to the tires. Ideally, you should be running 4.10s (or 4.56s for very spirited performance) with 35s. 3.73s can pass with a big, torquey 5.4L if you don't tow or haul much weight. Most people, me included, think 3.55s are too tall in any circumstance matched with 35s. Not so bad if all you do is cruise at freeways speeds, but not so hot around town or in hilly country. It's kinda like riding a 10 speed around in 10th gear all the time. Engine works harder in stop and go and the trans works harder too. Not so bad on the turnpike. In fact you might see a slight MPG uptick.

 

I have the 3.73's in my truck and i do tow quite a bit.. The heaviest is my toy hauler empty it is around 5600lbs both big quads and gear about 7600lbs... It dose it... hills i feel it other then that it's fine. I would like to have 4.10's in it as i had a 01 ranger that had 4.10's and that was an alsome truck.


MArk

 

So both Tire Size & Gears effect mileage? I got a used 2006 Lariat that has 20"w and 3.73ls. As far as I know, this is how the truck came from the factory - upgrades when originally purchased. Is this going to give my MPG a hit from the 14c-19h advertised with these trucks?

 

engass: It's overall tire diameter that counts, not the wheel rim diameter. It's easy enough to look up the factory tire/wheel size on your truck (hint: try the glovebox or the tire placard on the door (: <). Tire diameter and gears make up the "effective" gear ratio. Going to a taller tires with a given axle ratio is like going to a taller axle ratio. And vice versa. To get the effective ratio back to where the factory designed it, after going to taller tires, you have to go to lower axle ratios. To find what ratio to use, the the equivalent ratio formula works great. To use it you need the axle ratio and the original tire diameter.

Divide the new tire diameter (inches) by the old diameter and multiply that result by the gear ratio. Say you have a 245/70R17 tire (31-in dia.) and you want to use a 285/70-17 (33-in) and you have 4.10 ratios. 33/31=1.0645 x 4.10= 4.36. From there you find the nearest available ring and pinion ratio for the axles on your truck. The ratio change puts the effective ratio back to stock, meaning at any given speed, your rpms will be the same (or nearly) as they were stock. Lifts and bigger tires increase rolling resistance and aero drag, so you don't always get all the stock mileage back.

If you want to find out the effective ratio of a tire change on your existing ratio, you use a similar formula but you divide the old tire diameter by the new tire diameter and multiply by the axle ratio. Using the numbers from above:

31/33x4.10=3.85

Which means that the above truck (mine in fact) with 33 inch tires and the stock 4.10 ratio will drive as if (or "feel" like) it had 3.85:1 ratios with the stock size tires.

Let's take a 3.55 truck that had 31s and 3.55 gears stock. The owner wants to install 35s. 31/35x3.55=3.14 That will "feel" like fairly tall 3.14:1 gears. Good for hiway cruising MPG but not good for town driving MPG or acceleration. Or towing or hauling.

With a big engine you can get by with tall gears more than a small engine because the bottom line is wheel torque (engine torque times the multipliers of the gearing). An 5.4L with 360 lbs-ft, in direct gear in the trans (3rd, 1:1) and 3.14:1 ratios has approximately the same wheel torque as a 4.6L with 290 lbs-ft and 3.73:1 gears.

 

Thanks for the answer... A bit confusing for a novice - I have 20" Rims with stock 275/55/R20 Pirelli Scorpions. Just wondering if that is having an effect on me only getting around 12MPG with local driving only. I live 5 miles from work and rarely go any distance above 40MPH. Back country roads with in town Stops and Lights. Is this kind of mileage fairly normal for this type of driving?

 

It's certainly not far off. Your truck is most efficient when it's locked into O/D, which in my truck doesn't happen under 40 MPH. Stopping and starting a 5-6,000 lb truck, especially with those heavy wheels, takes lots o' juice!

 

ok back to my question...what would be the best affordable way to bump up the mpg 3-4.. programmers? air filter?

 

One thing you want to do is do the math for your actual MPG. I don't know what size tires you used to have, but say you increased the tire diameter by 10%. If you drove 200 miles on the odometer before the next fill up, add 10% to that total because you really drove 220 miles. Then divide by the gallons and that will give you your true MPG because yes, the odometer is effected.

You say your looking for 3-4 MPG increase. If you are gettint 15 mpg right now, that means you want to increase your MPG by 20%. That's a lot. I would say in general, intake and exhaust are good upgrades and that might get you half way there. The programmer may get you the rest of the way, but by the time you add up the cash you just shelled out, you're going to have to drive the truck like that for 10 years to pay for it, although you''ll be nicer to the polar bears.

The gears will actually help you gain some of your mileage back because you won't be ******* the engine and it will be in it's happy place, I mean, sweet spot of the power band as designed.

Byt the way, Is that THE Jim Allen of automotive book fame?