I need some advice. I've got a 2003 F-150 Lariat SuperCrew FX4 with a 5.4 and 3.73 gears. I recently put on some 285x70x17 BFGs. It also has a Flow Master muffler and a drop in K & N breather. My problem is that my gas milage is terrible. I'm getting around 13.5 or 14 at present. Does anyone have any ideas that would help me squeeze some more milage out of it? Any advice would be greatly appreciated.

 

When you put those larger tires on your supercrew, your odemeter will read slower and your speedometer will read slower than you actually traveling. This means that fo say you went 10 miles on the road, your larger tires made the odemter rea about 8.9 to 9.5 miles for example. So this means that your odemeter is reading less miles and would work out your so called poor milage.

 

I agree with sk8ate

Did the exact same thing bigger tires and I went from 15.0 to 13.5 and thought WTF's up with that!

I went from 30.05 to 31.65 tires and doing the math in rotations per mile and distance traveled per rotation.

I have to add 5 miles per 100 to get my odometer correction. So you see over 300 miles 15 extra miles makes a big difference. it's like using 1 gallon less gas.

So Don't worry about it it's still there. Or if You are bored at work one day figure out how to do the math and you'll see.

 

so bigger tires are a good way to reduce the amount of driving i do , looks like my job got a few miles closer to home.. cool

 

While the fundemental is true about the larger tire size, you only changed circumfrence by 3.5% so that is not your problem. 3.5% more mileage for the same amount of gas is only not even going to change your numbers by 0.5mpg. THe larger impact of performacne and fuel economy is due to the heavier tires over stock which take more power to rotate. Inertia sucks.

What kind of mileage were you getting before you changed the tires? I have the exact same truck with the same tires and typically get 12 in mixed driving. In 19k miles I have gotten a best of 14.2 and 13.8mpg, otherwise 10-12mpg. Your window sticker says 13/16 I think so you are getting within your range which I would say isn't terrible. You have a 3 ton pickup with a 350lb-ft V8 and 33" tires. I think your expectations may be set too high.

The best way to improve mileage is change driving habits. That is the single biggest influence. Anything else, will cost you money that most likely will take 75k+ miles to recover the fuel economy savings. Regardless, a Microtuner and electric fans typically help fuel economy, but the most benefit from the tuner comes at the cost of premium fuel which does not help out of pockect expenses.

 

Eeeyye Wrong APT


5.3 Percent more circumfrence.


And I know it's hard to believe but 5.3 percent is a big difference in 300 miles.


I was getting 15.5 mpg now 14.6 almost exactly 5.3 percent less mileage than before. Even if these bigger tires weighed 200 pounds more so what. Hard to believe 200 pounds would make a 1 mpg difference.

If anything would make a difference it would be the tire tread and wind resistance. The tires I have on now are pretty knobby and when they were spun balanced at 35 mph the wind coming off of them was incredible so I can imagine the power they eat up at 80 mph.. It's called fan effect. Well known in the snowmobile world for years, deeper lugged tracks eat up alot of power just from wind resistance.

 

265/70R17 = 99.29412" in circumference
285/70R17 = 102.7573" in circumference

102.7573/99.29412 = 1.034878% difference

Over 300 miles that means 10.5 miles further driven tham indicated.

Sorry, extra inertia causes uses more fuel than the larger size. Google will prove it, if you care to look.

Snowmobiles are a little different than cars that drive on paved roads, so your comparison is not accurate.

 

Newton's first law of motion states that "An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force."


265/ 75-16's = 31.65 x 3.14 = 99.38 circumfrence

255/70-16's = 30.05 x 3.14 = 94.36


99.38/94.36 = 1.053 5.3 %


300 miles x 1.053 (5.3%) = 315.9


315.9 / 3 (per 100 miles) = 105.3

105.3 - 100 (miles) = 5.3 extra miles per 100 miles

So in summary I have to add 5.3 miles per 100 to get my

accurate mileage.


300 miles / 20.5 gallons = 14.63 mpg

315.9 corrected miles/ 20.5 gallons = 15.41 mpg

Now just because your odometer mileage changes by 5.3 percent obviously doesn't mean your mileage changes 5.3 percent.

This is where the (little) extra weight, rolling resistance, and fan effect come into play.

 

I have my differences and you gave yours. You have mods to offset (in efficiency) the larger and heavier tires. I have none. My last F-150 had the exact same drivetrain, but weighed 250 less. It got on average 2mpg better than this truck, which was mostly unaffected when I had a 400 pound ATV in the bed as extra static weight. 14mpg instead of 12mpg is more than the 3.5% larger tire difference.

Regardless, the original posted staid he gets 13.5-14mpg with larger than stock tires which is well within the EPA estimates as well as what owwers of similar F-150 owners get.

 

APT, that was fun!


I mean no disrespect to you at all!


I have no mods at all on my truck. And I think 15 mpg on a 5200 lb truck really isn't that bad, thinking back to the old trucks, bronco's and blazers, that got 11 weighed about the same and had a 100 horsepower less. (shrug) waddah ya gonna do....

 

Hmm, I think I clicked on sk8inrj1's gallery and thought it was yours. Sorry about that.

 

When I went from the stock 16" wheel on my 01 2WD SCrew to L wheels with 285/60R18's I noticed a drop in mpg. Looking at the entire range of mods, I found out that I was really making the engine work at highway speeds, and a slight pedal down caused the VAC gauge to drop to 2IN/HG. Might as well be pouring the gas out of a hole in the tank.

I tried an experiment driving at highway speeds with the truck out of OD, and guess what...my VAC gauge stayed in the 12 to 18 range, and my MPG went up. Now unless I can drive at 85 MPH or better, OD is not an option, if I want to keep the mpg up.

Temp in a VAC gauge and try to keep it between 12 and 18, and see where your MPG goes to.
You will be shocked how hard it is to keep it in that range when taking off the line ( worse for you with 33" ), it is way hard to do. I figured out it was my combo of mods, and driving habits that took the MPG into the dumper. Now that I know it is me, not a problem with the truck, I am back to driving it the way I want, and getting about 9 to 11 MPG. Go figure if I wanted to save gas money I would have bough a Honda InSight, not a SCrew.

Oddly enough both of my bikes get crappy MPG when I hammer them off the line......go figure Not like the Zrex was for high MPG commuting

 

I found a solution to my gas milage problem. I let the wife drive the truck (she only drive 10KM per day) and take her car to work(about 40KM). The cost for fuel is about 14 cents per KM in my 2003 SCREW.

I do find that I get cut off a lot more while driving to work. Never happened when I drove the truck

Don't worry I drive the truck on weekends when I can really enjoy the truck!